Synaptic computation in the visual system. (360G-Wellcome-102905_Z_13_Z)

How does a circuit of neurons process sensory information? And how are transformations of neural signals altered by changes in synaptic strength? These questions will be investigated in the context of the visual system. A distinguishing feature of our approach will be the imaging of activity across populations of synapses - the fundamental elements of signal transfer within all brain circuits [1-5]. Our guiding hypothesis is that the plasticity of neurotransmission plays a major part in controlling the input-output relation of sensory circuits, regulating the tuning and sensitivity of neurons to allow adaptation or sensitization to particular features of the input [6-9]. We will focus on computations carried out in the visual system because these are defined in sufficient detail to allow a quantitative analysis of the underlying circuitry and are also likely to have parallels in other brain regions [10-15]. How does a population of connected neurons detect the different temporal frequencies in a fluctuating input? Or the direction of motion of a moving object? Or the orientation of that object? In parallel, we will ask how these computations are modified in response to i) changes in the visual input that lead to adaptive changes in processing, and ii) neuromodulators that alter circuit function on longer time-scales.