The lateral posterior-pulvinar complex modulation of stimulus-dependent oscillations in the cat visual cortex.

It has been suggested that binding coherent targets depends on the capacity of excited cortical cells to fire in synchrony at approximately 40 Hz. However, the origin of stimulus-related cortical oscillations is still not clear. We hypothesized that 40 Hz oscillations might propagate to the visual cortex from the lateral posterior-pulvinar complex (LP-P) whose cells send fibers to the visual cortex and have a tendency to exhibit oscillations. To test our hypothesis, we recorded single unit activity in areas 17 and 18 of anaesthetized cats. The activity of neurons which showed oscillations evoked by optimal visual stimuli was analysed before, during and after a reversible inactivation of the LP-P with GABA. Such inactivation was found to markedly modify the strength of oscillatory activity of cortical neurons whose visual responses were affected by LP-P blockade. In contrast, the oscillation frequencies of cortical neurons were not modified by such inactivation. However, in some cells (three of nine), oscillatory activity was found to be completely abolished by injection of GABA into the LP-P. Collectively, these findings demonstrate that inputs from the LP-P play a key role in modulating the oscillatory activity of visual cortex neurons. Assuming that cortical neurons utilize oscillatory activity to encode perceptual aspects of the visual stimulus, our findings underscore the contribution of the LP-P in this process.