Cerebral Cortex Advance Access originally published online on April 27, 2005
Cerebral Cortex 2006 16(2):162-177; doi:10.1093/cercor/bhi094
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Functional Response Properties of Neurons in the Dorsomedial Visual Area of New World Monkeys (Callithrix jacchus)
1 Department of Physiology, Monash University, Clayton, VIC 3800, Australia and 2 Monash University Centre for Brain and Behaviour, Monash University, Clayton, VIC 3800, Australia
Address correspondence to Dr Marcello Rosa, Department of Physiology, Monash University, Clayton VIC 3800, Australia. Email: Marcello.Rosa{at}med.monash.edu.au.
The dorsomedial visual area (DM), a subdivision of extrastriate cortex located near the dorsal midline, is characterized by heavy myelination and a relative emphasis on peripheral vision. To date, DM remains the least understood of the three primary targets of projections from the striate cortex (V1) in New World monkeys. Here, we characterize the responses of DM neurons in anaesthetized marmosets to drifting sine wave gratings. Most (82.4%) cells showed bidirectional sensitivity, with only 6.9% being strongly direction selective. The distribution of orientation sensitivity was bimodal, with a distinct population (corresponding to over half of the sample) formed by neurons with very narrow selectivity. When compared with a sample of V1 units representing a comparable range of eccentricities, DM cells revealed a preference for much lower spatial frequencies, and higher speeds. End inhibition was extremely rare, and the responses of many cells summated over distances as large as 30°. Our results suggest clear differences between DM and the two other main targets of V1 projections, the second (V2) and middle temporal (MT) areas, with cells in DM emphasizing aspects of visual information that are likely to be relevant for motor control.
Key Words: dorsal stream • parietooccipital • primate • receptive fields • visual cortex
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