Deep brain stimulation (DBS) of the subthalamic nucleus (STN) and antiparkinsonian medication have proved to be effective treatments for tremor in Parkinson's disease. To date it is not known how and to what extent STN DBS alone and in combination with antiparkinsonian medication alters the pathophysiology of resting and postural tremor in idiopathic Parkinson's disease. The purpose of this study was to examine the effects of STN DBS and antiparkinsonian medication on the neurophysiological characteristics of resting and postural hand tremor in Parkinson's disease. Resting and postural hand tremor were recorded using accelerometry and surface electromyography (EMG) from 10 Parkinson's disease patients and 10 matched control subjects. The Parkinson's disease subjects were examined under four treatment conditions: (i) off treatment; (ii) STN DBS; (iii) medication; and (iv) medication plus STN DBS. The amplitude, EMG frequency, regularity, and 1-8 Hz tremor-EMG coherence were analysed. Both STN DBS and medication reduced the amplitude, regularity and tremor-EMG coherence, and increased the EMG frequency of resting and postural tremor in Parkinson's disease. STN DBS was more effective than medication in reducing the amplitude and increasing the frequency of resting and postural tremor to healthy physiological levels. These findings provide strong evidence that effective STN DBS normalizes the amplitude and frequency of tremor. The findings suggest that neural activity in the STN is an important modulator of the neural network(s) responsible for both resting and postural tremor genesis in Parkinson's disease.

Whereas pharmacologic and thalamic lesions have previously failed to change characteristics of ET beyond amplitude reduction, VIM DBS modified multiple features of ET. The changes in ET after VIM DBS provide strong evidence for clinical efficacy.

. The purpose of this investigation was to determine the effects of healthy aging on the regularity of physiological tremor under rest and postural conditions. Additionally, we examined the contribution of mechanical reflex factors to age-related changes in postural physiological tremor. Tremor regularity, tremorelectromyographic (EMG) coherence, tremor amplitude, and tremor modal frequency were calculated for 4 age groups (young: 20 -30 yr, young-old: 60 -69 yr, old: 70 -79 yr, and old-old: 80 -94 yr) under resting and loaded postural conditions. There were 6 important findings from this study: 1) there were no differences between the young and elderly subjects for any of the dependent variables measured under the rest condition; 2) postural physiological tremor regularity was increased in the elderly; 3) postural physiological tremor-EMG coherence was also increased in the elderly, and there was a strong linear relation between peak tremor-EMG coherence in the 1-to 8-Hz frequency band and regularity of tremor. This relation was primarily driven by the increased magnitude of tremor-EMG coherence at 5.85 and 6.83 Hz; 4) enhanced mechanical reflex properties were not responsible for the increased magnitude of tremor-EMG coherence in the elderly subjects; 5) tremor amplitude was not different between the 4 age groups, but there was a slight decline in tremor modal frequency in the oldest age group in the unloaded condition; and 6) despite the increases in postural physiological tremor regularity and the magnitude of low frequency tremor-EMG coherence with age, there was a clear demarcation between healthy aging and previously published findings related to tremor pathology.

We investigated the control of movement in 12 patients with Parkinson's disease (PD) after they received surgically implanted high-frequency stimulating electrodes in the subthalamic nucleus (STN). The experiment studied ankle strength, movement velocity, and the associated electromyographic patterns in PD patients, six of whom had tremor at the ankle. The patients were studied off treatment, ON STN deep brain stimulation (DBS), on medication, and on medication plus STN DBS. Twelve matched control subjects were also examined. Medication alone and STN DBS alone increased patients' ankle strength, ankle velocity, agonist muscle burst amplitude, and agonist burst duration, while reducing the number of agonist bursts during movement. These findings were similar for PD patients with and without tremor. The combination of medication plus STN DBS normalized maximal strength at the ankle joint, but ankle movement velocity and electromyographic patterns were not normalized. The findings are the first to demonstrate that STN DBS and medication increase strength and movement velocity at the ankle joint.Keywords deep brain stimulation; subthalamic nucleus; bradykinesia; electromyography; Parkinson's disease; tremor Deep brain stimulation (DBS) of the subthalamic nucleus (STN) minimizes tremor, rigidity, and bradykinesia in Parkinson's disease (PD). 1 STN DBS restores basic upper limb motor functions, such as arm movement speed, 2,3 grip force control, 4 and wrist strength, 5 reduces tremor, 6 and improves oral force control. 7 Similar studies of the lower extremities are lacking. This is surprising since the volitional control of the ankle joint is critical in motor behaviors such as postural stance and walking. PATIENTS AND METHODSTwelve PD patients participated 4 -9 months after quadripolar stimulating electrodes were implanted unilaterally in the STN (Table 1). Six patients had tremor in the off state, and six did not. The stimulator pulse width was 60 μsec and the frequency was 185 Hz. Also, 12 age-and gender-matched control subjects were examined (mean age: 52 years).Patients were included if they had idiopathic PD by accepted criteria 11 and postoperative reduction of greater than 15% in the UPDRS motor section off treatment compared to STN DBS. Six of the 12 patients were previously studied at the elbow joint, 3 and 8 were previously studied for hand tremor. 6 All subjects gave informed consent in accordance with the local institutional review board and Declaration of Helsinki. Treatment DesignThe experiments were performed on consecutive days in each treatment condition: (1) off treatment; (2) STN DBS; (3) Meds; and (4) Meds plus STN DBS. On day 1, condition 1 occurred between 9 and 11 am and condition 2 between 1 and 3 pm. On day 2, the same testing schedule as day 1 was set for conditions 3 and 4, respectively. The control subjects were tested on 1 day.Patients were tested after a 12-hour withdrawal from the specific treatment. 12,13 The UPDRS motor section was administered 90 minutes after activation of ...

We quantified the effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN) and medication on Parkinsonian rigidity using an objective measure of work about the elbow joint during a complete cycle of imposed 1-Hz sinusoidal oscillations. Resting and activated rigidity were analyzed in four experimental conditions: 1) off treatment; 2) on DBS; 3) on medication; and 4) on DBS plus medication. Rigidity at the elbow joint was also assessed using the Unified Parkinson's Disease Rating Scale (UPDRS). We tested ten patients who received STN DBS and ten age-matched neurologically healthy control subjects. The activated rigidity condition increased work in both Parkinson's disease (PD) patients and control subjects. In PD patients, STN DBS reduced both resting and activated rigidity as indicated by work and the UPDRS rigidity score. This is the first demonstration that STN stimulation reduces rigidity using an objective measure such as work. In contrast, the presurgery dose of antiparkinsonian medication did not significantly improve the UPDRS rigidity score and reduced work only in the activated rigidity condition. Our results suggest that STN DBS may be more effective in alleviating rigidity in the upper limb of PD patients than medications administered at presurgery dosage level.