Adaptation-induced plasticity in the sensory cortex

For medical and fundamental reasons, we need to understand adult brain plasticity at several levels: structural, physiological, and behavioral. Historically, brain plasticity has been mostly investigated by weakening or removing sensory inputs. The visual system has been extensively used because diminishing visual inputs, i.e., visual deprivation-induced plasticity, permits more tractable findings. The present review is centered on the reverse strategy, by imposing a novel stimulus, i.e., adaptation-induced plasticity. Adaptation refers to the constant (milliseconds to hours) presentation of a nonoptimal stimulus (adapter) within the receptive field (RF, spatial area that modulates neuronal firing) of the neuron under observation. We specifically focus on how adaptation impacts the tuning of visual neurons with other associated properties. After adaptation, visual cortical neurons respond robustly to the adapter (before adaptation it typically evokes feeble responses) by developing alternate tuning curves that outlast the adaptation time. Here, with dendritic structure as foundation, we synthesize a push-pull mechanism of development and acquisition of novel tuning curves following adaptation. We then explain how these changes apply at the global level across different brain regions and species with a short description of underlying neurochemical changes. Finally, we discuss physiopathological consequences and conclude with some gaps and questions that need to be addressed to further comprehend such neuroplasticity.