ABSTRACT

The somatosensory system is an adaptive system: perturbations in signals from peripheral receptors can lead to adaptive changes in the response characteristics of central somatosensory neurons. Additional experimental evidence for a role of tonic inhibition in restricting receptive field size has been obtained from peripheral inactivation studies in the rat dorsal column nuclei (DCN). Lidocaine injections resulted in decreased activity in DCN neurons that could not be antidromically activated from the thalamus Although experimental data suggest that somatosensory receptive fields are restricted by local, tonic inhibition, there is little direct evidence for an inhibitory influence on receptive field structure in the DCN. In somatosensory cortex, blockade of GABAa receptors results in receptive field enlargement in approximately 85% of rapidly adapting neurons and 35% of slowing adapting neurons. A second mechanism that could be involved in restricting receptive field size is shunting of dendritic potentials by open channels at active synapses.