Modified sensory processing in the barrel cortex of the adult mouse following chronic whisker stimulation

Chronic stimulation of a mystacial whisker follicle for 24h induces structural and functional changes in layer IV of the corresponding barrel, with an insertion of new inhibitory synapses on spines and a depression of neuronal responses to the stimulated whisker (Knott et al. 2002). Under urethane anaesthesia, we analyzed how sensory responses of single units are affected in layer IV and layers II&III of the stimulated barrel column as well as in adjacent columns. In the stimulated column, spatiotemporal characteristics of the activation evoked by the stimulated whisker are not altered; however, spontaneous activity and response magnitude to the stimulated whisker are decreased. The sensitivity of neurons for the deflection of this whisker is not altered but the dynamic range of the response is reduced as tested by varying amplitudeand repetition rate of the deflection. Responses to deflection of non-stimulated whiskers remain unaltered with the exception of in-row whisker responses that are depressed in the column corresponding to the stimulated whisker. In adjacent non-stimulated columns, neuronal activity remains unaltered except for a diminished response of units in layers II & III to deflection of the stimulated whisker. From these results we propose that an increased inhibition within the stimulated barrel reduced the magnitude of its excitatory output and accordingly the flow of excitation towards layers II&III and the subsequent spread into adjacent columns. In addition, the period of uncorrelated activity between pathways from the stimulated and non-stimulated whiskers weakens synaptic inputs from in-row whiskers in the stimulated barrel column. Page 1 of 47 Articles in PresS. J Neurophysiol (November 22, 2006). doi:10.1152/jn.00338.2006 Copyright © 2006 by the American Physiological Society.