Responses from outside classical receptive fields of dorsal lateral geniculate cells in rabbits

The effects of stimuli at locations remote from classic receptive fields (CRF) of lateral geniculate cells were examined in rabbits. In anesthetized rabbits, small targets positioned well outside the CRF either facilitated or decreased responses evoked by a stimulus positioned within the most active area of the CRF in 51% of the cells tested, in spite of the fact that when presented in isolation the remote target failed to modify the spontaneous activity of the recorded cell. Late components of the discharge pattern evoked by the central stimulus were mostly influenced by the peripheral target. Focal or ectopic areas surrounding the CRF are thus identified. These areas were not a direct extension of the CRF, since the normal evoked response was unchanged when the remote stimulus moved closer to the CRF. Cells whose CRF were centrally located reacted with an augmented response in the presence of the additional stimulus, whereas units whose CRF was more eccentric exhibited a weaker response when the peripheral target was introduced in the visual field. We also investigated whether superior colliculus afferents to the lateral geniculate nucleus could be associated with these ectopic areas (EA). Depressing superior colliculus activity produced two types of results: (a) often the late component of the response pattern was modified; and (b) the influence of the remote stimulus disappeared with collicular blockade in 80% of tested neurons. These results provide evidence that the CRF of geniculate cells may be surrounded by satellite zones, which modify the responses to the central target when invaded by circumscribed stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)