Laboratory of Mriganka Sur
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Dynamics and Plasticity in Adult Cortex

Synaptic integration in the visual cortex
cortical maps The Sur lab studies cortical networks, which take simple inputs and make complex outputs. In the visual cortex, these outputs are manifested as selective responses to specific visual features. These features are mapped systematically across the cortex - we have shown that feature maps in V1 share important relationships with each other to account for continuity of representation and coverage of the visual field. The maps in turn influence the way response selectivity is generated: by recording intracellularly from neurons that lie in different locations within the map of orientation preference, we have demonstrated that orientation selectivity requires a balance of excitation and inhibition. The tuning of excitatory and inhibitory conductances varies from pinwheel centers to orientation domains, but the exquisite balance between the two ensures that spike outputs are sharply tuned for orientation at all locations. We are now using molecular genetic and calcium imaging tools, combined with two-photon and intrinsic signal imaging, to examine the mechanisms by which visual cortex neurons and networks process and represent information.

Beata Jarosiewicz Caroline Runyan James Schummers Hongbo Yu
Bottom up and top down dynamics in the visual cortex
cortical maps Cortical processing of sensory information integrates not only bottom up inputs from the sensory surface but also top down information about internal state, including attention, expectation and memory. We propose that top down 'learning' signals modulate responses in early cortical areas in accord with predictions about bottom up inputs. Thus, we have shown that orientation-specific responses of V1 neurons in alert monkeys can be modulated according to Bayesian estimates of stimulus location. Using multiple electrode recording and optical imaging in alert monkeys combined with computational models, we are now examining other predictive top down influences, including those due to location based attention and feature based expectation.
Scott Gorlin Jitendra Sharma Hiroki Sugihara
Influence of electrical activity on cortical networks in vivo
neuronal networks Specific rules underlie the generation and maintenance of cortical networks. These include principles of balanced excitation and inhibition, homeostasis or regulation of total drive, and synaptic plasticity based on patterns of input and output activity. We are examining several of these rules in isolation or in combination. The experiments utilize novel materials and technologies to grow networks in vitro, in which we can control the size, neuronal density, linkage, or the efficacy of synaptic connections.
Nathan Wilson
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