Frequency Based Mapping of the STN Borders

During deep brain stimulation (DBS) surgery for Parkinson disease, the target is the subthalamic nucleus (STN). STN is small, (9\(\,\times \,\)7 x 4 mm) and typically localized by a series of parallel microelectrodes. As those electrodes are in steps advanced towards and through the STN, they record the neurobiological activity of the surrounding tissues. By careful inspection and analysis of such recordings one can obtain a range of depth at which given electrodes passed through the STN. Both human made inspection and computer based analysis are performed during surgery in the environment of the operation theatre. There are several methods for the STN detection, one of them – developed by the authors – is described in [8]. While the detection of the STN interior can be obtained with good certainty its borders can be slightly fuzzy and sometimes it is difficult to classify whether given depth should be regarded as belonging to the STN proper or lying outside of it. Mapping of the borders is important as the tip of the final permanent stimulating electrode is often placed near the ventral (bottom) border of the STN [12]. In this paper we are showing that analysis focusing on narrow frequency bands can yield better discrimination of the STN borders and STN itself.