Recently, many groups have reported on the occurrence of brain shift in stereotactic surgery and its impact on the procedure. A shift of deep brain structures by only a few millimeters can potentially increase the number of required microelectrode and/or macroelectrode tracks. This can cause complications and potentially affect implantation accuracy. Detecting intra-operative brain shift and, more significantly correcting for it intra-operatively can thus impact the procedure and its outcome. In this study, we have used intra-operative stimulation response data to assess brain shift. Using a shift free functional atlas containing therapeutic response to stimulation (efficacy) data from a population of patients we build statistical efficacy maps on new patients. We then compare the information provided by the maps with the actual intra-operative responses of those patients to detect brain shift. Our preliminary results show that by maximizing the correlation between statistical maps and intra-operative observations, it may be possible to detect intra-operative brain shift and potentially correct for it.