Abstract
Interplay between the cerebral hemispheres is vital for coordinating perception and behavior. One influential account holds that the hemispheres engage in rivalry, each inhibiting the other. In the somatosensory domain, a seminal paper claimed to demonstrate such interhemispheric rivalry, reporting improved tactile detection sensitivity on the right hand after transcranial magnetic stimulation (TMS) to the right parietal lobe (Seyal, Ro, & Rafal, 1995). Such improvement in tactile detection ipsilateral to TMS could follow from interhemispheric rivalry, if one assumes that TMS disrupted cortical processing under the coil and thereby released the other hemisphere from inhibition. Here we extended the study by Seyal et al. (1995) to determine the effects of right parietal TMS on tactile processing for either hand, rather than only the ipsilateral hand. We performed two experiments applying TMS in the context of median-nerve stimulation; one experiment required somatosensory detection, the second somatosensory intensity discrimination. We found different TMS effects on detection versus discrimination, but neither set of results followed the prediction from hemispheric rivalry that enhanced performance for one hand should invariably be associated with impaired performance for the other hand, and vice-versa. Our results argue against a strict rivalry interpretation, instead suggesting that parietal TMS can provide a pedestal-like increment in somatosensory response.
Highlights
There was a significant interaction between transcranial magnetic stimulation (TMS) intensity and side, such that high- vs. low-intensity TMS affected sensitivity more on the ipsilateral side than on the contralateral side [F(1,70) = 5.11, p = 0.027; Fig. 3]
Experiment 2: Somatosensory discrimination In Experiment 1 we found enhanced somatosensory detection ipsilateral to right parietal TMS; but we did not find decreased performance in the contralateral hand, contrary to what should be predicted by the rivalry seesaw
We found that high- vs. low-intensity TMS did not affect contralateral detection, but did disrupt contralateral discrimination
Summary
More than 200 million axons transmit information between homologous regions on opposite sides, making the corpus callosum the brain’s largest connective tract (Banich, 1995; Tomasch, 1954). Lesions to this tract—whether due to disease, surgery, or congenital condition—result in a complex set of deficits, indicating that interhemispheric connections are vital to coordinate sensory, cognitive, and motor processing (for review, see Gazzaniga, 2005). It has long been known that each half of the body-surface projects information initially to the contralateral hemisphere of the brain (Maldjian, Gottschalk, Patel, Detre, & Alsop, 1999; Penfield & Rasmussen, 1950). If information from a given body-part is blocked
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
