PRECISELY CORRELATED FIRING IN CELLS OF THE LATERAL GENICULATE-NUCLEUS

SIMPLE cells within layer IV of the cat primary visual cortex are sele ctive for lines of a specific orientation, It has been proposed that t heir receptive-field properties are established by the pattern of conn ections that they receive from the lateral geniculate nucleus (LGN) of the thalamus(1-5). Thalamic inputs, however, represent only a small p roportion of the synapses made onto simple cells(6-8), and others have argued that corticocortical connections are likely to be important in shaping simple-cell response properties(9,11). Here we describe a mec hanism that might be involved in selectively strengthening the effect of thalamic inputs, We show that neighbouring geniculate neurons with overlapping receptive fields of the same type (on-centre or off-centre ) often fire spikes that are synchronized to within 1 millisecond, Mor eover, these neurons often project to a common cortical target neuron where synchronous spikes are more effective in evoking a postsynaptic response. We propose that precisely correlated firing within a group o f geniculate neurons could serve to reinforce the thalamic input to co rtical simple cells.