Parkinson's disease patients who would otherwise be undergoing subthalamic nucleus (STN) deep brain stimulation (DBS) will have dual hemispheric stimulation of the STN and globus pallidus interna (GPi).

Study will be utilizing multiple brain electrodes simultaneously. The study will require at least two electrodes to be placed in one cerebral hemisphere (one for motor improvement and one for potential cognitive implications).

Memory will be assessed with the Hopkins Verbal Learning Test. The test consists of a set of six forms. Each test includes a list of 12 nouns; the examiner reads the list to the examinee, who repeats as many words as remembered. This process is repeated three times; 20-25 minutes later, examinees are asked again to recall as many words as possible; for the final task, the examiner reads a list of 24 words (including the 12 words from the list) and asks the examinee after each whether the word was on the list. For interpreting findings, in each metric listed on a scale from 0 to 12 with zero being worse and 12 being best (total recall, delayed recall, retention), higher scores reflect better learning efficiency (total recall) and memory (delayed recall, retention). Since this is a longitudinal study, follow-up scores will be compared to baseline. A positive direction of change would be interpreted as "improved" and a negative direction of change would be interpreted as "declined".

Parkinson's disease subjects with dual hemispheric stimulation of the subthalamic nucleus (STN) and fornix/hypothalamus

Memory will be assessed with the Hopkins Verbal Learning Test. The test consists of a set of six forms. Each test includes a list of 12 nouns; the examiner reads the list to the examinee, who repeats as many words as remembered. This process is repeated three times; 20-25 minutes later, examinees are asked again to recall as many words as possible; for the final task, the examiner reads a list of 24 words (including the 12 words from the list) and asks the examinee after each whether the word was on the list. For interpreting findings, in each metric listed on a scale from 0 to 12 with zero being worse and 12 being best (total recall, delayed recall, retention), higher scores reflect better learning efficiency (total recall) and memory (delayed recall, retention). Since this is a longitudinal study, follow-up scores will be compared to baseline. A positive direction of change would be interpreted as "improved" and a negative direction of change would be interpreted as "declined".

Parkinson's disease subjects with dual hemispheric stimulation of the subthalamic nucleus (STN) and fornix/hypothalamus