Reciprocal lateral inhibition of on- and off-center neurones in the lateral geniculate body of the cat

In the lateral geniculate body (LGB), intra- and quasi-intracellular records were done. With small light stimuli shone into different parts of the receptive field, EPSPs and IPSPs could be elicited. Stimulation of the exact center of an on-center cell produced a pure excitatory response, that of an off-center neurone pure inhibition. This response lasted throughout the stimulus. At light off, inhibition was elicited in on-center cells and excitation in off-center cells. A stimulus in the field periphery produced a mixed response with a small and short excitation followed by large inhibition in on-center cells, and a short inhibition followed by postsynaptic depolarization in off-center cells. At light off, on-center cells showed depolarization after a short polarizing phase, and off-center cells a broad polarization which interrupted the initial small excitation. The latencies of both the excitatory and inhibitory center responses at light on and off characteristic for the two types of neurones, were 20–30 msec shorter than the reversed responses elicited by stimulation of the receptive field surround. The findings are compatible with a model in which each geniculate on-center cell gets its major excitatory input from one optic tract on-center fibre and inhibitory input from several off-center fibres with nearby receptive fields. An off-center LGB-cell receives its main excitation essentially from one offcenter fibre and inhibition from several on-center cells. The responses to moving stimuli also agreed with this model. The presence of recurrent inhibition within the LGB could be confirmed by electrical stimulation. But it could not be decided whether the reciprocal inhibition of on- and off-center cells was due to forward or backward inhibition. The spontaneous activity of on- and off-center cells which were simultaneously recorded with one electrode, showed a mutual inhibition 6–8 msec after one cell had fired. Anatomical data relevant to the model are discussed and some functional implications are suggested.