CHRONIC ELECTRICAL-STIMULATION OF THE LEFT VENTROINTERMEDIATE (VIM) THALAMIC NUCLEUS FOR THE TREATMENT OF PHARMACOTHERAPY-RESISTANT PARKINSONS-DISEASE - A DIFFERENTIAL IMPACT ON ACCESS TO SEMANTIC AND EPISODICMEMORY

Thalamotomy for medically refractory Parkinson's disease (PD) is consi dered to be efficacious and relatively safe. Because a minority of pat ients experience decrements in language and memory (often mild and tra nsient) after thalamotomy, chronic thalamic deep brain stimulation (DB S) might be a safer treatment given its reversibility and the modifiab ility of stimulation parameters. Two preliminary studies support the r elative cognitive safety of unilateral DBS of the ventral intermediate (Vim) thalamic nucleus, but it is unclear whether possibly subtle cha nges in language and memory represent effects of ''microthalamotomy'' or of stimulation per se. This report provides preliminary data concer ning effects of left thalamic stimulation on information processing sp eed, semantic memory (verbal fluency and visual confrontation naming), and verbal episodic memory in a patient with PD. In addition to being evaluated before and 3 and 6 months after surgery, the patient was te sted 18 months after surgery either on or off medications and with the stimulator turned either on or off (order counterbalanced across medi cation conditions). Test performance differences between the stimulati on conditions were attenuated ''off'' as compared to ''on'' medication . Vim stimulation consistently, albeit subtly, improved semantic verba l fluency but interfered with immediate recall of word lists. Parallel s to findings from acute, intraoperative thalamic stimulation studies are explored. The hypothesis is offered that left Vim stimulation migh t facilitate access to semantic memory, but interfere with episodic me mory processes, (C) 1998 Academic Press.