Learning of tactile frequency discrimination in humans.

Learning is based on the remodeling of neural connections in the brain. The purpose of the present study was to examine the extent to which training-induced improvements in tactile frequency discrimination in humans are correlated with an increase of cortical representations in the primary somatosensory cortex. Healthy male subjects (n = 16) were trained in a tactile frequency discrimination task of the left ring finger. During the first 15 days of training, there was a steep improvement in frequency discrimination, which generalized from the trained finger to its homologue on the opposite hand, and to a lesser extent, to the other fingers on both hands. During the following 15 days of training, there was only a minor improvement in tactile frequency discrimination. Retention of improved performance in frequency discrimination 30 days after training was demonstrated for all digits. Cortical finger representation in the primary somatosensory cortex, as measured by magnetic source imaging, did not change during training. Because of the generalized training effect and the lack of detectable increase in the cortical field evoked from the trained finger, we assume that skill improvement was mediated predominantly by regions outside the primary somatosensory cortex.