Abstract
Repetitive Magnetic Stimulation (rTMS) has shown to modify the metabolism of specific cortical regions, thus altering activity along extended brain networks. In both, intact, and injured cats with unilateral parietal ablations, we applied rTMS trains on the visuoparietal (VP) cortex, which is crucial for visuo-spatial attention. All animals were intensively trained (<10% errors) in a set of visuo-spatial tasks consisting in the detection and localization of moving or static targets. In two of them, a TMS coil was centered on the VP cortex and 1200 pulses of 1 Hz rTMS were unilaterally delivered. rTMS significantly increased the number of errors in orienting responses towards static but not moving targets, only when presented at the contrastimulated visual hemifield (38±4%; and 48±3%; p<0.05 vs. baseline). Performance went back to baseline error levels 45 minutes after the end of the stimulation (4±2; 6±1%). In the 2 other animals, the right or left parietal and primary visual cortices were surgically removed, generating a complete visuo-spatial neglect syndrome in the contralesional field (100±0% errors; p<0.05). Daily stimulation with 1 Hz rTMS on the intact VP region resulted in a progressive reduction of detection-orienting mistakes to moving but not static stimuli (34±5% and 28±4% errors; p<0.05). We conclude that rTMS can interact with attentional brain networks in both ways; transiently disrupting visuo-spatial processing in normal subjects, and also canceling spatial neglect after lesions of the same area. It constitutes, thus, a non-invasive ‘surgery-less’ method to manipulate brain activity and promote recovery after injuries.
Supported in part by the National Institutes of Health (NS32137, NS33975 and NS47754 to BRP/MM. AV-C was supported by grants from ‘La Caixa’ (Spain) and the Spanish Ministry of Education, Culture and Sports EX2002-041).