What made you want to look up negative valence? Please tell us where you read or heard it (including the quote, if possible).
WBS is nothing but Work Breakdown Structure. It is mainly used in Project System (PS) module. Tcode: CJ20N. For any project defined we must have atleast one WBS. Within this WBS we can have networks. Networks are nothing but the series of activities. Material are used to perform the activities.
DBS is also used in research studies to treat chronic pain and has been used to treat various affective disorders, including major depression; neither of these applications of DBS have yet been FDA-approved. While DBS has proven effective for some patients, potential for serious complications and side effects exists.