Table 1. Demographic characteristics of subjects.
| SID | Age (years) | PD duration (years) | Levodopa (mg) | DBS duration (months) | Left amp (volts) | Right amp (volts) | H and Y (off) | H and Y (on) | UPDRS III (off) | UPDRS III (on) |
|---|---|---|---|---|---|---|---|---|---|---|
| 103 | 54 | 14 | 250 | 44 | 3.2 | 2.8 | 3.0 | 2.0 | 51.0 | 25.0 |
| 104 | 57 | 16 | 400 | 27 | 3.0 | 3.0 | 5.0 | 4.0 | 57.0 | 55.5 |
| 106 | 59 | 10 | 600 | 09 | 3.0 | 3.0 | 2.5 | 2.5 | 27.5 | 19.0 |
| 107 | 62 | 15 | 600 | 02 | 2.5 | 2.6 | 2.5 | 2.0 | 26.0 | 23.0 |
| 109 | 49 | 09 | 300 | 04 | 2.6 | 2.5 | 2.5 | 2.0 | 23.5 | 21.5 |
| 110 | 62 | 11 | 600 | 56 | 3.0 | 3.3 | 4.0 | 3.0 | 52.5 | 31.0 |
| 111 | 56 | 11 | 400 | 37 | 3.0 | 3.0 | 2.0 | 1.0 | 11.5 | 4.0 |
PD, Parkinson's disease; STN-DBS, deep brain stimulation of the subthalamic nucleus; UPDRS III, United Parkinson's Disease Rating Scale III.
All subjects were right-handed males and all but one subject were native speakers of English (106 was a native speaker of Italian who immigrated to the United States as an adolescent). In all cases, the stimulation frequency was 185 Hz, pulse width 60 μ seconds. The medical indications for STN-DBS were advanced, medically refractory PD with marked clinical swings between medication doses (i.e., on/off effects), as well as levodopa-induced dyskinesias. Both on and off evaluations were performed at least 12 hours after the last dose of levodopa, which was taken the evening before the study. On and off studies were performed on different days separated by at least 1 week. Subject 104 had maximum scores on the rigidity items on the UPDRS III, which were not responsive to DBS. Given the unknown washout time of DBS effects, the UPDRS on–off differences may underestimate the therapeutic effects.