Cholinergic gating of improvement of tactile acuity induced by peripheral tactile stimulation.

As shown in many animal experiments, cholinergic mechanisms participate in N-methyl-d-aspartate (NMDA) receptor-dependent neuroplasticity. Acetylcholine is thought to play a similar role in humans, where it modulates attention and learning. Here, we tested the cholinergic action on non-associative learning in the tactile domain. We studied the influence of scopolamine, a cholinergic antagonist, on changes in tactile acuity as induced by peripheral tactile coactivation. Coactivation is a non-associative tactile learning protocol and has been shown to improve tactile two-point discrimination of the stimulated finger in addition to selective changes of cortical processing. Under placebo conditions, tactile two-point discrimination was improved on the stimulated index finger. After application of scopolamine, tactile improvement was completely eliminated and tactile acuity was even impaired. No drug effects were found on the left index finger indicating that the drug had no effect on performance per se. The current results provide further evidence that in humans cholinergic mechanisms are also involved in non-associative learning induced by passive stimulation protocols.