Journal of Neuroscience, Vol 14, 2080-2088, Copyright © 1994 by Society for Neuroscience
Responses in macaque visual area V4 following inactivation of the parvocellular and magnocellular LGN pathways
VP Ferrera, TA Nealey and JH Maunsell
Department of Physiology, University of Rochester, New York 14642-8642.
A substantial body of evidence has suggested that signals transmitted
through the magnocellular and parvocellular subdivisions of the LGN remain
largely segregated in visual cortex. This hypothesis can be tested directly
by selectively blocking transmission through either the magnocellular or
parvocellular layers with small injections of lidocaine or GABA while
recording cortical responses to a visual stimulus. In a previous study, we
found that responses in the middle temporal visual area (MT) were almost
always greatly reduced by blocks of magnocellular LGN, but that few MT
neurons were affected by parvocellular blocks. In the present study, we
have examined magnocellular and parvocellular contributions to area V4,
which lies at the same level of processing in the cortical hierarchy as
does MT and is thought to be a major recipient of parvocellular input. We
found that inactivation of parvocellular layers usually resulted in a
moderate reduction of visual responses (median reduction, 36%). However,
comparable reductions in V4 responses were also seen following
magnocellular blocks (median reduction, 47%). Directionally selective
responses in V4 were not found to depend specifically on either
subdivision. We conclude that area V4, unlike MT, receives strong input
from both subdivisions of the LGN. These results suggest that the
relationship between the subcortical magnocellular and parvocellular
pathways and the parietal and temporal streams of processing in cortex is
not one-to-one.
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