The location and retinotopic organization of visual areas in the cat cortex were determined by systematically mapping visual cortex in over 100 cats. The positions of the receptive fields of single neurons or small clusters of neurons were related to the locations of the corresponding recording sites in the cortex to determine the representations of the visual field in these cortical areas. In this report, the first of a series, we describe the organization of area 17. A single representation of the cat's entire visual field corresponds closely to the cytoarchitectonically defined area 17. This area has the largest cortical surface area (380 mm2) and the highest cortical magnification factor (3.6 mm2/degree2 at area centralis) of all the cortical areas we have studied. There was perfect agreement between the borders of area 17 determined electrophysiologically and cytoarchitecturally. This area contains a first order transformation of the visual hemifield in which every adjacent point in the visual field is represented as an adjacent point in the cortex. Some variability exists among cats in the extent and retinotopic representation of the visual field in area 17.

The retinotopic organization of area 17 (striate cortex) in the cat.

THE DORSAL lateral geniculate nucleus (LGNd) of the cat is a principal relay nucleus on the direct pathway from the retina to the visual cortex, and several parameters of its organization as a relay are well established. First, relay cells of the LGNd have either onor off-center receptive fields (16), because each relay cell receives direct excitatory drive from either onor off-center retinal ganglion cells (6, 16). Second, retinal ganglion cells fall into two groups (X-cells and Y-cells) according to whether they sum the influences of the center and surround regions of their receptive fields linearly or nonlinearly (8). Most LGNd relay cells can be similarly classified because most receive direct excitatory drive from either Xor Y-type retinal ganglion cells (6). Third, each relay cell receives direct excitatory drive from either fastor slow-conducting retinal afferents, and its own axon is correspondingly either fast or slow conducting (6, 36). The two latter parameters are closely correlated since Y-cells have been shown to have fast axons and Xcells, slow axons (6, 11). The on/off organization is independent of the other two parameters, however. Roth Y-cells and Xcells can have either onor off-center fields. This report examines several features of the LGNd relay in the normal cat, extending previous concepts and establishing a spectrum of normal properties against which the properties of the LGNd in deprived cats (described in the following paper (3W can be compared. First, the separate relay in the LGNd of the Xand Y-cell activity of the retina is described. Second, several properties of Xand Y-cells of the LGNd were observed to vary con-

Relay of receptive-field properties in dorsal lateral geniculate nucleus of the cat.

Cyto- and myeloarchitectonic investigation of the temporal operculum and the exposed superior temporal gyrus was combined with a connection study of the projection fibers of the pertinent areas in the rhesus monkey. A belt-like organization of the auditory region with a koniocortex core (corresponding to AI) surrounded by belt areas was revealed. This organization principally resembled that of the auditory region of the cat (Rose and Woolsey, 1949; Woolsey, 1961) and that of other sensory regions (Sanides, 1972; Sanides and Krishnamurti, 1967). The belt is composed of one prokoniocortex area (proA, corresponding to AII) in parinsular location and of a caudal (paAc), lateral (paAlt) and rostral (paAr) parakoniocortex area. The latter has a particular character. It was found to be the target of thalamic projections of the caudalmost portion of GMpc. In contrast to the other parakonio areas it does not receive associations of the koniocortex. The belt areas, including the prokoniocortex, are ipsilaterally and transcallosally interconnected as in the somatic sensory (Jones and Powell, 1969a, b; Pandya and Kuypers, 1969; Pandya and Vignolo, 1969) and visual regions (Myers, 1962; Kuypers et al., 1965; Karol and Pandya, 1971). The koniocortex core is formed by two areas, Kam and Kalt, corresponding to the architectonic organization hitherto only known in man. The medial area (Kam) has a large number of homotopical callosal projections except at its medial border (to proA). The lateral area receives less callosal fibers, particularly most of its lateral portion is devoid of terminations. Since the belt areas are rich in callosal projections the supratemporal plane shows a pattern of three stripes of callosal terminations with two intermittent stripes void of terminations. While the projections of the koniocortex into the belt areas terminate prevalently in layer IV, the parakoniocortex sends fibers only into layers I and II of the koniocortex. This corresponds to results in somatic sensory (Pandya and McKenna, unpublished observations) and visual regions (Kuypers et al., 1965; Sanides and Vitzthum, 1965b; Spatz, personal communication). In contrast to other sensory regions the auditory koniocortex receives its exceptionally dense, homotopic callosal connections in the whole outer stratum with emphasis on layer III, as opposed to layer IV in the somatic sensory region.

Architectonic parcellation of the temporal operculum in rhesus monkey and its projection pattern

Small lesions were placed in visual cortical areas 17, 18, 19, 20, 21, 7, and Clare-Bishop in the cat, and the sites of terminal degeneration seen with Fink-Heimer technique were plotted in thalamus, pretectum and superior colliculus. No degeneration was found in these sites after area 20 lesions; lesions in the other cortical areas gave different patterns of degeneration. Two major patterns were present, one from lesions in 17–18, one from lesions in 21, 7 and C-B, with degeneration from 19 forming a transition between the two groups.



Areas 17, 18 and 19 project to the dorsolateral geniculate nuclear complex (LGNd); areas 21, C-B and 7 do not. Area 17 projects to the laminar part, area 18 to both laminar and interlaminar (NIM) parts, and 19 only to NIM. The corticogeniculate projections from all three areas are topically organized anteroposteriorly, and at least that from area 17 is topically organized mediolaterally.



Areas 17 and 18 project topically to a columnar locus of the medial pulvinar (=lateral posterior) nucleus which ventrally includes that area known as the posterior nucleus. Area 19 has a double columnar projection to this part of the thalamus, one in the medial and one in the lateral pulvinar area. The medial column lies medial to that from 17–18, and appears to overlap the termination of the ascending projection from the superior colliculus. Cortical areas 21, C-B and 7 also have a double projection to the pulvinar.



These findings indicate that the corticorecipient neurons in both medial and lateral sectors of the pulvinar are organized so that dorsal neurons are activated by stimuli in upper visual fields (lower retina) and ventral neurons by stimuli in lower fields (upper retina).



Areas 17 and 18 project to the external layer of the ventrolateral geniculate (LGNv) nucleus, 19 to both external and internal layers, and 21, C-B and 7 to internal layer only.



The pretectal projection from 17–18 is limited to its caudal pole chiefly in the posterior pretectal nucleus (NPP), and also in the nucleus of the optic tract (NOT). Area 19 fibers terminate in NPP, NOT and also in the reticular part of the anterior pretectal nucleus (NPAr). Those from 21 and C-B end primarily in NPAr, and from area 7 in both reticular and compact parts of NPA. These corticopretectal systems all appear to be organized topically.



Areas 17, 18 and 19 have a double termination in the superior colliculus, a focal pattern in the superficial layers (chiefly lamina II), and a diffuse pattern in deeper layers (laminae IV, V, VI). The superficial pattern only provides the retinotopical matching with the optic afferents. All other cortical areas project diffusely to the deep layers. After lesions in 21 and C-B, the superficial foci are larger and centered in lamina III; after area 7 lesions this focal degeneration is centered in laminae III and IV and spread over much of the width of the colliculus. Degeneration to pontine nuclei and inferior olive was not examined.

Corticofugal projections from the visual cortices to the thalamus, pretectum and superior colliculus in the cat.

A comparative survey shows that lamination is a basic feature of the mammalian dorsal lateral geniculate nucleus. Relay laminae receive input from the retina, project to the cerebra

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Some Principles of Organization in the Dorsal Lateral Geniculate Nucleus; pp. 253–267

The organization in the cat of the projection of the visual field onto the medial part of the central half of dorsal lateral geniculate nucleus (LGNd), the medial interlaminar nucleus (MIN) and the posterior nucleus of the thalamus (PN) has been studied by systematically plotting the receptive fields of single units isolated in the nuclei by tungsten microelectrodes. Using a grid of verticals (azimuth) and horizontals (elevation), projection maps were prepared by locating the recording sites of the units in serial histological sections. We have plotted three separate but related topographical projections of the visual field, one in each nucleus. Particular attention was paid to the projection of the visual axis in the LGNd. With the possible exception of the upper periphery, the whole of the visual field is represented in the MIN, the topographical organization with respect to azimuths being the mirror-image of that in the LGNd. There were very few binocularly activated units in the MIN and no evidence was found of a laminar segregation of crossed and uncrossed optic tract terminals. The topographical projection onto the PN resembled that in the MIN except that the upper visual field was even more restricted and the organization of azimuth values was again reversed such that the central visual field projected inferomedially and the peripheral field dorsolaterally. In all three nuclei a naso-temporal overlap was found with receptive fields located across the midline in the ipsilateral hemifield for about 2° in the case of LGNd units and 6° or more in the case of the MIN and PN. Some observations are made on visually active units in the lateral posterior nucleus of the thalamus and the pulvinar, many responding binocularly.

Multiple projection of the visual field to the medial portion of the dorsal lateral geniculate nucleus and the adjacent nuclei of the thalamus of the cat

M. A. Vadas

Papers

Multiple projection of the visual field to the medial portion of the dorsal lateral geniculate nucleus and the adjacent nuclei of the thalamus of the cat