THE JOURNAL OF COMPARATIVE NEUROLOGY 501:243–259 (2007)
Occipital Sulci of the Human Brain:
Variability and Probability Maps
GIUSEPPE IARIA1,2* AND MICHAEL PETRIDES1
Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada
2
Dipartimento di Psicologia, Università di Roma “La Sapienza,” CAP 00185 Rome, Italy
1
ABSTRACT
The morphological variation of the sulci of the occipital region of the human brain was
examined in both the left and the right hemispheres in 40 normal adult human brains on
magnetic resonance images. We identified the occipital sulci and marked their corresponding
gray matter voxels on the magnetic resonance images, which had been transformed into the
Montreal Neurological Institute standard proportional stereotaxic space in order to construct
probability maps. In the medial occipital region, the calcarine sulcus was the longest and
most constant sulcus. We identified, in the inferior part of the medial occipital lobe, the
lingual sulcus and the posterior collateral sulcus, and, in the superior part, the inferior and
superior sagittal sulci of the cuneus. On the lateral surface of the occipital lobe, the lateral
occipital, the lunate, and the transverse and inferior occipital sulci were identified. The
parieto-occipital fissure and the temporo-occipital incisure were also identified on the lateral
and medial surfaces. Finally, the patterns of the occipital sulci and gyri were examined in 20
post-mortem human hemispheres fixed in formalin. Probability maps of the occipital sulci
were constructed, which provide a quantitative description of the variability of the sulci in
standard stereotaxic space and may be used to identify the location of voxels in other
magnetic resonance images transformed into the same streotaxic space. These maps are a
useful tool in the study of functional activations related to visual processing. J. Comp. Neurol.
501:243–259, 2007. © 2007 Wiley-Liss, Inc.
Indexing terms: sulcus; visual cortex; morphology; lunate sulcus; calcarine sulcus; lateral
occipital sulcus; transverse occipital sulcus
The occipital region of the human brain is traditionally
defined as extending from the occipital pole to the parietooccipital fissure, dorsally, and to the temporo-occipital incisure, ventrally. In both the human and the nonhuman primate brain, the occipital region is involved in visual
information processing. By the beginning of the Twentieth
Century, it was clearly established that the distinct cortex
comprising the stripe of Gennari (i.e., the striate cortex),
which lies on the banks of the calcarine sulcus, was involved
in visual cortical processing (see, e.g., Bolton, 1900). The
sulcal and gyral patterns of the occipital region of the human
brain became the subject of investigation during the latter
part of the Nineteenth Century and the first half of the
Twentieth Century (see, e.g., Cunningham, 1892; Eberstaller, 1890; Elliot Smith, 1904a– c; Retzius, 1896). Much of
this early work focused on the calcarine sulcus and its relation to the striate cortex, producing a number of publications
in which the detailed morphological relations of striate cortex, the calcarine sulcus, and the immediately surrounding
sulci were outlined (see, e.g., Bolton, 1900; Elliot Smith,
1904a– c; Shellshear, 1926).
© 2007 WILEY-LISS, INC.
Architectonic studies at the beginning of the Twentieth
Century established that the striate cortex (area 17 in the
Brodmann map, 1909; area OC in the Economo and Koskinas map, 1925) was surrounded by a ring of cortex with
different architecture (area 18 in the Brodmann map; area
OB in the Economo and Koskinas map) and then another
larger region (area 19 in the Brodmann map; area OA in
the Economo and Koskinas map). Thus, the architectonic
studies had already implied the presence of more than one
visual area in the occipital cortex. Beginning in the 1960s,
Grant sponsor: Canadian Institutes of Health Research (CIHR); Grant
number: MOR 14620.
*Correspondence to: Giuseppe Iaria, PhD, Cognitive Neuroscience Unit,
Montreal Neurological Institute, McGill University, 3801 University St.,
Montreal, Quebec, Canada H3A 2B4.
E-mail: giuseppe.iaria@mcgill.ca
Received 16 August 2006; Revised 12 October 2006; Accepted 31 October
2006
DOI 10.1002/cne.21254
Published online in Wiley InterScience (www.interscience.wiley.com).
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244
G. IARIA AND M. PETRIDES
neurophysiological investigations mapping the receptive
fields of single neurons responding to visual stimuli in the
occipital region of nonhuman primates identified several
visual areas that surround and extend anterior to the
striate cortex that now came to be referred to as area V1
(see, e.g., Allman and Kaas, 1971; Zeki, 1969, 1974,
1978a,b). In nonhuman primates, these additional visual
areas hold an excellent relation to sulcal and gyral landmarks. For instance, in the dorsal occipital region, area V2
occupies the posterior bank of the lunate sulcus, V3 and
V3A are found on the annectant gyrus that is buried in the
lunate sulcus, area V4 is located on the prelunate gyrus,
area V5/MT is found on the posterior bank of the caudal
superior temporal sulcus, and area V6 is found within the
parieto-occipital fissure (for reviews see Felleman and
Van Essen, 1991; Kaas, 2004; Sereno and Tootell, 2005).
In recent years, developments in functional neuroimaging in normal human subjects, such as functional magnetic resonance imaging (fMRI), have permitted the mapping of several visual areas of the human brain and have
already provided provisional identification of some of the
visual areas that were first described in nonhuman primates (see Sereno and Tootell, 2005). These areas are V1,
V2, V3, V3A, V4, V5/MT, and V6 (e.g., Anderson et al.,
1996; Barton et al., 1996; Bense et al., 2006; de Jong et al.,
1994; DeYoe et al., 1996; Dougherty et al., 2003; Dumoulin
et al., 2000; Dupont et al., 1994; Hadjikhani et al., 1998;
Hasnain et al., 1998; Itoh et al., 2005; Sack et al., 2006;
Sereno et al., 1995; Shipp et al., 1995; Shulman et al.,
1998; Stiers et al., 2006; Tootell et al., 1996, 1997; Tootell
and Hadjikhani 2001; Vallines et al., 2006; Walters et al.,
2003; Watson et al., 1993; Zeki et al., 1991). The first
visual area outside the striate cortex that was identified in
the human brain was the motion area V5/MT, for which a
reasonably good relation with certain sulcal landmarks
was noted (Watson et al., 1993; Zeki et al., 1991). The
V5/MT motion area lay within a sulcus that had variously
been named the anterior occipital sulcus or an ascending
branch of the inferior temporal sulcus (Cunnigham, 1892).
Watson and colleagues (1993) noted the lack of standard
terminology and adequate description of the sulci of the
occipital region of the human brain with the exception of
the calcarine sulcus.
The lack of an adequate description of the sulcal patterns of the human occipital region, with the exception of
the calcarine sulcus, which is evident from inspection of
any one of several modern standard textbooks of neuro-
Abbreviations
acc
ACS
AOS
BCS
IOS
ISGS
LiS
LOS
LuS
PCS
POF
RCS
SSGS
TO
TOS
accessory lateral occipital sulci
anterior calcarine sulcus
anterior occipital sulcus
body of the calcarine sulcus
inferior occipital sulcus
inferior sagittal sulcus
lingual sulcus
lateral occipital sulcus
lunate sulcus
posterior collateral sulcus, i.e., the occipital extension of
the collateral sulcus
parieto-occipital fissure
retrocalcarine sulcus
superior sagittal sulcus
temporo-occipital incisure
transverse occipital sulcus
anatomy (see, e.g., Carpenter, 1996; Nolte, 2002), makes it
difficult to establish clear relations between sulcal landmarks and identified visual areas with modern functional
neuroimaging. There have been no examinations of the
sulcal patterns of the occipital region of the human brain
in recent years, with the exception of the studies by Ono
and colleagues (1990) on 25 human cadaver brains. Ono
and colleagues (1990) examined the patterns formed by
the calcarine sulcus and its relation to the parietooccipital fissure as well as the sagittal sulci of the cuneus
and the lingual gyrus that immediately border the calcarine sulcus on the medial surface of the hemisphere. The
sulci of the lateral part of the occipital region, however,
were not investigated by Ono and colleagues.
The aim of the present investigation was to examine the
sulcal patterns on the medial and lateral surface of the
human occipital region and to provide a quantitative description of the variability of these sulci in standard stereotaxic space in the form of probability maps. Modern
functional neuroimaging studies have relied on the Talairach and Tournoux (1988) atlas to determine the location of functional activity in the human brain resulting
from functional neuroimaging studies. Because the Talairach and Tournoux atlas is based on one hemisphere of
a single brain, it does not provide any measure of anatomical variability. The proper use of a standard stereotaxic
space requires statistical statements of the variability of
the location of a given brain structure (e.g., a sulcus)
within that space in order to account for individual differences. Probability maps have already been provided for
the cingulate and paracingulate sulci (Paus et al., 1996),
the primary auditory region (Penhune et al., 1996), the
pars opercularis of the inferior frontal gyrus (Tomaiuolo et
al., 1999), the sulci of the orbital frontal cortex (Chiavaras
et al., 2001), and the precentral sulci (Germann et al.,
2005). The present study examines the anatomical variability of the sulci of the human occipital region. The
findings can be used to relate activation foci of visual
processing obtained from functional neuroimaging studies
in a precise quantitative manner.
MATERIALS AND METHODS
Subjects
Magnetic resonance imaging (MRI) scans of both the left
and the right hemispheres of 40 human brains were examined. The sample consisted of 17 females (mean age
25.5 years, SD 5.3) and 23 males (mean age 25 years, SD
5.3). All subjects were right-handed, and none had a positive history of neurological and psychiatric disorders. The
subjects were randomly selected from the International
Consortium for Brain Mapping project (Mazziotta et al.,
1995a,b). All subjects gave informed consent. We also examined 10 post-mortem human brains fixed in formalin
(six females, four males; mean age 70.5 years, SD 9.2) to
investigate the patterns of the occipital sulci and gyri.
Photographs of the sulci patterns on the post-mortem
brain were taken with a digital camera, and modifications
of the images (contrast and brightness) were made in
Adobe Photoshop.
MRI
The MRI scans were performed on a Philips Gyroscan
1.5-T superconducting magnet system. A fast-field echo
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3-D acquisition sequence was used to collect 160 contiguous 1-mm T1-weighted images (Tr ⫽ 18 msec, Te ⫽ 10
msec, flip angle ⫽ 30°) in the sagittal plane. To normalize
and correct the images for interindividual differences in
gross brain size, each MR volume was transformed into
the Montreal Neurological Institute (MNI) standardized
stereotaxic space (Evans et al., 1992; Mazziotta et al.,
1995a,b), which is based on that of Talairach and Tournoux (1988). For each MR volume, the transformation was
determined by an automated registration using 3D crosscorrelation (Collins et al., 1994) to a target image that was
the intensity average of 305 brain volumes previously
aligned to the Talairach atlas (Evans et al., 1992). The
image data were then resampled onto a standard grid
with cubical voxels 1 mm wide. The mediolateral (left–
right) axis was defined by using the x-coordinate (positive ⫽ right hemisphere), the rostrocaudal (anterior–
posterior) axis by using the y-coordinate (positive ⫽
rostral to anterior commisure), and the dorsoventral
(superior–inferior) axis by using the z-coordinate (positive ⫽ superior to a horizontal line drawn through anterior and posterior commissures).
Localization of the occipital sulci
The occipital sulci were manually identified using DISPLAY, an interactive 3-D imaging software package (MacDonald, 1996). The software displays a 3-D view of the
brain surface as well as sections in the coronal, horizontal,
and sagittal planes. The sections on the screen are automatically updated as the cursor is moved from voxel to
voxel in order to mark the location of the sulcus investigated. This automatic updating of the views on the screen
allows the investigator to identify accurately the extent
and direction of a particular sulcus. DISPLAY also generates a histogram of the image intensity values, which is
used to determine the upper intensity threshold for voxels
of the cerebrospinal fluid (CSF). All voxels were automatically classified according to tissue type (Kollokian, 1996).
Initially, the voxels considered to contain CSF between
the sulcal banks were marked by the investigator. The
gray-matter voxels extending for 1 mm on either side of
the banks of the sulcus, adjacent to those in the sulcal
CSF, were automatically included in the set of voxels
constituting the sulcus. The lateral and medial surfaces of
the occipital lobe of the formalin-fixed post-mortem human hemispheres were examined and photographed to
identify the typical sulcal and gyral patterns, as described
in the classical literature.
Probability mapping
After labeling of the voxels forming each of the sulci of
interest, 3-D probability maps were constructed. For each
sulcus, the probability values are displayed by means of a
color scale. The minimum value of each scale is 0.1 (10% of
the subjects included in this study). The highest probability value varied for different sulci. The maps were constructed by dividing, at each particular 3-D stereotaxic
location, the number of times that a voxel belonged to the
sulcus of interest by the number of subjects examined.
These probability values, which are displayed in colorcoded maps, thus represent the likelihood that any voxel
in MNI space will be classified as part of the sulcus. For
example, if the value at the given x,y,z location is 0.6, then
this location was occupied by a voxel that belong to that
sulcus in 60% of the subjects examined. The probability
245
maps are then superimposed on the intensity-averaged
target image of 305 brains (Evans et al., 1992), and the
stereotaxic x,y,z coordinate values are provided in the
MNI standard proportional space. In other words, these
maps quantify the spatial variability of the sulci in a
standard stereotaxic space.
RESULTS
We identified 11 occipital sulci in 80 hemispheres and
marked the gray-matter voxels that constituted these
sulci in the MNI space. In addition, we identified and
marked the gray-matter voxels around the parietooccipital fissure (POF) and the temporo-occipital incisure
(TO). Figures 1– 4 present photographs of the medial, lateral, basal, and dorsal surfaces, respectively, of the occipital lobe in post-mortem human hemispheres, illustrating
patterns of the occipital sulci. Figures 5–7 present coronal,
horizontal, and sagittal sections, respectively, through the
occipital region of one MRI brain to identify the location of
the sulci of interest. Examples of probability maps of the
POF and TO are provided in coronal section (POF, Fig. 8;
TO, Fig. 9).
Calcarine sulcus
The main sulcus on the medial part of the occipital lobe
is the calcarine sulcus, which extends from just below the
splenium of the corpus callosum all the way to the occipital pole. The parieto-occipital fissure extends from the
dorsal surface of the hemisphere all the way down in an
oblique direction to join the anterior part of the calcarine
sulcus, thus delimiting the upper part of the medial occipital lobe known as the cuneus (see Fig. 1). The anterior
part of the calcarine sulcus, extending in an anteroventral
direction in front of the point of intersection with the
parieto-occipital fissure (see asterisk in Figs. 1, 3), has
been referred to as the sulcus calcarinus proprius by Elliot
Smith (1904) and as the trunk of the calcarine and parietooccipital fissures by Economo and Koskinas (1925). In the
present description, we refer to this part of the calcarine
sulcus as the anterior calcarine sulcus (ACS; Fig. 1). Elliot
Smith (1904) referred to the part of the calcarine sulcus
that extends posterior to the point of intersection with the
parieto-occipital fissure as the retrocalcarine sulcus (sulcus retrocalcarinus). The term retrocalcarine sulcus, however, was gradually restricted by other investigators (Duvernoy, 1999; Economo and Koskinas, 1925) to the most
posterior tail of the calcarine sulcus, which often fans out
into an upper and a lower part (see Fig. 1a,b). We also use
the term retrocalcarine sulcus (RCS) to refer to the tailend of the calcarine sulcus, and we refer to the remaining
main part as the body of the calcarine sulcus (BCS; see
Fig. 1). The retrocalcarine sulcus may remain on the medial surface (Fig. 1a,b) of the occipital lobe or extend to the
lateral surface (Fig. 1c,d). The appearance of the different
parts of the calcarine sulcus on the coronal, horizontal,
and sagittal MRI sections can be visualized in Figures
5–7. Examples of probability maps of the RCS and the
BCS in coronal section are provided in Figure 8. Similarly,
examples of probability maps of and the ACS are available
in coronal section (Fig. 9).
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G. IARIA AND M. PETRIDES
Fig. 1. a– d: Sulci on the medial surface of the occipital lobe. The figure shows the sulci present on the
medial surface of four post-mortem human hemispheres fixed in formalin. *Intersection of the anterior
calcarine sulcus with the parieto-occipital fissure. For abbreviations see list. Scale bars ⫽ 1 cm.
Inferior and superior sagittal sulci
of the cuneus
Just dorsal to the body of the calcarine sulcus, there is
frequently a sulcus running, more or less, parallel to it.
This sulcus has been referred to as the inferior sagittal
sulcus (ISGS) of the cuneus by Economo and Koskinas
(1925) to distinguish it from another, somewhat less frequent superior sagittal sulcus of the cuneus (SSGS). Duvernoy (1999) referred to the inferior sagittal sulcus of the
cuneus as the paracalcarine sulcus, but this term is probably best avoided, because the same name has been used
for a sulcus that lies on the posterior bank of the parietooccipital fissure (Elliot Smith, 1904a). In the present
study, we have adopted the terminology of Economo and
Koskinas (1925) for the sulci of the cuneus. The appearance of the different patterns of these two sulci of the
cuneus can be visualized in Figure 1 (photographs of postmortem human brains) and in Figure 5–7 displaying the
coronal, horizontal, and sagittal MRI sections, respectively. Examples of probability maps of the ISGS and
SSGS are provided in coronal section (ISGS, Fig. 9; SSGS,
Fig. 10).
Posterior collateral and lingual sulci
In the inferior part of the occipital lobe (below the calcarine sulcus), the posterior branch of the collateral sulcus
(PCS) runs, more or less, parallel to the body of the calcarine sulcus, thus delimiting the lingual gyrus (Figs. 3,
7). Occasionally, within the lingual gyrus, there is a sulcus
running, more or less, parallel to the body of the calcarine
sulcus, dividing it into a superior and an inferior lingual
gyrus. This sulcus has been referred to as the lingual
sulcus (LiS) in the classical literature (e.g., Economo and
Koskinas, 1925) and, more recently, as the intralingual
sulcus by Ono and coauthors (1990). We have retained the
classical term lingual sulcus (Figs. 3, 7). The probability
maps of the PCS and the LiS are available in coronal
section (Fig. 10).
Lunate, lateral, inferior, and transverse
occipital sulci
At the most caudal part of the lateral occipital lobe lies
a dorsoventrally oriented sulcus, often forming a concavity
directed toward the occipital pole, namely the lunate sulcus (LuS; see Fig. 2). In MRI images, it is very hard to
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247
Fig. 2. a– d: Sulci on the lateral surface of the occipital lobe. The figure shows the sulci present on the
lateral surface of four post-mortem human hemispheres fixed in formalin. For abbreviations see list.
Scale bars ⫽ 1 cm.
identify this sulcus because of both its shape and its location on the lateral to medial curvature of the occipital pole
(see Figs. 5–7). Immediately anterior to the lunate sulcus,
the horizontally oriented lateral occipital sulcus (LOS) can
be identified (see Fig. 2; Duvernoy, 1999; Eberstaller,
1890; Economo and Koskinas, 1925; Ono et al., 1990).
Elliot Smith (1904a) referred to this sulcus as the prelunate sulcus (sulcus praelunatus). This sulcus usually
blends, more or less, with the middle part of the lunate
sulcus and divides the lateral surface of the occipital lobe
into a superior and an inferior part. In the inferior part of
the occipital region, close to the base of the hemisphere, is
the inferior occipital sulcus (IOS), the caudal end of which
runs close to the most ventral part of the lunate sulcus
(see Fig. 2). In the superior part of the occipital region, the
transverse occipital sulcus (TOS) can be identified (see Fig.
2; Duvernoy, 1999; Elliot Smith, 1904a). This sulcus,
which is more or less dorsoventrally oriented, lies caudal
to the parieto-occipital fissure and joins the occipital extension of the intraparietal sulcus. Economo and Koskinas
(1925) referred to this sulcus as the sulcus occipitalis
primus. The appearance of these sulci on coronal, horizontal, and sagittal MRI sections can be appreciated in Figures 5–7, respectively. Examples of probability maps of
the LuS and LOS are displayed in coronal section (LuS,
Fig. 10; LOS, Fig. 8). Similarly, examples of probability
maps of the IOS and TOS are available in coronal section
(IOS, Fig. 8; TOS, Fig. 10).
Gray-matter volumes of the occipital sulci
We analyzed the volumes of the intrasulcal gray matter
obtained from each of the sulci identified in the occipital
lobe. Two-way repeated-meausures analyses of variance
(ANOVA) were performed to evaluate the effect of gender
(female, male) and side (left and right hemisphere; with cc
volume as repeated measures) on each of the occipital
sulci. The main effect of the gender was statistically significant for the IOS (F1,38 ⫽ 6.4, P ⫽ 0.016) and LiS
(F1,38 ⫽ 5.02, P ⫽ 0.031). On the other hand, the main
effect of side was statistically significant for the RCS
(F1,38 ⫽ 6.25, P ⫽ 0.168), SSGS (F1,38 ⫽ 4.61, P ⫽ 0.038),
TOS (F1,38 ⫽ 10.33, P ⫽ 0.003), and PCS (F1,38 ⫽ 6.73, P ⫽
0.013). Post hoc comparison (Duncan’s test) of these effects showed that the larger gray-matter volumes were
found in males (vs. females) and in the left hemisphere
(vs. right). No other significant main or interaction effects
were found for the other sulci. In Table 1 we report the
volumes of the occipital sulci in individual sulci and the
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Fig. 3. a– d: Sulci identified on the basal surface of the occipital lobe. The figure shows the sulci
present on the basal surface of four post-mortem human hemispheres fixed in formalin. Asterisks
indicate intersection of the anterior calcarine sulcus with the parieto-occipital fissure. For abbreviations
see list. Scale bars ⫽ 1 cm.
mean values according to gender (females, males) and
hemisphere (left, right).
DISCUSSION
Although classic and modern descriptions of the morphology of the medial surface of the occipital region of the
human brain are reasonably consistent with each other,
descriptions of its lateral surface have generated considerable confusion. The same sulcus is frequently identified
with different names, and two obviously different sulci are
referred to by the same name (see below). Indeed, most
modern neuroanatomy textbooks avoid any description of
the sulci of the lateral occipital region of the human brain,
providing only a general definition of the lateral occipital
lobe as being that part of the posterior hemisphere that is
bounded by the parieto-occipital fissure dorsally and by
the temporo-occipital incisure ventrally (see, e.g., Carpenter, 1996; Nolte, 2002). The present examination of the
morphology of the occipital region in the MRIs of 80 cerebral hemispheres (40 left and 40 right), as well as 20
hemispheres of post-mortem brains, showed that, despite
the existence of considerable morphological variation, a
basic pattern governs the variability and can be used to
identify most of the sulci consistently. We provide below a
description of the basic pattern of the sulci of the lateral
occipital region, which is clearly illustrated in Figure 2a,
with comments on the variability that this pattern exhibits (Fig. 2b– d), and then we describe the less controversial
medial occipital region (Fig. 1).
Just anterior to the dorsoventrally directed lunate sulcus, which is situated close to the occipital pole, extends a
more or less horizontally arranged sulcus, the lateral occipital sulcus. The lateral occipital sulcus (Fig. 2), which
has also been called the praelunate sulcus by Elliot Smith
(1904a– c), is a very important sulcus for the definition of
the overall morphology of the lateral surface of the occipital region of the human brain because it divides it into a
superolateral and an inferolateral portion. The lunate sulcus is often difficult to identify in MRIs because of its
position on the curvature of the occipital pole, but the
lateral occipital sulcus can be reliably identified in coronal
MRI sections and can, therefore, be used to define the
superolateral and inferolateral portions of the lateral occipital lobe. Ventral or dorsal to the main lateral occipital
sulcus, there may be accessory lateral occipital sulci that
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249
Fig. 4. a– d: Sulci on the dorsal surface of the occipital lobe. The figure shows the sulci present on the
dorsal surface of four post-mortem human hemispheres fixed in formalin. For abbreviations see list. Scale
bars ⫽ 1 cm.
are shallower, shorter, and inconsistent (Fig. 2). By contrast, it has never proved difficult to identify the main
lateral occipital sulcus, which has a rostral end that approaches the anterior occipital sulcus and often blends
with it (superficially) and a caudal part that approaches
and often blends, approximately, with the midpoint of the
lunate sulcus (Fig. 2). The lunate sulcus is sometimes
divided into an upper and a lower branch by a submerged
or an exposed narrow gyrus (the translunate gyrus), and,
when this happens, either the dorsal or the ventral branch
of the lunate sulcus may blend with the lateral occipital
sulcus. Occasionally, the lunate sulcus blends with the
lateral occipital sulcus in such a manner that it appears as
the caudal tail of the lateral occipital sulcus (Fig. 2c).
The sulcus that marks the morphology of the superolateral portion of the human occipital region is the transverse occipital sulcus that runs in a dorsoventral direction
above the lateral occipital sulcus (Fig. 2a). The transverse
occipital sulcus emerges from the occipital extension of the
intraparietal sulcus just caudal to the parieto-occipital
fissure and often forms a branch running in a dorsomedial
direction (i.e., above the intraparietal sulcus) and a
branch running in ventrolateral direction below the intraparietal sulcus. These dorsomedial and ventrolateral
branches may blend (Fig. 2a,d) or remain separate (Fig.
2b,c) on the surface of the brain. The ventrolateral branch
of the transverse occipital sulcus may extend ventrally to
just above the lateral occipital sulcus and anterior to the
upper part of the lunate sulcus (Fig. 2), but in some brains
it may, superficially, appear to join the upper part of the
lunate sulcus because it extends beneath the posterior
bank of the lunate sulcus. Various names have been used
to refer to the transverse occipital sulcus: Economo and
Koskinas (1925) refer to the dorsomedial branch of the
transverse occipital sulcus as the sulcus parietalis transversus and its ventrolateral branch as the sulcus occipitalis primus. Elliot Smith (1904a) treats the transverse
occipital sulcus as the tail of what he calls the paroccipital
sulcus (i.e., the occipital extension of the intraparietal
sulcus). Eberstaller (1892) has referred to the transverse
occipital sulcus as the fissura occipitalis anterior, but this
name has been used for a completely different sulcus that
lies anterior to it by Wernicke (1876) and Elliot Smith
(1904a), and this terminology has been adopted by most
modern investigators (see, e.g., Malikovic et al., 2006; Ono
et al., 1990) and in the present study (see Fig. 2).
Since the completion of our study, an article on the
lunate sulcus of the human brain has been published by
The Journal of Comparative Neurology. DOI 10.1002/cne
Fig. 5. a–j: Coronal view of the occipital sulci. Coronal sections through the magnetic resonance
imaging volume of a single subject with the sulci of interest identified. The level in the rostrocaudal
dimension (y) in millimeters is shown within each image. For abbreviations see list.
The Journal of Comparative Neurology. DOI 10.1002/cne
Fig. 6. a–n: Horizontal view of the occipital sulci. Horizontal sections through the magnetic resonance
imaging volume of a single subject with the sulci of interest identified. The level in the dorsoventral
dimension (z) in millimeters is shown within each image. For abbreviations see list.
The Journal of Comparative Neurology. DOI 10.1002/cne
252
G. IARIA AND M. PETRIDES
Fig. 7. Sagittal view of the occipital sulci. Sagittal sections of the left (a– h) and right (i–n) hemisphere in the magnetic resonance imaging volume of a single subject with the sulci of interest identified.
The level in the mediolateral dimension (x) in millimeters is shown within each image. For abbreviations
see list.
The Journal of Comparative Neurology. DOI 10.1002/cne
THE HUMAN OCCIPITAL LOBE
Fig. 8. Probability maps on coronal sections of the parieto-occipital
fissure (POF), the retrocalcarine sulcus (RCS), and the lateral occipital sulcus (LOS) are displayed in Aa–f. Probability maps of the body
of the calcarine sulcus (BCS) and the inferior occipital sulcus (IOS)
253
are displayed in Ba–f. The probability maps of the sulci are superimposed on the average brain of the MNI (Evans et al., 1992), and the
coordinates provided are within the MNI standard proportional stereotaxic space.
The Journal of Comparative Neurology. DOI 10.1002/cne
254
G. IARIA AND M. PETRIDES
Fig. 9. a– h: Probability maps on coronal sections of the anterior calcarine sulcus (ACS), the inferior
sagittal sulcus (ISGS), and the temporo-occipital incisure (TO). The probability maps of the sulci are
superimposed on the average brain of the MNI (Evans et al., 1992), and the coordinates provided are
within the MNI standard proportional stereotaxic space.
Allen and colleagues (2006). These investigators note the
high variability in the shape of the lunate sulcus and
report that, when present, it is most often not a single
sulcus but rather a composite of two or more sulcal segments. They defined the lunate as a continuous sulcus
that traverses a substantial portion of the lateral surface
of the posterior occipital lobe. This definition would include not only the lunate sulcus as defined by Elliot Smith
(1904a– c) and by ourselves but also the transverse occipital sulcus and even the caudal part of the lateral occipital
sulcus. Indeed, Allen and colleagues (2006, p 871) point
out that, if a typical pattern can be identified in the composite lunate sulci they identified, “it is one in which the
superior portion is formed by the extension of intraparietal sulcus (i.e., the transverse occipital sulcus), which
then extends downward to form a junction with another
occipital sulcus (e.g., the lateral occipital sulcus or occipitopolar sulcus, sensu Duvernoy, 1999).” If one were to
adopt such a definition, the lunate sulcus of the human
brain would clearly not be homologous to the lunate sulcus
in nonhuman primate brains. We have defined the lunate
sulcus as a short sulcus on the occipital pole that may
blend, superficially, with the ventralmost part of the
transverse occipital sulcus or the caudalmost part of the
lateral occipital sulcus, but it is clearly distinct from these
other two sulci. Because in nonhuman primate brains the
lunate sulcus lies close to the lateral border of the striate
cortex, its homologue in the human brain can be considered to be a sulcus only at the very posterior part of the
lateral occipital lobe, where a small fraction of the striate
cortex extends. We agree with Allen and colleagues (2006)
that there has been considerable development of the occipital region of the human brain. We believe that the
transverse occipital and lateral occipital sulci found on the
human occipital lobe are new sulci and are related to
prestriate cortical areas (see below), which, in the macaque monkey brain, lie on the annectant gyrus that is
hidden within the nonhuman lunate sulcus and the prelunate gyrus that extends anterior to it.
Allen and colleagues (2006) report that the composite
lunate sulcus, as they defined it for the human brain, was
observed in 32.7% of the left hemispheres and 26.4% of the
right hemispheres. These percentages are much lower
than those reported by Ono et al. (1990) for the lunate
The Journal of Comparative Neurology. DOI 10.1002/cne
THE HUMAN OCCIPITAL LOBE
Fig. 10. Probability maps on coronal sections of the superior sagittal sulcus (SSGS) and the posterior collateral sulcus (PCS) are
displayed in Aa– c. Ba–f displays the probability maps of the lingual
sulcus (LiS) and the lunate sulcus (LuS). Finally, Ca– c displays the
255
probability maps of the transverse occipital sulcus (TOS). The probability maps of the sulci are superimposed on the average brain of the
MNI (Evans et al., 1992), and the coordinates provided are within the
MNI standard proportional stereotaxic space.
The Journal of Comparative Neurology. DOI 10.1002/cne
256
G. IARIA AND M. PETRIDES
TABLE 1. Volume (cc) of the Occipital Sulci for Individual Subjects and Mean Values According to Gender and Hemisphere1
POF
S1 (female)
S2 (female)
S3 (female)
S4 (female)
S5 (female)
S6 (female)
S7 (female)
S8 (female)
S9 (female)
S10 (female)
S11 (female)
S12 (female)
S13 (female)
S14 (female)
S15 (female)
S16 (female)
S17 (female)
S18 (female)
S19 (female)
S20 (female)
S21 (male)
S22 (male)
S23 (male)
S24 (male)
S25 (male)
S26 (male)
S27 (male)
S28 (male)
S29 (male)
S30 (male)
S31 (male)
S32 (male)
S33 (male)
S34 (male)
S35 (male)
S36 (male)
S37 (male)
S38 (male)
S39 (male)
S40 (male)
F Mean
F SD
M Mean
M SD
Mean
SD
MEAN (SD)
L
R
27.5
15.4
25.3
26.6
16.6
28.8
19.2
22.0
24.6
42.9
11.8
38.3
20.1
37.4
19.2
38.7
13.3
24.3
22.5
27.0
11.2
19.8
14.9
27.2
25.6
29.2
22.2
23.3
14.8
13.0
39.5
32.8
24.7
41.2
25.8
20.4
30.9
40.5
14.3
9.3
25.2
9.5
24.1
9.0
24.5
9.1
24.0
18.4
18.7
29.0
30.5
16.7
27.2
18.0
18.6
27.5
38.9
13.3
39.4
18.7
20.0
22.0
35.1
8.7
25.8
19.9
30.2
17.9
13.3
18.1
16.6
20.8
21.6
8.7
27.2
24.7
20.9
31.1
37.0
17.3
41.2
15.5
14.1
25.5
42.5
40.4
11.4
23.6
8.7
23.5
9.7
23.6
9.2
(9.1)
TO
L
BCS
R
2.5 3.4
2.2 1.3
1.3 0.6
2.2 1.0
0.9 0.8
1.0 0.7
0.8 0.8
0.6 0.7
1.3 0.8
1.1 0.8
0.9 0.7
1.0 1.9
1.0 0.9
2.1 0.8
1.2 1.2
0.8 0.8
0.5 1.0
1.6 1.4
0.7 0.4
0.8 0.8
1.6 4.7
1.0 1.6
2.3 2.7
0.0 0.8
0.9 1.3
0.8 2.4
0.5 0.6
0.5 0.7
0.6 0.7
1.3 0.8
0.9 0.9
1.2 1.3
1.2 0.7
2.0 0.7
1.1 0.7
0.6 1.3
1.7 0.5
1.2 1.0
1.0 0.3
0.3 0.9
1.2 1.1
0.5 0.3
1.1 1.2
0.5 1.0
1.2 1.1
0.6 0.8
1.1 (0.7)
L
R
14.1
5.3
10.0
11.2
6.4
15.8
10.9
8.9
10.1
14.5
7.1
17.3
11.8
18.6
7.6
0.0
8.3
22.2
10.0
8.8
7.2
8.9
10.1
8.9
11.3
8.0
10.8
4.8
11.7
8.3
15.4
16.3
12.2
19.1
14.1
15.1
8.7
19.4
4.3
6.7
11.1
4.8
11.4
4.7
11.3
4.4
11.2
9.8
8.5
11.0
10.7
12.9
13.4
7.0
8.1
8.1
11.2
2.8
17.8
10.1
12.4
9.5
41.0
11.3
15.0
12.3
7.3
9.0
12.1
8.2
10.6
5.4
8.9
10.9
4.7
10.5
11.7
13.3
13.2
6.5
17.1
13.5
9.0
11.5
20.7
7.9
3.5
12.1
8.1
10.5
4.0
11.2
6.0
(5.4)
ACS
L
R
RCS
L
R
5.6
4.5 4.1 1.2
3.6
5.0 0.0 1.5
4.1
6.6 2.2 1.7
7.0
7.9 6.7 4.4
8.0
7.7 0.7 1.1
9.8
9.4 7.3 4.0
4.1
6.2 5.6 0.0
9.9
6.5 1.5 2.6
8.0
7.8 2.6 2.4
12.1 10.6 2.1 2.5
3.3
3.0 0.8 2.6
6.1
5.4 10.2 4.0
6.9
5.4 1.4 0.3
9.5
3.5 4.6 4.0
3.1
5.4 1.7 1.2
6.9 12.1 3.5 2.9
4.0
3.7 2.2 1.3
6.5
4.4 1.4 1.0
10.5 7.5 3.2 0.6
7.0
8.3 2.2 2.4
3.3
4.0 2.4 2.0
5.5
9.0 8.0 3.8
3.7
4.1 2.9 0.0
4.8
4.8 2.2 2.0
7.3
4.5 2.7 9.6
7.3
5.6 2.7 0.7
5.8
5.5 1.6 1.9
15.1 0.0 1.6 0.7
6.6
6.4 3.4 1.0
18.3 0.0 1.3 0.0
10.4 10.3 1.4 5.0
8.6 12.7 5.1 4.5
9.2
6.7 2.8 1.2
7.6
7.0 3.1 4.4
11.3 12.7 2.8 2.6
8.8
8.3 2.0 1.2
10.1 14.6 4.4 3.1
18.3 10.9 2.0 1.6
5.9
9.0 0.9 0.6
6.8
6.1 2.8 1.3
6.6
6.5 3.6 2.3
2.7
2.5 2.7 1.3
8.6
7.7 2.7 2.4
4.0
3.1 1.5 2.1
7.8
7.2 3.1 2.4
3.6
2.9 2.1 1.8
7.5 (3.4)
2.7 (2.0)
ISGS
L
R
0.4 0.7
2.9 1.3
3.0 3.0
1.5 2.2
5.3 1.5
1.5 0.8
0.4 2.4
0.7 2.1
0.7 1.0
1.9 2.5
0.8 0.4
1.8 1.8
0.6 1.5
4.5 2.6
0.7 1.6
1.9 4.3
1.1 1.8
8.3 1.8
0.7 5.4
0.9 0.8
1.0 1.3
3.5 1.9
3.8 1.5
0.6 1.1
1.1 0.8
1.3 0.9
1.5 0.8
0.0 2.0
2.8 2.6
2.8 1.3
0.8 2.1
2.3 2.4
0.4 0.3
0.8 2.5
4.0 2.2
3.1 1.6
2.9 2.1
3.2 1.2
0.2 0.9
3.0 2.0
1.7 1.8
2.1 0.9
2.2 1.7
1.8 1.0
2.0 1.8
1.7 1.0
1.9 (1.4)
SSGS
L
R
1.3 1.0
0.6 1.8
1.6 1.2
0.8 2.1
1.3 4.1
0.4 2.0
1.0 0.8
6.4 0.9
1.7 1.2
1.6 0.6
1.3 0.3
1.8 2.7
2.5 1.2
1.8 1.2
1.0 1.0
4.1 1.2
0.4 1.6
1.6 2.2
1.5 2.8
3.5 1.4
1.1 1.4
2.5 0.4
2.4 1.2
0.3 2.1
0.5 0.7
6.2 0.4
6.2 1.3
3.6 0.4
2.7 1.7
0.6 1.5
1.5 1.4
1.1 0.6
3.9 3.0
2.6 2.4
1.5 0.9
2.1 1.8
4.9 3.1
1.1 0.7
0.9 0.6
5.4 2.1
1.7 1.5
1.5 0.9
2.5 1.5
1.8 0.9
2.2 1.5
1.7 0.9
1.8 (1.4)
TOS
L
R
7.0
3.2
7.2
5.0
12.9 12.6
19.6 15.7
3.8
2.8
5.3
6.8
8.3
6.8
12.5 12.4
6.3 10.4
19.5 5.0
3.3
4.3
5.6
6.4
4.4
3.4
11.4 5.3
6.6
3.8
10.6 10.6
6.3
4.2
4.8
5.0
4.8
2.6
2.6
0.8
7.3
8.0
10.4 12.0
5.3
6.3
2.0
2.6
12.5 7.0
3.2
4.9
1.7
1.9
14.3 8.7
11.4 6.8
11.6 7.0
3.9
7.3
12.2 8.6
9.1
7.9
21.4 9.1
6.4
2.2
5.0
5.2
7.0
6.7
8.4
7.3
5.8
2.4
5.4
2.7
8.8
7.0
5.0
3.8
7.7
5.8
4.7
2.9
8.2
6.3
4.8
3.3
7.2 (4.2)
LOS
L
R
1.5 2.9
1.6 1.6
7.1 17.0
4.8 19.8
2.4 1.2
4.1 5.9
8.2 5.2
5.4 3.8
4.6 3.6
8.1 1.8
1.8 1.5
10.2 6.3
2.0 0.5
11.4 9.8
2.0 3.3
10.8 10.1
0.6 1.1
36.3 12.1
1.1 0.8
9.5 2.7
8.0 9.6
13.1 6.3
3.6 6.4
4.3 7.9
14.2 10.9
6.6 5.6
1.1 3.8
6.9 1.4
6.8 5.2
5.5 4.0
6.6 7.9
6.4 2.6
3.2 1.6
10.3 0.7
6.3 6.0
4.3 3.0
7.0 4.2
7.6 1.0
6.4 2.4
0.7 0.6
5.1 5.6
8.3 5.8
7.6 4.6
7.1 3.3
6.6 5.0
5.9 4.4
5.8 (5.3)
IOS
L
R
1.1 0.3
1.5 0.2
2.1 7.6
4.8 1.0
0.9 0.9
1.0 0.4
1.8 2.1
0.3 0.3
1.1 1.1
1.1 0.5
0.7 0.9
1.2 1.0
0.2 0.5
2.2 1.9
1.4 0.2
1.0 1.5
0.5 0.2
9.3 1.7
6.6 2.9
2.9 4.1
3.1 3.8
4.5 3.8
4.2 2.4
1.1 1.9
4.1 2.6
1.7 0.7
0.8 1.2
4.2 2.0
9.3 1.7
0.6 0.7
3.1 1.0
3.8 3.3
0.8 0.8
1.7 0.9
1.4 1.8
1.0 0.4
0.9 2.7
1.3 0.9
0.7 2.4
0.2 0.5
1.4 1.2
2.2 1.7
2.9 1.9
2.6 1.1
2.3 1.6
2.2 1.5
1.9 (1.9)
PCS
L
R
4.4 2.9
0.5 1.3
7.7 5.3
12.5 8.6
3.1 1.9
1.2 1.4
9.3 3.9
6.6 2.4
3.9 1.4
4.5 4.8
1.3 1.6
5.1 5.1
2.0 1.1
1.6 6.9
0.4 0.9
1.7 1.3
0.2 0.4
7.5 5.5
5.9 5.1
2.4 1.5
10.2 4.6
3.8 3.0
3.9 6.3
4.3 2.4
7.7 1.0
5.2 5.8
0.9 1.6
4.6 4.0
2.0 5.5
3.1 3.5
10.6 5.7
4.6 1.2
7.2 1.6
5.6 5.8
1.4 1.3
2.0 1.2
2.7 3.7
7.0 3.2
3.2 3.7
1.1 0.7
3.9 3.0
3.6 2.4
4.6 3.4
2.7 1.9
4.3 3.2
3.0 2.1
3.8 (2.6)
LiS
L
R
1.4 1.8
1.8 1.6
2.1 2.6
1.9 0.8
2.3 1.8
0.9 1.1
1.8 0.6
0.7 0.8
0.6 2.3
4.9 1.3
0.8 0.4
3.0 1.0
0.8 0.4
0.2 1.0
1.1 0.6
0.5 0.3
0.3 0.1
2.7 3.6
3.2 7.1
1.4 0.3
0.6 1.7
1.9 0.6
2.5 3.4
3.6 2.5
1.6 3.4
5.6 3.1
2.5 3.5
0.7 0.9
2.0 2.5
1.7 0.3
1.6 0.6
1.9 1.2
5.2 3.0
3.6 0.7
1.0 0.8
0.7 0.4
1.3 1.1
0.9 1.0
3.9 0.6
1.7 0.8
1.5 1.1
1.2 0.9
2.3 1.9
1.4 1.6
1.9 1.5
1.3 1.4
1.7 (1.4)
LuS
L
R
0.0 0.0
1.0 0.0
0.0 0.0
2.0 0.0
1.0 1.3
5.6 2.6
3.6 0.7
0.0 0.0
0.0 0.0
2.5 0.0
1.4 1.0
0.0 0.0
0.0 0.0
3.9 4.0
0.0 0.0
0.0 0.0
0.0 0.0
1.2 0.5
2.9 0.8
0.0 0.0
4.4 0.0
0.6 1.7
0.0 0.0
0.0 1.7
0.0 0.0
0.8 5.0
0.0 0.0
1.4 0.0
3.7 3.8
0.6 0.2
13.0 7.6
1.0 2.1
0.0 0.0
5.5 0.9
0.0 1.7
0.0 0.9
0.0 0.0
0.0 0.0
3.4 0.6
0.0 0.0
2.6 1.9
1.6 1.3
3.2 2.0
3.5 2.1
3.0 1.9
2.9 1.9
2.5 (2.1)
1
F mean, mean for female subjects; F SD, standard deviation for female subjects; M mean, mean for male subjects; M SD, standard deviation for male subjects; mean, mean M ⫹
F by hemisphere; SD, standard deviation M ⫹ F by hemisphere; MEAN (SD), mean and standard deviation for total volumes; L, left hemisphere; R, right hemisphere; POF,
parieto-occipital fissure; TO, temporo-occipital incisure; BCS, body of the calcarine sulcus; ACS, anterior calcarine sulcus; RCS, retrocalcarine sulcus; ISGS, inferior sagittal sulcus;
SSGS, superior sagittal sulcus; TOS, transverse occipital sulcus; LOS, lateral occipital sulcus; IOS, inferior occipital sulcus; PCS, posterior collateral sulcus; LiS, lingual sulcus;
LuS, lunate sulcus.
sulcus in cadaver brains: 64% in the left hemisphere and
60% in the right hemisphere. In the MRIs that we examined, the lunate sulcus could be unambiguously defined in
50% of the left hemispheres and 45% of the right hemispheres. We must point out, however, that these percentages are underestimates of the true incidence of the lunate
sulcus because of the difficulty in identifying this sulcus,
which lies on the curvature of the occipital pole, in MRI
volumes.
The morphology of the medial surface of the occipital
region is dominated by the calcarine sulcus (Fig. 1). The
dorsal part of the medial occipital region that lies above
the calcarine sulcus and posterior to the parieto-occipital
fissure (POF) is known as the cuneus. The ventral part of
the medial occipital region that lies below the calcarine
sulcus as far as the occipital extension of the collateral
fissure is the lingual gyrus. Within the cuneus, a number
of more or less horizontally running sulci, the inferior and
superior sagittal sulci can be identified (Ono et al., 1990).
Immediately above the calcarine sulcus, the ISGS of the
cuneus can be identified and, farther dorsally, the SSGS of
the cuneus. Duvernoy (1999) has referred to these sulci as
the paracalcarine sulci, but this term should be avoided
because the term has been used to refer to sulci within or
adjacent to the parieto-occipital fissure (see, e.g., Elliot
Smith, 1904a). Within the lingual gyrus that lies between
the calcarine sulcus and the occipital extension of the
collateral sulcus, one can sometimes identify a sulcus that
is more or less well developed, the lingual (intralingual)
sulcus. This sulcus can be clearly seen in Figure 1c and
faintly in Figure 1a,b,d.
Neurophysiological studies in nonhuman primates beginning in the 1960s have identified many cortical visual
areas in the occipital lobe, i.e., many separate representations of the visual field (Kaas, 2004; Zeki, 1978), and
various schemes for naming these visual areas have been
proposed (Kaas, 2004; Zeki, 1978). In all these schemes,
the striate cortex (Brodmann’s area 17) is referred to as
the first cortical visual area, i.e., V1. Although it was
known since the beginning of the Twentieth Century that
the striate cortex (i.e., Brodmann’s area 17 or V1), with its
distinct and easily identified architectonic feature, the
The Journal of Comparative Neurology. DOI 10.1002/cne
THE HUMAN OCCIPITAL LOBE
stripe of Gennari, lies along both banks of the calcarine
sulcus (see, e.g., Bolton, 1900; Elliot Smith, 1904a), the
location of the many other functional visual areas that
have been identified in the monkey during the last 40
years has only now began to be tentatively identified in
the human brain thanks to modern functional neuroimaging (see e.g., Tootell and Hadjikhani, 2001; Tootell et al.,
1993, 1996; Walters et al., 2003; Watson et al., 1993; Zeki
et al., 1991). The current identifications of homologues in
the human occipital lobe of the visual areas established in
the monkey should be treated with caution and should be
regarded as tentative suggestions, because the methodologies used in studies with monkeys and humans are very
different. In the monkey, the definition of a cortical visual
area is based on mapping of the visual field representation
at the single-neuron level with microelectrode recording
(Kaas, 2004; Zeki, 1978). In the human brain, attempts to
map these same areas are usually based on global signal
changes in fMRI, i.e., indirect measures of functional activity based on blood flow, and the precise location of an
area is likely to be affected by the details of blood vessel
distribution. Despite these limitations, several interesting
studies have already been carried out that have provided
a tentative identification of many visual cortical areas in
the human occipital cortex that may be homologous to
areas previously identified in monkeys. We shall comment
here on the possible relation of the sulci of the occipital
region and these functionally defined visual cortical areas,
although much work remains to be carried out before we
can be reasonably certain that these identifications are
correct.
In the classic anatomical studies conducted at the beginning of the Twentieth Century, the relation of the
calcarine sulcus to the striate cortex was the subject of
intense investigation (see, e.g., Bolton, 1900; Elliot Smith,
1904a). These studies showed that the anterior calcarine
sulcus (Fig. 1), i.e., the extension of the calcarine sulcus
anterior to the point of intersection with the parietooccipital fissure, is the border between limbic cortex lying
on the isthmus and the striate cortex, which is found only
on the ventral bank of the calcarine sulcus at this point.
Caudal to the point of convergence of the parieto-occipital
fissure with the calcarine sulcus, i.e., on the body of the
calcarine sulcus (Fig. 1), the striate cortex extends on both
banks of the sulcus (see, e.g., Antoni, 1914; Bolton, 1900;
Brodmann, 1909; Economo and Koskinas, 1925; Elliot
Smith, 1904a). The striate cortex extends outside the calcarine sulcus farther caudally, i.e., close to the occipital
pole. According to Elliot Smith (1904a,b), in about 70% of
the brains, the striate cortex extends around the occipital
pole to reach the lateral surface of the occipital region, and
it is limited, more or less, by the lunate sulcus. Note that,
unlike the brain of the macaque monkey, in which the
lunate sulcus is always the border of area V1 with area
V2, the striate cortex in the lateral part of the human
occipital pole may be close to the lunate sulcus (as in the
macaque monkey), or it may stay behind it (see, e.g., Elliot
Smith, 1904a). In other words, area V2, which in the
monkey lies always within the posterior bank of the lunate sulcus, may spread in the human brain outside the
posterior bank of the lunate sulcus onto the occipital pole.
The relation of the striate cortex (Brodmann’s area 17)
to the calcarine sulcus was recently reexamined by
Amunts and coauthors (2000). These investigators examined 10 brains and in all cases area 17 (i.e., V1) was
257
located mainly in the depth of the calcarine sulcus, extending onto the free surface in the most caudal sections.
Area 18 (V2) surrounded area 17 dorsally and ventrally.
Clarke and Miklossy (1990) studied the location of callosal
connections in the human occipital cortex because they
are known to provide an anatomical indication of the
vertical meridian (i.e., the boundary) between V1 and V2.
Area 17 (V1) occupied both banks of the calcarine sulcus
and posteriorly (toward the occpital pole) extended onto
both lips of the calcarine sulcus. The boundary of area 17
(V1) and area 18 (V2) extended in an anteroposterior
direction close to the superior saggital sulcus, dorsally,
and the lingual sulcus, ventrally. Below the lingual sulcus
and still on the lingual gyrus, the ventral part of area V3
(also known as VP) could be established on the basis of
callosal connections (Clarke and Miklossy, 1990).
Functional neuroimaging studies have also identified
the primary visual cortical area along the calcarine sulcus
(V1) of the human brain (see, e.g., DeYoe et al., 1996;
Hadjikhani et al., 1998; Sereno et al., 1995; Tootell et al.,
1997). These studies have shown that, proceeding dorsally
in the cuneus, strips of cortex running in an anteroposterior direction along the calcarine sulcus can be identified
as the dorsal part of V2, V3, and V3A (accessory V3; DeYoe
et al., 1996; Hadjikhani et al., 1998; Sereno et al., 1995;
Tootell et al., 1997). All these areas extend beyond the
cuneus onto the superior-lateral surface of the occipital
lobe. The most dorsal area, V3A, runs along the transverse
occipital sulcus (Fig. 2) on the superior-lateral surface of
the occipital lobe (Tootell et al., 1997). Recently, Pitzalis
and coauthors (2006) have shown that, in the dorsalmost
part of the parieto-occipital sulcus of the human brain, the
contralateral visual hemifield could be mapped anterior
and medial to areas V2, V3, and V3A. This newly mapped
area is thought to be the human homologue of macaque
area V6 (Galletti et al., 1996, 1999).
Below the calcarine sulcus, on the lingual gyrus, again a
series of anteroposterior strips of cortex has been linked
with the ventral part of V2 and the ventral part of V3 (also
known as VP; DeYoe et al., 1996; Hadjikhani et al., 1998;
Sereno et al., 1995; Tootell et al., 1997). More ventrally,
close to the collateral sulcus and extending lateral to it on
the fusiform gyrus, a visual area related to the processing
of color has been identified via functional neuroimaging
(Lueck et al., 1989; Zeki et al., 1991). This color-related
area was originally interpreted as the homologue of macaque monkey area V4 (Zeki et al., 1991), but others have
argued that it is not area V4 but a separate area, which
was named V8 (Hadjikhani et al., 1998). Some neuroimaging studies have located the ventral part of area V4
(V4v) immediately after ventral area V3 and medial to the
color area, which was originally found on the fusiform
gyrus (DeYoe et al., 1996; Hadjikhani et al., 1998; Sereno
et al., 1995; Tootell et al., 1997). These studies suggest
that the most ventral part of the lingual gyrus may in fact
contain the ventral part of area V4 (i.e., V4v), which is
separate from the color area found on the fusiform gyrus.
According to the coordinates provided by Tootell and
Hadjikhani (2001), dorsal area V4 (V4d) would lie at the
rostral part of the lateral occipital sulcus, extending dorsally behind the anterior occipital sulcus. Recall that area
V3A (i.e., area V3 accessory), which in the monkey lies in
the dorsal prestriate region between areas V3 and V4
(Van Essen and Zeki, 1978; Zeki, 1978b), has been identified in the human brain in the dorsal prestriate region
The Journal of Comparative Neurology. DOI 10.1002/cne
258
G. IARIA AND M. PETRIDES
along the transverse occipital sulcus (Tootell et al., 1997),
i.e., just posterior to the location of dorsal area V4 on the
dorsal part of the lateral occipital sulcus (Tootell and
Hadjikhani, 2001). If these interpretations are correct,
then the superior lateral occipital cortex that lies above
the lateral occipital sulcus includes the dorsal parts of
areas V2, V3, and V4 and the complete contralateral representation of area V3A. This would make this region of
the human occipital cortex comparable to the cortex that
is hidden in the lunate sulcus and extending onto the
prelunate gyrus in the macaque monkey, where areas V2,
V3, V3A, and V4 can be found. The ventral parts of areas
V2, V3 (VP), and V4 would then occupy the lingual gyrus.
Anterior to the transverse occipital sulcus lies the anterior occipital sulcus (Fig. 2). The anterior occipital sulcus has also been referred to as the posterior ascending
branch of the second temporal sulcus (Eberstaller, 1892;
Economo and Koskinas, 1925) or the posterior ascending
branch of the inferior temporal sulcus (Cunningham, 1982;
Watson et al., 1993). The cortical region close to the point
of intersection of the anterior occipital sulcus and the
lateral occipital sulcus has been shown, via functional
neuroimaging methods (Dumoulin et al., 2000; Watson et
al., 1993; Zeki et al., 1991), to be the locus of the human
homologue of the visual cortical motion area demonstrated in the rhesus monkey by Zeki (1974) and named
V5 and in the owl monkey by Allman and Kaas (1971) and
named MT. In a recent study, Malikovic and coauthors
(2006) have shown a distinct architectonic area in this
region of the cortex that is located most often in the depth
of the sulci, i.e., the posterior bank of the anterior occipital
sulcus and the ventral bank of the lateral occipital sulcus.
These investigators consider this distinct architectonic
area as the putative human visual motion area, i.e., the
homologue of monkey V5/MT.
Although many details remain to be established regarding the number of visual areas in the human occipital lobe
and their correspondence to comparable areas in the monkey, as well their relation to the morphology of the human
occipital region, the available evidence has produced a
preliminary scheme that is in line with what is known
from the monkey. The qualitative and quantitative description of the sulci of the occipital lobe of the human
brain that is provided here may help in evaluating any
relations that might exist between functional areas and
the sulcal and gyral morphology of the human brain.
ACKNOWLEDGMENTS
We thank Steve Robbins and Mallar Chakravarty for
help with the construction of the probability maps and
figures and Emily Rubin-Ferreira for technical assistance.
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