Involvement of the ipsilateral hemisphere during planning of reachingmovements is still matter of debate.
While it has beendemonstrated that the contralateral hemisphere is dominant in visuo-motor integration,
involvement of the ipsilateral hemisphere has also been proposed. Furthermore, a dominant role for left
posterior parietal cortex has been shown in this process, independently of the hand and visual field
involved. In this study, the possible involvement of ipsilateral parieto-occipital cortex in planning of
reaching movements was investigated by transcranial magnetic stimulation (TMS). TMS was applied on
four points of the parietal and occipital cortex at 50% (Time 1), 75% (Time 2) and 90% (Time 3) of reaction
time from a go-signal to hand movement. The only effect observedwas an increase in reaction time when
a region around the parieto-occipital junction was stimulated at Time 2. These results provide further
support to the hypothesis that, in the posterior parietal cortex, planning of reaching movements also
relies on the ipsilateral hemisphere, in addition to the contralateral or dominant one.
