The relationship between mother and child is one of the

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1 Mothers Neural Activation in Response to Pictures of Their Children and Other Children Ellen Leibenluft, M. Ida Gobbini, Tara Harrison, and James V. Haxby Background: Considerable literature has focused on neural responses evoked by face viewing. We extend that literature and explore the neural correlates of maternal attachment with an fmri study in which mothers view photographs of their own children. Method: Seven mothers performed a one-back repetition detection task while viewing photographs of their own child, friends of their child, unfamiliar children, and unfamiliar adults. Results: Viewing one s own child versus a familiar child was associated with activation in the amygdala, insula, anterior paracingulate cortex, and posterior superior temporal sulcus (STS). Viewing familiar versus unfamiliar children elicited increased activation in regions associated with familiarity in adults. Viewing unfamiliar children versus unfamiliar adults was associated with activation in the fusiform gyrus, intraparietal sulcus, precuneus, and posterior STS. Conclusions: The sight of one s own child versus that of a familiar child activates regions that mediate emotional responses (amygdala, insula) and are associated with theory of mind functions (anterior paracingulate cortex, posterior superior temporal sulcus). These activations may reflect the intense attachment, vigilant protectiveness, and empathy that characterize normal maternal attachment. The sight of an unfamiliar child s face compared with that of an unfamiliar adult engages areas associated with attention as well as face perception. Key Words: Amygdala, emotion, face processing, fmri, insula, theory of mind The relationship between mother and child is one of the most important human attachments, but the biological basis of this bond and, in particular, the neural mechanisms that support it in humans are poorly understood. Extensive research has demonstrated that peptide and steroid hormones mediate maternal behavior in rodents and nonhuman primates, but as yet this has been a difficult line of research to extend to humans (Fleming et al 1997; Nelson and Panksepp 1998; Pedersen 1997). To better understand the neurobiology of maternal attachment in people, it may be possible to use functional magnetic resonance imaging (fmri) and build on the considerable literature concerning the neural responses evoked by face viewing. The thoughts and emotions that are evoked when a mother sees or hears her child are colored by the maternal relationship. This is a particular example of a more general phenomenon in that social cognitive studies have shown that simple face viewing is associated with the spontaneous activation of knowledge, attitudes, and emotions linked to the perceived individual (Bargh et al 1996; Greenwald and Banaji 1995; Todorov and Uleman 2002). In a recent fmri study, we found that viewing the faces of close friends and immediate family, compared with viewing the familiar faces of people with whom one has no personal relationship (i.e., celebrities), is associated with modulation of neural responses in brain areas that mediate emotional responses, episodic memory, and the representation of the mental states of others ( theory of mind ; Gobbini et al, in press). Specifically, personal familiarity was associated with activation of the posterior cingulate precuneus region, the superior temporal From the Pediatrics and Developmental Neuropsychiatry Branch (EL, TH) and Laboratory of Brain and Cognition (MIG, JVH), National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland. Address reprint requests to Dr. Ellen Leibenluft, 10 Center Drive, MSC 1255, Bethesda, MD ; Leibs@mail.nih.gov. Received December 9, 2003; revised March 15, 2004; accepted May 21, /04/$30.00 doi: /j.biopsych sulcus (STS), and the anterior paracingulate. Other investigators have noted that the latter two regions are activated during theory of mind tasks (for a review, see Gallagher and Frith 2003). In addition to Gobbini et al, several other studies have found greater posterior cingulate and precuneus activation in response to familiar faces, names, or voices (Gorno-Tempini et al 1998; Leveroni et al 2000; Nakamura et al 2001; Shah et al 2001). Studies have also found differences in anterior middle temporal, hippocampal, and lateral prefrontal activation associated with face familiarity, possibly due to the spontaneous retrieval of biographical information associated with a familiar individual (Gorno-Tempini et al 1998; Leveroni et al 2000; Sergent et al 1992; Sugiura et al 2001). Finally, Bartels and Zeki (2000) have shown that seeing one s lover, compared with seeing a personal friend, evokes a distinctive pattern of brain activation that reflects emotional response (in particular, decreased amygdala activation). The latter work is consistent with a body of literature demonstrating increased amygdala activation in response to novel, as opposed to familiar, stimuli (Phillips et al 1998; Schwartz et al 2003; Wright et al 2001). All of this previous work demonstrating the impact of personal familiarity and emotional attachment on brain activation suggests that an fmri study of mothers while they view pictures of their children may reveal neural correlates of the maternal relationship. Thus, we decided to study the maternal relationship with an event-related fmri study in which we compared activation when mothers view pictures of their own child (aged 5-12 years) compared with pictures of another familiar child (i.e., one of their child s friends). Because no previous neuroimaging study has used children s faces as stimuli, we also investigated whether the neural processing of faces differs according to whether the stimulus is the face of a child or that of an adult, and whether familiarity affects the processing of children s faces in a manner similar to its effects on the processing of adult faces. We predicted that viewing one s own child would be associated with activation in areas associated with emotional responses and in areas associated with the representation of episodic memories, biographical knowledge, and the mental states of others (specifically, amygdala, insula, superior temporal sulcus, posterior cingulate and precuneus, anterior paracingulate, hippocampus, and dorsolateral prefrontal cortex). BIOL PSYCHIATRY 2004;56: Society of Biological Psychiatry

2 226 BIOL PSYCHIATRY 2004;56: E. Leibenluft et al Methods and Materials Subjects The study was approved by the National Institute of Mental Health Institutional Review Board, and all subjects gave written informed consent before participating. Subjects were recruited by advertisement and were paid for their participation. Participants were right-handed women aged years whose firstborn (nonadopted) child was 5 12 years old. Handedness was assessed by self-report, and vision 20/30 or better was ascertained by use of a Snellen eye chart. All subjects were without psychiatric or medical illness, as ascertained by a structured psychiatric diagnostic interview (Williams et al 1992), medical history, and physical examination. Subjects were excluded if they took any prescribed medications (including birth control pills), if they were pregnant, or if their vision was inadequate to see the visual stimulus. Task Subjects were asked to provide two pictures of their child and two pictures each of six of their child s friends who were also aged 5 12 years. The photographs were all taken within the past year. In all pictures, the children were facing the camera straight on and had a neutral to mildly positive facial expression. The pictures were digitized and cropped, if necessary, to show only the face. Photographs of each subject s own child and those of her child s friends were used to provide unfamiliar children for other subjects, and pictures of unfamiliar adults were obtained from another study (Gobbini et al, unpublished data). Investigators have demonstrated that neural activation can vary depending on the relationship between the race of a person viewing faces and the race of the facial stimuli (Hart et al 2000; Phelps et al 2000). To control for this possible confound, the racial composition of each subject s unfamiliar picture set was matched to that of her familiar picture set. Control nonsense stimuli were created by phase-scrambling the pictures of faces. Before entering the scanner, subjects were asked to rate their subjective response to the pictures that they were going to see in the scanner. Using the Self-Assessment Manikin (Bradley and Lang 1994), subjects were asked to use a button press to rate the pictures in terms of valence ( How pleasant or unpleasant does the picture make you feel? with 1 being positive, 3 neutral, and 5 negative) and arousal ( How excited does the picture make you feel? with 1 being most calm and 5 most aroused). In the scanner, subjects performed a one-back repetition detection task in which they indicated whether each photograph depicted the same or a different person than the previous photograph. Participants responded by pressing a button with either the right thumb (same) or left thumb (different). Subjects saw 12 runs of stimuli, with each run consisting of three blocks separated by 12-sec intervals. Each block consisted of 30 stimuli and was introduced by a cue. Stimuli were presented for 1.5 sec with a 1.5-sec interstimulus interval. In this event-related paradigm, each subject viewed pictures of her own child, six of her child s friends, six unfamiliar children, five unfamiliar adults, and scrambled faces, presented in a random order. There were eight stimulus conditions with 135 stimulus presentations per condition. Four conditions involved 135 presentations of pictures of a single individual: the subject s own child, a friend of the child, an unfamiliar child, and an unfamiliar adult. The pictures of the friend, unfamiliar child, and unfamiliar adult were chosen randomly from the set of available pictures, with the constraint that they were all matched racially to the subject s child. Three conditions involved presentation of pictures of five individuals from each category: friends of the subject s child, unfamiliar children, and unfamiliar adults. There were two pictures of each individual face. One condition involved scrambled pictures. Imaging Scanning was performed on a 1.5-T GE scanner (General Electric, Milwaukee, Wisconsin). Responses to different faces and scrambled pictures were measured using blood oxygen level dependent (BOLD) contrast fmri with T2*-weighted gradient echo-planar images. Twelve time series were obtained in each subject in a single fmri session. Each time series began and ended with a 12-sec rest. During the rest condition, subjects saw a blank screen and were instructed to keep their eyes open. In each time series, three blocks of 30 stimuli were presented, and images of the whole brain were acquired 114 times. Each volume consisted of 22 contiguous 5-mm-thick axial slices (repetition time 3 sec, echo time 40 msec, flip angle 90, field of view (FOV) 24 cm). High-resolution T1-weighted spoiled gradient recall anatomic images ( mm-thick sagittal images, FOV 24 cm, matrix) were also obtained for each subject. Statistics Behavioral data (valence and arousal ratings and reaction time data) for the five types of pictures (one s own child; the familiar child whose face was shown as many times as the subject s own child; all familiar children (excluding the subject s own child); unfamiliar children; unfamiliar adults) were compared using a repeated-measures analysis of variance. Post hoc analyses were performed using paired t tests with Bonferroni correction for multiple comparisons. Significance was set at p.05. Image data were analyzed with the Analysis of Functional NeuroImages software package (AFNI; gov/afni). The impulse response to each stimulus type was determined using the program 3dDeconvolve. For each stimulus type, a separate regressor modeled the response for each TR following stimulus onset to 15 sec. The magnitude of the response to each stimulus condition was indexed by the area under the curve of the impulse response from 3 9 sec, calculated as the sum of the b-weights for the corresponding regressors. Maps of response magnitudes for each condition in each subject were resampled into Talairach space (Talairach and Tournoux 1988) and matched sample t tests were calculated for each voxel to test contrasts between responses to different stimulus conditions. These tests are simple random effects tests in which each subject represents a single degree of freedom. The following contrasts were evaluated: 1) face of one s own child versus face of a friend of one s own child with the same number of stimulus repetitions as one s own child; 2) faces of familiar children (excluding one s own child) versus faces of unfamiliar children; and 3) faces of unfamiliar children versus faces of unfamiliar adults. Clusters of voxels with p.025 and a minimum volume of 250 ml volume were considered significant. Because of the small volume of the amygdala and prior hypotheses regarding its role in the recognition of familiar faces with high emotional valence, our criteria for significance was relaxed to include clusters of any size in this structure. We performed a conjunction analysis to identify areas that showed a consistent response to familiar individuals across different conditions. Specifically, we performed a conjunction analysis on the contrasts own child versus familiar child and

3 E. Leibenluft et al BIOL PSYCHIATRY 2004;56: Table 1. Valence and Arousal Ratings (n 7 subjects) Across Picture Types familiar children versus unfamiliar children. These contrasts involve different conditions with different stimuli and therefore are statistically independent, but both contrasts identify regions in which activation is associated with an increased degree of familiarity. Regions of overlap were identified as voxels that had a z score 1.96 (p.05, two-tailed) for both individual contrasts and a z score for the conjoint probability 3.89 (p.0001, two-tailed). Maximum z scores for each region were based on the conjoint probability for the two contrasts. The conjunction analysis is conservative because it uses a strict statistical threshold and tests whether identical voxels are activated in independent data sets. Results Picture Type Valence a Arousal b Mean SD Mean SD Own Child Familiar Child Repeat All Familiar Children Unfamiliar Children Unfamiliar Adults a Rated 1 5, with 1 being most positive and 5 most negative. Repeatedmeasures analysis of variance (ANOVA): F 38.61, df 4, p.007. b Rated 1 5, with 1 being most arousing and 5 least arousing. Repeatedmeasures ANOVA: F 12.83, df 4, p.031. Ten women who met inclusion criteria were scanned. Data from three subjects were excluded from further analysis. In one, there was significant imaging artifact. In two others, there were no response differences for faces, averaging over familiar and unfamiliar faces, compared with scrambled images, calling into question the compliance of the subjects with the task. This contrast (i.e., faces vs. scrambled images) is orthogonal to the contrasts of interest for our study of the effect of familiarity. The mean age of the seven women whose data are reported here is years. Mean arousal and valence ratings across the five picture types are shown in Table 1. The difference in valence and arousal ratings was significant (for valence, F 38.61, df 4, p.007; for arousal, F 12.83, df 4, p.031), with increasing familiarity being associated with more positive valence ratings and increased arousal. Post hoc analyses showed that differences were significant between valence ratings of one s own child versus unfamiliar adults (t 8.66, df 6, corrected p.001), one s own child versus unfamiliar children (t 5.50, df 6, corrected p.02), and familiar children versus unfamiliar adults (t 4.94, df 6, corrected p.03). No post hoc analyses of arousal ratings were significant after corrections were made for multiple comparisons. An examination of reaction times during the one-back task that subjects performed in the scanner revealed no significant difference in reaction time across picture types. Tables 2 4 show all significant areas of activation for the following contrasts: face of one s own child versus face of a familiar child (Table 2), faces of familiar children versus faces of unfamiliar children (Table 3), and faces of unfamiliar children versus faces of unfamiliar adults (Table 4). Table 5 shows the results of the conjunction analysis on the contrasts own child versus familiar child and familiar children versus unfamiliar children. All significant activations are shown in the tables, but in the text below we focus particularly on those regions for which we anticipated activation because they have been reported to have a role in the perceptual representation of faces, in emotional responses, in the retrieval of images from long-term memory, or in social cognition, as noted earlier in the article. Face of One s Own Child Versus the Face of a Familiar Child Compared with the face of a familiar child, there was a significantly stronger response to the face of one s own child bilaterally in the anterior paracingulate and the dorsolateral prefrontal cortex, as well as in the left insula, the left posterior fusiform gyrus, the left STS, and the right posterior cingulate precuneus (Table 2; Figure 1). In addition, there was increased activation in the right amygdala. Faces of Familiar Children Versus Faces of Unfamiliar Children Compared with the faces of unfamiliar children, the faces of familiar children evoked a stronger response in the right anterior paracingulate, the left insula, the left STS, and the posterior cingulate precuneus bilaterally (Table 3). In the same contrast, the faces of familiar children evoked a significantly weaker response than those of unfamiliar children in the ventral occipital regions bilaterally, the right fusiform gyrus, and the left amygdala. Faces of Unfamiliar Children Versus Faces of Unfamiliar Adults Compared with faces of unfamiliar adults, faces of unfamiliar children evoked a significantly stronger response in the left fusiform gyrus, the right STS, the left posterior cingulate precuneus, and the left insula (Table 4; Figure 2). Conjunction Analysis of Own Child Versus Familiar Child and Familiar Children Versus Unfamiliar Children The conjunction analysis confirmed that identical voxels in a number of the areas noted earlier were activated in both the own child versus familiar child and familiar children versus unfamiliar children contrasts (Table 5). In other words, activation in these regions was associated with increased familiarity. Significant activation was observed in the bilateral paracingulate cortex, left posterior STS, right posterior cingulate precuneus, and left anterior insula. Deactivation with increasing familiarity was seen in the intraoccipital sulcus and thalamus. Discussion The results of this study show that simple viewing of one s child s face evoked a unique pattern of neural responses in mothers that may reflect how the maternal relationship differs from other social attachments. This pattern was revealed by comparing neural activation while viewing one s own child to activation while viewing another very familiar child with whom the mother does not have a biological relationship (i.e., her child s friend). Viewing one s own child evoked stronger responses in areas associated with emotional responses, such as the amygdala and the insula and in areas associated with representing the mental states of others (theory of mind), namely, the anterior paracingulate, posterior superior temporal, and precuneus posterior cingulate cortices. In addition, prefrontal areas known to be associated with episodic memory were more activated by a picture of one s own child rather than that of familiar children. The uniqueness of this pattern of response may reflect how the maternal relationship differs from other social attachments.

4 228 BIOL PSYCHIATRY 2004;56: E. Leibenluft et al Table 2. Results for the Own Child Versus Familiar Child Comparison Area BA R/L x y z z Score Frontal Anterior paracingulate 9 R L Anterior cingulate 32 L Precentral sulcus L Superior frontal gyrus 6 R L Middle frontal gyrus 9 R L L R L Inferior frontal gyrus 47 L Gyrus rectus 11 L Temporal Posterior superior temporal sulcus 39 L Superior temporal gyrus 22 R Middle temporal gyrus 21 R L Inferior temporal gyrus 37 R Parietal Posterior cingulate 23 R Precuneus 31 R Supramarginal gyrus 40 L Medial parieto-occipital fissure R Occipital Occipitotemporal sulcus 20 R Inferior gyrus 19 L Subcortical Amygdala R Insula L Thalamus R R L L L Globus pallidus R L Putamen R Cerebellum R L BA, Brodmann s area; L, left; R, right. The threshold for significance was contiguous voxels with a volume of 250 ml and p.025. Previous fmri studies of face perception have used only pictures of adult faces. To complement this literature and provide background for the interpretation of the mothers responses to the sight of their own child, we also examined whether viewing children s faces generally was associated with unique responses. We found that viewing personally familiar (but unrelated) children, versus viewing unfamiliar children, produced a pattern of responses that was remarkably similar to the pattern we found in another study when subjects viewed personally familiar (vs. unfamiliar) adult faces. Specifically, the personally familiar condition was associated with activation of the anterior paracingulate, insula, STS, and posterior cingulate precuneus, as well as deactivation of the amygdala (Gobbini et al, in press). In addition to the original contrasts, we performed a conjunction analysis of the contrasts own child versus familiar child and familiar children versus unfamiliar children. This analysis identifies specific voxels whose activation is associated with increased familiarity in both of the individual contrasts and thus decreases the probability of Type I errors. The conjunction analysis identified the anterior paracingulate cortex, posterior STS, posterior cingulate precuneus, and insula as areas that were activated in the setting of increased familiarity. The conjunction analysis did not yield a significant finding for the amygdala, a result that is not surprising given that amygdala activation was associated with viewing a picture of one s own child in the own child versus familiar child contrast but with viewing pictures of unfamiliar children in the familiar versus unfamiliar children contrast. As discussed subsequently, this may reflect a unique pattern of activation in the amygdala relative to other brain structures, as well as the unique nature of the maternal relationship. Viewing one s own child modulated activity in a number of cortical and subcortical regions. We focus our discussion on areas that mediate emotional responses, representations of the

5 E. Leibenluft et al BIOL PSYCHIATRY 2004;56: Table 3. Results for the Familiar Versus Unfamiliar Children Comparison Area BA R/L x y z z Score Frontal Anterior paracingulate 10 L Anterior cingulate 32 R R Superior frontal gyrus 8 R Middle frontal gyrus 46 R L L R R Inferior frontal gyrus 45 R L Posterior orbital gyrus 11 L Temporal Posterior superior temporal sulcus 39 L Middle temporal gyrus 21 R Parietal Posterior cingulate/precuneus 23/31 L Supramarginal parietal gyrus 40 R L Intraparietal sulcus 40 R L Inferior parietal gyrus 40 R L Occipital Middle occipital gyrus 18 R Lingual gyrus 19 L Fusiform gyrus 37 R Subcortical Amygdala L Insula R L Thalamus R L Caudate R Cerebellum R R R L L L BA, Brodmann s area; L, left; R, right. The threshold for significance was contiguous voxels with a volume of 250 ml and p.025. personality and mental states of others, and episodic memory. Viewing one s own child, versus a familiar child, was associated with stronger responses in both the right amygdala and the left anterior insula. Both of these regions are associated with emotional responses. The amygdala is associated most strongly with the representation of fear (Breiter et al 1996; Morris et al 1996; Phelps et al 2001), leading to the hypothesis that this structure plays a key role in modulating vigilance in response to threatening emotional stimuli (Davis and Whalen 2001); however, the amygdala is also activated during positive emotional states, such as those induced by winning a game (Zalla et al 2000), seeing a smiling face or another pleasant visual stimulus (Breiter et al 1996; Canli et al 2002; Hamann et al 2002; Lane et al 1997; Liberzon et al 2003), or hearing positively valenced words (Hamann and Mao 2002). With regard to the insula, fmri experiments have shown that the insula responds to negatively valenced stimuli that evoke emotions such as anger and disgust (Calder et al 2001; Phillips et al 2003). This structure also responds during autonomic arousal (Critchley et al 2002), during negotiation games when one feels unfairly treated (Sanfey et al 2003), and during imitation of facial expressions (Carr et al 2003). The amygdala and insula responses seen here when mothers view pictures of their children stand in contrast to results obtained when subjects view other individuals with whom they have a close personal relationship. In fact, pictures of close friends and immediate family, compared with those of famous familiar faces, evoke a weaker response in the amygdala and no response in the insula (Gobbini et al, in press). Seeing a picture of one s lover, compared with that of a close friend, evokes a weaker response in the amygdala but a stronger response in the insula (Bartels and Zeki 2000). The activations seen in this study may reflect the mixture of intense attachment and vigilant protectiveness that characterizes the maternal relationship but not these other close personal relationships.

6 230 BIOL PSYCHIATRY 2004;56: E. Leibenluft et al Table 4. Results for the Unfamiliar Children Versus Unfamiliar Adults Comparison Area BA R/L x y z z Score Frontal Frontopolar gyrus 10 L Inferior frontal gyrus 45 R Posterior orbital gyrus 11 L Gyrus ambiens 34 L Temporal Posterior superior temporal sulcus 39 R Middle temporal gyrus 21 L Parietal Posterior cingulate/precuneus 23/31 L Supramarginal gyrus 40 R Intraparietal sulcus 19 R R L Occipital Fusiform gyrus 37 L Subcortical Insula L Thalamus R BA, Brodmann s area; L left; R right. The threshold for significance was contiguous voxels with a volume of 250mL and p.025. Viewing the face of one s own child, compared with the face of a familiar, unrelated, child, also evoked a stronger response in areas associated with theory of mind. Theory of mind refers to the capacity to predict and explain other people s behavior based on a representation of their intentions and mental states. There is evidence that specific areas are associated with theory of mind, such as the anterior paracingulate cortex, the posterior STS, and the posterior cingulate precuneus (Ferstl and von Cramon 2002; Fletcher et al 1995; Gallagher and Frith 2003; Johnson et al 2003, but see also Gusnard and Raichle 2001). Activation of the anterior paracingulate cortex and the posterior STS have been associated with interpretation of cartoons and stories that require understanding the mental state of the characters (Gallagher et al 2000) or with viewing moving geometrical shapes that evoke attribution of a mental state (Castelli et al 2000). Activation in the anterior paracingulate region was also reported by Lorberbaum et al (2002) in an fmri study of mother s responses to their newborn baby s cry. In our study, the anterior paracingulate cortex and the posterior STS, in addition to responding more strongly to the face of one s own child than to that of a familiar child, also responded more strongly to familiar children than to unfamiliar children. Combined with the results in Gobbini et al (in press), these findings support the hypotheses that familiarity with a face is related not only to the face s appearance, but also to the representation of that person s mental state and personality, and that this information is spontaneously retrieved when viewing a familiar individual. The question of whether stimuli associated with close personal attachment evoke activation in theory of mind areas could be explored further using other stimuli associated with loved ones (i.e., songs, pictures of relevant places, etc.). Finally, viewing unfamiliar children s faces was associated with a different pattern of response than that associated with viewing unfamiliar adult faces. Specifically, a stronger response for children s faces was detected in areas associated with face perception, such as the fusiform gyrus, and with attention, such as the intraparietal sulcus and the precuneus. A stronger response for unfamiliar children was also detected in the posterior STS, an area that has been associated with processing of biological motion, facial movements, judgment of intention, and theory of mind (Castelli et al 2000; Frith and Frith 1999; Winston et al 2002). In a recent study, Carr et al (2003) observed a stronger activity in the posterior STS and insula during imitation of facial emotional expressions, leading the authors to hypothesize that these areas are part of a neural network associated with empathy. The posterior cingulate precuneus is also activated during judgments requiring empathy (Farrow et al 2001). These results raise the intriguing possibility that the sight of a Table 5. Results of Conjunction Analysis for Own Child Versus Familiar Child and Familiar Children Versus Unfamiliar Children Area BA R/L x y z z Score Anterior Paracingulate Cortex 9 R Anterior Paracingulate Cortex 9 L Posterior Superior Temporal Sulcus 39 L Posterior Cingulate/Precuneus 31 R Anterior Insula L Intraoccipital Sulcus 19 R Thalamus R BA, Brodmann s area; L, left; R, right. Regions were identified as voxels that had a Z score greater than 3.89 (p.0001, two-tailed) for both contrasts. Maximum z scores for each region are based on the conjoint probability for the two contrasts.

7 E. Leibenluft et al BIOL PSYCHIATRY 2004;56: child s face, even that of an unfamiliar child, might be experienced with stronger sympathetic interest than the sight of an unfamiliar adult s face. More broadly, these results suggest that mothers process the faces of children in a manner that differs in important ways from the manner in which they process the faces of adults. Lorenz (1937) suggested that mammalian maternal behavior is in part elicited by the babyish appearance of the infant s face. This biased perception of children s faces has obvious evolutionary value and may be reflected in a specific alteration of neural response. In addition to replication with a larger sample, an important extension of this line of research would involve conducting a similar study in fathers to ascertain whether the pattern of activation observed when mothers view their child reflects the parental, rather than the maternal, relationship. Similarly, further study could determine whether the findings reported here for the unfamiliar child versus unfamiliar adult comparison vary according to the gender of the subject. Finally, it is possible that the pattern of activation occurring when a mother views a picture of her child may change as that child grows into adulthood. In any case, our results suggest widespread differences in activation when a mother views a picture of her own child compared with that of another familiar child. In addition, they provide preliminary evidence that, among mothers, the age of the person depicted in a face stimulus may modulate neural activation. Finally, they provide further evidence of the utility of face processing as a window into the neural circuitry mediating social cognition. Figure 1. Areas that showed stronger activation in the own child versus familiar child comparison. (A) Amygdala: maximum at 26, 7, 16. (B) Insula: maximum at 41, 28, 9. 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