Tuesday,
November 08, 2011 - 12:30
Schmidt Lecture Hall
Prof. Jeff Daskalakis
Centre for Addiction and Mental Health, University of Toronto
Repetitive transcranial magnetic stimulation (rTMS) has been shown to induce neurophysiological changes in the cortex that can be recorded through electroencephalography. Oscillatory activity in the gamma (30-50 Hz) frequency range represents a neurophysiological process that has been shown to be altered during working memory, a cognitive process that is mediated by the dorsolateral prefrontal cortex (DLPFC). We examined the effect of 20 Hz rTMS applied bilaterally to the DLPFC on gamma oscillations elicited during the N-back working memory task in 22 healthy subjects and 24 patients with schizophrenia. Patients with SCZ then continued to receive rTMS (active or sham) for an additional 4 weeks (i.e., 20 treatments in total). Compared to sham rTMS, active rTMS produced a significant increase in gamma oscillations in healthy subjects that was most pronounced in the 3-back condition, the condition associated with greatest cognitive demand. In patients with schizophrenia, by contrast, active rTMS reduced gamma oscillations compared to sham. Neither group demonstrated significant changes in other frequency ranges, suggesting that rTMS selectively modulates only gamma oscillations. In addition, after an additional 4 weeks of active rTMS evidence suggests a potentiation of N-back performance compared to sham but no significant changes in negative symptoms. These findings suggest that patients with schizophrenia demonstrate altered gamma modulation which may be normalized in response to rTMS and over time translate into improved cognitive performance. These findings may also provide important insights into the mechanisms that lead to enhanced cognitive performance.
