Submitted on December 23, 2007
Accepted on March 4, 2008
Baseline cortical excitability determines whether TMS disrupts or facilitates behavior
Juha Silvanto1*, Zaira Cattaneo2, Lorella Battelli3, and Alvaro Pascual-Leone3
1 Harvard Medical School, Boston, Massachusetts, United States; Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
2 Department of Psychology, University of Pavia, Italy; Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
3 Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, Massachusetts, United States
* To whom correspondence should be addressed. E-mail: juha_silvanto{at}yahoo.com.
Transcranial magnetic stimulation (TMS) is increasingly used to modify brain activity noninvasively and to study brain-behavior relations. However, results can be variable and the conditions that affect the functional efficacy of TMS remain unclear. Here we show that online TMS can either facilitate or suppress perceptual functions depending on the baseline level of activity of the targeted brain region. When TMS was applied over the motion selective region V5/MT during a simple motion detection task, motion detection ability was impaired. Similarly, suppression of V5/MT activity using offline 1 Hz rTMS disrupted performance in a subsequent motion detection task. However, paradoxically, online V5/MT TMS had a facilitatory effect on motion detection if V5/MT had been suppressed by offline 1 Hz rTMS prior to the motion detection task. These results demonstrate that TMS can have an unexpected facilitatory effect on behavior when the targeted neural population is in a suppressed state. Our findings support the view that the effects of TMS are modulated by the initial activation state of the targeted neural population.
