Cortical Connections of the Inferior Parietal Cortical Convexity of the Macaque Monkey

Transcription

1 Cerebral Cortex October 2006;16: doi: /cercor/bhj076 Advance Access publication November 23, 2005 Cortical Connections of the Inferior Parietal Cortical Convexity of the Macaque Monkey Stefano Rozzi, Roberta Calzavara 1, Abdelouahed Belmalih, Elena Borra, Georgia G. Gregoriou 2, Massimo Matelli and Giuseppe Luppino Dipartimento di Neuroscienze, Sezione di Fisiologia, Universita` di Parma, I Parma, Italy 1 Current address: Department of Pharmacology and Physiology, School of Medicine and Dentistry, University of Rochester, Rochester, NY, USA 2 Current address: Laboratory of Neuropsychology, NIMH, NIH, Bethesda, MD, USA We traced the cortical connections of the 4 cytoarchitectonic fields Opt, PG, PFG, PF forming the cortical convexity of the macaque inferior parietal lobule (IPL). Each of these fields displayed markedly distinct sets of connections. Although Opt and PG are both targets of dorsal visual stream and temporal visual areas, PG is also target of somatosensory and auditory areas. Primary parietal and frontal connections of Opt include area PGm and eye-related areas. In contrast, major parietal and frontal connections of PG include IPL, caudal superior parietal lobule (SPL), and agranular frontal armrelated areas. PFG is target of somatosensory areas and also of the medial superior temporal area (MST) and temporal visual areas and is connected with IPL, rostral SPL, and ventral premotor arm- and face-related areas. Finally, PF is primarily connected with somatosensory areas and with parietal and frontal face- and arm-related areas. The present data challenge the bipartite subdivision of the IPL convexity into a caudal and a rostral area (7a and 7b, respectively) and provide a new anatomical frame of reference of the macaque IPL convexity that advances our present knowledge on the functional organization of this cortical sector, giving new insight into its possible role in space perception and motor control. Keywords: area 7a, area 7b, dorsal visual stream, space coding, visuomotor transformations Introduction The posterior parietal cortex of the macaque contains a multiplicity of areas involved in the analysis of visual information necessary for motor planning and execution of eye, limb, and body movements (see, e.g., Rizzolatti and others 1997; Colby 1998). The rich parietofrontal connections of these areas mediate the transformation of visual information into action, and a series of parietofrontal circuits has been so far identified, linking visually related areas of the caudal superior parietal lobule (SPL) and of the intraparietal sulcus (IPS) with different sectors of the agranular frontal cortex or with the frontal eye fields. These circuits are involved in the visual guidance of reaching, grasping, or eye movements (Colby 1998; Rizzolatti and others 1998). Within this general framework, there are still several aspects of the anatomical organization of the cortical convexity of the inferior parietal lobule (IPL) and its possible role in visuomotor transformations and/or space coding that need to be elucidated. This cortical sector is usually subdivided according to the architectonic studies of Vogt O and Vogt C (1919) into a caudal and a rostral area, 7a and 7b, respectively, considered as functional and hodological different entities (see, e.g., Andersen and others 1997; Siegel and Read 1997a). According to this view, 7a is a visually responsive area, located at the vertex of the occipitoparietal visual information flow (dorsal visual stream, Ungerleider and Mishkin 1982), linked with oculomotor area lateral intraparietal area (LIP) and the rostral prearcuate cortex and where retinal and extraretinal signals are combined to construct a representation of space. In contrast, 7b is mostly related to the analysis of somatosensory information, connected with the ventral premotor cortex, and involved in the control of arm and face movements. Area 7a, however, is also involved in the control of armreaching movements (Mountcastle and others 1975; Blum 1985; MacKay 1992; Battaglia-Mayer and others 2005), and according to Hyva rinen (1981) there is a functional segregation in this area between a more rostral, visually and somatosensory responsive, arm field and a more caudal field, in which eye movement signals predominate. Furthermore, in the rostral IPL convexity (area 7b) there is a visual and somatosensory responsive arm/ hand and face field (Hyva rinen 1981; Ferrari and others 2003), where visual neurons appear to be involved in higher order visuomotor processings (Gallese and others 2002; Yokochi and others 2003; Fogassi and others 2005). These data, therefore, suggest, first, that area 7a is not homogeneous and, second, that 7b is not exclusively involved in somatomotor functions. In their architectonic study, Pandya and Seltzer (1982) indeed suggested that the IPL convexity contains at least 3 distinct areas: a rostral, an intermediate, and a caudal one, defined as PF, PG and Opt, respectively, plus a transitional area located between areas PF and PG and named PFG. Accordingly, areas 7a and 7b are both cytoarchitectonically not homogeneous and, in particular, area 7a would consist of at least 2 areas, PG and Opt. This subdivision, however, was never validated by clear connectional and/or functional data, and it is common practice in the literature to refer to areas 7a and PG as synonyms (Siegel and Read 1997a). In the present study we used cytoarchitectonic data to guide the location of neural tracer injections to study the cortical connections of the IPL convexity. Specific aims were 1) to examine whether patterns of connections validate the subdivision of this sector into more than 2 distinct areas, 2) to identify all the possible sources of sensory information to each of these areas, and 3) to trace their projections to the frontal lobe, where there are multiple representations of different effectors (see, e.g., Rizzolatti and others 1998; Rizzolatti and Luppino 2001) and identify all the several possible parietofrontal circuits involving the IPL convexity and their possible role in space representation and motor control. The results provide strong support for a subdivision of the IPL convexity into 4 distinct areas, referred, in agreement with Pandya and Seltzer (1982), to as PF, PFG, PG, and Opt. Preliminary data have been presented in abstract form (Luppino, Belmalih, and others 2004). Ó The Author Published by Oxford University Press. All rights reserved. For permissions, please journals.permissions@oxfordjournals.org

2 Rozzi Methods The experiments were carried out on 6 macaque monkeys (3 Macaca nemestrina and 3 Macaca fascicularis) in which neural tracers were injected in cytoarchitectonic fields PF, PFG, PG, and Opt. Additional data from 2 M. nemestrina, in which retrograde tracers were injected in the lateral funiculus of the spinal cord, were used for the definition of the corticospinal projections from the IPL. The brains of 5 additional monkeys (4 M. nemestrina and 1 M. fascicularis, 8 hemispheres), 2 of them used in tracing experiments not related to the present one, were used for preliminary cytoarchitectonic analysis of the IPL convexity. All experimental procedures were approved by the Veterinarian Animal Care and Use Committee of the University of Parma and complied with the European law on the care and use of laboratory animals. Surgical Procedures and Tracers Injections Each animal was anasthetized with ketamine hydrochloride (15 mg/kg intramuscularly) and placed in a stereotaxic apparatus. In all animals in which tracers were injected in the IPL areas, under aseptic conditions, an incision was made in the scalp, the skull was trephined over the target region, and the dura was opened to expose the IPL convexity. Injection sites were chosen by using cytoarchitectonic data as frame of reference, referred in terms of stereotaxic coordinates and location of anatomical landmarks such as the IPS, the lateral fissure (LF), and the superior temporal sulcus (STS). Once the appropriate site was chosen, fluorescent tracers (Fast Blue [FB] 3% in distilled water, Diamidino Yellow [DY] 2% in 0.2 M phosphate buffer at ph 7.2, True Blue [TB] 5% in distilled water, EMS-POLYLOY GmbH, Gross-Umstadt, Germany), wheat germ agglutinin--horseradish peroxidase conjugated (WGA-HRP, 4% in distilled water, SIGMA, St. Louis, Missouri), biotinilated dextran amine (BDA, 10% phosphate buffer 0.1 M, ph 7.4; Molecular Probes, Eugene, Oregon), and cholera toxin B subunit, gold conjugated (CTB-g, 0.5% in distilled water, LIST, Campbell, California) or conjugated with Alexa 488, Alexa 555, or Alexa 594 (CTB- A, 1% in phosphate-buffered saline, Molecular Probes) were slowly pressure injected at about mm below the cortical surface as described in detail in previous studies (e.g., Luppino and others 2003). Table 1 summarizes the locations of injections, the injected tracers, and their amounts. After the injection, the dural flap was sutured, the bone replaced, and the superficial tissues sutured in layers. In the 2 animals in which tracers were injected in the spinal cord, under aseptic conditions, following a laminectomy, the dura was opened and the segment of the spinal cord selected for the injection exposed. Retrograde tracers were, then, pressure injected with a 5 ll Hamilton microsyringe in the left lateral funiculus. In 1 animal (Case 10), DY (2%, 8 injections, total amount 12 ll) was injected at the T6 spinal level and 26 days later (HRP, 30% in 2% lysolecithin, SIGMA, 6 injections, total amount 10 ll) at the C4--C5 spinal level. In the second animal (Case 21), HRP was injected at the C3--C5 level. Upon the completion of the Table 1 Monkey species, localization of the cortical injections and tracers employed in the experiments Monkey Species Hemisphere Area Tracer Amount (ll) Case 13 Macaca Fascicularis L PFG WGA-HRP 4% R PF CTB-g 0.5% Case 14 Macaca Nemestrina R PFG BDA 10% Case 20 Macaca Nemestrina R PG WGA-HRP 4% Case 23 Macaca Fascicularis L Opt WGA-HRP 4% Case 27 Macaca Nemestrina R PF FB3% R PFG CTB-A 488 1% R PG CTB-A 594 1% R Opt DY 2% R Opt TB 5% Case 29 Macaca Fascicularis L PG BDA 10% R PF DY 2% R PFG FB 3% R PFG CTB-A 555 1% R PG CTB-A 488 1% R PG TB 5% Note: L 5 left; R 5 right. injections, the spinal cord was covered with Gelfoam and wounds were closed in layers. During surgeries, hydration was maintained with saline (about 10 cc/h, intravenously) and temperature with a heating pad. Heart rate, blood pressure, respiratory depth, and body temperature were continuously monitored. Upon recovery from anesthesia, the animals were returned to their home cage and closely monitored. Histological Procedures After appropriate survival periods following cortical (28 days for BDA, days for fluorescent tracers and CTB-A, 7 days for CTB-g and 2 days for WGA-HRP) or spinal cord (29 days for DY and 3 days for HRP) injections, each animal was anesthetized with ketamine hydrochloride (15 mg/kg intramuscularly) followed by an intravenous lethal injection of sodium thiopental and perfused through the left cardiac ventricle with saline, % paraformaldehyde, and 5% glycerol in this order. All solutions were prepared in phosphate buffer 0.1 M, ph 7.4. Each brain was then blocked coronally on a stereotaxic apparatus, removed from the skull, photographed, and placed in 10% buffered glycerol for 3 days and 20% buffered glycerol for 4 days. Finally, it was cut frozen in coronal sections 60 lm thick. In Cases 10 and 21 (spinal cord injections) the spinal cord was removed and, after cryoprotection, cut transversally at 60 lm. In Cases 27 and 29, 1 section of 5 was mounted, air-dried, and quickly coverslipped for fluorescence microscopy. In Cases 13, 20, and 23, 1 section of 5 was processed for WGA-HRP histochemistry with tetramethylbenzidine as chromogen (Mesulam 1982). In Case 13, in 1 section of 5, CTB-g was revealed by the silver-intensification protocol described by Kritzer and Goldman-Rakic (1995). In Cases 14 and 29, 1 series of each fifth section was processed for the visualization of BDA, using a Vectastain ABC kit (Vector Laboratories, Burlingame, California) and 3,39-diaminobenzidine (DAB) as a chromogen. The reaction product was intensified with cobalt chloride and nickel ammonium sulfate. In all cases, 1 series of each fifth section was stained with the Nissl method (thionin, 0.1% in 0.1 M acetate buffer ph 3.7), and in Cases 23, 27, and 29 a further series was stained for myelin (Gallyas 1979). All the other brains, but Case 1, used for cytoarchitectonic analysis were processed as described above and cut frozen in coronal (5 hemispheres) or parallel to the direction of the IPS (2 hemispheres) sections, 60 lm thick. The 2 hemispheres of Case 1, embedded in celloidin, were cut, one in a plane perpendicular to the direction of the IPS, the other in a plane parallel to the direction of the IPS, both at 40 lm. In all cases, 1 series of each fifth section was stained with the Nissl method. Data Analysis Injection Sites and Distribution of Retrogradely Labeled Neurons Injection sites were defined according to criteria previously described in detail (Luppino and others 2001, 2003) and attributed to the architectonic areas of the IPL convexity with analysis of adjacent Nissl-stained sections. The injection sites presented in this study (listed in Table 1) were all restricted within the limits of a single cytoarchitectonic area. One WGA-HRP injection in Case 27 involved both PG and PFG and was not considered for this study. FB, DY, TB, WGA-HRP, and CTB-g labeling was identified as described in detail in Luppino and others (2001, 2003). CTB-A labeling was analyzed by using standard fluorescein (for CTB-A 488) or rhodamine (for CTB-A 555 and CTB-A 594) sets of filters. CTB-A 488--labeled neurons were identified for a green granular fluorescence in the cytoplasm and CTB-A and CTB-A 594--labeled neurons for a red-- orange and a red granular fluorescence in the cytoplasm, respectively. These 2 last tracers were never used in the same animal. The distribution of retrograde and anterograde (for WGA-HRP and BDA injections) labeling was analyzed in each section every 300 lm and plotted in each section every 600 lm, together with the outer and inner cortical borders, by using a computer-based charting system. Data from individual sections were then imported into a three-dimensional (3D) reconstruction software (Bettio and others 2001), creating volumetric reconstructions of the hemispheres from individual histological sections containing connectional and/or architectonic data. The results of this processing allowed us to obtain realistic visualizations of the d 1390 Connections of the Macaque IPL and others

3 labeling distribution for a more precise comparison of data from different hemispheres. Distribution of labeling on exposed cortical surfaces was visualized in standard mesial, dorsolateral, or bottom views of the hemispheres. Distribution of labeling within sulci was visualized in nonstandard views of the hemispheres in which sulcal banks were exposed with appropriate dissections of the 3D reconstructions (Fig. 1). Areal Attribution of the Labeling Retrograde and anterograde labeling was found in several areas of the parietal, temporal, cingulate, agranular frontal, and prefrontal cortices. In the parietal cortex, outside the IPL convexity, connections were attributed, when possible, to functional areas that, although in many cases still lack a clear architectonic definition, have been well established in electrophysiological studies. Accordingly, the lateral bank of the IPS was subdivided into a caudal (LIP), a rostral (anterior intraparietal, AIP), and a ventral (ventral intraparietal, VIP) area, according to Blatt and others (1990), Murata and others (2000), and Colby and others (1993), respectively. The SPL and the posterior cingulate cortex were subdivided as in Matelli and others (1998) (see also Marconi and others 2001) where functional areas V6A (Galletti and others 1999) and medial intraparietal (MIP) (Colby and others 1988; Colby and Duhamel 1991) were included in the map of Pandya and Seltzer (1982). Area V6A was Figure 1. Dissection procedures of the reconstructed hemispheres to expose sulcal banks. In each panel, nonstandard views of an intact right hemisphere show in darker gray the brain sectors removed to expose the medial and the lateral banks of the intraparietal sulcus, the posterior bank of the arcuate sulcus, and the upper and lower banks of the lateral fissure and of the superior temporal sulcus. In each dissected view of the hemisphere, the exposed bank is shown in darker gray. The upper bank of the lateral fissure is shown in a bottom view of the dissected hemisphere, where arrowed lines mark the level of the rostral end of the intraparietal sulcus and the rostralmost level of the central sulcus. AI = inferior arcuate sulcus; AS = superior arcuate sulcus; C = central sulcus; Cg = cingulate sulcus; IP = intraparietal sulcus; LF = lateral fissure; Lu = lunate sulcus; P = principal sulcus; ST = superior temporal sulcus. Cerebral Cortex October 2006, V 16 N

4 Rozzi subdivided into a dorsal (V6Ad) and a ventral (V6Av) sector according to Luppino and others (2005). For the parietal operculum the functional maps of the SII region and neighboring areas of Robinson and Burton (1980a, 1980b) and Krubitzer and others (1995) were considered, although these areas could not be precisely distinguished one from another. In cases of uncertain functional correspondence, labeling was attributed according to the architectonic maps of Pandya and Seltzer (1982) and Lewis and Van Essen (2000a). Temporal areas of the STS and inferior temporal gyrus were defined according to Boussaoud and others (1990) and Saleem and Tanaka (1996). In the frontal lobe, agranular frontal and cingulate areas were cytoarchitectonically defined according to Matelli and others (1985, 1991) and Geyer and others (2000). The prefrontal cortex was subdivided according to the cytoarchitectonic map of Walker (1940) and the prearcuate cortex also according to Stanton and others (1989) and Petrides and Pandya (2002). Quantitative Analysis and Laminar Distribution of the Labeling To obtain more objective information on the relative strength of the connections observed within the same case or across different cases, for each cortical injection, but those of BDA (because of the paucity of retrograde labeling observed with this tracer), we counted the number of labeled neurons plotted in the ipsilateral hemisphere in one section every 600 lm and located beyond the limits of the injected field. Because the absolute number of labeled neurons was largely variable across cases, mainly because of differences in amount, spread, and sensitivity of injected tracers, afferents to the injected field were expressed in terms of percent of labeled neurons found in a given cortical area or sector, with respect to the total number of labeled neurons. The percent distribution of the retrograde labeling observed for each area was then used for guiding the qualitative description of its connections. In this analysis, some sectors (e.g., parietal operculum) in which labeling extended across adjacent areas, which could not be precisely defined, were considered as a whole. To obtain information on possible hierarchical relationships of the observed cortical connections, labeling attributed to a given area and reliably observed across different sections and cases, was analyzed in each section every 300 lm, in terms of laminar distribution of the anterogradely labeled terminals and in terms of percent of labeled neurons located in the superficial (I--III) versus deep (V--VI) layers. These data were then analyzed according to the criteria reviewed by Felleman and Van Essen (1991) (see also Andersen and others 1990). Based on the laminar distribution of labeled terminals, projections were classified as feedforward when mostly concentrated in layer IV and lower III, feedback when distributed in superficial and deep layers, but avoiding layer IV, lateral when fairly even distributed in all cortical layers, and mixed when patches of feedforward projections were found together with patches of feedback projections. Based on the laminar distribution of labeled neurons, connections were classified as feedforward or feedback when labeled neurons in the superficial layers were >70% or <30%, respectively. More equal distributions were classified as bilaminar. This last pattern has been generally used to infer that 2 given areas are located at the same hierarchical level. However, as noted by Felleman and Van Essen (1991) (see also Andersen and others 1990; Boussaoud and others 1990; Lewis and Van Essen 2000b), bilaminar connections, at least at the level of parietal and temporal areas, can be compatible with different types of hierarchical relationship, according to the disposition of the anterograde labeling. Because most of the connections observed in the present study, as already noticed by Andersen and others (1990) and Lewis and Van Essen (2000b) in their connectional studies of different parietal areas, showed a bilaminar projection pattern, where not otherwise specified, possible hierarchical relationships as suggested by Felleman and Van Essen (1991) and following Andersen and others (1990) were established on the basis of the laminar distribution of labeled terminals (data available for Opt, PG, and PFG). In the agranular frontal and cingulate areas, the lack of layer IV forced us to modify these criteria and connections characterized by retrograde labeling mostly in layers III and VI, and anterograde terminals mostly in layers III and V were considered as feedforward connections. In some cases, connections were characterized by retrograde labeling mostly in layers III and VI, and terminal labeling was densest in layers I and II and very weak in layer VI. This pattern only partially fits with the criteria used for the definition of feedback connections and was left undefined. Photographic Presentation Photomicrographs shown in the present study were obtained by capturing images directly from the sections with a digital camera attached to the macroscope or to the microscope. Individual images were then imported in Adobe Photoshop in which they could be processed, eventually assembled into digital montages, and reduced to the final enlargement. In most of the cases, image processing required lighting, contrast, brightness, and contrast adjustments. Results Cytoarchitecture of the IPL Convexity and Location of Injection Sites The cytoarchitectonic analysis of the IPL convexity showed, in substantial agreement with Pandya and Seltzer (1982), that in this cortical sector 4 different fields can be defined and located at different rostrocaudal levels. Following the nomenclature of Pandya and Seltzer (1982) these fields will be here referred, from rostral to caudal, to as PF, PFG, PG and Opt. The major cytoarchitectonic criteria used in defining these fields are illustrated in Figure 2, in low-power photomicrographs of 4 Nisslstained coronal sections taken at different rostrocaudal levels from Case 10 and in Figure 3 (upper part) in higher magnification views of representative fields from the same sections. In PF, a radial pattern is recognizable in lower layer III as well as in layers V and VI. Cells in layer III display a size gradient with medium-sized pyramids spread in its lower half. Layer IV is homogeneous and lacks a sharp upper border with layer III. Layer V is relatively poor and thin, with rather small pyramids, and layer VI is broad and subdivided into 2 sublayers. In PFG a columnar organization is evident only in layer III. In this layer, medium-sized pyramids are mainly concentrated in its lowest part. A well-developed layer V is evident, even in lowpower views. This layer is populated mainly not only by medium-sized pyramids but also by scattered larger pyramids, which represent a major distinctive feature of PFG, compared with PF and PG. Layer VI is rather uniform. In PG, the overall cellular density in layer III appears higher, compared with the more rostral areas. This layer is mainly formed by small pyramids, and the almost complete absence of larger cells gives it a rather uniform appearance. Layer V is well developed and populated by densely packed small pyramids. Layer VI is relatively homogeneous. Opt displays a clear, broad columnar pattern particularly evident in layer III. A size gradient is present in layer III with many medium-sized pyramids occupying its lowest part. Layer IV is sharply defined, and it is denser than in PG. Cell size is also increased in layer V, compared with that of PG, with many medium-sized pyramids. Layer VI has a clear border with layer V and can be subdivided into 2 sublayers. All these fields enter medially in the IPS for about 2 mm, whereas laterally PF, PFG, and PG border with opercular areas extending in the dorsal bank of the LF (PFop and PGop of Pandya and Seltzer 1982). In general, architectonic features were found to change gradually from one field to another, in the range of less than 1 mm. For this reason, cytoarchitectonic borders presented in this study represent the intermediate point of the transitions and were found to run roughly in the coronal stereotaxical plane, slightly obliquely in caudoventral direction. d 1392 Connections of the Macaque IPL and others

5 Figure 2. Low-power photomicrographs of 4 Nissl-stained coronal sections from Case 10 through cytoarchitectonic fields PF (A), PFG (B), PG (C), and Opt (D). Dorsal is up and lateral on the right. Arrows mark cytoarchitectonic borders. The level at which the sections were taken and the location of the photomicrographs is shown in the lower part of the figure. Scale bar (shown in A) = 500 lm. The average location along the IPL convexity of the identified cytoarchitectonic fields was quantitatively estimated in 13 hemispheres of M. nemestrina and 8 hemispheres of M. fascicularis. Cytoarchitectonic borders, set as the intermediate points of the transitional zones, were measured in terms of antero-posterior stereotaxic coordinates (AP), according to the M. nemestrina atlas of Winters and others (1969) (AP values referred to the interaural line), and to the M. fascicularis atlas of BrainInfo (2000) (AP values referred to the anterior commissural line, AC). Average cytoarchitectonic maps, shown in Figure 3 (lower part) were, then, generated separately for the 2 species by plotting the average AP values on a dorsolateral view of a standardized hemisphere. To provide an estimate of the interindividual variability across hemispheres of the same species, standard Cerebral Cortex October 2006, V 16 N

6 Rozzi Figure 3. Upper part: Higher magnification views of representative fields of cytoarchitectonic fields PF, PFG, PG, and Opt taken from the sections shown in Figure 2. Scale bar (shown in PF) = 300 lm. Lower part: cytoarchitectonic map of the macaque IPL convexity plotted onto an enlarged dorsolateral view of a standard hemisphere of a Macaca nemestrina (left) and of a Macaca fascicularis (right), showing AP stereotactic coordinates according to the atlases of Winters and others (1969; M. nemestrina) and of BrainInfo (2000; M. fascicularis). Dashed lines mark the averaged location of cytoarchitectonic borders. Numbers inside the map indicate the standard deviations of the AP values of the cytoarchitectonic borders in correspondence of the shoulder of the intraparietal sulcus and of the opercular cortex. Abbreviations as in the caption of Figure 1. deviation values of the mean AP position of the borders at the level of the lateral crown of the IPS and at the level of the border with the opercular areas are also shown in the maps. The result of this analysis showed that the location of these fields was quite constant across different cases and similar to that shown by Pandya and Seltzer (1982). In selecting the location of the injection sites our aim was not only to involve different parts of each IPL field but also the more Figure 4. Location of representative injection sites. The location of each tracer injection is shown on a dorsolateral view of the hemisphere and in drawings of 3 representative coronal sections taken through the core (shown in darker gray) and through the caudal and rostral part of the halo (shown in lighter gray). For the sake of comparison, all the reconstructions in this and in the subsequent figures are shown as a right hemisphere. Abbreviations as in the caption of Figure 1. d 1394 Connections of the Macaque IPL and others

7 Cerebral Cortex October 2006, V 16 N

8 Rozzi peripheral transitional zones to avoid spread of tracers across different fields. All the injection sites considered for this study (most of them shown in Fig. 4, in drawings of representative sections through the core and the rostral and caudal part of the halo) were restricted to a single architectonic field, only in few cases marginally involving transitional zones. For this reason, the patterns of connections described in this study mostly concern much more the core of each field rather than the transitional zones. Given the relatively low interindividual variability in the location of cytoarchitectonic borders, only in 1 case a WGA-HRP injection in Case 27 was found to be not restricted to a single field, involving both PG and PFG. The labeling distribution observed of in this case was fully compatible with an almost equal involvement of both these fields and, therefore, not considered in this study. At least 3 tracer injections were placed in each field, which yielded consistent distributions and patterns of labeling across different cases and animals, the main differences lying in the overall number of marked neurons, depending on the injected tracer. Furthermore, quantitative analysis showed similar percent distributions of the labeling. Injections of retrograde-- anterograde tracers in all fields, but PF, showed that all neocortical connections of Opt, PG, and PFG were reciprocal. For this reason, the general pattern of connectivity of each field will be mainly described on the basis of the distribution of the retrograde labeling, whereas the anterograde labeling will be mainly considered in terms of laminar distribution in the various connected areas. Connections of Area Opt Three tracer injections were placed in Opt in 2 different monkeys (Case 23 WGA-HRP and Case 27 DY and TB). Figure 5A shows the location of the WGA-HRP injection site in Case 23 placed in the mid-rostral part of this field (see also Fig. 4). The adjacent Nissl-stained section in Figure 5A1 shows architectural features, for example, columnar organization, evident size gradient in layer III and dense layer V, populated by mediumsized pyramids, typical of Opt. In Case 27, the DY and TB injections were relatively close to each other, with the TB one located slightly more dorsal and caudal to the DY injection. The distribution of DY and TB labeling largely overlapped, without any clear topographic organization. The general distribution of the retrograde labeling observed in Cases 23 and 27 DY and TB and drawings of representative coronal sections from Case 23 are presented in Figures 6 and 7, respectively. The percent distribution of the labeled neurons observed in Cases 23 and 27 DY, as well as the mean values of all the 3 Opt injections, are shown in Table 2. Representative patterns of the laminar distribution of retrograde and anterograde labeling observed in Case 23 are illustrated in Figure 8. Parietal and Posterior Cingulate Cortices In the IPL very strong lateral connections of Opt were observed with PG (Figs. 6, 7, section f, and 8, PG), whereas PFG was only very marginally labeled. Weak, lateral connections were observed in the parietal operculum, only with its outermost and caudalmost part, corresponding to area PGop of Pandya and Seltzer (1982). Caudal to Opt, moderate feedback connections were observed with the dorsal aspect of the prelunate gyrys (area DP, Andersen and others 1990). In the lateral bank of the IPS, numerous and dense patches of marked cells were observed in its caudal part in both the dorsal (LIPd) and the ventral (LIPv) subdivisions of area LIP (Blatt and others 1990). In this area, the anterograde labeling showed a feedback pattern, and retrograde labeling in layers I--III was >70% (Fig. 8, LIP). In the SPL, connections were limited to the mesial surface of the hemisphere and to the anterior wall of the parietooccipital sulcus (Fig. 6). In particular, these very strong connections extensively involved, with some variability in the relative distribution across cases, area PGm (Fig. 7, sections b--e), extending caudally in V6Av (Luppino and others 2005; Fig. 7, section a) and rostrally, in the caudal part of the cingulate gyrus (posterior cingulate cortex, CGp; Olson and others 1996). In all these areas the anterograde labeling showed a feedback pattern, and in PGm the labeled neurons in layers I--III were >70% (Fig. 8, PGm). Some labeling was also found more rostrally, in areas 23a and 23b. Temporal Cortex, Including Area MST and Insula Opt was connected with different STS and inferotemporal areas. In the caudal part of the STS (Fig. 6) very strong feedback connections (retrograde labeling in layers I--III >70%) were found in area MST (Figs. 7, section e, and 8, MST), mostly in its dorsal and caudal part (presumably dorsal MST, MSTd; Komatsu and Wurtz 1988). Weak labeling was observed in the middle temporal area (MT) (Fig. 7, sections d and e) and very sparse labeled cells in the fundal superior temporal area (FST). In the upper bank of the STS robust, lateral, or mixed connections (Fig. 8, superior temporal polysensory area, STP) were observed in restricted sectors lateral and rostral to MST, attributable to both the posterior (STPp; Fig. 7, section e) and anterior (STPa; Fig. 7, sections h, i, and n) subdivisions of the superior temporal polysensory area, respectively. Ventral to STPa, feedforward connections were observed with the fundal region of the sulcus (area IPa; Fig. 7, section l; Fig. 8, IPa), extending also in the ventral bank, in the medial part of area TE (TEm) (Fig. 7, sections m and n). Additional labeling in the inferotemporal cortex, showing a lateral pattern, was observed in the postero-ventral part of area TE (TEpv) (Figs. 6 and 7, sections g and h), on the lateral lip and the fundus of the occipitotemporal sulcus. With the only exception of a small cluster of marked neurons observed in the postero-dorsal part of area TE (TEpd) in Case 27 (Fig. 6), in both Cases 23 and 27, labeling in TEm and TEpv was observed in very similar locations, suggesting that Opt is target of specific subsectors of these inferotemporal areas. Spots of labeling were also observed at different rostrocaudal levels in the parahippocampal area TF, and few scattered marked neurons were located in the perirhinal cortex (Figs. 6 and 7, sections g, i, l, and m). In Case 23, some purely anterograde labeling was found in the caudal part of the presubiculum. Very poor labeling was inconstantly located in the granular insula (Fig. 7, sections l and n). Agranular Frontal and Cingulate Cortices Two agranular frontal sectors, located in the dorsal premotor cortex (PMd) and ventral premotor cortex (PMv), respectively, showed relatively weak connections with Opt (Fig. 6). In PMd (Fig. 7, section o), labeling was consistently observed in the lateral part of the rostral PMd area F7, not including the supplementary eye field (F7 non-sef [Luppino and others 2003]). In this premotor sector, anterograde labeling was very weak in deep layers, and much denser in layers I and II (Fig. 8, F7). In PMv (Fig. 7, section p), labeling, with some variability across cases, was found in the rostral area F5, in a relatively d 1396 Connections of the Macaque IPL and others

9 Figure 5. Low-power photomicrographs of pairs of adjacent coronal sections showing, in the left column, representative injection sites in Opt (A, Case 23, WGA-HRP), PG (B, Case 20, WGA-HRP), PFG (C, Case 13, WGA-HRP), and PF (D, Case 29, DY). In the right column, higher magnification views from the adjacent Nissl-stained sections show the general cytoarchitectonic features of the injected areas. Calibration bars: in A--D = 1 mm; in A1--D1 = 500 lm. Abbreviations as in the caption of Figure 1. rostral part of the posterior bank of the arcuate sulcus, the anterograde labeling being mostly focused in layer III ( feedforward pattern). In the agranular cingulate cortex, sparse labeling was observed in area 24b. Prefrontal Cortex Several relatively weakly labeled sectors were observed in the prefrontal cortex (Figs. 6 and 7, sections p--r). In both Cases 23 and 27, some labeling was located relatively Cerebral Cortex October 2006, V 16 N

10 Rozzi Figure 6. Distribution and areal attribution of retrogradely labeled neurons observed following injections in area Opt in Cases 23 (WGA-HRP) and 27 (DY and TB) shown in dorsolateral, mesial, and bottom (Case 23 only) views of the injected hemispheres and in 3D views of the lateral bank of the IPS of the upper and lower bank of the STS and of the postarcuate cortex. The core of the WGA-HRP, DY, and TB injection sites is shown in black, green, and red, respectively, surrounded by a gray region corresponding to the halo. In Case 27, DY- and TB-labeled neurons are shown in green and red, respectively. Each dot corresponds to one labeled neuron. Dashed lines mark borders between IPL convexity or agranular frontal areas. AMT = anterior middle temporal sulcus; IO = inferior orbital sulcus; OT = occipitotemporal sulcus; R = rhinal fissure. Other abbreviations as in the caption of Figure 1. caudally in the principal sulcus, mostly in the ventral bank and much weaker labeling was found on the mesial surface of the hemisphere, in medial area 8B. Some labeling was also found in the ventral prearcuate cortex, in area 45 ventral to the frontal eye field (FEF), as defined cytoarchitectonically in adjacent Nissl-stained sections (area 45b of Petrides and Pandya 2002). Part of the labeling was also observed on the dorsal lip of the principal sulcus (dorsal area 46) and in the dorsalmost part of area 8A. Finally, a very weak connection was also observed with the orbitofrontal area 12o (Fig. 6). All d 1398 Connections of the Macaque IPL and others

11 Figure 7. Drawings of representative coronal sections from Case 23, in caudal to rostral order (a--r), showing the distribution and areal attribution of retrogradely labeled neurons observed following WGA-HRP injection in area Opt. The levels at which the sections were taken are indicated in the dorsolateral view of the injected hemisphere shown in the upper left part of the figure. PMT = posterior middle temporal sulcus. Conventions and other abbreviations as in the captions of Figures 1 and 4. prefrontal connections of area Opt showed a feedforward pattern (Fig. 8, 45). Connections of Area PG Five tracer injections in 3 animals (Case 20, WGA-HRP; Case 27, CTB-A 594; Case 29, TB and CTB-A 488; Case 29, BDA) were placed in different parts of area PG. Figure 5B shows the location of the WGA-HRP injection in Case 20, placed in the middle of the inferior parietal gyrus (see also Fig. 4), in a sector where cytoarchitectonic features typical of area PG, for example, a layer III quite homogeneous in cell size and density, a layer V densely populated by relatively small pyramids, could be observed in the adjacent Nissl-stained section (Fig. 5B1). The general distribution of retrograde labeling observed in Cases 20 (WGA-HRP) and 27 (CTB-A 594) and drawings of representative coronal sections from Case 20 are presented in Cerebral Cortex October 2006, V 16 N

12 Rozzi Table 2 Percent distribution (%) and total number (n) of labeled neurons observed following representative tracer injections and mean percent distribution (in bold) of all cases of retrograde tracer injections in Opt, PG, PFG, and PF Injected area Opt (%) PG (%) PFG (%) PF (%) Case C23 C27DY Mean (all cases) C20 C27CTB-A594 Mean (all cases) C13 C29FB Mean (all cases) C27FB C29DY Mean (all cases) IPL PF * 0.7 * / / / PFG * * * / / / PG / / / * VIP 0.5 * * AIP * * Parietal operculum Opt / / / LIP * * MST * * Total IPL SPL PEa 0.8 * * PE * * * * * * * * PEc * * * * MIP * * * * * * PEci * * * * V6Ad * V6Av * * PGm * * Total SPL Area 2 * * * Total parietal Temporal STP * * C, Tpt * * * * * IPa, TE * * * * Pr/PH * * * * * FST * 0.6 * * 0.5 * * Total temporal * * AFG, ACC F4 * * * F F2 * * * * * * * F * * * * * 24d 1.0 * 0.65 * * * Others * * * * * * Total AFG þ ACC Prefrontal 46d, * * 1.0 * * 46v, 45b, 12o Total prefrontal Others MT, DP * 0.60 * * * CGp, * 1.05 Insula 0.5 * * a þ b * * * * * * PrCO * * * 0.6 * Total n Note: / 5 injected area; 5 no labeling; * 5 labeling \0.5%; AFC 5 agranular frontal cortex; ACC 5 agranular cingulate cortex. Figures 9 and 10, respectively. The percent distribution of the labeled neurons observed in these 2 cases, as well the mean values of all the PG injections, but the BDA one, is shown in Table 2. Representative patterns of laminar distribution of retrograde and anterograde labeling observed in Cases 29, BDA, and 20 are illustrated in Figure 11. Parietal and Posterior Cingulate Cortices In the IPL, strong lateral connections were observed with areas PFG, PGop, and the rostral part of area Opt (Figs. 9, 10, sections d--g, and 11, Opt). A few marked neurons were also found in area PF and in area DP. In the parietal operculum, in addition to PGop, very strong connections showing a feedback pattern were observed with the retroinsular cortex, but also more rostrally and deeply, with area SII (Figs. 9, 10, sections f--h, and 11, SII). A more rostral, minor labeling can be attributed to area PV. In the lateral bank of the IPS, moderate lateral connections were observed with the mid-rostral part of it, mostly involving area AIP and, at a very minor extent, area VIP (Figs. 9 and 10, sections f--h). Area LIP, which was heavily connected with Opt, was virtually devoid of marked neurons. Moderate to rich connections showing a lateral pattern (Fig. 11, PEci) were observed in different areas of the caudal part of the SPL, with some variability in their relative distribution across cases. These connections involved the caudal part of the ventral bank of the cingulate sulcus (area PEci), area V6Ad (Figs. 9 and 10, sections a and b) and area PEc. Area PGm and the CGp were virtually devoid of labeling. Dense patches of lateral connections (Fig. 11, MIP) were also observed in the medial bank of the IPS, where, although with some variability across cases, most of them were observed in the mid-caudal part of it, attributable mostly to area MIP. In the cingulate area 23, rich lateral d 1400 Connections of the Macaque IPL and others

13 Figure 8. Upper part: camera lucida drawings of representative examples of laminar distribution of retrograde and anterograde labeling observed following WGA-HRP injection in Opt in Case 23 taken from the areas indicated in each panel. The anterograde labeling is shown in gray, and retrogradely labeled neurons are shown in black. Dashed lines mark borders between cortical layers. Calibration bar (below TEpv) = 500 lm (applies to all drawings). Lower part: photomicrographs from Case 23 showing examples of WGA-HRP labeling observed in areas LIP, PGm, and TEpv. Calibration bar (shown in LIP) = 500 lm (applies to all photomicrographs). connections (Fig. 11, 23c) were observed with the ventral bank of the cingulate sulcus (area 23c) and the dorsal part of the cingulate gyrus (area 23b). Temporal Cortex, Including Area MST and Insula Very rich labeling was observed in MST (Figs. 9 and 10, sections d and e), which extended also more rostrally (and deeply) with respect to Opt injections, possibly involving also the lateral part of MST (MSTl, Komatsu and Wurtz 1988). Dense, but restricted labeling was also found at different rostrocaudal levels of area STP attributable to both STPp and STPa (Figs. 9 and 10, sections f, i, and o). In particular, the labeling in STPa shown in Figure 10, section i, appears to occupy a location similar to the labeling observed following injections in Opt. In both MST and STP the anterograde labeling showed a feedback pattern (Fig. 11, MST and STP). Very weak feedforward connections (more evident following BDA injection) were also observed in area IPa (Figs. 10, section m, and 11, IPa). Very sparse labeling was observed in area MT (Fig. 10, section c) and in perirhinal and parahippocampal cortices (Fig. 10, section l). In 2 cases (Case Cerebral Cortex October 2006, V 16 N

14 Rozzi Figure 9. Distribution and areal attribution of retrogradely labeled neurons observed following injections in area PG in Cases 20 (WGA-HRP) and 27 (CTB-A594) shown in dorsolateral and mesial views of the injected hemispheres and in 3D views of the medial and lateral banks of the IPS of the upper and lower banks of the STS and lateral fissure and of the postarcuate cortex. Conventions and abbreviations as in the captions of Figures 1 and 6. d 1402 Connections of the Macaque IPL and others

15 Figure 10. Drawings of representative coronal sections from Case 20, in caudal to rostral order (a--q), showing the distribution and areal attribution of retrogradely labeled neurons observed following WGA-HRP injection in area PG. Ca = calcarine sulcus; OI = inferior occipital sulcus. Conventions and other abbreviations as in the captions of Figures 1, 6, and BDA and 29 TB), some labeling was observed in area TEav, close to the anterior medial temporal sulcus. In Case 29 BDA, labeled terminals were also observed in the caudal part of the presubiculum. One additional and distinctive relatively strong connection of PG, showing a feedback pattern (retrograde labeling in layers I--III >70%), was located caudally, in the ventral bank of the LF, extending also on the adjacent part of the superior temporal gyrus (Figs. 9, 10, sections f and g, and 11, C), involving areas C of Morel and others (1993) and Tpt of Pandya and Sanides (1973; see also Lewis and Van Essen 2000a). Rich feedforward connections (retrograde labeling in layers I--III <70%) were also observed in insular area Ig (Figs. 9 and 10, section l). Agranular Frontal and Cingulate Cortices Minor connections were observed with several agranular frontal areas. In PMv, clusters of marked cells, with labeled terminals densest in layer III ( feedforward pattern; Fig. 11, F5), were Cerebral Cortex October 2006, V 16 N

16 Rozzi Figure 11. Upper part: camera lucida drawings of representative examples of laminar distribution of retrograde and anterograde labeling observed following BDA injection in Case 29. Conventions as in Figure 8. Calibration bar (below SII) = 500 lm (applies to all drawings). Lower part: photomicrographs from Case 29 BDA and 20 WGA-HRP showing examples of labeling observed in areas IPa and F2vr (Case 29) and in areas PEci and STP (Case 20). Calibration bar (shown in IPa) = 500 lm (applies to all photomicrographs). located along the entire extent of the posterior bank of the inferior arcuate sulcus (area F5; Figs. 9 and 10, sections n and o). In PMd, labeling was consistently observed in the ventrorostral part of area F2 (F2vr; Luppino and others 2003), close to the spur of the arcuate sulcus (Figs. 9 and 10, sections m--o), and additional, sparse labeling was located in area F6/pre-supplementary motor area (pre-sma) (Fig. 9). Finally, clusters of labeled cells were also found in the cingulate motor area 24d (Fig. 10, section n), mainly in the ventral bank of the cingulate sulcus and in area 24b (Fig. 9). In F2vr, F6 and area 24, labeled terminals were mostly confined to layers I and II (Fig. 11, F2vr). Prefrontal Cortex The only prefrontal sector consistently labeled following PG injections was the ventral part of area 46 (Figs. 9 and 10, sections p and q). In particular, lateral connections (Fig. 11, 46v) were found mostly in the ventral bank of the principal sulcus, partially overlapping with the sector connected with d 1404 Connections of the Macaque IPL and others

17 Opt, but also extending more dorsally to include the ventral lip of the sulcus and the adjacent cortical convexity. Connections of Area PFG Five tracer injections were placed in 4 animals in different parts of area PFG (Case 13, WGA-HRP; Case 14, BDA; Case 27, CTB-A 488; Case 29, FB and CTB-A555). Figure 5C shows the location of the WGA-HRP injection site in Case 13, placed in the mid-ventral part of the inferior parietal gyrus (see also Fig. 4), where cytoarchitectonic features typical of area PFG, for example, medium-sized pyramids in the lowest part of layer III and a welldeveloped layer V, with occasional relatively large pyramids, could be observed in the adjacent Nissl-stained section (Fig. 5C1). The distribution of the retrograde labeling observed in Cases 13, WGA-HRP, and 29, FB (shown in light blue), is illustrated in Figure 12. The percent distribution of the labeled neurons observed in these 2 cases, as well as the mean values of all the PFG injections, but the BDA one, is shown in Table 2. Threedimensional reconstructions of Case 29 in Figure 12 also show in red the distribution of the neurons marked following TB injection in PG to provide direct comparison between the differential patterns of cortical connectivity of PFG and PG found in the present study. Drawings of representative coronal sections from Case 13 are presented in Figure 13, and representative patterns of the laminar distribution of retrograde and anterograde labeling observed in Cases 14, BDA, and 13 are illustrated in Figure 14. Parietal and Posterior Cingulate Cortices Following PFG injections, the labeled territory extended to the adjacent caudal and rostral areas PG and PF, respectively (Figs. 12 and 13, sections b, c, and f). The strong, lateral connections between PFG and PG (Fig. 14, PG) were very evident in Case 29, where retrograde tracers were injected in both these areas (Fig. 12). In the parietal operculum, similarly to PG, very dense labeling ( lateral connections) was found more caudally in correspondence of PGop (Fig. 13, sections c and d) and retroinsular cortex, and more rostrally ( feedback connection; Fig. 14, SII) in correspondence of SII (Fig. 12, sections e--h) and PV. In the lateral bank of IPS, strong lateral connections were observed in areas AIP and VIP (Figs. 12, 13, sections d--g, and 14, VIP). The dense labeling in VIP extended also in the rostral part of the medial bank of the IPS, in the rostral part of area PEa, rostral to MIP, corresponding to the medial IPS sector source of corticospinal projections (area PEip of Matelli and others 1998; Figs. 12, 13, sections d, e, and h, and 14, PEa). In contrast, in areas MIP and V6Ad, source of rich afferents to PG (Fig. 12, Case 29, TB, red labeling) marked neurons were poor. Weak connections ( lateral pattern) were observed with areas PEci and 23. Temporal Cortex, Including Area MST and Insula Feedback connections (retrograde labeling in layers I--III >70%), weaker than those observed following PG injections, were observed in area MST in all cases of injections in PFG (Figs. 12, 13, section b, and 14, MST). In STP restricted but relatively robust labeling showing a mixed type of connections (Fig. 14, STP) was found in both STPp and STPa (Figs. 12 and 13, sections c, g, and h). In particular, the labeled STPa sector in Figure 13, section g, appeared to largely overlap with the STPa sector connected with PG and Opt. In the ventral bank of the STS, in addition to few marked neurons found in area MT (Fig. 13, section a), some labeling was also located in area FST (Fig. 13, section d). More rostrally, some clusters of marked neurons were consistently observed, in all cases, in areas IPa and TEm, where labeled terminals showed a feedforward pattern (Figs. 12, 13, sections e and f, and 14, TEm). Robust feedforward connections (retrograde labeling in layers I--III <70%) were observed in the insular area Ig. Agranular Frontal and Cingulate Cortices Connections of PFG with the agranular frontal cortex were rich and by far densest in PMv. (Figs. 12 and 13, sections i--m). In F4, which is virtually not connected with PG, relatively weak labeling was almost completely confined to the dorsal part of it, whereas in F5 a rich labeling involved the whole posterior bank of the arcuate sulcus, extending also on the cortical convexity. Labeled terminals in both these areas tended to be relatively evenly distributed across all layers ( lateral connections, Fig. 14, F5). Weak labeling (with high degree of variability among cases) was observed, especially in Case 14, BDA, in F2vr, where terminals were mostly concentrated in the superficial layers (Fig. 14, F2vr) and even sparser labeling could also be observed in F6/pre-SMA, F3 and F1. In area 24 labeling showing a lateral pattern was observed in areas 24d and 24b. Prefrontal Cortex Substantial connections, with some variability across cases, were observed with ventral area 46 in a location similar to that labeled following injections in PG (Figs. 12 and 13, sections o and p). Additional and distinctive connections of area PFG, with respect to PG (although with some variability in their strength among cases), were observed in the caudal and lateral part of the orbitofrontal cortex (area 12o of Carmichael and Price 1994) and in the disgranular, precentral opercular area (PrCO) ventral to F5. All these connections could be classified as lateral (Fig. 14, 46v). Corticospinal Projections from the IPL Convexity Figure 15 shows the distribution of the labeled corticospinal neurons observed in the hemispheres of Cases 10 and 21 contralateral to large HRP injections in the lateral funiculus of the spinal cord at upper cervical levels. Considering the size and the level of the injections, the distribution of labeled neurons can be considered, in both cases, quite representative of the origin of projections to all spinal levels caudal to C4--C5. In the IPL convexity a cortical sector, very well corresponding to area PFG, was found to be a source of corticospinal projections. These projections represent a distinctive connectional feature of this area with respect to the other IPL convexity areas. In Case 10, DY was also injected in the same lateral funiculus at the upper thoracic level to identify the origin of projections to the thoracic and lumbar spinal levels. The results (not shown in the figure) showed that DY-labeled neurons were virtually absent in PFG, thus suggesting that this area is a source of corticospinal projections mostly directed to the cervical levels of the spinal cord. Connections of Area PF Three tracer injections were placed in area PF in 3 different monkeys (Case 13 CTB-g, Case 27 FB, and Case 29 DY), which produced remarkably similar distributions of retrograde labeling. Figure 5D shows the location of the DY injection site in Case 29, placed in the middle of the inferior parietal gyrus (see Cerebral Cortex October 2006, V 16 N

18 Rozzi Figure 12. Distribution and areal attribution of retrogradely labeled neurons observed following injections in area PFG in Cases 13 (WGA-HRP) and 29 (FB) shown in dorsolateral and mesial views of the injected hemispheres and in 3D views of the postarcuate cortex of the upper and lower bank of the STS, of the medial and lateral banks of the IPS, and of the upper bank of the lateral fissure. Reconstructions from Case 29 also show the distribution of the labeled neurons observed following TB injection in area PG. The core of the WGA- HRP, FB, and TB injection sites is shown in black, light blue, and red, respectively, surrounded by a gray region corresponding to the halo. In Case 29, FB- and TB-labeled neurons are shown in light blue and red, respectively. Abbreviations and other conventions as in the captions of Figures 1 and 6. d 1406 Connections of the Macaque IPL and others

19 Figure 13. Drawings of representative coronal sections from Case 13, in caudal to rostral order (a--p), showing the distribution and areal attribution of retrogradely labeled neurons observed following WGA-HRP injection in area PFG. Conventions and abbreviations as in the captions of Figures 1 6 and 7. also Fig. 4), in a cortical sector showing a dense layer III with medium-sized pyramids in the lower half, a well-developed layer IV, and a relatively poor layer V (area PF, Fig. 5D1). Figure 16 shows the results observed in Case 29 DY in 3D reconstructions of the injected hemisphere and in drawings of representative coronal sections. The percent distribution of the labeled neurons observed in Case 29 DY and 27 FB, as well as the mean values of all the PF injections, is shown in Table 2. In general, PF displayed connections with a much more limited set of cortical areas, with respect to the other IPL convexity fields, virtually all confined to the parietal and frontal cortices. Parietal Cortex The major feature of the cortical connections of PF was the very strong connection with the postcentral gyrys (Fig. 16, dorsolateral view and sections d and e). In this sector, retrograde labeling was very dense and almost completely confined to area 2, in its ventral part. In the IPL convexity, the connections with area PFG were very strong, extending also more caudally to involve, at a minor extent, area PG (Fig. 16, dorsolateral view and sections a and b). In the parietal operculum (Fig. 16, upper bank of the LF and sections d--f), very dense labeling was found in the SII region, with substantial labeling involving, presumably, also Cerebral Cortex October 2006, V 16 N

20 Rozzi Figure 14. Left: camera lucida drawings of representative examples of laminar distribution of retrograde and anterograde labeling observed following BDA injection in PFG in Case 14. Conventions as in Figure 8. Calibration bar (shown below MST) = 500 lm (applies to all drawings). Right: photomicrographs from Case 13 showing examples of WGA-HRP labeling observed in areas VIP and STP. Calibration bar (shown in VIP) = 500 lm (applies to both photomicrographs). Figure 15. Distribution of retrogradely labeled corticospinal neurons observed following HRP injections in the lateral funiculus of the spinal cord at upper cervical levels shown in dorsolateral views of the hemispheres of Cases 10 and 21 contralateral to the injections. Conventions and abbreviations as in the captions of Figures 1 and 6. area PV. In the IPS, connections were quite strong with areas AIP and VIP (Fig. 16, sections a--c) but weak with rostral PEa. Weak labeling was observed in the insular cortex (Fig. 16, section f). Frontal Cortex In the agranular frontal cortex the labeling was quite dense in both PMv areas F4 and F5. In F4, labeling was densest in the dorsal part of this area, close to the spur of the arcuate sulcus d 1408 Connections of the Macaque IPL and others

21 Figure 16. Upper part: distribution and areal attribution of retrogradely labeled neurons observed following injections in area PF in Case 29 (DY) shown in a dorsolateral view of the injected hemispheres and in 3D views of the postarcuate cortex and of the upper bank of the lateral fissure. Lower part: drawings of representative coronal sections from the same case, in caudal to rostral order (a--m), showing the distribution and areal attribution of retrogradely labeled neurons. Conventions and abbreviations as in the captions of Figures 1, 6, and 7. (Fig. 16, dorsolateral view and sections f and g). In F5 (Fig. 16, postarcuate cortex and sections f--i), it included the whole extent of the posterior bank of the inferior arcuate sulcus and the cortical convexity, where labeled neurons appeared to extend also more ventrally with respect to those observed following injections in PFG. Relatively weak labeling was also found ventral to F5 in area PrCO and in ventral area 46 (Fig. 16, dorsolateral view and section m). In all cortical areas, but the granular insula, the distribution of the retrograde labeling was bilaminar. In the granular insula, marked cells showed a feedback pattern. Discussion In this study we traced the cortical connections of the 4 architectonic fields PF, PFG, PG, and Opt forming the macaque IPL cortical convexity by placing tracer injections aimed to involve different parts of each field, but the more peripheral, transitional ones. The results showed that each of these fields is robustly connected with the neighboring ones and displays markedly different patterns of connections with visual-, somatosensory-, auditory-, and limbic-related areas and with parietal and frontal areas related to the control of different effectors. Figure 17 summarizes the main results of this study. Cerebral Cortex October 2006, V 16 N