Abstract
We studied the multiunit responses to moving and static stimuli from 585 cell clusters in area MT using multi-electrode arrays. Our aim was to explore if MT columns exhibit any larger-scale tangential organization or clustering based on their response properties. Neurons showing both motion and orientation selectivity were classified into four categories: 1- Type I (orientation selectivity orthogonal to the axis of motion); 2- Type II (orientation selectivity coaxial to the axis of motion); 3- Type DS (significant response to moving stimuli, but non-significant response to static stimuli); and 4- Type OS (significant orientation selectivity, but non-significant direction selectivity). Type I (34%), Type II (24%) and Type DS (32%) clusters were the most predominant and may be associated with different stages of motion processing in MT. On the other hand, the rarer Type OS (9%) may be integrating motion and form processing. Type I and unidirectional sites were the only classes to exhibit significant clustering. Type OS sites showed a trend for clustering, which did not reach statistical significance. We also found a trend for unidirectional sites to have bidirectional sites as neighbors. In conclusion, neuronal clustering associated with these four categories may be related to distinct MT functional circuits.
Highlights
Intrinsic circuits and feedforward projections give rise to receptive field properties that are increasingly more complex as one advances along the visual hierarchy (Hubel & Wiesel 1968, Gross et al 1972, Gattass et al 2005)
In order to investigate the hypothesis that these different cell types are part of distinct middle temporal area (MT) modules participating in distinct stages of motion processing, we investigated the distribution of these four cell types across the tangential dimension of area MT in the capuchin monkey
We worked with the assumption that the few nearby neurons recorded at a single electrode tip had very similar response properties, prompting them to be classified as a homogeneous ‘cell type’, or a site with a homogeneous selectivity to stimulus motion
Summary
Intrinsic circuits and feedforward projections give rise to receptive field properties that are increasingly more complex as one advances along the visual hierarchy (Hubel & Wiesel 1968, Gross et al 1972, Gattass et al 2005). The extrastriate cortex in primates contains multiple visual areas (Van Essen & Zeki 1978, Gattass & Gross 1981, Gross et al 1981, Gattass et al 1988, Kaas 1989, Neuenschwander et al 1994) The study of their receptive field properties has shown results that are compatible with both parallel (Martin & Whitteridge 1984) and serial (Hubel & Wiesel 1962) neuronal processing. While the processing of the visual attributes is distributed across multiple areas (Zeki 1969, Van Essen & Zeki 1978) and streams (Ungerleider & Mishkin 1982), receptive field size becomes gradually larger at each successive hierarchical stage (Gattass et al 1985).
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