Modified Sensory Processing in the Barrel Cortex of the Adult Mouse After Chronic Whisker Stimulation

1 Département de Biologie Cellulaire et de Morphologie, Université de Lausanne, Lausanne, Switzerland; and 2 Department of Neuroscience, Queen Mary Westfield College, University of London, London, United Kingdom Submitted 31 March 2006; accepted in final form 16 November 2006 Chronic stimulation of a mystacial whisker follicle for 24 h 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. Under urethane anesthesia, 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, although 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 the amplitude and repetition rate of the deflection. Responses to deflection of nonstimulated whiskers remain unaltered with the exception of in-row whisker responses that are depressed in the column corresponding to the stimulated whisker. In adjacent nonstimulated columns, neuronal activity remains unaltered except for a diminished response of units in layer 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 toward layers II & III and the subsequent spread into adjacent columns. In addition, the period of uncorrelated activity between pathways from the stimulated and nonstimulated whiskers weakens synaptic inputs from in-row whiskers in the stimulated barrel column. Address for reprint requests and other correspondence: E. Welker, DBCM, Rue du Bugnon 9, 1005 Lausanne, Switzerland (E-mail: egbert.welker{at}unil.ch )