title: Medial forebrain bundle stimulation as a pathophysiological mechanism for hypomania in subthalamic nucleus deep brain stimulation for Parkinson's disease.
abstract: OBJECTIVE
  Hypomania accounts for approximately 4% to 13% of psychotropic adverse events during subthalamic nucleus (STN) deep brain stimulation (DBS) for Parkinson's disease. Diffusion of current into the inferior and medial "limbic" STN is often reported to be the cause. We suggest a different explanation, in which the coactivation of the medial forebrain bundle (MFB), outside the STN, leads to hypomania during STN DBS.
  
  
  METHODS
  Six patients with advanced Parkinson's disease (age, 54 +/- 11 years) underwent bilateral STN DBS surgery. Preoperative diffusion tensor imaging scans for fiber tracking of the MFB were conducted on a 3T magnetic resonance imaging scanner. After implantation, the electrode positions were determined with computed tomography and integrated in a diffusion tensor imaging software environment.
  
  
  RESULTS
  The medial STN was shown to send tributaries to the MFB using it as a pathway to connect to the reward circuitry. One patient, who had a transient, stimulation-induced acute hypomanic episode, showed a direct contact between 1 active electrode contact and these putative limbic STN tributaries to the MFB unilaterally on the left. In 5 asymptomatic patients, the active contacts were between 2.9 and 7.5 mm distant from the MFB or its limbic STN tributaries.
  
  
  CONCLUSIONS
  We hypothesize that STN DBS-induced reversible acute hypomania might be elicited by inadvertent and unilateral coactivation of putative limbic STN tributaries to the MFB. These findings may provide insight into the neural pathways of hypomania and may facilitate future investigations of the pathophysiology of mood disorders.
authors.affiliation: Surgical Center for Movement Disorders, University of British Columbia, Vancouver, BC, Canada. vacoenen@aol.com
authors.forename: Volker A
authors.initials: VA
authors.lastname: Coenen
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Honey
authors.forename: Trevor
authors.initials: T
authors.lastname: Hurwitz
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Rahman
authors.forename: Jacqueline
authors.initials: J
authors.lastname: McMaster
authors.forename: Uli
authors.initials: U
authors.lastname: Bürgel
authors.forename: Burkhard
authors.initials: B
authors.lastname: Mädler
mesh_terms: D000328:Adult; D000368:Aged; D046690:Deep Brain Stimulation / Q000009:adverse effects* / Q000379:methods*; D003863:Depression / Q000209:etiology* / Q000628:therapy*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008474:Medial Forebrain Bundle / Q000502:physiology*; D008875:Middle Aged; D010300:Parkinson Disease / Q000628:therapy; D020531:Subthalamic Nucleus / Q000502:physiology