Layer IVB Research Articles

Layer IVA of Rhesus Monkey Primary Visual Cortex

Layer IVA of rhesus monkey striate cortex contains pyramidal cells arranged in distinct groups. Their cell bodies are in a configuration of flat cones, each with an average diameter of 60 microns, and their apical dendrites aggregate into bundles that ascend toward the pial surface. Nissl-stained sections suggest that these pyramidal cell cones have their bases in layer IVB, with their tops extending into layer IVA. The neurons in the cones are readily apparent in MAP2 antibody-stained material, and in cytochrome oxidase-reacted tissue it is evident that the pyramidal cell cones occupy the pale spaces that are surrounded by the darkly reactive honeycomb lattice. This lattice of neuropil around the cones contains some axons and boutons that are immunoreactive for parvalbumin, and it is within the lattice that other investigators have shown afferents from the parvocellular (P)-layers of the dLGN to terminate. Because of this input, it is likely that the pyramidal cell cones of layer IVA are involved with color and form perception. The relationship between the layer IVA cones of neurons and the underlying system of previously described pyramidal cell modules (Peters and Sethares, 1991) is discussed, as well as the possibility that the pyramidal cell cones might represent aggregations of neurons, which receive input from basic sets of P-like afferents originating from color-responsive ganglion cells of the retina, as described by Schein and de Monasterio (1987).

Terminal arbors of individual, physiologically identified geniculocortical axons in the tree shrew's striate cortex

We studied the terminal patterns of single, physiologically identified geniculocortical axons in the striate cortex of the tree shrew by using intracellular recording and labeling methods. Axons were classified by their response to the onset (ON-center) or offset (OFF-center) of a light stimulus presented to the ipsilateral or contralateral eye. Then, we attempted to penetrate each axon for labeling with horseradish peroxidase. We recovered 23 axons and studied 16 of these in detail. Light microscopic reconstructions of these axons revealed several distinct terminal patterns within cortical layer IV. ON-center axons had terminal arbors that ended mainly in the upper part of layer IV (IVa), while OFF-center axons ended in the lower part of layer IV (IVb). Within layers IVa and IVb, axons driven by the ipsilateral eye and those driven by the contralateral eye had overlapping distributions. However, their terminal arbors differed in size, in shape, and in the number of boutons. Compared with contralateral eye arbors, ipsilateral eye axons were on average three times larger in lateral extent (925 microns vs. 325 microns), spread over four times the surface area (0.13 mm2 vs. 0.03 mm2), and supported one and one-half times as many terminal boutons (1,647 vs. 1,086). The ipsilateral eye axons had more boutons at the edges of layer IV (i.e., the upper part of layer IVa and the lower part of layer IVb), while those from the contralateral eye axons were more evenly distributed. These results show that each functional class of geniculocortical fiber has a different laminar and areal arrangement of boutons and we consider the significance of these differences for visual cortical function.

Quantitative analysis of a vulnerable subset of pyramidal neurons in Alzheimer's disease: II. Primary and secondary visual cortex

In this study we investigated the primary and secondary visual areas of normal and Alzheimer's disease brains by using the SMI32 antibody. It is known that in Alzheimer's disease primary sensory areas are usually less devastated than association cortices, although visual symptomatology has been documented early in the course of the disease. In area 17, the SMI32 antibody primarily labeled the perikarya and dentritic tree of the large Meynert cells and cells in layer IVB. Smaller neurons in layers III, V, and VI were also immunoreactive (ir). In area 18, very large SMI32-ir pyramidal neurons in layers III and V were observed. In both areas, staining intensity was correlated with cell size, the largest neurons being the most intensely stained. Only a few changes were observed in the Alzheimer's disease cases. The only statistically significant differences in SMI32-ir neuron counts between control and Alzheimer's disease brains occurred in layer IVB cells and Meynert cells in area 17, and in layer III cells in area 18. In contrast with association cortices, there were no changes in staining intensity in the visual areas. There were fewer neurofibrillary tangles and neuritic plaques in these areas than in prefrontal and inferior temporal cortex, and a correlation between neurofibrillary tangle counts and SMI32-ir neuron loss was only observed in layer III of area 18. These observations show that in the primary and secondary visual cortex, SMI32 also labeled a distinct subset of pyramidal cells that are known from data obtained in the monkey brain to furnish long corticocortical as well as subcortical projections. Interestingly, although there is much less cell and/or neurofibrillary tangle formation in these occipital regions than in prefrontal and temporal association areas, there is significant loss within key subsets of pyramidal cells. The selective loss of this particular subpopulation of pyramidal neurons will disrupt association pathways linking primary visual cortex with areas involved in higher level visual processing. The partial disconnection of such pathways may be relevant to the visual symptomatology frequently observed in Alzheimer's disease patients. These data further support the hypothesis that subtypes of pyramidal neurons with specific anatomical and molecular profiles may display a differential vulnerability in Alzheimer's disease.

Interlaminar and lateral excitatory amino acid connections in the striate cortex of monkey

The intrinsic excitatory amino acid pathways within the striate cortex of monkeys were studied by autoradiographic detection of retrogradely labeled somata following microinjections of D-3H-aspartate (D-3H-Asp) into different layers. The labeled amino acid was selectively accumulated by subpopulations of neurons and, to a small extent, by glial cells, the latter mainly in the supragranular layers. Immunocytochemical detection of neurons containing GABA showed that, apart from a few cells exclusively in layer I, GABAergic neurons do not accumulate D-3H-Asp. Several lines of evidence suggest that D-3H-Asp uptake occurred only at nerve terminals; thus, the pattern of perikaryal labeling allowed the delineation of interlaminar and lateral projections. Neurons in layer I probably project laterally, and layer I receives wide-ranging projections from layer IVB and layer V from cells up to 1300 microns laterally. Some neurons in layer II send a focused projection to lower layer VI. Some neurons in layers II/III project up to 1 mm laterally within their own layer, but relatively few neurons can be labeled in these projections. Similarly, in layers II/III few neurons can be retrogradely labeled from layers V and upper VI, and this projection is organized such that cells closer to the pia project deeper in layer V/VI. The connections of layer IVA could not be revealed separately because of the difficulty of confining injections to this thin sublamina. Neurons in layer IVB project up to 1300 microns within IVB itself. A small number of cells from IVB also project to layers III, IVC-alpha, V, and VI with much more restricted lateral spread. Neurons in upper IVC-alpha send axons to layer IVB with at least 600-800 microns lateral spread. Neurons in lower IVC-alpha/upper IVC-beta project to layer III with at least 300-500 microns lateral spread. The bottom 50-80 microns of layer IVC-beta contains neurons with a very focused projection, apparently exclusively to the layer III/IVA border region. Both layers IVC alpha and beta have rich connections within themselves, the beta sublayer having more restricted lateral connections. Some neurons in layer IVC-beta give a laterally restricted small input to layers IVC-alpha and IVB. Both IVC-alpha and -beta project to layers V and VI, and these projections are spread at least 400 microns laterally. Neurons in layer V project to all layers, but the projection to layers I-III and within layer V itself spread much further laterally than the projections to layers IV and VI.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal synchrony in monkey striate cortex: interocular signal flow and dependency on spike rates.

A hypercolumn of monkey striate cortex was studied with an array of 30 closely spaced microelectrodes. Prominent broad peaks appearing in spike train correlograms are considered here. These were not due to shared stimulation, were mostly 30 to 100 ms wide, and were presumably the consequence of intraretinal lateral interactions. The correlogram peak areas were found to be predictable from the products of the spike rates, to which they were proportional. One can conclude that the correlation occurs before the overall reduction of spike rates from retina to cortex takes place. Furthermore, when a neurone dominated by one eye was stimulated via that eye, the correlogram formed with a neurone dominated by the other eye showed a displaced peak, indicating that excitation traveled from the well-responding to the unresponsive neurone in about 10 ms. When a left-eye stimulus was delivered, the same pair of neurones had a correlogram with a reversed peak displacement. This effect was only observed in layers IVb and c, indicating that in these layers the paths from the two eyes to a given cell are of unequal length, whereas in other layers, cells receive input from both eyes via similar connections differing only in strength.

Histochemical localization of cytochrome oxidase activity in the visual system of the tree shrew:normal patterns and the effect of retinal impulse blockage.

The tree shrew Tupaia belangeri has three functional pathways (ON-center, OFF-center, and W-like cells) that arise in the retina and proceed through separate LGN laminae to separate cortical targets. To determine whether these pathways have consistent differences in activity, cytochrome oxidase (C.O.) patterns were examined in the retina, LGN, and striate cortex. In six normal tree shrews the outer and inner plexiform layers of the retina were highly reactive for C.O. A pale, vascularized cleft zone separated the a (OFF) and b (ON) inner plexiform sublaminae, which seemed about equally reactive for C.O. In the LGN, laminae 1 and 2 (ON-center cells) and laminae 4 and 5 (mostly OFF-center cells) were highly reactive for C.O. LGN lamina 3 and 6 are part of an W-like afferent pathway. Lamina 3 was distinctly paler than laminae 1, 2, 4, and 5 while lamina 6 was intermediate. In the striate cortex, layer IV was the most reactive layer. Sublayer IVb (predominantly an OFF region) was consistently more reactive than sublayer IVa (predominantly ON). The middle portion, layer IVm, was paler than either IVa or IVb. This paler region includes, but extends above and below, the cell-sparse "cleft" region. Thus, considering all three levels of the retinogeniculostriate pathway, the ON and OFF systems were equally active until they reached the striate cortex, where the OFF system appeared to be more active than the ON. The W-cell laminae in the LGN exhibited the lowest level of activity. The contribution of ganglion cell activity to these patterns was assessed by intravitreal administration of tetrodotoxin (TTX) blockade either monocularly (three animals) or binocularly (two animals). In the TTX-treated retinae, the inner plexiform a and b sublaminae were paler for C.O., although visible, and were still separated by the pale cleft. The ganglion cell layer was very pale in comparison to the normal. In the LGN, monocular TTX blockade reduced the C.O. reactivity in the ON and OFF laminae that received input from the treated eye but had little effect on the W-like cell laminae. The ipsilaterally innervated ON and OFF laminae were more affected than were the contralaterally innervated laminae. Binocular TTX treatment resulted in a decrease of C.O. activity in the binocular segment of the ON and OFF LGN laminae. In the striate cortex, the most marked changes following TTX treatment occurred in layer IV.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of neuropeptide Y immunoreactivity in human visual cortex and underlying white matter

Immunocytochemical techniques have been used to study neuropeptide Y (NPY) distribution in the human visual cortex (Brodman's areas 17, 18 and 19) NYP cell bodies belong mostly to inhibitory (multipolar and bitufted) but also to excitatory (bipolar and some pyramidal) neuronal types. Their distribution is similar in the three cortical areas studied: 20 to 40% of the NPY perikarya are located in the cortical gray matter, mostly in the deep layers, while the remaining 60 to 80% are located in the underlying white matter. Immunoreactive NPY processes form a rich network of intersecting fibers throughout the entire visual cortex. A superficial plexus (layers I and II) and a deep plexus (deep layer V and layer VI) of NPY fibers are present in areas 17, 18 and 19. In area 17, an additional well developed plexus is present in layers IVb and IVc. These plexuses receive branches from long parallel fibers arising from deep cortical layers or underlying white matter and terminating in superficial layers. Local or extrinsic NPY terminals wind around vessels in the cortex as well as in the white matter, and either penetrate them or form clusters of club endings on their walls. Our results suggest a role for NPY in human visual circuitry and in cortical blood flow regulation.

Ocular dominance columns and retinal projections in New World spider monkeys (Ateles ater).

Retinal projections and the degree of ocular segregation in the striate cortex were examined by transneuronal autoradiography following unilateral intraocular injections of 3H-proline in a New World primate, the spider monkey (Ateles ater). The results show that, within the lateral geniculate nucleus (LGN), retinal fibers terminate in six principal layers and within the interlaminar spaces adjacent to the magnocellular layers, as well as the S layers ventral to the magnocellular layers. Projections to the superior colliculus, both ipsilateral and contralateral to the injected eye, were patchy and restricted to the superficial gray layer. Our main result shows that, in the striate cortex, LGN projections terminate in well-defined ocular dominance columns in layer IV. Labelled columns were most clearly delimited in layer IVb, where they averaged 373 + 42 micron in width in both the ipsilateral and contralateral hemispheres, slightly smaller than those reported originally from electrophysiological studies of striate cortex in spider monkeys (Hubel and Wiesel, '68). Unlabelled intercolumns were significantly narrower than labelled columns, which suggests that there may be overlap between input from the two eyes between columns. Quantitative measures showed above-background label also in cortical layers IIIb, V, and VI. Our results support the idea that among primates, ocular dominance columns are not limited to Old World species. At the same time, it is apparent that spider monkeys are exceptional among New World primates in having sharply delimited columns. The functional significance of the variation in the degree of ocular segregation in the cortex and its relation to primate evolution are discussed.

Projection patterns of individual X- and Y-cell axons from the lateral geniculate nucleus to cortical area 17 in the cat.

Horseradish peroxidase was injected intracellularly into single, physiologically-identified X- and Y-cell geniculocortical axons projecting to area 17 of the cat. This injection anterogradely labeled the axon terminal fields in cortex and retrogradely labeled the somata of these same axons in laminae A and A1 of the lateral geniculate nucleus (LGN). The laminar projections of 21 X- and 15 Y-cell axons were analyzed. For these, the laminar terminations of ten X- and seven Y-cell axons were also related to their cells' positions in the A-laminae. The terminal fields of X- and Y-cell axons overlapped substantially in layers IV and VI of area 17. Some X-cells terminated mainly in IVb, others mainly in IVa, and still others throughout IVa and IVb. The latter two groups also projected up to 100 micron into lower layer III. Y-cells terminated primarily in layer IVa and projected up to 200 microns into lower layer III. Some also arborized throughout the depth of layer IVb. Both X- and Y-cell axons terminated throughout the depth of layer VI, although more so in the upper half. We found no relationship between the diameter of the parent axon and its sublaminar projection within layer IV. Within layer IV, X-cell axons generally terminated within a single, continuous clump and had surface areas of 0.6 to 0.9 mm2. Axons of Y-cells often terminated in two to three separate clumps, separated by terminal free gaps 400 to 600 micron wide. Their total surface areas, including gaps, were 1.0 to 1.8 mm2, roughly 1.6 times the surface areas of X-cell axons. Despite considerable overlap, Y-cell arbors contained significantly more boutons than did X-cell arbors. The sublaminar projections of the X- and Y-cell axons within layer IV reflected the locations of the cells' somata within the depth of the A-laminae. X-cells located in the dorsal or ventral thirds of the depths of the laminae projected mainly to layer IVa or throughout layer IV in cortex. Those located in the central thirds projected mainly to layer IVb. Y-cells showed a similar positional relationship, but they appeared to follow different rules. Y-cells in the outer thirds of the A-laminae projected mainly to layer IVa; those in the central thirds, in addition, expanded their projections to include layer IVb. In general, larger sized somata in the LGN gave rise to more widely spreading terminal arbors and greater numbers of boutons in cortex than did smaller somata.(ABSTRACT TRUNCATED AT 400 WORDS)

Termination patterns of individual X- and Y-cell axons in the visual cortex of the cat: projections to area 18, to the 17/18 border region, and to both areas 17 and 18.

Horseradish peroxidase was injected intracellularly into single, physiologically identified X- and Y-cell geniculocortical axons that projected to area 18, to the 17/18 border region, or to both areas 17 and 18 via branching axons. The axon terminal fields in cortex were labeled anterogradely, and the cell bodies of the axons in the A-laminae, lamina C, and the medial interlaminar nucleus (MIN) of the dorsal lateral geniculate nucleus (LGN) were labeled retrogradely. The laminar projections in area 18 of eight Y-cells and one geniculate, non-Y-cell were analyzed. Most of the cells arborized densely within layer IVa and the lower 200 to 400 microns of layer III. Most provided little or no input to layer IVb or layer VI. Thus, the laminar projections of Y-cells to layer IV of area 18 were similar to those of their area 17 counterparts, although the input to layer III was greater and rose much higher in area 18 than in area 17. The terminal arbors in area 18 were two to three times larger in lateral extent than those in area 17. They spread over 2.0 to 2.8 mm2 of layer IV and occupied proportionately much greater regions of area 18 than the Y-cell arbors in area 17. This may partially account for the large receptive fields of cortical cells in area 18, and it indicates that a small region of area 18 may receive converging inputs from a relatively wide retinotopic region of the LGN. The terminal arbors were also highly asymmetric, generally being two to four times longer anteroposteriorly than mediolaterally. These asymmetric arbors may form the structural basis for the anisotropic organization of the retinotopic map in area 18. We recovered three cells (two Y, one X) whose axons arborized in the border zone between areas 17 and 18. One Y-cell axon had a receptive field located in the ipsilateral visual hemifield and it arborized in a small region restricted almost exclusively to the border zone. The other two cells had receptive fields on or adjacent to the vertical meridian, and they terminated on either side of the 17/18 border region as well as within it. Thus, geniculate afferents representing the ipsilateral hemifield or the vertical meridian appear to have different patterns of termination on and adjacent to the 17/18 border zone. Also, some X-cell input may invade area 18 in the region immediately adjacent to the border zone.(ABSTRACT TRUNCATED AT 400 WORDS)

ON and OFF regions in layer IV of striate cortex

In vertical penetrations through the striate cortex in the tree shrew ( Tupaia belangeri), we found regions where neural activity was evoked predominantly by light ON. These were followed by regions where responses were evoked predominantly by light OFF. Histological reconstructions indicated that the ON regions were correlated with layer IVa and the OFF regions were correlated with layer IVb. Local application of cobalt chloride produced a transient cessation of visually evoked activity, suggesting that the electrodes sampled cortical activity rather than lateral geniculate nucleus afferents. These data demonstrate that separate ON and OFF regions are present in the tree shrew striate cortex and suggest that spatially separate, parallel ON and OFF afferent channels extend, in this species, at least through the first synapse in the striate cortex.

Postnatal development of laminar innervation patterns by monoaminergic fibers in monkey (Macaca fascicularis) primary visual cortex

Immunohistochemical methods are used to characterize the distribution of noradrenergic and serotonergic fibers in primary visual cortex of cynomolgus monkeys (Macaca fascicularis) at various postnatal ages. Previous studies in adult squirrel monkeys have shown that serotonergic fibers are generally restricted to the upper four cortical laminae and are especially dense in layer IV, whereas noradrenergic fibers are especially dense in layers V and VI, moderate in layers I, II, and III, and virtually absent in layer IV (Morrison, J. H., S. L. Foote, M. E. Molliver, F. E. Bloom, and H. G. W. Lidov (1982) Proc. Natl. Acad. Sci. U.S.A. 2401-2405; Morrison, J. H., S. L. Foote, D. O'Connor, and F. E. Bloom (1982) Brain Res. Bull. 9: 309-319). Since these monoamines, especially norepinephrine, have been hypothesized to play an essential role in the developmental plasticity of visual cortex organization (e.g., Kasamatsu, T., and J. D. Pettigrew (1976) Science 194: 206-209; Pettigrew, J. D., and T. Kasamatsu (1978) Nature 271: 761-763), the present study examined the postnatal development of these innervation patterns, especially just before and just after the reported "critical period" for visual plasticity. A dense serotonergic innervation of layer IV is present at birth along with sparse innervation of other laminae. The adult pattern of serotonergic innervation, which is similar to that in the squirrel monkey but even more specifically laminated, becomes evident by 6 weeks of age. In the adult pattern, the most dense innervation remains in layers IVb and IVc. A much lower density of noradrenergic than of serotonergic fibers is evident at all ages examined. As with serotonin, the lowest density of fibers is observed at birth. By about 2 months of age these noradrenergic fibers have become more dense, and their laminar distribution is similar to that of adult cynomolgus which is similar to adult squirrel monkey. These studies indicate that: (1) both types of innervation display a continuum of development, with no abrupt changes, (2) serotonergic innervation is more dense than noradrenergic innervation at every age examined, (3) these two transmitter systems exhibit very different laminar innervation patterns as early as birth, and (4) the greater laminar specialization of area 17 in cynomolgus versus squirrel monkeys is accompanied by corresponding enhanced laminar specialization of these monoaminergic afferents.

Serotonin nerve fibers in the primary visual cortex of the monkey. Quantitative and immunoelectronmicroscopical analysis.

A quantitative and immunoelectronmicroscopical analysis of serotonin nerve fibers in the primary visual cortex of the monkey (Macaca fuscata) was made using a sensitive immunoperoxidase method for serotonin. The overall numerical density of serotonin-containing varicosities in the primate striate cortex was approximately 770,000/mm3 and the highest concentration of immunoreactive varicosities (ca. 1,400,000/mm3) was observed in the upper portion of layer IVc, the next highest concentration being in layer IVb (ca. 1,180,000/mm3). At the ultrastructural level, the electron dense immunoreactive products were observed in the small granules (10-65 nm in diameter). The varicosities were usually small (0.5-1.0 micron in diameter) and made contact with both stellate and pyramidal cells. Serotonin fibers were often in close apposition to the poorly myelinated axons in layers IVb, V, and VI, and they rarely formed distinct synaptic structures with unlabelled neuronal elements.

The laminar organization of the lateral geniculate body and the striate cortex in the tree shrew (Tupaia glis)

The organization of geniculostriate projections in Tupaia was studied using three separate methods, anterograde transport from the lateral geniculate, retrograde transport from the striate cortex, and reconstruction of single geniculostriate axons. The results show that each layer of the lateral geniculate body has a unique pattern of projections to the striate cortex, and each pattern consists of a major and a minor target. The two ipsilateral layers project to thin subtiers of layer IV: the major target of geniculate layer 1 is the top of IVa; the major target of geniculate layer 5 is the base of IVb. The minor target of layer 1 is the major target of layer 5. Two of the contralateral layers can be matched to the ipsilateral layers. Layers 1 and 2 are a matched pair and project to IVa; layers 4 and 5 are a matched pair and project to IVb. Thus, projections of a matched pair overlap. The remaining two contralateral layers, 3 and 6, project chiefly to cortical layer III. Layer 3 projects to layers IIIb and I and seems to be the counterpart of the parvocellular C layers in the cat and the intercalated layers in primates. Layer 6 projects to the base of IIIc in a zone contiguous with IVa. This contiguity raises the issue of whether the base of IIIc might actually be a part of layer IV. If this were the case, the two tiers of layer IV which are separated by a conspicuous cleft might be considered two subdivisions of layer IVb.

Morphology of geniculo-striate afferents in a prosimian primate

In order to analyze the arborization pattern of single axons innervating layer of striate cortex in Galago (a prosimian primate), injections of horseradish peroxidase were made into the white matter below visual cortex. Two distinct fiber types were identified which ramify within different subdivisions of layer IV. Fibers with large axons (type I) have relatively wide terminal arbors which ramify in layer IVa and lower layer III, while those with small axons (type II) arborize in restricted zones of layer IVb. Evidence from previous investigations suggest that terminals of these two fiber types represent the axon terminals of X-like and Y-like geniculate relay cells.

An anterograde degeneration study of the tangential spread of axons in cortical areas 17 and 18 of the squirrel monkey (Saimiri Sciureus)

AbstractIn area 17 of squirrel monkey, lamina IVB of Brodmann is divided into three sublaminae by a thin, dense row of cell bodies, the largest of which have apical poles. Study of the 17/18 border suggests that these are a group of pyramidal cells, continuous with the large border pyramids in the depth of layer III in area 18. In contrast, the densely packed granule cells of layers IVA and IVC appear to be continuous with those of layer IV of area 18. It is thus proposed that in area 17, the third and fourth neocortical layers not only divide into sublaminae, but that these in turn interdigitate and intermingle their cell types. The tangential extent of intracortical fibers has been studied by making perpendicular slits in both areas and measuring the spread of anterograde degeneration to each side of the lesion. In area 17, this spread is always the same whatever the orientation of the fibers with respect to visual field representation. Degenerating fibers are few in number and found mainly in layers I, IVB and VI. In layers IVB and VI they extend for 0.5–1.0 mm. In layer I, some reach as far as 2.0 mm. In area 18, degenerating fibers are more numerous and longer. They are plentiful in layer I, diminish considerably in layer II, increase again in number till the depth of III, are slightly less numerous in layer IV and are again plentiful in layers V and VI. Their length varies with orientation. In a direction corresponding to a visual field sector, they extend for 1.5–2.0 mm, a distance representing only a fraction of the total representation of a sector in the cortex. In a direction corresponding to a visual field zone, they extend further and the combined degeneration of the two sides spans the whole distance of area 18 from the vertical to the horizontal meridian (6 mm). It is suggested that at least some of the fibers of the stria of Gennari subserve binocular interaction and that the differential fiber lengths in area 18 are related to foveal acquisition or to a directional anisotropy of visual movement perception along sector‐zone axes.

On the striate area of the human isocortex. A Golgi- and pigmentarchitectonic study.

The distribution pattern of the pigment in various layers of the primary visual cortex of man is described by means of a method for the stereomicroscopical demonstration of neurolipofuscins in sections up to 1,000 mum thick. This paper presents the striate area as being composed of 12 cellular layers, which can be clearly delineated by a successive examination of both the Nissland the pigment preparations. Layers I, II, and III resemble more or less the corresponding laminae of other isocortical fields. The pyramids within the deep portion of layer III are unusually small and additionally are intermingled with thorny stellate cells which are a characteristic component of layer IV. Accordingly, this band of cells is called IIIc-IVa. The subjacent layers IVb and IVcalpha are poorly pigmented. In Nissl-preparations layer IVb, which contains only a few cells, is followed by a broad band of cells tightly packed together, which includes layers IVcalpha, IVcbeta, IVd, and Va. These layers cannot be reliably delineated in Nissl-preparations but appear in pigment preparations as distinct and sharply limited laminae. Particularly, layer IVcbeta, which is built up by minute thorny stellate cells, is marked by coarse and intensely stained lipofuscin granules, whereas IVd is mainly populated by minute pyramids which are almost devoid of pigment deposits. A remarkably narrowed layer Va, the pyramids of which store a medium number of lipofuscin grains, completes this series (IVcalpha, IVcbeta, IVd, Va). The cell-sparse layer Vb is almost devoid of pigment granules. Layer VIa has specialized pyramidal cells containing finely grained pigment. The relatively broad layer VIb shows loosely arranged cells poorly endowed with lipofuscin granules.