The distribution of mislocalizations across fingers demonstrates training-induced neuroplastic changes in somatosensory cortex

The somatosensory system has been shown to alter its cortical activation pa tterns in reaction to changes in the attended sensory input to certain body parts. Whether these modifications in the functional organization of the s omatosensory cortex of humans also result in perceptual changes has rarely been investigated. Here we used near-threshold tactile stimuli to the cente r of the fingertips to evoke mislocalizations to fingers other than the sti mulated. In healthy untrained subjects, the distribution of the mislocaliza tions from each of the fingers was different from a distribution expected i f the subjects were purely guessing the position of the stimulus. The di-it s next to the stimulated one receive a higher number of mislocalizations th an digits further away from the stimulated digits. This decrease can be acc ounted for by digit-overlapping receptive fields in combination with the se quential representation of the digits in the primary somatosensory cortex. In a second experiment subjects received 20 h of simultaneous stimulation o f the left thumb and little finger in the context of a perceptual task. For both hands, the distribution of mislocalization from these fingers was ana lyzed at the beginning and the end of the training. For the left hand, the number of assigned mislocalizations to the most distant neighbor digit (i.e ., the simultaneously stimulated digit in the training) increased while the number of mislocalizations toward the direct neighboring digit decreased w ith the training. This change did not occur in the untrained right hand, or in the untrained subjects. We conclude that the distribution of mislocaliz ation to fingers other than the stimulated can be used to investigate perce ptual changes paralleling training-induced modifications in the activation patterns of the somatosensory cortex.