Quantitative aspects of the state-dependent co-variation of cat lateral geniculate and perigeniculate visual activity.

The quantitative relationship between EEG-related changes in the visual activity of perigeniculate (PGN) and lateral geniculate (LGN) neurons with overlapping receptive fields was analyzed in the anesthetized and paralyzed cat. While transient response peaks were independent of the EEG state, we found opposite changes in spontaneous activity and tonic visual responses, with PGN cells increasing and LGN cells decreasing their spontaneous/tonic activity with increasing EEG delta activity in most cases. The tonic firing rates of PGN and LGN cell pairs were clearly correlated with a slope of about -0.5. Thus, LGN firing was low when PGN activity was high and vice versa. With a change from low to high EEG delta activity the difference between the tonic responses of PGN and LGN cells increased on average by 50 spikes/s, both for the whole population and at the single cell level, indicating that state-dependent changes in retino-geniculate transmission are regulated by a distinct ratio of PGN-LGN activity.