Abstract
The crossed-uncrossed difference (CUD) estimates the interhemispherictransfer time (ITT) through the corpus callosum. Previous research hasshown that transcranial magnetic stimulation (TMS) to the occipitalcortex determines an increased CUD during cognitive tasks. The aim ofthe present study was to investigate whether TMS stimulation applied at amotor stage can interfere with the ITT, comparing the performance ofleft- and right-handed people. Results showed a significant TMS effect,i.e. increasing reaction times were reported when stimulation wasdelivered on the left primary motor area. Effects were more evident wheninformation was primarily perceived through the dominant hemisphere.Both left and right stimulations increased CUD times in right-handedsubjects; however, left-handed subjects showed significant effectsassociated with left stimulation only. Furthermore, in both groups, TMSproduced larger effects in the crossed than in the uncrossed condition.TMS stimulation increased reaction times, thus supporting the idea thatthe interhemispheric transfer of visuo-motor information occurs at amotor processing stage. The dominant hemisphere seems to play a majorrole within this process: our data indicates that left- and right-handedpeople have different ITT latencies associated with the transfer ofinformation to the contralateral hemisphere.