Representations of faces and body parts in macaque temporal cortex: a functional MRI study.

Abstract

Human neuroimaging studies suggest that areas in temporal cortex respond preferentially to certain biologically relevant stimulus categories such as faces and bodies. Single-cell studies in monkeys have reported cells in inferior temporal cortex that respond selectively to faces, hands, and bodies but provide little evidence of large clusters of category-specific cells that would form "areas." We probed the category selectivity of macaque temporal cortex for representations of monkey faces and monkey body parts relative to man-made objects using functional MRI in animals trained to fixate. Two face-selective areas were activated bilaterally in the posterior and anterior superior temporal sulcus exhibiting different degrees of category selectivity. The posterior face area was more extensively activated in the right hemisphere than in the left hemisphere. Immediately adjacent to the face areas, regions were activated bilaterally responding preferentially to body parts. Our findings suggest a category-selective organization for faces and body parts in macaque temporal cortex.

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study
Representations of faces and body parts in macaque temporal cortex: A functional MRI
Mark A. Pinsk, Kevin DeSimone, Tirin Moore, Charles G. Gross, and Sabine Kastner
doi:10.1073/pnas.0502605102
2005;102;6996-7001; originally published online Apr 28, 2005;
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Representations of faces and body parts in macaque
temporal cortex: A functional MRI study
Mark A. Pinsk*†‡, Kevin DeSimone*†, Tirin Moore§, Charles G. Gross*, and Sabine Kastner*†
*Department of Psychology and†Center for the Study of Brain, Mind, and Behavior, Princeton University, Green Hall, Princeton, NJ 08544; and§Department
of Neurobiology, Stanford University School of Medicine, Sherman Fairchild Building, Stanford, CA 94305
Contributed by Charles G. Gross, March 30, 2005
Human neuroimaging studies suggest that areas in temporal cor-
tex respond preferentially to certain biologically relevant stimulus
categories such as faces and bodies. Single-cell studies in monkeys
have reported cells in inferior temporal cortex that respond selec-
tively to faces, hands, and bodies but provide little evidence of
large clusters of category-specific cells that would form ‘‘areas.’’
Weprobedthecategoryselectivityofmacaquetemporalcortexfor
representations of monkey faces and monkey body parts relative
to man-made objects using functional MRI in animals trained to
fixate. Two face-selective areas were activated bilaterally in the
posterior and anterior superior temporal sulcus exhibiting differ-
ent degrees of category selectivity. The posterior face area was
more extensively activated in the right hemisphere than in the left
hemisphere. Immediately adjacent to the face areas, regions were
activated bilaterally responding preferentially to body parts. Our
findings suggest a category-selective organization for faces and
body parts in macaque temporal cortex.
non-human primate ? visual category representations
H
ronments. In humans, neuroimaging studies have shown that
object information is represented in a large swath of ventral
temporal and lateral occipital cortex that is characterized by
stronger responses to objects than to non-objects (1, 2). Within
these object-selective activations, discrete regions have been
identified that respond preferentially to some biologically rele-
vant stimulus categories such as faces [the ‘‘fusiform face area,’’
FFA (3–6)] or bodies [the ‘‘extrastriate body area,’’ EBA (7)],
suggesting a category-specific and anatomically segregated mod-
ular organization of neural representations related to certain
classesofobjectstimuli.Thesestudiesareconsistentwithreports
of patients with lesions of temporooccipital cortex, who show
selective impairments in recognizing familiar faces [prosopag-
nosia (8)] or body parts (9) but not other objects.
In the macaque, much less is known about the large-scale
representation of object information. Single-cell physiology
studies have shown that neurons in inferior temporal (IT) cortex
typically respond to complex stimuli with some selectivity for
shape, color, and texture (10, 11). A small proportion of IT
neurons were found to respond selectively to faces (10–16),
hands (14, 17), or human bodies (18). These neurons were more
common in the portion of cytoarchitectonic area TE on the
ventral bank of the superior temporal sulcus (STS) and in the
superior polysensory area on the dorsal bank of the STS. They
were also found on the lateral and ventral surfaces of area TE.
Even though face-selective neurons were found clustered to-
gether, or sometimes even formed columns (19, 20), there was
noevidenceforanorganizationintoface-orbody-selectiveareas
in monkey IT cortex, similar to the human FFA or EBA.
However, this view has recently been challenged by the
demonstration of discrete face-selective areas in the posterior
and anterior STS by using functional MRI (fMRI) in anesthe-
tizedandawakemacaques(21,22).Theface-selectiveareaswere
embedded in a large object-selective activation extending from
uman and non-human primates have a remarkable ability to
recognize a large variety of different objects in their envi-
areaV4torostralTE(22).Thesestudieswerethefirsttoprovide
evidence of category-selective areas in monkey IT cortex. Here,
we probe the neural representations of two classes of biologically
relevant stimuli, monkey faces and body parts, using fMRI in
behaving macaques.
Methods
Subjects. Subjects were three adult, male macaque monkeys
(Macaca fascicularis) weighing 4–9 kg. All procedures were
approved by the Princeton University Animal Care and Use
Committee and conformed to National Institutes of Health
guidelines for the humane care and use of laboratory animals.
Details regarding surgery, experimental setup, data acquisi-
tion, and analysis are described by Pinsk et al. (23) and will only
be briefly summarized here. Each animal was surgically im-
planted with a plastic head bolt by using ceramic screws and
dental acrylic. Monkeys were placed in an MR-compatible
primate chair prone with their heads erect and rigidly fixed in a
head-holding apparatus. The animals were acclimated to the
MRI environment through the use of a mock scanner. Monkeys
were trained to fixate on a small dot at the center of a display
screen by using an infrared eye-tracking system (Applied Science
Laboratories, Bedford, MA). By providing the animals with
regular juice rewards while they maintained fixation within a 4°
square window, and systematically increasing the reward rate
during the course of a trial, the animals were trained to fixate for
as long as 4 min.
Visual Stimuli and Experimental Design. Color pictures of monkey
faces, monkey body parts, and man-made objects were presented
on a screen while the animals maintained fixation (see Fig. 4,
which is published as supporting information on the PNAS web
site). The stimuli subtended 12 ? 12° and were presented for 1 s
foveally behind the fixation point (0.5° diameter), followed by a
1-s blank interval during which only the fixation point was
present. Several additional categories of stimuli (food, labora-
toryscenes)werepresentedduringeachtrial,theresultsofwhich
willbedescribedinaseparatereport.Blocksofstimulifromeach
category were presented interleaved with blank periods, each
lasting for 12 s. Each category block was repeated twice within
a trial, resulting in trials of 240 s each. Monkey M3 was only
tested for faces in relation to pictures of houses instead of
man-made objects and not for body parts. Stimulus presentation
and eye position recordings were synchronized to the beginning
of each scan by using a trigger pulse from the scanner.
Data Acquisition. Structural and functional images were acquired
with a 3-T head-dedicated scanner (Magnetom Allegra, Sie-
mens, Erlangen, Germany), using a 12-cm transmit?receive
surface coil (NMSC-023, Nova Medical, Wakefield, MA). For
Abbreviations:aBody,anteriorbodypart;aFace,anteriorface;EBA,extrastriatebodyarea;
FFA, fusiform face area; fMRI, functional MRI; IT, inferior temporal; pBody, posterior body
part; pFace, posterior face; STS, superior temporal sulcus.
‡To whom correspondence should be addressed. E-mail: mpinsk@princeton.edu.
© 2005 by The National Academy of Sciences of the USA
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cortical surface reconstructions, a high-resolution (0.5 ? 0.5 ?
0.5 mm) structural scan was acquired in a separate session during
which the animals were anesthetized with Telazol (tiletamine?
zolazepam, 10 mg?kg i.m.) [MPRAGE sequence; field of view
(FOV) ? 128 ? 128 mm; 256 ? 256 matrix; TR ? 2,500 ms;
TE ? 4.4 ms; TI ? 1,100 ms; flip angle ? 8°; 20 acquisitions]. All
other scan sessions were performed with awake animals. Func-
tional images were taken with a gradient echo, echo planar
imaging sequence (FOV ? 80 ? 80 mm; 64 ? 64 matrix; TR ?
2,400 ms, TE ? 32 ms, flip angle ? 90°, bandwidth ? 2,112 Hz
per pixel). Twenty-seven contiguous coronal slices (thickness of
2 mm without gap; in-plane resolution of 1.25 ? 1.25 mm) were
acquired in six to eight series of 100 images each, starting from
the posterior pole and covering the brain up to the region of the
principal sulcus. An in-plane magnetic field map image was
acquired to perform echo planar imaging undistortion (FOV ?
80 ? 80 mm; 64 ? 64 matrix; TR ? 600 ms, TE ? 8.8?11.3 ms;
flip angle ? 45°). An anatomical scan was also acquired in the
samesessiontofacilitatecorticalsurfacealignments(0.5?0.5?
1.0 mm, MPRAGE sequence; FOV ? 128 ? 128 mm; 256 ? 256
matrix; TR ? 2,500 ms; TE ? 4.4 ms; TI ? 1,100 ms; flip angle ?
8°; 1 acquisition).
In total, 4,400 and 4,800 functional volumes were acquired in
monkeys M1 and M2 in a total of six scan sessions per animal.
In monkey M3, 600 functional volumes were acquired in a single
session. The reliability of activations was investigated in monkey
M1, who repeated the experiment twice with 3,000 functional
volumes acquired in five and four scan sessions, respectively.
Data Analysis. Data were analyzed by using AFNI (http:??
afni.nimh.nih.gov?afni), FREESURFER (http:??surfer.nmr.mgh.
harvard.edu), and SUMA (http:??afni.nimh.nih.gov?afni?suma).
Scans during which the animal broke fixation ?20 times and for
longer than 500 ms each time were excluded from fMRI analysis.
The functional images were motion-corrected to the image
acquired closest to the anatomical scan, undistorted by using the
field map scan (24), and spatially filtered with a 2-mm Gaussian
kernel. Each time series was normalized to its mean to input all
of the time series across scan sessions into a single multiple
regression analysis. Square-wave functions matching the time
courseoftheexperimentaldesignwereconvolvedwithagamma-
variate function (25) and used as regressors of interest in a
multiple regression model in the framework of the general linear
model (26). Additional regressors to account for variance due to
baseline shifts between time series, linear drifts within time
series, and head motion were included in the regression model.
Brain regions responding more strongly to faces or body parts
were identified by contrasting presentation blocks of faces with
objects and body parts with objects, respectively, similar to
definitions used in previous human fMRI studies (3, 4, 6, 27).
The statistical maps were thresholded at a Z score of 2.33 (P ?
0.01) and overlaid on anatomical scans or cortical surface
reconstructions.
Regions of interest within temporal cortex were defined as
clusters of 10 or more contiguous voxels. Clusters smaller than
10 voxels were included as regions of interest only if a larger
cluster (?10 voxels) was found in the same anatomical location
of the other hemisphere. The raw, unsmoothed fMRI signals
were averaged across all activated voxels within a given region of
interest and across scans, and normalized to the mean intensity
obtained during the blank periods. Statistical significance was
determined by two-sample t tests assuming unequal variances on
the averaged peak intensities of fMRI signals for each condition
obtained in a given scan session and in both monkeys. The
selectivity of each area for the different stimulus categories
was assessed by computing a category selectivity index [CSI ?
(Rcat? Rctrl)?(Rcat? Rctrl), where Rcatis the averaged response
of peak MRI intensities obtained during face or body part
conditions and Rctrlis the averaged response obtained during
the object condition].
Eye-movement analysis was performed with ILAB software
(28) and confirmed that the animals maintained fixation for
almost all of the time during scanning sessions. For example,
during a typical session, monkey M2 maintained fixation within
the 4° window for 97 ? 1% of the time and made an average of
2.5 ? 1 eye movements outside the window that lasted for ?500
ms before returning to the window.
Results
To identify brain regions that responded more strongly to faces
than man-made objects, we contrasted face and object condi-
tions and compared the resulting activations in monkeys M1–
M3. This contrast revealed two activated regions in temporal
cortex (Z ? 2.33, P ? 0.01). A posterior face (pFace) area was
activated bilaterally along the fundus and banks of the posterior
STS (slice 1 in Fig. 1A), and an anterior face (aFace) area, also
activated bilaterally, was found in the anterior STS and on the
Fig.1.
temporal cortex. (A) Coronal slices of monkeys M1 and M2 depicting voxels
activated significantly more by faces compared to objects. (B) Same coronal
slices depicting voxels activated significantly more by body parts compared
withobjects.Approximatelocationsofthecoronalslices(1,2)areindicatedon
a sagittal slice. Scale indicates Z-score values of functional activity in colored
regions. R, right hemisphere.
Category-selectiverepresentationsoffacesandbodypartsinmonkey
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middle temporal gyrus (MTG) (slice 2 in Fig. 1A). There was
some variability in the locations of these areas among the three
animals. For example, M1’s aFace area was located on both
banks and fundus of the STS, whereas M2’s aFace area was
located only on the right MTG (Fig. 1A). Activations in similar
locations were also found in M3 (Fig. 5, which is published as
supporting information on the PNAS web site).
Brain regions that responded more strongly to body parts than
toman-madeobjectswereidentifiedbycontrastingmonkeybody
part and object conditions and comparing the resulting activity
in monkeys M1 and M2. This contrast revealed two activated
regions in the temporal cortex (Z ? 2.33, P ? 0.01). A posterior
body part (pBody) area was found along the banks and fundus
of the STS in M1 (slice 1 in Fig. 1B) but not in M2. A second
region was found more anterior along the STS. This anterior
body part (aBody) area was activated bilaterally in both monkeys
and located on the banks and the fundus of the STS (slice 2 in
Fig. 1B).
It is important to note that the differences in activation
patterns could not be attributed to systematic differences in eye
movements while viewing the three categories of stimuli. Fixa-
tion performance was similar for the three monkeys, and there
were no significant differences in the amount of horizontal and
vertical eye movements made while viewing stimuli of the three
different categories [e.g., monkey M2: horizontal eye move-
ments, F0.05(2,45) ? 1.16, P ? 0.32; vertical eye movements,
F0.05(2,45) ? 0.52, P ? 0.59].
The anatomical relationship between the face and body part
areas was examined by determining the responsiveness of each
voxel shown in the activation maps of Fig. 1 for M1 and M2 to
faces (color-coded in red), body parts (color-coded in yellow), or
both stimuli (color-coded in blue). The color-coded voxels were
then projected onto inflated and flattened cortical surface
reconstructions (Fig. 2). With this presentation format, there
appears to be a larger number of category-selective areas
compared to those shown in Fig. 1. However, this is a result of
the data-display procedures. When neighboring voxels touch
cortically distant regions (e.g., upper and lower banks of a
sulcus), they tend to separate when projected onto the cortical
surface. Face-selective regions in M1 were located in the lower
and upper banks of the posterior STS in the left and right
hemispheres, respectively (Fig. 2A). Interestingly, the more
anterior activations in M1 for faces and body parts appeared to
be continuous and also partially overlapping. The body part-
selective area in the anterior STS in M2 was located on both
banks, and the aFace-selective area was found to be adjacent and
ventral to it on the right MTG (Fig. 2B). Overall, this topography
suggests a representation of the appearance of the monkey body
in the anterior STS and MTG. It is possible that there is a second
representation in the posterior STS, as suggested by the findings
in M1, but this will need further study.
To examine the extent of the category-selective activations,
the volumes of the activated regions in the left and right
hemisphere were analyzed and compared in the three animals
(Table 1). The size of the face activations ranged from 3 mm3to
103 mm3, and the size of the body part activations ranged from
87 mm3to 121 mm3. There were no significant differences in
activated volumes between the right and left hemisphere in any
of the category-selective areas except for the pFace area, which
showed a larger activation volume in the right than in the left
hemisphereineachofthethreemonkeys[t(2)?13.85,P?0.01].
The reliability of activations for the face and body part areas
in the STS was examined in monkey M1, who participated in two
additional experiments (Exps. 2 and 3 in Fig. 6, which is
published as supporting information on the PNAS web site) that
were similar to our original study (Exp. 1 in Fig. 6). Exp. 2 was
identical to Exp. 1 in terms of the experimental design but
involved a higher-resolution echo planar imaging sequence
Table 1. Activated volumes in category-selective areas
MonkeyArea
Activated volume, mm3
RHLH
M1pFace
aFace
pBody
aBody
56.25
18.75
21.88
121.88
12.5
103.13
6.25
87.5
M2 pFace
aFace
aBody
56.25
53.13
56.25
6.25
0
121.88
M3* pFace
aFace
56.25
31.25
0
3.13
Mean ? SEpFace
aFace
aBody
56 ? 0
34 ? 10
89 ? 33
6 ? 4
35 ? 34
105 ? 17
*Face responsive regions in monkey M3 were defined in a single scan session
by comparing faces to houses rather than to objects.
Fig. 2.
flattenedcorticalsurfacerepresentationsoftheleftandrighthemispheresof
monkeys M1 (A) and M2 (B). Activated voxels are color-coded according to
their preferred category. Faces ? objects, red; body parts ? objects, yellow;
overlap of the two, blue. sts, superior temporal sulcus; sf, sylvian fissure; ios,
inferior occipital sulcus; ots, occipitotemporal sulcus; ls, lunate sulcus; ips,
inferior parietal sulcus; cs, central sulcus; as, arcuate sulcus.
Topographic relationship of face and body part areas. Inflated and
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(1.25?1.25?1.25mminsteadof1.25?1.25?2.0mm).InExp.
3, we probed only the face and object, but not the body part
condition. Both the pFace and the aFace areas were activated
acrossthethreeexperiments(Fig.6A).Furthermore,thevolume
of the pFace area in the right hemisphere was larger than in the
corresponding area of the left hemisphere in both additional
experiments (Exp. 2: 97 mm3vs. 0 mm3; Exp. 3: 53 mm3vs. 16
mm3), thus replicating the right hemisphere asymmetry found
across the three monkeys in Exp. 1. The aBody area, but not the
pBody area, was activated in Exp. 2 (Fig. 6B), suggesting that
activations of the aBody area were more robust and reliable than
those of the pBody area.
The response properties and category selectivity of face- and
body part-related activations were studied by performing a time
course analysis of fMRI signals (Fig. 3A). fMRI signals were
averaged across all activated voxels within each region, across
hemispheres, scans, and monkeys M1 and M2 and normalized to
the average signals obtained during blank periods. This analysis
revealed that both face areas responded two to three times as
strongly to faces than objects [pFace: faces vs. objects, t(128) ?
3.20, P ? 0.01; aFace: faces vs. objects, t(142) ? 4.22, P ? 0.01].
However, the pFace area was as responsive to faces as to body
parts [pFace: faces vs. body parts, t(119) ? 0.68, not significant],
whereasbodypartsdidnotevokesignificantlystrongerresponses
than objects in the aFace area [aFace: body parts vs. objects,
t(141) ? ?0.62, not significant] (Fig. 3A). Both the posterior and
aBody areas responded more strongly to body parts than to
objects and faces [pBody: body parts vs. objects, t(61) ? 2.48, P ?
0.05; body parts vs. faces, t(61) ? 2.91, P ? 0.01; aBody: body
parts vs. objects, t(138) ? 4.76, P ? 0.01; body parts vs. faces,
t(138) ? 4.65, P ? 0.01]. However, objects and faces both evoked
a considerable and similar response in the posterior area,
whereas almost no activity was elicited by these stimuli in the
aBody area (Fig. 3A). The differences in category selectivity
were further quantified with a category selectivity index (CSI).
Values close to 1 indicate strong selectivity for a given stimulus
category (faces and body parts) relative to the control category
(objects). Values around 0 indicate no preference between the
stimulus category and the control category. And negative values
indicate a greater preference for the control category than the
probed stimulus category. It is striking that the aFace and aBody
areasaswellasthepBodyareawerehighlyselectiveforfacesand
body parts, respectively, whereas the pFace area did not dis-
criminate between faces and body parts (Fig. 3B and Table 2,
which is published as supporting information on the PNAS web
site).
Discussion
Our results confirm previous fMRI studies reporting face-
selective activations in apparently similar anatomical locations in
anesthetized (21) and awake macaques (22). They extend these
results by demonstrating an area responding selectively to body
parts adjacent to the face-selective area in the anterior STS. In
addition, our results suggest a more extensive activation of the
pFace area in the right hemisphere than in the left hemisphere.
The differences in activations that we obtained with face, body
part, and object stimuli are unlikely to reflect differences in the
attentional state of the animals performing the passive viewing
task. On such an account, one would not predict reliable
activations of the same regions across different experiments,
high test-retest reliability in the same experiment, or consistent
activations across individual monkeys, all of which were dem-
onstrated in our study.
Neuronsrespondingmorestronglytofacesthantoothervisual
stimuli have been found, on both banks and the floor of the STS,
and less prominently on the lateral and ventral convexity of IT
cortex (10–16). These STS ‘‘face cells’’ were often found clus-
tered together in patches and sometimes formed columns (19,
20). However, their overall proportion was reported to be small,
20% of visually responsive cells at the most (15), and no evidence
for a ‘‘face area’’ consisting of chiefly face responsive cells was
found. Indeed, bilateral lesions of the STS did not induce specific
impairments in face discrimination but led only to mild impair-
ments in discrimination of eye gaze (29, 30). Our results, on the
other hand, suggest that a large proportion of neurons that are
regionally clustered together in the anterior and posterior STS
must be activated selectively in response to faces to evoke
sufficiently strong blood oxygenation level-dependent signals.
Single-cell physiology studies in animals, in which the face-
selective blood oxygenation level-dependent signals will guide
the electrode placement, will be necessary to address this
apparent discrepancy.
In humans, functional brain imaging studies have demon-
strated a distributed neural system activated specifically by faces
consistingofareasinthelateralfusiformgyrus(theFFA),lateral
inferior occipital gyrus, and STS (3, 31). These different areas
appear to be involved in different aspects of the perceptual
analysis of faces. Perception of face identity was shown to be
associated with regions in the inferior occipital and fusiform
gyri,andperceptionofeyegaze,eye,andmouthmovements,and
facial expressions was associated with the STS region (32–35).
Our finding of several face-responsive areas exhibiting different
degrees of category-selectivity raises the possibility that face
Fig.3.
from the pFace, pBody, aBody, and aFace areas averaged across two monkeys
(M1 and M2). The duration of the visual stimulation epoch is indicated by the
black bar. The pBody area was activated only in M1. Note the y-axis scale
change for the time courses in the pFace and the aBody areas. (B) Selectivity
ofeachareatofaces(red)andbodyparts(black)relativetoobjects,computed
with an index (see Methods and Results).
TimecoursesoffMRIsignalsfromcategory-selectiveareas.(A)Signals
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perception in the macaque may also be mediated by a distributed
network of areas as in humans. Interestingly, in single-cell
studies, neurons responding more strongly to facial expression
were found more frequently in the STS, whereas neurons
responding to facial identity were found more frequently in the
IT gyrus (36), suggesting such a dissociation of function with
respect to different aspects of face perception. Neurons in the
anterior STS have been shown to respond to cues that are
important for social communication such as eye gaze or emo-
tional face expression (35, 37, 38). Therefore, it is possible that
the macaque anterior STS face area serves a similar function to
that of the human STS face area. Tsao and colleagues (22) have
proposed in a related monkey fMRI study that the face area in
the posterior STS may be homologous to the human FFA.
However, the human FFA has been shown to respond differen-
tially to faces and human bodies (39), whereas the pFace area
that we identified in the macaque did not discriminate monkey
faces and body parts.
We found a more extensive activation of the pFace area in the
right than in the left hemisphere, suggesting a hemispheric asym-
metry in the processing of face information in the macaque. This
findingisconsistentwithseveralstudiesreportingrighthemisphere
superiorityinmonkeysforprocessingfacialinformation(40–42).In
humans,thereisconvergingevidencefromneuropsychologicaland
neuroimaging studies for a right hemispheric dominance in face
perception. Damage to the posterior right hemisphere is often
sufficient to produce prosopagnosia (43). Neuroimaging studies
have shown that face-selective areas are often more strongly
activated in the right hemisphere than in the left hemisphere (3–5).
These findings are paralleled by behavioral studies demonstrating
thathumansubjectsprocessfaceinformationfasterwhenpresented
to the left hemifield than to the right hemifield, the so-called ‘‘left
field advantage’’ (44).
Neurons in the anterior STS have also been found to respond to
body parts such as hands (14, 17) and to static views of human
bodies with and without heads (18, 45). Our finding of an area in
the anterior STS that responded more strongly to body parts than
to faces and objects is in agreement with these physiology studies,
although, as with faces, the proportion of neurons responding
selectively to body parts or bodies was found to be rather small
(?10% of visually responsive neurons) and did not suggest the
existence of a category-selective area. Neurons in the anterior STS
have also been shown to respond to complex body movements such
as walking patterns (12, 46) or biological motion (45), suggesting
that this high-level extrastriate area integrates form and motion
aspects of biologically relevant visual stimuli (45). Tsao and col-
leagues (22) demonstrated an area responding more strongly to
headless human bodies relative to human body parts such as faces
and hands as well as man-made objects in posterior STS but not in
anterior STS, using fMRI in awake macaques. Their body area is
likely different from the pBody area of monkey M1 given that our
stimulus set contained monkey body parts including hand stimuli.
Whereas several of our findings regarding face-selective activa-
tions suggest similarities in the functional organization of face
representation in human and macaque, our findings regarding the
representations of body parts in the two species indicate a number
of differences. Although both species appear to have category-
specificrepresentationsofbodyparts,thehumanEBAislocatedin
Brodmann area 18, possibly in retinotopically organized visual
cortex (7), whereas the monkey body part area is located in the
anteriorSTS,ahigh-levelvisualprocessingareawithinthetemporal
cortex. The human EBA has been implicated not only in the
processing of the appearance of the body, but also in the coding of
goal-directed movements of the observer’s body parts (47). This
area does not, however, carry signals that can differentiate biolog-
ical from nonbiological motion (48), whereas neurons in the
anteriorSTShavebeenshowntorespondtobiologicalmotion(45).
Most importantly, the EBA and face-selective areas such as the
FFA were found in widely separated locations of cortex in the
human (ref. 7; but see ref. 39). In contrast, the body part-selective
regioninmacaqueanteriorSTSwasfoundtobeadjacentinM2and
partially overlapping with face-selective activations in M1, suggest-
ing a more continuous representation of the appearance of the
monkey body in the anterior STS.
In conclusion, we present evidence for category-selective neural
representations in macaque IT cortex for object stimuli that are of
particular biological significance to the animal, namely monkey
faces and body parts, suggesting a modular organization of certain
classes of object stimuli in the ventral visual pathway.
We thank Michael Benharrosh, Jonathan D. Cohen, Rhodri Cusack,
Michael S. A. Graziano, James V. Haxby, and Kimberly J. Montgomery.
This work was supported by National Institutes of Health Grants R01
EY-11347 (to C.G.G.), R01 MH-64043 (to S.K.), and P50 MH-62196 (to
S.K.) and a grant from the Whitehall Foundation (to S.K.).
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