Cerebral Cortex October 2006;16:1389--1417 doi:10.1093/cercor/bhj076 Advance Access publication November 23, 2005
Cortical Connections of the Inferior Parietal Cortical Convexity of the Macaque Monkey
Stefano Rozzi, Roberta Calzavara1, Abdelouahed Belmalih, Elena Borra, Georgia G. Gregoriou2, Massimo Matelli and Giuseppe Luppino
We traced the cortical connections of the 4 cytoarchitectonic fields—Opt, PG, PFG, PF—forming the cortical convexity of the macaque inferior parietal lobule (IPL). Each of these fields displayed markedly distinct sets of connections. Although Opt and PG are both targets of dorsal visual stream and temporal visual areas, PG is also target of somatosensory and auditory areas. Primary parietal and frontal connections of Opt include area PGm and eye-related areas. In contrast, major parietal and frontal connections of PG include IPL, caudal superior parietal lobule (SPL), and agranular frontal armrelated areas. PFG is target of somatosensory areas and also of the medial superior temporal area (MST) and temporal visual areas and is connected with IPL, rostral SPL, and ventral premotor arm- and face-related areas. Finally, PF is primarily connected with somatosensory areas and with parietal and frontal face- and arm-related areas. The present data challenge the bipartite subdivision of the IPL convexity into a caudal and a rostral area (7a and 7b, respectively) and provide a new anatomical frame of reference of the macaque IPL convexity that advances our present knowledge on the functional organization of this cortical sector, giving new insight into its possible role in space perception and motor control.
Ungerleider and Mishkin 1982), linked with oculomotor area lateral intraparietal area (LIP) and the rostral prearcuate cortex and where retinal and extraretinal signals are combined to construct a representation of space. In contrast, 7b is mostly related to the analysis of somatosensory information, connected with the ventral premotor cortex, and involved in the control of arm and face movements. Area 7a, however, is also involved in the control of armreaching movements (Mountcastle and others 1975; Blum 1985; MacKay 1992; Battaglia-Mayer and others 2005), and according to Hyva¨rinen (1981) there is a functional segregation in this area between a more rostral, visually and somatosensory responsive, arm field and a more caudal field, in which eye movement signals predominate. Furthermore, in the rostral IPL convexity (area 7b) there is a visual and somatosensory responsive arm/ hand and face field (Hyva¨rinen 1981; Ferrari and others 2003), where visual neurons appear to be involved in higher order visuomotor processings (Gallese and others 2002; Yokochi and others 2003; Fogassi and others 2005). These data, therefore, suggest, first, that area 7a is not homogeneous and, second, that 7b is not exclusively involved in somatomotor functions. In their architectonic study, Pandya and Seltzer (1982) indeed suggested that the IPL convexity contains at least 3 distinct areas: a rostral, an intermediate, and a caudal one, defined as PF, PG and Opt, respectively, plus a transitional area located between areas PF and PG and named PFG. Accordingly, areas 7a and 7b are both cytoarchitectonically not homogeneous and, in particular, area 7a would consist of at least 2 areas, PG and Opt. This subdivision, however, was never validated by clear connectional and/or functional data, and it is common practice in the literature to refer to areas 7a and PG as synonyms (Siegel and Read 1997a). In the present study we used cytoarchitectonic data to guide the location of neural tracer injections to study the cortical connections of the IPL convexity. Specific aims were 1) to examine whether patterns of connections validate the subdivision of this sector into more than 2 distinct areas, 2) to identify all the possible sources of sensory information to each of these areas, and 3) to trace their projections to the frontal lobe, where there are multiple representations of different effectors (see, e.g., Rizzolatti and others 1998; Rizzolatti and Luppino 2001) and identify all the several possible parietofrontal circuits involving the IPL convexity and their possible role in space representation and motor control. The results provide strong support for a subdivision of the IPL convexity into 4 distinct areas, referred, in agreement with Pandya and Seltzer (1982), to as PF, PFG, PG, and Opt. Preliminary data have been presented in abstract form (Luppino, Belmalih, and others 2004).
Keywords: area 7a, area 7b, dorsal visual stream, space coding, visuomotor transformations Introduction The posterior parietal cortex of the macaque contains a multiplicity of areas involved in the analysis of visual information necessary for motor planning and execution of eye, limb, and body movements (see, e.g., Rizzolatti and others 1997; Colby 1998). The rich parietofrontal connections of these areas mediate the transformation of visual information into action, and a series of parietofrontal circuits has been so far identified, linking visually related areas of the caudal superior parietal lobule (SPL) and of the intraparietal sulcus (IPS) with different sectors of the agranular frontal cortex or with the frontal eye fields. These circuits are involved in the visual guidance of reaching, grasping, or eye movements (Colby 1998; Rizzolatti and others 1998). Within this general framework, there are still several aspects of the anatomical organization of the cortical convexity of the inferior parietal lobule (IPL) and its possible role in visuomotor transformations and/or space coding that need to be elucidated. This cortical sector is usually subdivided according to the architectonic studies of Vogt O and Vogt C (1919) into a caudal and a rostral area, 7a and 7b, respectively, considered as functional and hodological different entities (see, e.g., Andersen and others 1997; Siegel and Read 1997a). According to this view, 7a is a visually responsive area, located at the vertex of the occipitoparietal visual information flow (dorsal visual stream, Ó The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail:
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Dipartimento di Neuroscienze, Sezione di Fisiologia, Universita` di Parma, I-43100 Parma, Italy 1 Current address: Department of Pharmacology and Physiology, School of Medicine and Dentistry, University of Rochester, Rochester, NY, USA 2 Current address: Laboratory of Neuropsychology, NIMH, NIH, Bethesda, MD, USA
Methods The experiments were carried out on 6 macaque monkeys (3 Macaca nemestrina and 3 Macaca fascicularis) in which neural tracers were injected in cytoarchitectonic fields PF, PFG, PG, and Opt. Additional data from 2 M. nemestrina, in which retrograde tracers were injected in the lateral funiculus of the spinal cord, were used for the definition of the corticospinal projections from the IPL. The brains of 5 additional monkeys (4 M. nemestrina and 1 M. fascicularis, 8 hemispheres), 2 of them used in tracing experiments not related to the present one, were used for preliminary cytoarchitectonic analysis of the IPL convexity. All experimental procedures were approved by the Veterinarian Animal Care and Use Committee of the University of Parma and complied with the European law on the care and use of laboratory animals. Surgical Procedures and Tracers Injections Each animal was anasthetized with ketamine hydrochloride (15 mg/kg intramuscularly) and placed in a stereotaxic apparatus. In all animals in which tracers were injected in the IPL areas, under aseptic conditions, an incision was made in the scalp, the skull was trephined over the target region, and the dura was opened to expose the IPL convexity. Injection sites were chosen by using cytoarchitectonic data as frame of reference, referred in terms of stereotaxic coordinates and location of anatomical landmarks such as the IPS, the lateral fissure (LF), and the superior temporal sulcus (STS). Once the appropriate site was chosen, fluorescent tracers (Fast Blue [FB] 3% in distilled water, Diamidino Yellow [DY] 2% in 0.2 M phosphate buffer at pH 7.2, True Blue [TB] 5% in distilled water, EMS-POLYLOY GmbH, Gross-Umstadt, Germany), wheat germ agglutinin--horseradish peroxidase conjugated (WGA-HRP, 4% in distilled water, SIGMA, St. Louis, Missouri), biotinilated dextran amine (BDA, 10% phosphate buffer 0.1 M, pH 7.4; Molecular Probes, Eugene, Oregon), and cholera toxin B subunit, gold conjugated (CTB-g, 0.5% in distilled water, LIST, Campbell, California) or conjugated with Alexa 488, Alexa 555, or Alexa 594 (CTBA, 1% in phosphate-buffered saline, Molecular Probes) were slowly pressure injected at about 1.2--1.5 mm below the cortical surface as described in detail in previous studies (e.g., Luppino and others 2003). Table 1 summarizes the locations of injections, the injected tracers, and their amounts. After the injection, the dural flap was sutured, the bone replaced, and the superficial tissues sutured in layers. In the 2 animals in which tracers were injected in the spinal cord, under aseptic conditions, following a laminectomy, the dura was opened and the segment of the spinal cord selected for the injection exposed. Retrograde tracers were, then, pressure injected with a 5 lL Hamilton microsyringe in the left lateral funiculus. In 1 animal (Case 10), DY (2%, 8 injections, total amount 12 lL) was injected at the T6 spinal level and 26 days later (HRP, 30% in 2% lysolecithin, SIGMA, 6 injections, total amount 10 lL) at the C4--C5 spinal level. In the second animal (Case 21), HRP was injected at the C3--C5 level. Upon the completion of the
Table 1 Monkey species, localization of the cortical injections and tracers employed in the experiments Monkey
Species
Hemisphere
Area
Tracer
Amount (lL)
Case 13
Macaca Fascicularis
Case Case Case Case
Macaca Macaca Macaca Macaca
L R R R L R R R R R L R R R R R
PFG PF PFG PG Opt PF PFG PG Opt Opt PG PF PFG PFG PG PG
WGA-HRP 4% CTB-g 0.5% BDA 10% WGA-HRP 4% WGA-HRP 4% FB 3% CTB-A 488 1% CTB-A 594 1% DY 2% TB 5% BDA 10% DY 2% FB 3% CTB-A 555 1% CTB-A 488 1% TB 5%
1 2 4 1 1 1 2 2 1 1 4 1 1 1 1 1
14 20 23 27
Case 29
Nemestrina Nemestrina Fascicularis Nemestrina
Macaca Fascicularis
Note: L 5 left; R 5 right.
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3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
0.1 1 1 0.1 0.1 0.2 1 1 0.2 0.2 1 0.2 0.2 1 1 0.2
injections, the spinal cord was covered with Gelfoam and wounds were closed in layers. During surgeries, hydration was maintained with saline (about 10 cc/h, intravenously) and temperature with a heating pad. Heart rate, blood pressure, respiratory depth, and body temperature were continuously monitored. Upon recovery from anesthesia, the animals were returned to their home cage and closely monitored. Histological Procedures After appropriate survival periods following cortical (28 days for BDA, 12--14 days for fluorescent tracers and CTB-A, 7 days for CTB-g and 2 days for WGA-HRP) or spinal cord (29 days for DY and 3 days for HRP) injections, each animal was anesthetized with ketamine hydrochloride (15 mg/kg intramuscularly) followed by an intravenous lethal injection of sodium thiopental and perfused through the left cardiac ventricle with saline, 3.5--4% paraformaldehyde, and 5% glycerol in this order. All solutions were prepared in phosphate buffer 0.1 M, pH 7.4. Each brain was then blocked coronally on a stereotaxic apparatus, removed from the skull, photographed, and placed in 10% buffered glycerol for 3 days and 20% buffered glycerol for 4 days. Finally, it was cut frozen in coronal sections 60 lm thick. In Cases 10 and 21 (spinal cord injections) the spinal cord was removed and, after cryoprotection, cut transversally at 60 lm. In Cases 27 and 29, 1 section of 5 was mounted, air-dried, and quickly coverslipped for fluorescence microscopy. In Cases 13, 20, and 23, 1 section of 5 was processed for WGA-HRP histochemistry with tetramethylbenzidine as chromogen (Mesulam 1982). In Case 13, in 1 section of 5, CTB-g was revealed by the silver-intensification protocol described by Kritzer and Goldman-Rakic (1995). In Cases 14 and 29, 1 series of each fifth section was processed for the visualization of BDA, using a Vectastain ABC kit (Vector Laboratories, Burlingame, California) and 3,39-diaminobenzidine (DAB) as a chromogen. The reaction product was intensified with cobalt chloride and nickel ammonium sulfate. In all cases, 1 series of each fifth section was stained with the Nissl method (thionin, 0.1% in 0.1 M acetate buffer pH 3.7), and in Cases 23, 27, and 29 a further series was stained for myelin (Gallyas 1979). All the other brains, but Case 1, used for cytoarchitectonic analysis were processed as described above and cut frozen in coronal (5 hemispheres) or parallel to the direction of the IPS (2 hemispheres) sections, 60 lm thick. The 2 hemispheres of Case 1, embedded in celloidin, were cut, one in a plane perpendicular to the direction of the IPS, the other in a plane parallel to the direction of the IPS, both at 40 lm. In all cases, 1 series of each fifth section was stained with the Nissl method. Data Analysis Injection Sites and Distribution of Retrogradely Labeled Neurons Injection sites were defined according to criteria previously described in detail (Luppino and others 2001, 2003) and attributed to the architectonic areas of the IPL convexity with analysis of adjacent Nissl-stained sections. The injection sites presented in this study (listed in Table 1) were all restricted within the limits of a single cytoarchitectonic area. One WGA-HRP injection in Case 27 involved both PG and PFG and was not considered for this study. FB, DY, TB, WGA-HRP, and CTB-g labeling was identified as described in detail in Luppino and others (2001, 2003). CTB-A labeling was analyzed by using standard fluorescein (for CTB-A 488) or rhodamine (for CTB-A 555 and CTB-A 594) sets of filters. CTB-A 488--labeled neurons were identified for a green granular fluorescence in the cytoplasm and CTB-A 555-- and CTB-A 594--labeled neurons for a red-orange and a red granular fluorescence in the cytoplasm, respectively. These 2 last tracers were never used in the same animal. The distribution of retrograde and anterograde (for WGA-HRP and BDA injections) labeling was analyzed in each section every 300 lm and plotted in each section every 600 lm, together with the outer and inner cortical borders, by using a computer-based charting system. Data from individual sections were then imported into a three-dimensional (3D) reconstruction software (Bettio and others 2001), creating volumetric reconstructions of the hemispheres from individual histological sections containing connectional and/or architectonic data. The results of this processing allowed us to obtain realistic visualizations of the
labeling distribution for a more precise comparison of data from different hemispheres. Distribution of labeling on exposed cortical surfaces was visualized in standard mesial, dorsolateral, or bottom views of the hemispheres. Distribution of labeling within sulci was visualized in nonstandard views of the hemispheres in which sulcal banks were exposed with appropriate dissections of the 3D reconstructions (Fig. 1). Areal Attribution of the Labeling Retrograde and anterograde labeling was found in several areas of the parietal, temporal, cingulate, agranular frontal, and prefrontal cortices.
In the parietal cortex, outside the IPL convexity, connections were attributed, when possible, to functional areas that, although in many cases still lack a clear architectonic definition, have been well established in electrophysiological studies. Accordingly, the lateral bank of the IPS was subdivided into a caudal (LIP), a rostral (anterior intraparietal, AIP), and a ventral (ventral intraparietal, VIP) area, according to Blatt and others (1990), Murata and others (2000), and Colby and others (1993), respectively. The SPL and the posterior cingulate cortex were subdivided as in Matelli and others (1998) (see also Marconi and others 2001) where functional areas V6A (Galletti and others 1999) and medial intraparietal (MIP) (Colby and others 1988; Colby and Duhamel 1991) were included in the map of Pandya and Seltzer (1982). Area V6A was
Figure 1. Dissection procedures of the reconstructed hemispheres to expose sulcal banks. In each panel, nonstandard views of an intact right hemisphere show in darker gray the brain sectors removed to expose the medial and the lateral banks of the intraparietal sulcus, the posterior bank of the arcuate sulcus, and the upper and lower banks of the lateral fissure and of the superior temporal sulcus. In each dissected view of the hemisphere, the exposed bank is shown in darker gray. The upper bank of the lateral fissure is shown in a bottom view of the dissected hemisphere, where arrowed lines mark the level of the rostral end of the intraparietal sulcus and the rostralmost level of the central sulcus. AI = inferior arcuate sulcus; AS = superior arcuate sulcus; C = central sulcus; Cg = cingulate sulcus; IP = intraparietal sulcus; LF = lateral fissure; Lu = lunate sulcus; P = principal sulcus; ST = superior temporal sulcus.
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criteria used for the definition of ‘‘feedback’’ connections and was left undefined.
subdivided into a dorsal (V6Ad) and a ventral (V6Av) sector according to Luppino and others (2005). For the parietal operculum the functional maps of the SII region and neighboring areas of Robinson and Burton (1980a, 1980b) and Krubitzer and others (1995) were considered, although these areas could not be precisely distinguished one from another. In cases of uncertain functional correspondence, labeling was attributed according to the architectonic maps of Pandya and Seltzer (1982) and Lewis and Van Essen (2000a). Temporal areas of the STS and inferior temporal gyrus were defined according to Boussaoud and others (1990) and Saleem and Tanaka (1996). In the frontal lobe, agranular frontal and cingulate areas were cytoarchitectonically defined according to Matelli and others (1985, 1991) and Geyer and others (2000). The prefrontal cortex was subdivided according to the cytoarchitectonic map of Walker (1940) and the prearcuate cortex also according to Stanton and others (1989) and Petrides and Pandya (2002).
Results
Quantitative Analysis and Laminar Distribution of the Labeling To obtain more objective information on the relative strength of the connections observed within the same case or across different cases, for each cortical injection, but those of BDA (because of the paucity of retrograde labeling observed with this tracer), we counted the number of labeled neurons plotted in the ipsilateral hemisphere in one section every 600 lm and located beyond the limits of the injected field. Because the absolute number of labeled neurons was largely variable across cases, mainly because of differences in amount, spread, and sensitivity of injected tracers, afferents to the injected field were expressed in terms of percent of labeled neurons found in a given cortical area or sector, with respect to the total number of labeled neurons. The percent distribution of the retrograde labeling observed for each area was then used for guiding the qualitative description of its connections. In this analysis, some sectors (e.g., parietal operculum) in which labeling extended across adjacent areas, which could not be precisely defined, were considered as a whole. To obtain information on possible hierarchical relationships of the observed cortical connections, labeling attributed to a given area and reliably observed across different sections and cases, was analyzed in each section every 300 lm, in terms of laminar distribution of the anterogradely labeled terminals and in terms of percent of labeled neurons located in the superficial (I--III) versus deep (V--VI) layers. These data were then analyzed according to the criteria reviewed by Felleman and Van Essen (1991) (see also Andersen and others 1990). Based on the laminar distribution of labeled terminals, projections were classified as ‘‘feedforward’’ when mostly concentrated in layer IV and lower III, ‘‘feedback’’ when distributed in superficial and deep layers, but avoiding layer IV, ‘‘lateral’’ when fairly even distributed in all cortical layers, and ‘‘mixed’’ when patches of ‘‘feedforward’’ projections were found together with patches of ‘‘feedback’’ projections. Based on the laminar distribution of labeled neurons, connections were classified as ‘‘feedforward’’ or ‘‘feedback’’ when labeled neurons in the superficial layers were >70% or 70% (Fig. 8, LIP). In the SPL, connections were limited to the mesial surface of the hemisphere and to the anterior wall of the parietooccipital sulcus (Fig. 6). In particular, these very strong connections extensively involved, with some variability in the relative distribution across cases, area PGm (Fig. 7, sections b--e), extending caudally in V6Av (Luppino and others 2005; Fig. 7, section a) and rostrally, in the caudal part of the cingulate gyrus (posterior cingulate cortex, CGp; Olson and others 1996). In all these areas the anterograde labeling showed a ‘‘feedback’’ pattern, and in PGm the labeled neurons in layers I--III were >70% (Fig. 8, PGm). Some labeling was also found more rostrally, in areas 23a and 23b. Temporal Cortex, Including Area MST and Insula Opt was connected with different STS and inferotemporal areas. In the caudal part of the STS (Fig. 6) very strong ‘‘feedback’’ connections (retrograde labeling in layers I--III >70%) were found in area MST (Figs. 7, section e, and 8, MST), mostly in its dorsal and caudal part (presumably dorsal MST, MSTd; Komatsu and Wurtz 1988). Weak labeling was observed in the middle temporal area (MT) (Fig. 7, sections d and e) and very sparse labeled cells in the fundal superior temporal area (FST). In the upper bank of the STS robust, ‘‘lateral,’’ or ‘‘mixed’’ connections (Fig. 8, superior temporal polysensory area, STP) were observed in restricted sectors lateral and rostral to MST, attributable to both the posterior (STPp; Fig. 7, section e) and anterior (STPa; Fig. 7, sections h, i, and n) subdivisions of the superior temporal polysensory area, respectively. Ventral to STPa, ‘‘feedforward’’ connections were observed with the fundal region of the sulcus (area IPa; Fig. 7, section l ; Fig. 8, IPa), extending also in the ventral bank, in the medial part of area TE (TEm) (Fig. 7, sections m and n). Additional labeling in the inferotemporal cortex, showing a ‘‘lateral’’ pattern, was observed in the postero-ventral part of area TE (TEpv) (Figs. 6 and 7, sections g and h), on the lateral lip and the fundus of the occipitotemporal sulcus. With the only exception of a small cluster of marked neurons observed in the postero-dorsal part of area TE (TEpd) in Case 27 (Fig. 6), in both Cases 23 and 27, labeling in TEm and TEpv was observed in very similar locations, suggesting that Opt is target of specific subsectors of these inferotemporal areas. Spots of labeling were also observed at different rostrocaudal levels in the parahippocampal area TF, and few scattered marked neurons were located in the perirhinal cortex (Figs. 6 and 7, sections g, i, l, and m). In Case 23, some purely anterograde labeling was found in the caudal part of the presubiculum. Very poor labeling was inconstantly located in the granular insula (Fig. 7, sections l and n). Agranular Frontal and Cingulate Cortices Two agranular frontal sectors, located in the dorsal premotor cortex (PMd) and ventral premotor cortex (PMv), respectively, showed relatively weak connections with Opt (Fig. 6). In PMd (Fig. 7, section o), labeling was consistently observed in the lateral part of the rostral PMd area F7, not including the supplementary eye field (F7 non-SEF [Luppino and others 2003]). In this premotor sector, anterograde labeling was very weak in deep layers, and much denser in layers I and II (Fig. 8, F7). In PMv (Fig. 7, section p), labeling, with some variability across cases, was found in the rostral area F5, in a relatively
Figure 5. Low-power photomicrographs of pairs of adjacent coronal sections showing, in the left column, representative injection sites in Opt (A, Case 23, WGA-HRP), PG (B, Case 20, WGA-HRP), PFG (C, Case 13, WGA-HRP), and PF (D, Case 29, DY). In the right column, higher magnification views from the adjacent Nissl-stained sections show the general cytoarchitectonic features of the injected areas. Calibration bars: in A--D = 1 mm; in A1--D1 = 500 lm. Abbreviations as in the caption of Figure 1.
rostral part of the posterior bank of the arcuate sulcus, the anterograde labeling being mostly focused in layer III (‘‘feedforward’’ pattern). In the agranular cingulate cortex, sparse labeling was observed in area 24b.
Prefrontal Cortex Several relatively weakly labeled sectors were observed in the prefrontal cortex (Figs. 6 and 7, sections p--r). In both Cases 23 and 27, some labeling was located relatively Cerebral Cortex October 2006, V 16 N 10 1397
Figure 6. Distribution and areal attribution of retrogradely labeled neurons observed following injections in area Opt in Cases 23 (WGA-HRP) and 27 (DY and TB) shown in dorsolateral, mesial, and bottom (Case 23 only) views of the injected hemispheres and in 3D views of the lateral bank of the IPS of the upper and lower bank of the STS and of the postarcuate cortex. The core of the WGA-HRP, DY, and TB injection sites is shown in black, green, and red, respectively, surrounded by a gray region corresponding to the halo. In Case 27, DY- and TB-labeled neurons are shown in green and red, respectively. Each dot corresponds to one labeled neuron. Dashed lines mark borders between IPL convexity or agranular frontal areas. AMT = anterior middle temporal sulcus; IO = inferior orbital sulcus; OT = occipitotemporal sulcus; R = rhinal fissure. Other abbreviations as in the caption of Figure 1.
caudally in the principal sulcus, mostly in the ventral bank and much weaker labeling was found on the mesial surface of the hemisphere, in medial area 8B. Some labeling was also found in the ventral prearcuate cortex, in area 45 ventral to the frontal eye field (FEF), as defined cytoarchitectonically in 1398 Connections of the Macaque IPL
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adjacent Nissl-stained sections (area 45b of Petrides and Pandya 2002). Part of the labeling was also observed on the dorsal lip of the principal sulcus (dorsal area 46) and in the dorsalmost part of area 8A. Finally, a very weak connection was also observed with the orbitofrontal area 12o (Fig. 6). All
Figure 7. Drawings of representative coronal sections from Case 23, in caudal to rostral order (a--r), showing the distribution and areal attribution of retrogradely labeled neurons observed following WGA-HRP injection in area Opt. The levels at which the sections were taken are indicated in the dorsolateral view of the injected hemisphere shown in the upper left part of the figure. PMT = posterior middle temporal sulcus. Conventions and other abbreviations as in the captions of Figures 1 and 4.
prefrontal connections of area Opt showed a ‘‘feedforward’’ pattern (Fig. 8, 45). Connections of Area PG Five tracer injections in 3 animals (Case 20, WGA-HRP; Case 27, CTB-A 594; Case 29, TB and CTB-A 488; Case 29, BDA) were placed in different parts of area PG. Figure 5B shows the location of the WGA-HRP injection in Case 20, placed in the
middle of the inferior parietal gyrus (see also Fig. 4), in a sector where cytoarchitectonic features typical of area PG, for example, a layer III quite homogeneous in cell size and density, a layer V densely populated by relatively small pyramids, could be observed in the adjacent Nissl-stained section (Fig. 5B1). The general distribution of retrograde labeling observed in Cases 20 (WGA-HRP) and 27 (CTB-A 594) and drawings of representative coronal sections from Case 20 are presented in Cerebral Cortex October 2006, V 16 N 10 1399
Table 2 Percent distribution (%) and total number (n) of labeled neurons observed following representative tracer injections and mean percent distribution (in bold) of all cases of retrograde tracer injections in Opt, PG, PFG, and PF Injected area
Opt (%)
PG (%)
Case
C23
C27DY
Mean (all cases)
C20
IPL PF PFG PG VIP AIP Parietal operculum Opt LIP MST Total IPL
— * 11.7 0.5 * 2.5 / 13.1 15.4 43.8
— * 17.4 * — 1.3 / 14.1 11.7 44.8
— * 12.83 * * 1.57 / 13.83 12.00 40.89
* 5.5 / 1.8 3.3 26.0 4.7 — 8.4 50.2
SPL PEa PE PEc MIP PEci V6Ad V6Av PGm Total SPL Area 2 Total parietal
— — — * * — 5.7 10.7 16.5 — 60.3
— — — * — 1.3 7.3 10.7 19.3 — 64.1
— — — * * 0.67 7.23 13.20 21.18 — 62.07
Temporal STP C, Tpt IPa, TE Pr/PH FST Total temporal
7.0 — 4.6 1.3 * 13.0
5.2 — 3.8 1.8 0.6 11.4
AFG, ACC F4 F5 F2 F7 24d Others Total AFG þ ACC
— 2.2 * 2.6 — * 5.1
PFG (%) Mean (all cases)
C13
C29FB
Mean (all cases)
C27FB
C29DY
Mean (all cases)
0.6 3.2 31.4 5.0 — 6.0 54.0
* 9.40 / 0.66 2.80 25.55 4.63 — 7.43 50.76
4.7 / 13.4 6.9 11.7 26.8 — * 1.8 65.3
6.8 / 13.6 6.0 10.7 29.8 — — 1.7 68.6
6.03 / 13.60 6.35 10.10 31.55 — * 1.55 69.18
/ 10.2 * 5.7 8.7 32.5 — — — 57.2
/ 10.3 1.5 4.6 12.7 29.9 — — * 59.0
/ 10.20 0.66 5.47 13.07 31.77 — — * 61.18
0.8 * 0.8 7.1 4.2 2.7 * — 15.9 — 66.1
* * 3.2 2.1 7.3 1.5 — * 14.6 — 68.6
* * 2.10 5.30 4.70 3.98 * * 16.77 — 67.53
4.3 * — * 1.4 — — — 6.1 * 71.5
3.8 * * 0.6 * — — — 4.8 * 73.5
3.50 * * 0.65 * * — — 5.31 * 74.56
1.0 — — — — — — — 1.0 18.2 76.4
1.4 * * * — — — — 2.2 17.1 78.3
1.10 * * * — — — — 1.36 16.60 79.14
5.77 — 4.07 1.90 * 12.16
4.8 8.2 — * — 13.4
4.9 5.6 0.6 — — 11.1
4.13 5.53 * * * 10.11
4.4 * * * 0.5 5.3
3.9 * * * * 4.5
3.53 * * * * 4.00
— — — — — —
* * — — — *
* * — — — *
— 1.8 * 2.6 — * 4.5
— 1.33 * 2.33 — * 3.79
* 1.8 1.2 * 1.0 * 4.3
* 1.3 0.8 * * * 2.9
* 2.35 1.60 * 0.65 * 5.03
1.5 7.1 * * * 0.5 9.5
3.0 6.4 1.1 — 1.0 1.2 12.7
1.78 6.70 1.23 * 0.89 0.83 11.44
5.5 12.5 * — — 2.1 20.1
4.9 11.1 * — * 1.4 17.7
4.00 10.27 * — * 1.27 15.63
3.5 3.6 7.1
2.9 3.0 5.9
2.47 2.43 4.90
* 1.5 1.8
— 1.0 1.0
* 1.75 1.93
1.0 5.7 6.7
* 4.4 4.5
* 3.35 3.64
— 0.9 0.9
— 1.0 1.0
— 1.77 1.77
Others MT, DP CGp, 23 Insula 24a þ b PrCO
1.9 11.5 0.5 * —
3.5 9.7 — * —
3.30 12.63 * * —
* 8.1 5.3 0.5 *
— 9.0 6.4 0.8 *
0.60 9.58 4.20 0.90 *
* 0.9 4.9 0.5 0.6
* * 3.7 0.7 *
* 1.05 4.08 0.70 0.55
— — * * 2.4
— — 1.2 * 1.6
— — 1.82 * 1.57
Total n
19.775
17.939
21.273
27.841
41.704
16.281
12.645
30.900
Prefrontal 46d, 8 46v, 45b, 12o Total prefrontal
C27CTB-A594
PF (%)
0.7 7.1 /
Note: / 5 injected area; — 5 no labeling; * 5 labeling \0.5%; AFC 5 agranular frontal cortex; ACC 5 agranular cingulate cortex.
Figures 9 and 10, respectively. The percent distribution of the labeled neurons observed in these 2 cases, as well the mean values of all the PG injections, but the BDA one, is shown in Table 2. Representative patterns of laminar distribution of retrograde and anterograde labeling observed in Cases 29, BDA, and 20 are illustrated in Figure 11. Parietal and Posterior Cingulate Cortices In the IPL, strong ‘‘lateral’’ connections were observed with areas PFG, PGop, and the rostral part of area Opt (Figs. 9, 10, sections d--g, and 11, Opt). A few marked neurons were also found in area PF and in area DP. In the parietal operculum, in addition to PGop, very strong connections showing a ‘‘feedback’’ pattern were observed with the retroinsular cortex, but also more rostrally and deeply, with area SII (Figs. 9, 10, sections f--h, and 11, SII). A more rostral, minor labeling can be attributed to 1400 Connections of the Macaque IPL
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area PV. In the lateral bank of the IPS, moderate ‘‘lateral’’ connections were observed with the mid-rostral part of it, mostly involving area AIP and, at a very minor extent, area VIP (Figs. 9 and 10, sections f--h). Area LIP, which was heavily connected with Opt, was virtually devoid of marked neurons. Moderate to rich connections showing a ‘‘lateral’’ pattern (Fig. 11, PEci) were observed in different areas of the caudal part of the SPL, with some variability in their relative distribution across cases. These connections involved the caudal part of the ventral bank of the cingulate sulcus (area PEci), area V6Ad (Figs. 9 and 10, sections a and b) and area PEc. Area PGm and the CGp were virtually devoid of labeling. Dense patches of ‘‘lateral’’ connections (Fig. 11, MIP) were also observed in the medial bank of the IPS, where, although with some variability across cases, most of them were observed in the mid-caudal part of it, attributable mostly to area MIP. In the cingulate area 23, rich ‘‘lateral’’
Figure 8. Upper part: camera lucida drawings of representative examples of laminar distribution of retrograde and anterograde labeling observed following WGA-HRP injection in Opt in Case 23 taken from the areas indicated in each panel. The anterograde labeling is shown in gray, and retrogradely labeled neurons are shown in black. Dashed lines mark borders between cortical layers. Calibration bar (below TEpv) = 500 lm (applies to all drawings). Lower part: photomicrographs from Case 23 showing examples of WGA-HRP labeling observed in areas LIP, PGm, and TEpv. Calibration bar (shown in LIP) = 500 lm (applies to all photomicrographs).
connections (Fig. 11, 23c) were observed with the ventral bank of the cingulate sulcus (area 23c) and the dorsal part of the cingulate gyrus (area 23b). Temporal Cortex, Including Area MST and Insula Very rich labeling was observed in MST (Figs. 9 and 10, sections d and e), which extended also more rostrally (and deeply) with respect to Opt injections, possibly involving also the lateral part of MST (MSTl, Komatsu and Wurtz 1988). Dense, but restricted labeling was also found at different rostrocaudal levels of area
STP attributable to both STPp and STPa (Figs. 9 and 10, sections f, i, and o). In particular, the labeling in STPa shown in Figure 10, section i, appears to occupy a location similar to the labeling observed following injections in Opt. In both MST and STP the anterograde labeling showed a ‘‘feedback’’ pattern (Fig. 11, MST and STP). Very weak ‘‘feedforward’’ connections (more evident following BDA injection) were also observed in area IPa (Figs. 10, section m, and 11, IPa). Very sparse labeling was observed in area MT (Fig. 10, section c) and in perirhinal and parahippocampal cortices (Fig. 10, section l). In 2 cases (Case Cerebral Cortex October 2006, V 16 N 10 1401
Figure 9. Distribution and areal attribution of retrogradely labeled neurons observed following injections in area PG in Cases 20 (WGA-HRP) and 27 (CTB-A594) shown in dorsolateral and mesial views of the injected hemispheres and in 3D views of the medial and lateral banks of the IPS of the upper and lower banks of the STS and lateral fissure and of the postarcuate cortex. Conventions and abbreviations as in the captions of Figures 1 and 6.
1402 Connections of the Macaque IPL
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Figure 10. Drawings of representative coronal sections from Case 20, in caudal to rostral order (a--q), showing the distribution and areal attribution of retrogradely labeled neurons observed following WGA-HRP injection in area PG. Ca = calcarine sulcus; OI = inferior occipital sulcus. Conventions and other abbreviations as in the captions of Figures 1, 6, and 7.
29 BDA and 29 TB), some labeling was observed in area TEav, close to the anterior medial temporal sulcus. In Case 29 BDA, labeled terminals were also observed in the caudal part of the presubiculum. One additional and distinctive relatively strong connection of PG, showing a ‘‘feedback’’ pattern (retrograde labeling in layers I--III >70%), was located caudally, in the ventral bank of the LF, extending also on the adjacent part of the superior temporal gyrus (Figs. 9, 10, sections f and g, and 11, C), involving areas C of Morel and others (1993) and Tpt of Pandya
and Sanides (1973; see also Lewis and Van Essen 2000a). Rich ‘‘feedforward’’ connections (retrograde labeling in layers I--III 70%), weaker than those observed following PG injections, were observed in area MST in all cases of injections in PFG (Figs. 12, 13, section b, and 14, MST). In STP restricted but relatively robust labeling showing a ‘‘mixed’’ type of connections (Fig. 14, STP) was found in both STPp and STPa (Figs. 12 and 13, sections c, g, and h). In particular, the labeled STPa sector in Figure 13, section g, appeared to largely overlap with the STPa sector connected with PG and Opt. In the ventral bank of the STS, in addition to few marked neurons found in area MT (Fig. 13, section a), some labeling was also located in area FST (Fig. 13,
section d). More rostrally, some clusters of marked neurons were consistently observed, in all cases, in areas IPa and TEm, where labeled terminals showed a ‘‘feedforward’’ pattern (Figs. 12, 13, sections e and f, and 14, TEm). Robust ‘‘feedforward’’ connections (retrograde labeling in layers I--III
