Exposure to even a brief train of TMS pulses can elicit an acute physiologic change (cf Siebner and Rothwell, 2003), and so a test procedure can be performed that will assess the distance from the standard treatment position to the point eliciting a maximal acute physiologic response. We propose a 9-locus mapping procedure, involving the assessment of changes in brain activity from stimulation at locations including and around the standard treatment target. The nine locations will be the usual treatment location and 8 other points, 1.5 and 3.0 cm anterior, posterior, rostral, and caudal of the primary target. Test stimulation will be for 15 seconds (=150 pulses @ 10 Hz) at each location, followed by 5 minutes of continuous EEG recording to examine acute changes in regional brain activity in response to a brief stimulation exposure. All therapeutic stimulations will take place in the standard location, and we will be able to evaluate what proportion of variance in clinical outcome is explained by distance from the location of maximal acute physiologic response.