NEUROREPORT Schutter et al. Vol 12 No 3 5 March 2001 1 Effects of slow rTMS at the right dorsolateral prefrontal cortex on EEG asymmetry and mood Dennis J.L.G. Schutter, Jack van Honk CA , Alfredo A.L. d’Alfonso, Albert Postma, Edward H.F. de Haan Psychological Laboratory, Utrecht University, Heidelberglaan 2, 3584 Cs Utrecht, The Netherlands CA Corresponding Author In a sham-controlled design (n=12), slow repetitive Transcranial Magnetic Stimulation (rTMS) was applied to the right dorsolateral prefrontal cortex during a period of 20 minutes, and the subsequent effects on mood and the EEG spectrum were investigated. Analysis revealed a significant left hemisphere increase in EEG theta activity between 25 to 35 and 55 to 65 minutes after stimulation. In addition, participants reported significant decrease in anxiety immediately after stimulation, as well as 35 and 65 minutes after rTMS. These findings indicate that reductions in anxiety after slow rTMS at the right dorsolateral prefrontal cortex are associated with a contralateral increase in theta activity. NeuroReport 12:445-447. Keywords: rTMS, dorsolateral prefrontal cortex, EEG power spectrum, mood INTRODUCTION There is now abundant evidence for the involvement of the prefrontal cortex in affective processes. According to the directional model of negative affect, the left anterior sector of the brain is involved in the approach-related emotion ‘anger’, whereas the right prefrontal sector is linked to the withdrawal-related emotion ‘anxiety’ 1,2 . Recently, D’Alfonso et al. 3 applied slow rTMS over the right dorsolateral prefrontal cortex. This method is commonly suggested to decrease neuronal activity in the stimulated area. Enhanced approach and reduced withdrawal-related motivation were found, as indexed by a motivational selective attention task. It was shown that right compared to left prefrontal stimulation induced vigilant attention for angry faces, in agreement with a line of findings in our laboratory in relation to low levels of social anxiety and high levels of anger 4 .