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Brain — Like us on Facebook. Follow us on Twitter. Subscribe to our YouTube channel. You can make a difference. Donate Not now. It is the anterior border of the superior parietal lobule and the supra marginal gyrus. Postcentral gyrus The gyrus is located between the central and postcentral sulci.
Occasionally it can be divided in two or more parts. Inferiorly, it is limited by the Sylvian fissure. It is connected to the frontal lobe by the subcentral gyrus and the paracentral lobule. Intraparietal sulcus The horizontal groove separating the superior and the inferior parietal lobules. It starts from the postcentral sulcus and it continues as the superior occipital sulcus. Numerous unnamed segments arise from this fissure, but It is often possible to recognize three different parts: the anterior, intermediate, and posterior segments.
Superior parietal lobule The lobule is located between the superior margin of the parietal lobe and the intraparietal sulcus. It is connected to the superior occipital gyrus by a transition area known as arcus parieto-occipitale. Inferior parietal lobule The lobule is located between the superior parietal lobule, superiorly, and the Sylvian fissure, inferiorly, which forms the parietal operculum.
It is divided into two different gyri: the anterior supramarginal gyrus and the posterior angular gyrus. Posteriorly, the parieto-occipital sulcus constitutes the limit with the occipital lobe. Supramarginal gyrus The anterior part of the inferior parietal lobule. It is limited superiorly by the intraparietal sulcus which separates it from the superior parietal lobule. Anteriorly it encircles the caudal part of the sylvian fissure, behind the postcentral gyrus, and it continues into the superior temporal gyrus.
Posteriorly, the intermediate sulcus separates it from the angular gyrus. Angular gyrus The posterior portion of the inferior parietal lobule. Rostrally, the intermediate sulcus separates it from the supramarginal gyrus. Inferiorly, it is bounded by the superior temporal sulcus, continuing into the caudal portion of the superior and the middle temporal gyri. Posteriorly, the parietal-occipital sulcus lies between the posterior portion of the angular gyrus and the superior occipital gyrus.
The superolateral surface presents a horizontal sulcus, called the lateral occipital sulcus, which limits :. The lateral surface turns medially as the posterior surface, which corresponds to the convexity of the occipital pole. Superior occipital sulcus The sulcus arising from the posterior segment of the intraparietal sulcus, also known as intraoccipital sulcus, which runs parallel to the interhemispheric fissure.
It intersects, forming an angle of 90 degrees, the transverse occipital sulcus, separating the superior occipital gyrus from the middle occipital gyrus.
Transverse occipital sulcus The fissure on the dorsal surface of the occipital lobe starting from the posterior segment of the parieto-occipital sulcus.
It separates the middle occipital gyrus from the middle temporal gyrus. Lunate sulcus The vertical sulcus on the lateral occipital surface, perpendicular to the lateral occipital sulcus. It can be divided into dorsal and ventral branches. The small horizontal sulcus on the inferior surface of the lobe. It separates the middle and the inferior occipital gyri.
The horizontal fissure that divides the middle occipital gyrus into the superior and inferior portions. It often arises from the middle segment of the lunate sulcus, and anteriorly it can be connected to the inferior temporal sulcus.
The small fissure that may arise from the preoccipital notch, connecting the inferior temporal sulcus and the lateral occipital sulcus. Pandya and colleagues Pandya and Seltzer ; Petrides and Pandya ; Seltzer and Pandya relied on a parcellation scheme similar to the one used in our study but placed injections that nevertheless were relatively large and involved, in the mid-caudal part of the IPL, both PG and Opt or both PFG and PG.
These studies, therefore, did not distinguish among possible differential patterns of connections of PFG, PG, and Opt.
In particular, data from caudal PG and Opt IPL injections are in substantial agreement with reports on 7a connections, whereas data from injections in the middle part of the IPL PFG and PG are difficult to interpret, the injection sites involving also part of the parietal operculum or of the lateral bank of the IPS.
The present data, based on injections restricted to areas PF, PFG, PG, and Opt provide a new, more detailed view of the connectivity of the IPL convexity, which only partially fits with the general scheme proposed by the abovementioned studies.
Our data on Opt and PG altogether roughly corresponding to 7a injections indicate that these areas are strongly interconnected with each other and are both connected with areas MST, DP, and with temporal areas of the STS, including different rostrocaudal sectors of area STP and area IPa.
As summarized in Figure 17 , the present data, however, clearly show that Opt and PG, have markedly different connections with parietal, frontal, limbic, and temporal areas other that STP and IPa, clearly supporting the notion that area 7a, at least as originally defined by Vogt O and Vogt C and usually delineated in the anatomical and functional literature, is not homogeneous. In particular, a major finding of our study is that the major connections of Opt, summarized in Figure 17 , nearly all coincide with those previously attributed to area 7a Neal and others a ; Cavada and Goldman-Rakic a ; b ; Andersen and others ; Neal and others or to PG and Opt Pandya and Seltzer ; Petrides and Pandya ; Seltzer and Pandya In contrast, although PG is clearly located within the limits of Vogts' area 7a, most of its connections described here and summarized in Figure 17 have never been attributed to area 7a in previous reports.
This discrepancy can be explained on the basis of the location of the injection sites. Cavada and Goldman-Rakic a , b placed an injection site in area 7a their Case 2 relatively caudally, very likely mostly in Opt. Furthermore, in the study of Andersen and others , area 7a is considerably smaller than the Vogts' area 7a see also Andersen and others , corresponding mostly to Opt, plus only a small part of PG. Accordingly, it is not surprising that also in this study, 7a injections reproduced, to a large extent, the connectivity observed in our study following Opt injections.
Finally, Pandya and Seltzer and Petrides and Pandya following a large tracer injection involving both PG and Opt their Case 16 also showed a labeling distribution basically very similar to those of Opt of the present study.
It is possible, therefore, that the distinctive pattern of connections of PG versus Opt, consistently observed in our study, was previously missed, mainly because of the location of the injection sites in most of the studies on 7a connections. Our data on PF and PFG injections altogether roughly corresponding to area 7b indicate that the rostral part of the IPL convexity is not homogeneous either.
The present data on PF connections, summarized in Figure 17 , are in full agreement with reports of Pandya and colleagues Pandya and Seltzer ; Petrides and Pandya in which the location of their area PF is very similar to that of the present study. In other studies this rostralmost part of the IPL convexity was clearly avoided or only partially involved by tracer injections, possibly because it was partially included by Vogt O and Vogt C within area 2.
The present data, as well as those of Pandya and colleagues, showing connections of PF with PMv and area 46, clearly support the notion that this rostralmost part of the IPL convexity should be considered as part of the posterior parietal cortex. One major finding of this study is that cytoarchitectonic area PFG displays a distinctive connectivity pattern. Finally, PFG is the only IPL convexity area that is a source of corticospinal projections, apparently mostly directed to the cervical levels.
Their data, therefore, cannot be compared with the present ones. Accordingly, 7b injections in this study clearly involved also area PG. However, on the basis of its location and extent, the 7b injection in the studies of Cavada and Goldman-Rakic a , b and Lewis and Van Essen b , appear to involve mostly PFG. In both these studies, connections attributed to 7b, appear to correspond, to a large extent, to the connections described here for PFG.
Finally, the finding that PFG is a source of corticospinal projections finds support in the study of Galea and Darian-Smith , which described corticospinal projections from a cortical sector defined as 7b but very likely coincident with PFG.
Area 7a is generally considered as a visually responsive area, placed at the apex of the dorsal visual stream, where retinal and extraretinal signals contribute to the construction of representations of surrounding space, according to head-, body- or world-centered coordinates, for space perception and guidance of motor behavior see, e. This view is supported by data showing that 7a neurons have large visual receptive fields, usually bilateral, modulated by the orbital position of the eye or by the position of the head see, e.
Furthermore, 7a, although lacking a reproducible retinotopic organization Heider and others , displays topography in terms of eye position gain fields Siegel and others , and neurons in this area appear to be involved in the analysis of different types of optic flow Siegel and Read b ; Phinney and Siegel These studies, however, appear to be mostly focused on the caudal part of the Vogts' area 7a, that is, where the inferior parietal gyrus narrows because of the upward bending of the STS, present in virtually all macaque brains.
This sector to a large extent coincides with Opt. Indeed, the connectivity pattern reported here for Opt suggests that this is the caudal IPL area in which representations of surrounding space according to head-, body-, or world-centered coordinates are constructed for space perception and the guidance of motor behavior.
In this context, it appears of interest to note is that recent optical imaging data have suggested a role of caudal 7a largely corresponding to Opt in the neural mechanisms underlying shifts of attention in space Raffi and Siegel Recent data suggested a novel role of caudal 7a in the guidance of motor behavior.
In particular, Battaglia-Mayer and others showed that in caudal 7a likely Opt, cfr. The presence of arm reaching—related activity in this sector has also been reported by Heider and others Indeed, Opt is connected strongly with PGm and weakly with F7, that is, areas where combined arm and eye movement—related activity was recorded Ferraina and others ; Fujii and others F7 is, in turn, a target of major projections from PGm Matelli and others and from dorsal area 46 Luppino and others a prefrontal sector, target of Opt, included into the so-called space memory domain by Wilson and others Furthermore, Opt is tightly connected with PG, which, as discussed below, may represent a major source of the arm-related signals recorded in this area.
Accordingly, Opt would represent a site of convergence of different types of sensory and eye- and arm-related motor signals used, as suggested by Battaglia-Mayer and others , to construct an integrated representation of the contralateral eye and arm motor space. All these last studies did not specifically aim to unequivocally dissociate arm-related from possible eye-related signals and the possibility that in PG neurons may be influenced by other types of motor signals cannot be at present completely ruled out.
However, our data on PG connections strongly support the view that this area is primarily an arm-related field. Indeed, virtually all the most important parietal connections of PG are with areas involved in visual or visual and somatosensory guidance of distal or proximal arm movements, that is, the hand-related area AIP Murata and others and the arm-related areas MIP Colby and Duhamel ; Johnson and others , PEc Battaglia-Mayer and others , and dorsal V6A Galletti and others ; Battaglia-Mayer and others Moreover, the relatively weak but consistent connections of PG with agranular frontal and cingulate areas where distal F5 or proximal and distal F2, 24d arm movements are represented see, e.
The possible functional role of PG appears to rely on the analysis of a large variety of sensory information. Moreover, PG appears to be a target also of MSTl, where there are neurons that appear to code object motion in world-centered coordinates Ilg and others and are supposed to be involved in the guidance of eye or arm movements Ilg and Schumann Finally, the strong connections with Opt may represent a further major source of visual input possibly related to space coding according to several different frames of reference.
Finally, PG is strongly connected with areas C and Tpt, potential sources of auditory information Pandya and Sanides ; Leinonen and others ; Morel and others Although auditory responses have never been observed in the IPL convexity, it is possible that, as shown in LIP Mazzoni and others , this information is used only when crucial for planning motor activity.
It is then possible that in PG there is a multimodal integration of visual, somatosensory, and auditory information, in which extrapersonal space coded on the basis of different frames of reference, is coregistered with arm-position signals for the control of arm movements. Altogether, our data strongly suggest that the rostral and the caudal part of 7a correspond to different cortical areas, Opt and PG, respectively.
This distinction is based not only on cytoarchitectural data, as previously also suggested by Pandya and Seltzer , but also by the markedly different connectivity patterns of these 2 areas, which cannot be simply explained in terms of any type of topographic organization.
This proposed subdivision is not in contrast with the possibility that PG and Opt, though primarily related to different aspects of motor control, cooperate in the mechanisms giving rise to representations of motor space through their strong reciprocal connections.
Future electrophysiological or optical imaging experiments focused on both these areas are highly desirable to clarify this issue. STP has been subdivided into a caudal sector STPp , target of parietal areas of the dorsal visual stream, and a rostral sector STPa , where inputs from dorsal and ventral visual stream areas converge Boussaoud and others ; Baizer and others ; see also Felleman and Van Essen ; Cusick It has been then suggested an that there is an involvement of this area in integration of information within and across modalities, subserving orienting behavior to novel stimuli Bruce and others ; Bayliss and others Furthermore, visually responsive neurons may have complex functional properties, extensively studied by Perrett and others for review, see, e.
In particular, STP visual neurons mostly in STPa may code whole-body or body-parts postures, particular types of body motion, may differentiate between self-produced actions and actions made by others, and may code movements in terms of goal-directed actions.
Finally, STPa neurons appear to code biological motion also implied from static postures and intentionality of actions Jellema and others ; Jellema and Perrett Thus, the possible functional role of PG and Opt but also PFG, as discussed later may also rely on these higher order perceptual processes of crucial importance in the social behavior of primates. These observations open the possibility that Opt and PG but also PFG may have a more specific effect on some premotor areas and a possible modulatory role on others.
First, the caudal part of 7b, likely PFG L. Fogassi, personal communication , contains visually responsive neurons active during the observation of arm, hand, and mouth goal-directed movements made by the experimenter parietal mirror neurons, Gallese and others , suggesting a role of this area in action recognition. Second, Fogassi and others recently showed that a class of these parietal mirror neurons appears to be engaged in understanding intentions of others.
The present data are fully in line with the apparent functional segregation in 7b. Connections of PF with the ventral part of area 2 and with SII and PV suggest a major role for this area mostly in somatomotor transformations for the guidance of face and mouth movements. Furthermore, PF could be a source of somatosensory information to the visual and somatosensory face-related area VIP Colby and others Frontal projections of PF are directed to F4, where many neurons have somatosensory and visual receptive fields around the face Fogassi and others , and also to ventral and dorsal sectors of F5, where the mouth and the hand are mostly represented, respectively Gentilucci and others These data, as well as the connections with PFG and AIP, suggest a role for PF also in somatomotor transformations related to the control of hand movements.
PFG is a newly defined cortical area with a distinctive pattern of connections. Connections with SII, parietal e. In this respect, particularly interesting are the connections with temporal areas mostly STPa , where neurons appear to code actual or implied biological motion and intentionality of actions or appear to code goal-directed hand actions Perrett and others ; see also Carey and others These connections provide a strong anatomical support to the hypothesis that PFG represents a step in a pathway linking STP with PMv, mediating the matching between the visual description of an observed action, coded in STPa, with corresponding motor representations, coded in F5 cortical mirror system, Rizzolatti and others The primate posterior parietal cortex consists of several areas, involved in parallel in the analysis of specific aspects of visual information, alone or in combination with the somatosensory one.
These areas are distributed over both the SPL and the IPL, in contrast to the classical notion that the dorsal visual stream involves only the IPL for reviews, see Caminiti and others ; Galletti and others ; Rizzolatti and Matelli A major result of this processing is the construction of multiple representations of space based on different frames of references used for the control of specific classes of actions Andersen and others ; Rizzolatti and others ; Colby Our data, showing that the IPL convexity is formed by several distinct areas, potential sites of convergence of multimodal sensory information and connected with parietal and frontal areas involved in motor control of different effectors, are congruent with such an organizational view.
Thus, the macaque IPL appears to be a site where visual information from both the dorsal and the ventral visual stream is integrated with information about motor programs. This view is in line with the possible homology of this region with the corresponding sector of the human brain, which, in the evolutionary processes leading to lateralization of functions, developed areas involved, in the right hemisphere, to perception of spatial relationships and, in the left hemisphere, to the storage of complex representations of actions.
Professor Massimo Matelli died on August The authors are profoundly indebted to him for his contribution to this study and agreed that his name had to be included as a coauthor in this manuscript. We wish to remember him not only as a scientist but also as a person contagious in his enthusiasm for research and as an example for all of us. The authors are also grateful to Leonardo Fogassi and Claudio Galletti for their suggestions and comments on a preliminary version of the manuscript.
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