The middle temporal visual area in the macaque: Myeloarchitecture, connections, functional properties and topographic organization

Abstract

The location, topographic organization, and function of the middle temporal visual area (MT) in the macaque monkey was studied using anatomical and physiological techniques. MT is a small, elliptically shaped area on the posterior bank of the superior temporal sulcus which can be identified by its direct inputs from striate cortex and by its distinctive pattern of heavy myelination. Its average surface area is 33 mm2, which is less than 3% of the size of striate cortex. It contains a complete, topographically organized representation of the contralateral visual hemifield. There are substantial irregularities in the detailed pattern of topographic organization, however, and the representation is significantly more complex than that found for MT in other primates. Much of MT is devoted to the representation of central visual fields, with the emphasis on central vision being similar to that found in striate cortex. Electrophysiological recordings have confirmed previous reports of a high incidence of direction selective cells in MT. The transition in functional properties, from cells lacking direction selectivity outside MT to direction selective cells within, occurs over a distance of 0.1-0.2 mm or less along the lateral border of MT. Such a transition does not occur along the medial border, however, as the cortex medial to MT contains many cells with strong direction selectivity. Nevertheless, this region differs from MT in its myeloarchitecture, its lack of inputs from striate cortex, and the large size of its receptive fields. These results demonstrate the existence of three distinct visual areas on the posterior bank of the superior temporal sulcus which can be distinguished on the basis of both physiological and anatomical criteria.

Cortical and cerebellar activation induced by reflexive and voluntary saccades

“…Neurons in the MT area of monkeys are speciWcally responsive to visual motion, selectively for both direction and speed, and have receptive Weld sizes of up to 25° in visual angle (Zeki 1974;Baker et al 1981;Van Essen et al 1981;Maunsell and Van Essen 1983;Felleman and Kaas 1984;Churchland and Lisberger 2001). Functional imaging studies in humans have shown that the human homologue, area MT/V5, is also highly responsive to visual motion stimuli (Zeki et al 1991;Watson et al 1993;Tootell et al 1995).…”

The pattern of interhemispheric connections and its relationship to extrastriate visual areas in the macaque monkey

“…Six of these areas contain topographically organized representations of all or part of the contralateral visual hemifield; these are V2, V3, V3A, V4, the middle temporal area (MT), and the ventral posterior area (VP) (Cragg, 1969;Zeki, 1969Zeki, , 1971Van Essen and Zeki, 1978;Ungerleider and Mishkin, 1979;Van Essen et al, 1981). Visual areas lacking obvious topographic organization include inferotemporal cortex (IT) (Gross et al, 1972;Desimong and Gross, 1979) and posterior parietal cortex (area 7) (Lynch et al, 1977;Robinson et al, 1978).…”

“…Precise determination of their borders in any given hemisphere generally has proven very difficult, however. MT is the only extrastriate area whose borders have as yet been determined accurately and completely on the basis of architectonic criteria (Van Essen et al, 1981), and its location is indicated in Figure 3B by a solid outline. For the other areas, the approximate boundaries are indicated by dashed lines in the figure and are discussed in greater detail below.…”

“…Two topographically organized visual areas, V4 and MT, have been identified within region D and the adjacent callosal recipient cortex. MT lies almost entirely within zone 7, with only a small portion extending into region D (Van Essen et al, 1981). MT contains a complete representation of the contralateral visual hemifield but with substantial disorderliness in the representation (Zeki, 1978d;Montero, 1980;Van Essen et al, 1981).…”

“…This asymmetry, in turn, reflects important differences in the organization of visual areas in dorsal and ventral parts of the hemisphere which have been revealed by the tracing of intrahemispheric cortical connections. The second objective was to determine whether there is any consistent relationship between the local irregularities known to exist in the pattern of callosal inputs and the disorderliness in topographic organization that has been demonstrated in several extrastriate areas (Zeki, 1971(Zeki, , 1978dVan Essen and Zeki, 1978;Van Essen et al, 1981). The third objective was to determine the distribution of the cells of origin of the callosal pathway.…”