Tactile coactivation-induced changes in spatial discrimination performance

We studied coactivation-based cortical plasticity at a psychophysical level in humans. For induction of plasticity, we used a protocol of simultaneous pairing of tactile stimulation to follow as closely as possible the idea o f Hebbian learning. We reported previously that a few hours of tactile coac tivation resulted in selective and reversible reorganization of receptive f ields and cortical maps of the hindpaw representation of the somatosensory cortex of adult rats (Godde et al., 1996). In the present study, simultaneo us spatial two-point discrimination was tested on the tip of the right inde x finger in human subjects as a marker of plastic changes. After 2 hr of co activation we found a significant improvement in discrimination performance that was reversible within 8 hr. Reduction of the duration of the coactiva tion protocol revealed that 30 min was not sufficient to drive plastic chan ges. Repeated application of coactivation over 3 consecutive days resulted in a delayed recovery indicating stabilization of the improvement over time . Perceptual changes were highly selective because no transfer of improved performance to fingers that were not stimulated was found. The results demo nstrate the potential role of sensory input statistics (i.e., their probabi lity of occurrence and spatiotemporal relationships) in the induction of co rtical plasticity without involving cognitive factors such as attention or reinforcement.