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.