Visuotopic organisation and neuronal response selectivity for direction of motion in visual areas of the caudal temporal lobe of the marmoset monkey (Callithrix jacchus): Middle temporal area, middle temporal crescent, and surrounding cortex

Abstract

On the basis of extracellular recordings in marmoset monkeys, we report on the organisation of the middle temporal area (MT) and the surrounding middle temporal crescent (MTc). Area MT is approximately 5-mm long and 2-mm wide, whereas the MTc forms a crescent-shaped band of cortex 1-mm wide. Neurones in area MT form a first-order representation of the contralateral hemifield, whereas those in the MTc form a second-order representation with a field discontinuity near the horizontal meridian. The representation of the vertical meridian forms the border between area MT and the MTc. In both areas, the fovea is represented ventrocaudally, and the visual field periphery is represented dorsorostrally. Analysis of single units revealed that 86% of cells in area MT show a strong selectivity for the direction of motion of visual stimuli. The proportion of direction-selective cells in the MTc (53%), whereas lower than that in area MT, is much higher than that observed in most other visual areas. Neurones in the cortex immediately rostral to area MT and the MTc are direction selective, with receptive fields predominantly located in the visual field periphery. In contrast, only a minority of the cells in the cortex ventral to the MTc are direction selective, and their receptive fields emphasise central vision. The results suggest that the MTc is functionally closely related to area MT, and distinct from the areas forming the dorsolateral complex. The MTc may have a role in combining information about motion in the visual field, processed by area MT, with information about stimulus shape, processed by the dorsolateral complex.

Visual Responses of Neurons in the Middle Temporal Area of New World Monkeys after Lesions of Striate Cortex

“…In a previous study (Rosa and Elston, 1998), we demonstrated that area MT in normal marmosets has a simple visuotopic organization that is remarkably constant among individuals. As demonstrated in Figure 3, at any anteroposterior level, a dorsoventral movement of the electrode results in a regular change in the polar angle of receptive field centers, which gradually move from the lower quadrant toward the upper quadrant.…”

“…In the right diagram, receptive fields from the same rostrocaudal level are connected in sequences that correspond to sites progressing from dorsal to caudal in the cortex (e.g., 1-8, 9 -15, etc.). For clarity, not every recording site or receptive field obtained in this case is illustrated (Rosa and Elston, 1998). spared region was confirmed by both the presence of responsive V2 cells covering that part of the visual field and histological reconstruction].…”

“…Six marmosets (Callithri x jacchus) received a unilateral lesion of V1, whereas six nontreated animals, used for a previous study (Rosa and Elston, 1998), served as controls. All animals were sexually mature and past the period of rapid changes in cellular, synaptic, and columnar organization of visual cortex that characterizes the first year of postnatal life in marmosets (Missler et al, 1993;Spatz et al, 1994).…”

“…The protocol and techniques were the same as those used in our study of MT in normal marmosets (Rosa and Elston, 1998). In each animal, several electrode penetrations were directed toward the approximate location of MT, using the caudal tip of the lateral sulcus as a landmark for the location of the peripheral representation in this area.…”

“…Part of the problem is that the visuotopic map in macaque MT is complex, including re-representations and local discontinuities, even in normal monkeys (Maunsell and Van Essen, 1987). For this reason, the simpler and more stereotyped map in MT of New World monkeys (Allman and Kaas, 1971;Rosa and Elston, 1998) provides a better model in which to study this issue. Here we report on the visuotopic organization and response properties of MT cells several weeks after lesions of V1 in the marmoset, a species of New World monkey with diurnal habits.…”