Abstract
Author SummaryThe adult brain is capable of learning new tasks and being shaped by new experiences. Evidence for experience-dependent plasticity of the adult cerebral cortex is seen in the functional rearrangement of cortical maps of sensory input and in the formation of new connections following alteration of sensory experience. The barrel cortex of the rodent receives sensory input from the whiskers and is an ideal model for examining the influence of experience on cortical function and circuitry. In the current study, we asked how experience alters cortical circuitry by examining excitatory and inhibitory axons within the adult whisker barrel cortex before and after plucking of a whisker and hence removal of its sensory input. By combining delivery of genes encoding fluorescent proteins, under the control of cell-type specific promoters, with two-photon imaging, we were able to directly examine subpopulations of axons and to determine when and to what extent experience altered specific connections in the adult living brain. Following whisker plucking we observed both the retraction of existing connections and an exuberant amount of growth of new axons. Axonal restructuring occurred rapidly and continued to undergo changes over the following weeks, with reciprocal sprouting of axons of excitatory neurons located in non-deprived cortex and of inhibitory neurons located in deprived cortex. The changes in the inhibitory circuits preceded those seen for excitatory connections.
Highlights
The adult cortex adapts to alterations in sensory experience
Detailed knowledge of the structural rewiring of cortical circuitry following sensory loss provides insight into the operation of cortical circuits: which circuits are involved in specific functions, how they can be altered by sensory deprivation and learning, and how they reorganize following nervous system damage
The presence of inhibitory responses establishes the beginning of the critical period [24,25], while the end of the critical period is dependent on inhibitory interneuron maturation [26]
Summary
The adult cortex adapts to alterations in sensory experience This experience-dependent plasticity is evidenced by the functional reorganization of the primary sensory maps of the brain [1,2,3,4,5,6,7,8,9,10,11,12], synaptogenesis in the adult brain [13,14,15,16], and reorganization of dendrites [17,18]. Pyramidal neurons in the superficial cortical layers form long-range horizontally projecting axons, which undergo a process of sprouting and synaptogenesis that parallels the functional reorganization of the cortex following altered sensory experience [6,13,14,19,20]. A reduction in inhibition could unmask a network of normally subthreshold horizontal connections, driving their influence above threshold as a consequence of sensory deprivation
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