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 cap acity of excited cortical cells to fire in synchrony at similar to 40 Hz. However, the origin of stimulus-related cortical oscillations is s till not clear. We hypothesized that 40 Hz oscillations might propagat e to the visual cortex from the lateral posterior-pulvinar complex (LP -P) whose cells send fibers to the visual cortex and have a tendency t o exhibit oscillations. To test our hypothesis, we recorded single uni t activity in areas 17 and 18 of anaesthetized cats. The activity of n eurons 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 streng th of oscillatory activity of cortical neurons whose visual responses were affected by LP-P blockade. In contrast, the oscillation frequenci es 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. Assum ing that cortical neurons utilize oscillatory activity to encode perce ptual aspects of the visual stimulus, our findings underscore the cont ribution of the LP-P in this process. Copyright (C) 1996 Elsevier Scie nce Ltd.