Visual recognition memory: A view from V1, by Marc Bear
Daily exposure of a mouse to a phase reversing, full-field visual grating stimulus reliably triggers a dramatic form of synaptic plasticity in primary visual cortex (V1) that alters the behavioral response of the mouse to this stimulus. This plasticity reveals itself in several different ways depending on how it is assayed. As the initially novel stimulus becomes familiar: (1) visual evoked potentials (VEPs) recorded in layer 4 grow via mechanisms shared with long-term synaptic potentiation (LTP), (2) activity in a network of parvalbumin-containing inhibitory interneurons decreases, changing the state of oscillations in the local field potential, and (3) evoked cellular responses revealed by calcium imaging of layer 4 principal neurons are depressed. Understanding how these puzzle pieces fit together promises to reveal the neurobiological substrate of a simple but crucial form of visual recognition memory, manifested behaviorally as long-term habituation to stimuli that portend neither reward nor punishment. In humans, habituation deficits are a common feature of neuropsychiatric disorders. Studying this phenomenon in mice carrying gene mutations linked to psychiatric disorders may reveal pathophysiology that points the way to novel therapeutic approaches.
Marc Bear is Professor at Picower Institute for Learning and Memory Department of Brain and Cognitive Sciences Massachusetts Institute of Technology, MA, USA