RESUMO
This study used extracellular unit recordings in behaving animals to evaluate thalamocortical response transformations in the rat whisker-barrel system. Based on previous acute studies using controlled whisker stimulation, we hypothesized that in a cortical barrel adjacent (non-principal) whiskers exert a net inhibitory effect. In contrast, in thalamic barreloid neurons, the effects of neighboring whiskers should be net facilitatory. We evaluated these hypotheses by recording unit activity at 21 sites in 17 animals trained to explore a wire mesh screen with their whiskers. In the middle of the recording session, selected vibrissae were clipped close to the skin surface. The absence of whiskers surrounding the principal whisker was associated with a mean 20% increase in cortical activity and, conversely, a 37% decrease in the thalamic activity. Removal of the principal whisker resulted in a 50% decrease in cortical unit firing. Findings are consistent with the idea that, in the behaving animal, each barrel uses multi-whisker thalamic inputs and local inhibitory circuitry to sharpen the receptive field properties of its constituent neurons. Cortical disinhibition as a consequence of selective whisker removal is likely to be an important factor underlying altered receptive field properties in sensory-deprived animals.
