The facilitatory influence of anterior cingulate cortex on ON-OFF responseof tactile neuron in thalamic ventrobasal nucleus

The structures of limbic system have been found to modulate the auditory, v isual and pain efferent signals in the related nuclei of thalamus. One of t hose structures is anterior cingulate cortex (ACC) that influences nocuous response of the pain-sensitive neurons in the ventropostero-lateral nucleus of thalamus. Thus, we inferred that ACC would also modulate tactile inform ation at the thalamic level. To test this assumption, single units were rec orded extracellularly from thalamic ventrobasal nucleus (VB), Tactile ON-OF F response and the relationship between different patterns of the responses and the parameters of tactile stimulation were examined. Furthermore, the influence of ACC on the tactile ON-OFF response was studied. ACC stimulatio n was found to produce a facilitatory effect on the OFF-response of ON-OFF neurons. It lowered the threshold of the off-response of that neuron, and t herefore changed the response pattern or enhanced the firing rate of the OF F-response of the neuron, The study on receptive fields of ON-OFF neurons s howed that the excitation of the ACC could change an ON-response on the ver ge of a receptive field into an ON-OFF response. The above results suggest that the ACC modulation sharpens the response of a VB neuron to a moving st imulus within its receptive field, indicating that the limbic system can mo dulate tactile ascending sensory information.