Next
Previous
Up
Mechanisms and neuropharmacology of visual attention in primate V1
Alex Thiele
University of Newcastle upon Tyne
Attention can selectively enhance neuronal responses and exclude
external noise, but the neuronal computations underlying these effects
and the neuropharmacology involved remain unknown. We hypothesized that
the effects of attention are mediated by increasing the synaptic
efficacy of feed-forward connections while simultaneously reducing the
synaptic efficacy of lateral connections, possibly through contributions
from cholinergic mechanisms. We tested this proposal by recording
neuronal activity and length tuning in macaque V1 when attention was
directed towards or away from stimuli presented in the neuron's
classical receptive field. For cells with central/parafoveal receptive
fields, attention indeed reduced spatial integration demonstrated by a
reduction in preferred length and in the size of the spatial summation
area. Conversely, in cells representing more peripheral locations,
attention increased spatial integration by increasing the cell's
summation area. This previously unknown dichotomy between central and
peripheral vision could support accurate analysis of attended foveal
objects and target selection for impending eye-movements to peripheral
objects. We further tested whether cholinergic mechanisms are an
integral part of attentional modulation in V1. Cholinergic antagonists
reduced the attentional modulation in the attend RF condition by means
of muscarinic receptor mechanisms. Nicotinic receptor mechanisms are
necessary for adequate sensory transmission, but do not seem to
contribute to attentional modulation. These data demonstrate that the
cholinergic system plays an important role in mediating effects of
attention in V1 of the macaque monkey. Supported by: Wellcome Trust,
BBSRC, MRC.