The Quiet Revolution of Existential Neuroscience. by Marco Iacoboni. Ahmanson-Lovelace Brain Mapping Center

Transcription

1 Iacoboni: Existential Neuroscience.1 The Quiet Revolution of Existential Neuroscience by Marco Iacoboni Ahmanson-Lovelace Brain Mapping Center Dept. of Psychiatry and Biobehavioral Sciences Neuropsychiatric Institute Brain Research Institute David Geffen School of Medicine at UCLA Address correspondence to: Marco Iacoboni, MD PhD Ahmanson Lovelace Brain Mapping Center David Geffen School of Medicine at UCLA 660 Charles E. Young Drive South Los Angeles, CA 90095, USA

2 Iacoboni: Existential Neuroscience.2 Introduction: Clarifying the Assumptions In the last two decades, we have witnessed the merging of scientific disciplines into novel, interdisciplinary enterprises. Cognitive science and neuroscience have produced the novel and quite successful field of cognitive neuroscience. Social psychology and neuroscience have produced in parallel the new exciting field of social neuroscience. Moreover, in the last decade, social psychologists and cognitive neuroscientists have effectively joined forces to create the fascinating field of social cognitive neuroscience. In this last field, the scientific approach that dominates is the one that uses functional imaging techniques to study brainbehavior relationships. Other approaches, for instance lesion studies in neurological patients, are also used to study the neural basis of social cognition but less frequently than the functional imaging approach. In this chapter, I will discuss some of the work that has been performed in my lab on mirror neurons, imitation, and social cognition. This work has been carried out mostly using imaging techniques. Before discussing this work, however, I would like to make explicit some tacitly held assumptions in the functional imaging and the social cognitive neuroscience field. The dominant underlying broadly shared assumptions of all the scientific fields mentioned above, and particularly of functional neuroimaging - those unsaid but implicitly held concepts that constitute a general framework for data interpretation and more generally for what make sense in the practice of science - are mostly derived from assumptions dominant in classical cognitive science

3 Iacoboni: Existential Neuroscience.3 and in what John Haugeland termed good old-fashioned artificial intelligence (GOFAI) (Haugeland 1985). The three main assumptions I will discuss here can be called the subject/world and inner/outer dichotomy, the strictly linked assumption on the role of representations in the mind of the cognitive subject contemplating the world, and finally the assumption, in turn linked to the second one, of the atomism of the input that the cognitive agent should receive from the world. The first two assumptions can be formulated as such: the cognitive agent or subject understands the objects of the world by using internal mental states that represent those objects of the world and by so doing produces knowledge. These internal mental states represent the outer objects of the world in an inner mental world, thus these representations do not really depend on the objects they represent. These assumptions fit naturally the experimental setup of brain imaging studies, in which a subject is isolated in a scanner and is presented with various stimuli that the subject must 'process', yielding some brain activity that reflects the brain 'representations' of the stimuli. Moreover, different kinds of elements (motion, color or even 'social' versus 'nonsocial') of what is presented to the subjects are assumed to be processed largely independently of each other (the assumption of the atomism of the input), thus yielding different types of brain activity related to different elements of the input. And this picture seems quite accurate, in that we can reliably induce activations in specific brain areas for specific kinds of stimuli. For instance, area V4 is activated by color, area MT/V5 is activated by motion, the so-called face fusiform area (FFA) is activated by watching a face. Even the empirical work and theoretical approach that

4 Iacoboni: Existential Neuroscience.4 challenges the notion that certain kinds of stimuli are processed by localized and specialized neural systems (Haxby et al. 2001) takes the assumption of the atomism of the input for granted. What I would like to suggest is that one can look at things with different eyes. In fact, some empirical work in the neuroscience of sociality seems to suggest - quietly, but resolutely - that the assumptions of the subject/world, inner/outer dichotomy, of representations independent of the things they represent, and of the atomism of the input may not be easily applied in some cases. Thus, rather than the picture of a meaning-giving brain that looks at the outside world and makes sense of it with a reflective and analytic approach, what emerges from some work in social cognitive neuroscience is the view of a human brain that needs a body to exist in a world of shared social norms in which meaning originates from being-in-the-world. This view is reminiscent of motives recurring in at least one flavor of what is called existential phenomenology (Heidegger 1927). For this reason, I call this view existential neuroscience. The Subject/World, Inner/Outer Dichotomy One of the most powerful aspects of human behavior is the tendency to imitate others. We do this very early in life (Meltzoff and Moore 1977) but we also tend to do it throughout adulthood (Chartrand and Bargh 1999). There is a developmental trajectory according to which a prepotent form of imitation earlier in life (Wapner and Cirillo 1968) is what one could call specular imitation. That is,

5 Iacoboni: Existential Neuroscience.5 when the imitator and the model are face-to-face, the imitator tends to imitate the model as if in front of a mirror. Thus, if the model raises the left hand, the imitator raises the right hand. In our imaging work, we had identified a fronto-parietal system relevant to imitation (Iacoboni et al. 1999; Koski et al. 2002) that is likely the human homologue of fronto-parietal areas in the macaque brain containing mirror neurons, that is, neurons that fire when the monkey performs an action and when she sees somebody else performing the same action (Rizzolatti and Craighero 2004). Within the human fronto-parietal mirror system activated during imitation, the activity in the frontal area (pars opercularis of the inferior frontal gyrus) seems particularly relevant to aspects of imitation associated with the goal of an action. For instance, a functional magnetic resonance imaging (fmri) study from our group shows that, when actions with visible goals are imitated, the activity in pars opercularis of the inferior frontal gyrus is higher compared to imitating the same movement in absence of a visible goal (Koski et al. 2002). In a subsequent study, we used frameless stereotaxy to guide repetitive Transcranial Magnetic Stimulation (rtms) over pars opercularis of the inferior frontal gyrus. The rtms approach allows experimenters to impair transiently the functions of the cortical areas directly stimulated. While stimulated over pars opercularis of the inferior frontal gyrus, subjects had a selective impairment in imitation but not in a visuo-motor task in which the motor output was identical to the imitation task (Heiser et al. 2003). Importantly, the deficit in imitation was selective for the goal of the action, but not for specific aspects of the movement such as movement time and trajectory. Thus, both fmri and rtms provide complementary evidence

6 Iacoboni: Existential Neuroscience.6 supporting the relevance of pars opercularis of the inferior frontal gyrus with regard to the goal of imitative actions. It turns out that this same cortical region shows higher activity during specular imitation (right hand imitation of a left hand action) compared to anatomical imitation (right hand imitation of a right hand action) (Koski et al. 2003). If one considers the relevance of goals for this cortical region, the dominance of specular imitation early in development, and the fact that specular imitation substantially means that both the imitator and the model share the same sector of space during imitative behavior, one is led to hypothesize that a general goal of imitating others seems to be 'directed toward' them, a process according to which a certain intimacy between model and imitator is achieved through space and action sharing. What is this intimacy if not the interdependence of both parties, model and imitator, rather than the expression of a separation between the perceiver (the imitator) and the perceived (the model)? Another example of how the relation between neural activity and space seems to map better onto a concept of being-amidst rather than onto the concept of a subject-world dichotomy comes from the neurophysiological work in primates of Graziano and collaborators. The classical and intuitive concept of space is that space is a unitary medium through which we move and operate and interact with others (here, a socially relevant practice that seems strongly culture-dependent is the practice to stand the appropriate distance from people) (Dreyfus 1991). This classical and intuitive concept of a unitary space, however, has been challenged in the last two decades by converging observations in clinical neurology and

7 Iacoboni: Existential Neuroscience.7 primate neurophysiology. Patients with hemi-inattention tend to neglect things located in the hemi-space contralateral to the cerebral lesion. Typically, the lesions associated with hemi-neglect are located in the right hemisphere and the hemi-inattention is for the left hemi-space. Some of these patients, however, show a double dissociation, such that some patients show hemi-neglect only for near space and some other patients show hemi-neglect only for far space (Bisiach et al. 1986; Halligan and Marshall 1991). Near space is practically definable by what is reachable with the hand. The boundaries between near and far space, however, are flexible. In fact, when a patient with near space neglect is given a long stick to bisect a line in far space, the patient shows the classical rightward bias typical of unilateral neglect also in far space. In contrast, if the patient bisects the line in far space with a lightpen, no rightward bias is observed (Berti and Frassinetti 2000). These data suggest that the use of the stick altered the near space map, stretching it at a much larger distance from the body of the patient. Neurophysiological data from Iriki and collaborators provide the singlecell mechanism for this phenomenon (Iriki et al. 1996). Iriki and colleagues trained monkeys to use a rake to get food. Monkeys were initially clumsy with the rake but eventually learned how to use it proficiently. Single-cell recordings in parietal bimodal neurons with a tactile receptive field at the hand and a visual receptive field around the hand and anchored to this body part demonstrated that after the monkey had learned how to master the tool, the visual receptive field of the parietal neuron had extended to incorporate the entire length of the rake. These data suggest that the kind of spatial maps provided by the primate brain

8 Iacoboni: Existential Neuroscience.8 are pragmatic maps, determined by the kind of actions that can be performed in that space sector. In fact, the fronto-parietal networks associated with near and far space have physiological properties in line with this concept. The frontoparietal cortical areas relevant to far space are the frontal and parietal eye fields, with neurons having properties associated with ocular movements and with sensory responses to non graspable stimuli like light flashes. The fronto-parietal cortical areas associated with near space have neurons active during reaching and grasping movements, and with sensory responses to three-dimensional, graspable objects (Rizzolatti et al. 1994; Rizzolatti et al. 1997). The work of Graziano and colleagues has initially defined the polysensory properties of premotor and posterior parietal neurons that seem relevant to creating a peripersonal space map (Graziano et al. 1994; Graziano et al. 1997; Graziano and Gross 1998; Graziano et al. 1999). Neurons in two polysensory areas in the frontal and parietal lobe that are also well connected anatomically, the ventral intraparietal area (VIP) and the polysensory zone (PZ) in the precentral gyrus, have tactile receptive fields mostly with respect to the arm and the head. These neurons also respond to visual and auditory stimuli located close to their tactile receptive field. These properties seem to suggest that these neurons provide a map of the space around us. This space map might as well be the map representing a space completely separated from us, albeit close. However, electrical stimulation of these two areas produces complex, coordinated movements that are identical to defensive movements occurring in natural conditions (Cooke and Graziano 2003; Cooke et al. 2003; Cooke and

9 Iacoboni: Existential Neuroscience.9 Graziano 2004). For instance, a set of polysensory neurons with tactile receptive fields on the face of the monkey and visual receptive fields around the tactile receptive field, when stimulated produce a defensive posture that includes '..a facial grimace, a squinting of the eye, a turning of the head away from the side of the sensory receptive fields, a hunching of the shoulders, a fast thrusting of the hand into the space beside the head, and a turning of the hand such that the palm faced outward, away from the head' (Graziano et al. 2002). The sensorymotor integration properties of these frontal and parietal areas suggest that, rather than implementing an abstract representation of an 'outer' near space, these neural ensembles are relevant to a direct sense of being-amidst, of beingin-the-world. One could argue, however, that after all these fronto-parietal cortical areas seem relevant to very basic aspects of sensory-motor behavior, but not so relevant to more complex behaviors that may play a more central role in human sociality. The following sections of this chapter will discuss increasingly more complex, and more 'social', aspects of human behavior to test whether or not we should abandon the mentalistic dominant assumptions I discussed above in favor of a more 'existential' (remember the dictum 'existence precedes essence') approach. The Assumption of Internal Representations A corollary of the inner/outer dichotomy is that the outer world must be represented internally. Recent data on motor facilitation during action

10 Iacoboni: Existential Neuroscience.10 observation, however, suggest that this idea, dominant in cognitive science, may not be entirely correct. Using TMS, Fadiga and colleagues (Fadiga et al. 1995) reported for the first time that action observation facilitates corticospinal excitability. They stimulated the primary motor cortex of normal volunteers while recording motor evoked potentials (MEPs) over muscles of the hand contralateral to the stimulated motor cortex. Fadiga and colleagues recorded greater MEPs while subjects observed actions, compared to control experimental conditions. These findings have been replicated in other labs, including ours (Strafella and Paus 2000; Gangitano et al. 2001; Aziz-Zadeh et al. 2002; Aziz-Zadeh et al. 2004). The most commonly accepted explanation for this effect is the following: watching an action activates inferior frontal mirror neurons in ventral premotor cortex. These neurons have a direct input onto primary motor cortex. Thus, the activation in inferior frontal mirror neurons modulates the sub-threshold membrane potential of primary motor neurons, such that these neurons are more readily excitable by the trans-cranial magnetic pulse. One of the most important aspects of this motor facilitation is that it is muscle-specific. That is, facilitation can be observed only in muscles involved in the observed action, but not in other muscles. This is true even for muscles of the same body part. That is, if subjects observe the extension of fingers, only muscles involved in finger extension, but not muscles involved in finger flexion, will show the facilitation. The specificity of the effect and the fact that the effect can be measured at the level of muscle activity in observing subjects not directly involved in any task suggest that this motor resonance behavior rather than

11 Iacoboni: Existential Neuroscience.11 being the correlate of a representation of actions of others, that is an entity with informational content about the actions of others that is completely independent of those actions is a dynamic, embodied, relational process of some form of imitation. Given that it would be highly inefficient to parrot others continuously, it is likely that there exist neural control mechanisms that suppress such embodied, imitation-like form of action recognition. In fact, there is evidence that patients with large prefrontal lesions may show uncontrolled imitative behavior (Lhermitte et al. 1986; De Renzi et al. 1996), likely due to the dysfunction of such control mechanisms. Similar phenomena have been observed even in the domain of language. Listening to speech sounds activates primary motor areas necessary to produce speech sounds, as reported in a recent fmri study performed in our lab (Wilson et al. 2004). Moreover, while listening to speech sounds, tongue muscles show facilitation when stimulated with TMS. Once again, this facilitation is specific to the muscles necessary to emit the sounds listened to (Fadiga et al. 2002). It seems that the only way we can perceive things is by using our motor system and our body to mimic those things. This seems to be true even in the domain of emotions and empathy. It is well known that humans have the automatic tendency to imitate each other while interacting socially, the so-called 'Chameleon Effect' (Hatfield et al. 1994). It has been shown that the tendency to imitate others in social situation correlates with the tendency to be empathic (Chartrand and Bargh 1999). At the level of neural systems, it is well known that the limbic system is very important for emotional

12 Iacoboni: Existential Neuroscience.12 behavior. In our work on imitation, we had identified a neural architecture for imitation comprising three major cortical systems, the superior temporal cortex, the rostral part of the posterior parietal cortex, and the inferior frontal cortex. Within this architecture, the superior temporal cortex would provide a higher order visual description of the action, the posterior parietal cortex would provide somatosensory information, and the inferior frontal cortex would code the goal of the action (Iacoboni 2003, in press; Iacoboni et al. in press). Thus, we have here two well-identified large-scale neural systems for emotion and imitation, but a strong functional link between the two, as suggested by the behavioral data on mimicry and empathy (Hatfield et al. 1994; Chartrand and Bargh 1999), suggest that these two systems must interact in an even larger scale network. Anatomical data on the insula suggest that the dysgranular sector of the insula connect the limbic system to the three major systems comprising the neural architecture for imitation, namely superior temporal cortex, posterior parietal cortex and inferior frontal cortex. To test whether these anatomical connections would result in a functionally significant large-scale network we used fmri while subjects were observing and imitating facial emotional expressions. What we observed (Carr et al. 2003) was a substantially similar pattern of activated areas during observation and imitation - with greater activity during imitation than observation - in all the critical areas outlined above, thus suggesting two main concepts: first, to perceive emotions of others we need to activate the same brain areas we use to express those emotions; second, we do this by using a large scale neural

13 Iacoboni: Existential Neuroscience.13 network comprising cortical areas relevant to imitation, the anterior insula and the limbic system. The assumption of the atomism of the input Another critical assumption that permeates cognitive neuroscience in general and social cognitive neuroscience in particular is what could be called the assumption of the atomism of the input. This basically means that one assumes the mind can process elements of the world independent of each other and of the context they are in. Thus, a given situation can be processed by using some combinatorial strategy over categories of fixed, self-standing, and contextfree elements. This assumption has been challenged on logical grounds (Andler 2000; Taylor 2000). Here I am providing some experimental neuroscience evidence that challenges the assumption of the atomism of the input as well. In area F5 of the macaque brain there are premotor neurons that fire during object-directed actions such as grasping, manipulating, holding, tearing (Rizzolatti et al. 1988). Some of these neurons have also sensory properties, in that the neurons fire while the monkey is not making any movement but is simply observing certain kinds of stimuli. There are at least two major classes of visuomotor neurons in F5, the so-called mirror neurons discussed above and canonical neurons. Canonical neurons have motor properties identical to mirror neurons, that is, both types of neurons fire during object-directed actions. Mirror and canonical neurons are distinguished by their sensory properties. As said

14 Iacoboni: Existential Neuroscience.14 above, mirror neurons fire at the sight of object-directed actions performed by others but not at the sight of pantomimed actions in absence of the object. Canonical neurons fire at the sight of graspable three-dimensional objects (Gallese et al. 1996). The commonly accepted interpretation of these sensory properties is that mirror neurons provide some form of action recognition, whereas canonical neurons provide some form of analysis of the affordance of the object, how-to-grab-that-thing. This interpretation is quite reasonable and at first sight it does not seem to go against the assumption of the atomism of the input. In fact, it looks like different kinds of things (actions and objects) are processed by different kinds of neurons. However, there is indeed a problem. Canonical neurons do not fire at the sight of an object-directed action, even though the object is visible. This neural property of canonical neurons, which is not well known (Vittorio Gallese made me aware of this property of canonical neurons during a conversation in Tucson in 2001 and Giacomo Rizzolatti has recently confirmed it in an ) is really problematic for the assumption of the atomism of the input, because there is no apparent reason why canonical neurons should not fire at the sight of a cup that somebody else is going to grasp. After all, these neurons do fire at the sight of the cup when nobody is going to grasp it. Thus, the neural activity in F5 while watching somebody grasping a cup rather than being a combinatorial activity of neurons that respond separately to elements of the scene, that is of mirror neurons responding to the sight of the action and of canonical neurons responding to the sight of the visible object mysteriously sums up to firing in mirror neurons and

15 Iacoboni: Existential Neuroscience.15 absence of firing in canonical neurons. This firing pattern is not readily explained by an account of processing of self-standing, context-free elements. It is much more readily explained by a holistic stance, which assumes that the nature of any given element is determined only by the 'whole' and that this 'whole' is never simply determined by the sum of its elements. Thus, when the cup is going to get grasped by somebody, it is no longer simply a cup, it belongs to the grasping action. This concept is reminiscent of the intentional arc of Merleau-Ponty ("From the outset the grasping movement is magically at its completion") (Merleau-Ponty 1945). A different kind of empirical evidence also seems in support of a holistic stance and much less of the atomism of the input. In a recent imaging study we investigated the role of mirror neurons in understanding the intentions of others (Iacoboni et al. 2004a). It has been proposed early on that mirror neurons may provide a neural mechanism for understanding the intentions of other people (Gallese and Goldman 1998). Most of the evidence on mirror neurons, however, could be interpreted more parsimoniously as suggesting that mirror neurons provide a relatively simple action recognition mechanism. Such a mechanism is reminiscent of some features of categorical perception (Liberman et al. 1957; Diehl et al. 2004). In fact, some mirror neurons do not discriminate between stimuli of the same category (i.e., the sight of different kinds of grasping actions can activate the same neuron) but do discriminate well between actions belonging to different categories even when the observed actions share several visual features. These properties seem more likely to support an action

16 Iacoboni: Existential Neuroscience.16 recognition mechanism ("that's a grasp") than an intention coding mechanism. This is because the same action can be associated with different intentions. We can grasp a cup in order to drink or in order to clean up the table. Given that there is not a one-to-one mapping between actions and intentions, one might conclude that mirror neurons are exclusively involved in action recognition or at least in some aspects of it. Typically, however, the context in which the actions occur is an important clue for clarifying the intentions of others (the "why" of an action). The same action done in two different contexts acquires different meanings and may reflect two different intentions. Thus, we investigated whether the observation of the same grasping action either embedded in contexts that cued the intention associated with the action or in absence of a context cuing the observer - elicited the same or differential activity in mirror areas for grasping in the human brain. If mirror neurons for grasping simply code the type of observed action, then the activity in mirror areas should not be influenced by the presence or the absence of context. If, in contrast, mirror neurons code the intention associated with the observed action, then the presence of a context that cues the observer should modulate activity in mirror areas. To test these competing hypotheses, we studied 23 normal volunteers with fmri while they watched three kinds of stimuli: grasping hand actions without a context, context only (a scene containing objects), and grasping hand actions embedded in contexts. The context cued the intention associated with the grasping action (either drinking or cleaning up) in the condition displaying both action and context. We found that observing

17 Iacoboni: Existential Neuroscience.17 grasping actions embedded in contexts yielded greater activity in inferior frontal cortex mirror areas than observing grasping action in absence of contexts and observing contexts only (Iacoboni et al. 2004a). This suggests that mirror neurons do not simply provide an action recognition mechanism, but rather they represent a neural system for coding the intentions of other people. Above all, the activity in inferior frontal mirror areas while subjects observed the action embedded in the context was above and beyond the sum of activity in the same area while subjects observed only the grasping action or only the context. Again, rather then the combinatorial processing of elements, this neural pattern seems to reflect more a holistic stance towards contexts, actions and intentions. A default human state: Being social We are skilled at existing. And skilled at existing certainly means the ability to negotiate a complex network of social interactions in which we are thrown into. In spite of this complexity, it seems we are able to understand the social relations between people automatically and effortlessly, even though we briefly glance at interacting people with our peripheral vision while we are engaged in our everyday activities, like driving, going to the mall, buying fresh produce at the Farmer's market. How do we do this? In a recent study, we asked subjects to watch 20-seconds videoclips depicting realistic everyday interactions. The clips were organized such that during the first twelve seconds only one person was shown (the single person segment), whereas in the last eight

18 Iacoboni: Existential Neuroscience.18 seconds there was an interaction between the first person and a second person (the relational segment). When compared to a resting baseline, both the single person and the relational segments yielded activation in areas known to be relevant to socially important stimuli, such as the face fusiform area, inferior frontal mirror areas and superior temporal areas responding to actions and biological motion. Moreover, two medial cortical areas, the dorsomedial prefrontal cortex and the medial parietal cortex, revealed signal increases compared to the resting baseline. The relational segment of the clip also yielded signal increases in all these areas compared to the single person segment of the clip (Iacoboni et al. 2004b). What is notable here is that the dorsomedial prefrontal and medial parietal cortices belong to a set of areas that are known collectively as the default state areas of the human brain. This is because these areas tend to show taskindependent de-activation in a wide variety of experimental conditions. This puzzling feature led researchers to assign functions to these regions on the basis of the experimental conditions that de-activated less these areas (Mitchell et al. 2002). However, this interpretational approach is quite unusual. Typically, functions to brain systems are assigned on the basis of the experimental conditions that increase activity in the neural systems under investigation. What we proposed on the basis of our findings is that one of the default state of humans is to 'think socially', explicitly or implicitly, and the cortical areas mostly engaged with this continuous social thinking are the ones that get de-activated when artificial laboratory tasks with very little ecological validity are used. Other

19 Iacoboni: Existential Neuroscience.19 reports have recently supported our suggestion (Greene et al. 2001; Mitchell et al. 2004; Rilling et al. 2004). Interestingly, these medial prefrontal and medial parietal areas show signal increase in politically sophisticated individuals while these subjects respond to political questions. In contrast, political novices (that is, people that know and care little about politics) show decreased activity in these medial areas while responding to political questions (Schreiber and Iacoboni, in preparation). These political novices behave like typical subjects in a typical cognitive experiment. Taken together, these findings suggest that the activity of these areas truly reflect an existential form of skill. Politically sophisticated people think about politics almost continuously. Politics is certainly one of the fabrics of their lives. We are all skilled at understanding social relationships, we do it all the time. The activity in these medial cortical areas seems to correlate with this existential form of skill. If this is correct, a prediction that can be made is that people with social problems, like autistic individuals, should show reduced activity in medial prefrontal and medial parietal cortex while watching social interactions, compared to control subjects. Conclusion In this chapter, I invited the reader to look at things with different eyes. We are so entrenched in our way of doing science that we take for granted assumptions that may need to be re-discussed. Some of these assumptions are

20 Iacoboni: Existential Neuroscience.20 so basic that often mold our own language, making it very difficult to see things differently. I hope I provided some evidence from the neuroscience of social behavior that will invite people to adopt, at least temporarily, a different interpretational perspective. This approach may disclose a whole new world.

21 Iacoboni: Existential Neuroscience.21 Acknowledgements Supported by Brain Mapping Medical Research Organization, Brain Mapping Support Foundation, Pierson-Lovelace Foundation, The Ahmanson Foundation, Tamkin Foundation, Jennifer Jones-Simon Foundation, Capital Group Companies Charitable Foundation, Robson Family, William M. and Linda R. Dietel Philanthropic Fund at the Northern Piedmont Community Foundation, Northstar Fund, and grants from National Center for Research Resources (RR12169, RR13642 and RR08655), National Science Foundation (REC ), and National Institute of Mental Health (MH63680).

22 Iacoboni: Existential Neuroscience.22 References Andler D (2000) Context and background: Dreyfus and cognitive science. In: Wrathall M, Malpas J, editors. Heidegger, coping, and cognitive science. Cambridge, MA: MIT Press. pp Aziz-Zadeh L, Maeda F, Zaidel E, Mazziotta J, Iacoboni M (2002) Lateralization in motor facilitation during action observation: a TMS study. Exp Brain Res 144(1): Aziz-Zadeh L, Iacoboni M, Zaidel E, Wilson S, Mazziotta J (2004) Left hemisphere motor facilitation in response to manual action sounds. Eur J Neurosci 19(9): Berti A, Frassinetti F (2000) When far becomes near: remapping of space by tool use. J Cogn Neurosci 12(3): Bisiach E, Perani D, Vallar G, Berti A (1986) Unilateral neglect: personal and extrapersonal. Neuropsychologia 24: Carr L, Iacoboni M, Dubeau MC, Mazziotta JC, Lenzi GL (2003) Neural mechanisms of empathy in humans: a relay from neural systems for imitation to limbic areas. Proc Natl Acad Sci U S A 100(9): Chartrand TL, Bargh JA (1999) The chameleon effect: The perception-behavior link and social interaction. Journal of Personality & Social Psychology 76(6): Cooke DF, Graziano MS (2003) Defensive movements evoked by air puff in monkeys. J Neurophysiol 90(5):

23 Iacoboni: Existential Neuroscience.23 Cooke DF, Graziano MS (2004) Sensorimotor integration in the precentral gyrus: polysensory neurons and defensive movements. J Neurophysiol 91(4): Cooke DF, Taylor CS, Moore T, Graziano MS (2003) Complex movements evoked by microstimulation of the ventral intraparietal area. Proc Natl Acad Sci U S A 100(10): De Renzi E, Cavalleri F, Facchini S (1996) Imitation and utilisation behaviour. J Neurol Neurosurg Psychiatry 61(4): Diehl RL, Lotto AJ, Holt LL (2004) Speech perception. Annu Rev Psychol 55: Dreyfus HL (1991) Being-in-the-world : a commentary on Heidegger's Being and time, division I. Cambridge, Mass.: MIT Press. xiv, 370 p. Fadiga L, Fogassi L, Pavesi G, Rizzolatti G (1995) Motor facilitation during action observation: a magnetic stimulation study. J Neurophysiol 73: Fadiga L, Craighero L, Buccino G, Rizzolatti G (2002) Speech listening specifically modulates the excitability of tongue muscles: a TMS study. Eur J Neurosci 15: Gallese V, Goldman A (1998) Mirror neurons and the simulation theory of mindreading. Trends Cogn Sci 2: Gallese V, Fadiga L, Fogassi L, Rizzolatti G (1996) Action recognition in the premotor cortex. Brain 119:

24 Iacoboni: Existential Neuroscience.24 Gangitano M, Mottaghy FM, Pascual-Leone A (2001) Phase-specific modulation of cortical motor output during movement observation. Neuroreport 12(7): Graziano MS, Gross CG (1998) Spatial maps for the control of movement. Curr Opin Neurobiol 8(2): Graziano MS, Yap GS, Gross CG (1994) Coding of visual space by premotor neurons. Science 266: Graziano MS, Hu XT, Gross CG (1997) Coding the locations of objects in the dark. Science 277: Graziano MS, Reiss LA, Gross CG (1999) A neuronal representation of the location of nearby sounds. Nature 397(6718): Graziano MS, Taylor CS, Moore T, Cooke DF (2002) The cortical control of movement revisited. Neuron 36(3): Greene JD, Sommerville RB, Nystrom LE, Darley JM, Cohen JD (2001) An fmri investigation of emotional engagement in moral judgment. Science 293(5537): Halligan PW, Marshall JC (1991) Left neglect for near but not for far space in man. Nature 350: Hatfield E, Cacioppo JT, Rapson RL (1994) Emotional contagion. Paris: Cambridge University Press. Haugeland J (1985) Artificial intelligence: The very idea. Cambridge, MA: MIT Press.

25 Iacoboni: Existential Neuroscience.25 Haxby JV, Gobbini MI, Furey ML, Ishai A, Schouten JL, et al. (2001) Distributed and overlapping representations of faces and objects in ventral temporal cortex. Science 293(5539): Heidegger M (1927) Being and time. New York: Harper & Row. Heiser M, Iacoboni M, Maeda F, Marcus J, Mazziotta JC (2003) The essential role of Broca's area in imitation. Eur J Neurosci 17(5): Iacoboni M (2003) Understanding intentions through imitation. In: Johnson SH, editor. Taking action: Cognitive neuroscience perspective on intentional acts. Cambridge, MA: MIT Press. pp Iacoboni M (in press) Understanding others: Imitation, language, empathy. In: Hurley S, Chater N, editors. Perspectives on imitation: From mirror neurons to memes. Cambridge, MA: MIT Press. Iacoboni M, Kaplan J, Wilson S (in press) A neural architecture for imitation and intentional relations. In: Nehaniv C, Dautenhahn K, editors. Imitation and social learning in robots, humans and animals: Behavioural, social and communicative dimensions. Cambridge, UK: Cambridge University Press. Iacoboni M, Woods RP, Brass M, Bekkering H, Mazziotta JC, et al. (1999) Cortical mechanisms of human imitation. Science 286(5449): Iacoboni M, Molnar-Szakacs I, Gallese V, Buccino G, Mazziotta J, et al. (2004a) Grasping intentions with mirror neurons. Abstract Viewer/Itinerary Planner, Society for Neuroscience, Online: Program No Iacoboni M, Lieberman MD, Knowlton BJ, Molnar-Szakacs I, Moritz M, et al. (2004b) Watching social interactions produces dorsomedial prefrontal and

26 Iacoboni: Existential Neuroscience.26 medial parietal BOLD fmri signal increases compared to a resting baseline. Neuroimage 21(3): Iriki A, Tanaka M, Iwamura Y (1996) Coding of modified body schema during tool use by macaque postcentral neurones. NeuroReport 7: Koski L, Iacoboni M, Dubeau MC, Woods RP, Mazziotta JC (2003) Modulation of cortical activity during different imitative behaviors. J Neurophysiol 89(1): Koski L, Wohlschlager A, Bekkering H, Woods RP, Dubeau MC, et al. (2002) Modulation of motor and premotor activity during imitation of targetdirected actions. Cereb Cortex 12(8): Lhermitte F, Pillon B, Serdaru MD (1986) Human autonomy and the frontal lobes. Part I: Imitation and utilization behavior. A neuropsychological study of 75 patients. Ann Neurol 19: Liberman AM, Harris KS, Hoffman HS, Griffith BC (1957) The discrimination of speech sounds within and across phoneme boundaries. J Exp Psychol 54: Meltzoff AN, Moore MK (1977) Imitation of facial and manual gestures by human neonates. Science 198: Merleau-Ponty M (1945) Phenomenology of perception. London: Routledge. Mitchell JP, Heatherton TF, Macrae CN (2002) Distinct neural systems subserve person and object knowledge. Proc Natl Acad Sci U S A 99(23):

27 Iacoboni: Existential Neuroscience.27 Mitchell JP, Macrae CN, Banaji MR (2004) Encoding-specific effects of social cognition on the neural correlates of subsequent memory. J Neurosci 24(21): Rilling JK, Sanfey AG, Aronson JA, Nystrom LE, Cohen JD (2004) The neural correlates of theory of mind within interpersonal interactions. Neuroimage 22(4): Rizzolatti G, Craighero L (2004) The Mirror-Neuron System. Annu Rev Neurosci 27: Rizzolatti G, Riggio L, Sheliga BM (1994) Space and selective attention. In: Umilta` C, Moscovitch M, editors. Attention and performance XV: Conscious and nonconscious information processing. Cambridge, MA: MIT Press. pp Rizzolatti G, Fogassi L, Gallese V (1997) Parietal cortex: from sight to action. Curr Op Neurobiol 7: Rizzolatti G, Camarda R, Fogassi M, Gentilucci M, Luppino G, et al. (1988) Functional organization of inferior area 6 in the macaque monkey. II. Area F5 and the control of distal movements. Exp Brain Res 71: Strafella AP, Paus T (2000) Modulation of cortical excitability during action observation: a transcranial magnetic stimulation study. NeuroReport 11: Taylor C (2000) What's wrong with foundationalism?: Knowledge, agency, and world. In: Wrathall M, Malpas J, editors. Heidegger, coping, and cognitive science. Cambridge, MA: MIT Press. pp

28 Iacoboni: Existential Neuroscience.28 Wapner S, Cirillo L (1968) Imitation of a model's hand movement: Age changes in transposition of left-right relations. Child Dev 39: Wilson SM, Saygin AP, Sereno MI, Iacoboni M (2004) Listening to speech activates motor areas involved in speech production. Nat Neurosci 7(7):