The long-term goal of the proposed research is to provide insight into how naturalistic stimuli are represented by ensembles of cortical neurons in the early visual system. We focus on a form of rapid adaptation by neurons in the primary visual cortex (V1) whereby neurons dynamically modify their receptive fields (RFs) in response to naturalistic stimuli. This proposal tests the hypothesis that STOP (spike-timing dependent plasticity) underlies this adaptation. We plan to test this hypothesis using a combination of novel stimuli, pharmacological intervention and multi-tetrode recordings in area V1 of the anesthetized and paralyzed monkey. In the first specific aim (S.A. 1), we test the prediction, made by our hypothesis, that the adaptation of RFs is driven only by stimuli which induce correlations between neurons. To do this, we will modify a natural vision stimulus set to reduce certain correlations. We will record neural responses to these stimuli in V1. Then, using a few different analytical techniques (Spike-Triggered Covariance and Maximally Informative Dimension analysis), we will examine the extent to which these stimuli evoke RF adaptation. In the second specific aim, we test the prediction that coordinated multi-neuron spike-timing is necessary (S.A. 2A) and sufficient (S.A. 2B) for the adaptation of V1 RFs. In S.A. 2A, we will use cannabinoid receptor agonists (known to disrupt synchronous neural activity in the cortex) to decrease interactions between neurons. Using the same stimulus set and analytical techniques as S.A. 1 we test the prediction that, under STOP, decreasing interactions between neurons will decrease the rate of adaptation of RFs to natural stimuli. In S.A. 2B, we alter a stimulus set (which is otherwise not adapting) so as to induce correlations between pairs of neurons from which we are recording. Our hypothesis predicts that these correlations should lead to adaptation to an otherwise non-adaptive stimulus set. This proposal provides data on an overlooked component to visual processing (multi-neuronal processing of naturalistic stimuli) and seeks to elucidate a mechanism for a novel, but significant component, to natural scene processing (adaptation to naturalistic stimuli). In addition, the proposed cannabinoid experiments potentially offer v;-sual neurophysiologists a new tool for disrupting multi-neuron interactions and provide data on the neural effect of a frequently abused drug, marijuana. Taken as a whole, this proposal contributes to our understanding of early visual cortical processing, a necessity for therapeutic interventions aimed at restoring sight to those with irreparable ocular or optic nerve damage.