The long-term objective of this project is to contribute to our understanding of the mechanisms of visual representation by cortical networks. Neuronal gain, measured as the continuous slope of the relationship between stimulus input and cellular output, is a measure of neuronal sensitivity to the stimulus and a defining element of the contribution of single neurons to network operations. Previous work has identified a role for network-driven synaptic activity in modulating the input-output gain of cortical neurons. In addition, synchrony between local network inputs may determine the magnitude of the impact of network activity on neuronal gain. Previous studies have also suggested that both neuronal gain and population synchrony play roles in mediating visual perception. However, even at the earliest stages of cortical visual processing, the relationship between individual neurons and the network in which they are embedded is poorly understood. [unreadable] [unreadable] The main goals of the work proposed here are therefore 1) to determine the relationship between cellular mechanisms of contrast gain control and network synchrony and 2) to examine the interaction between population synchrony and discrimination between visual stimuli. To that end, the first Aim will focus on many simultaneous recordings of cortical neurons during presentation of stimuli with varying properties. In a subset of experiments, these recordings will be paired with intracellular recordings to test the impact of network activity on postsynaptic cells. The second Aim will use a behavioral task in which awake, behaving animals discriminate between visual stimuli of varying contrast. In one series of experiments, this task will be combined with population recordings from primary visual cortex. The results of these experiments are expected to provide novel insights into the relationship between the temporal dynamics of population activity and cellular mechanisms of gain control. In addition, they will generate a better understanding of the role of synchronous cortical network activity in visual perception. [unreadable] The overall objective of this research is to characterize the patterns of activity at the early stages of visual processing in the brain in response to differing stimulus contexts and relate those patterns of activity to the visual stimulus sensitivity of individual neurons. Our continuing goal is to advance understanding of global functions of the central nervous system in perceptual processing. [unreadable] [unreadable] [unreadable] [unreadable]