Minna Hong

A Kinematic and Electromyographic Analysis of Turning in People With Parkinson Disease

Background. Parkinson disease frequently causes difficulty turning that can lead to falls, loss of independence, and diminished quality of life. Turning in tight spaces, which may be particularly impaired in Parkinson disease, is an essential part of our daily lives, yet a comprehensive analysis of in-place turning has not been published. Objective. This study was conducted to determine whether there are objective differences in turning between people with Parkinson disease and unimpaired people. Methods. In-place turning with kinematics and electromyographic measures was characterized in 11 participants with Parkinson disease and 12 healthy people. Kinematic data were recorded using a 3-dimensional motion capture system in synchrony with electromyographic data from lower extremity muscles as participants turned 180°. Those with Parkinson disease were tested after overnight withdrawal of medication. Results. Both groups used 2 distinct turning strategies. In one, the foot ipsilateral to the turning direction initiated the turn; in the other, the foot contralateral to the turning direction initiated the turn. Kinematic analysis demonstrated a craniocaudal sequence of turning in the unimpaired group, whereas those with Parkinson disease had a simultaneous onset of yaw rotation of the head, trunk, and pelvis. They also took a longer time and more steps to complete turns. Overall, lower extremity muscle activation patterns appeared similar between groups. Conclusion. Differences between the groups were noted for axial control, but lower extremity muscle patterns were similar. This work may provide the foundation for development of new treatments for turning difficulty in Parkinson disease.

Unilateral Subthalamic Nucleus Stimulation Has a Measurable Ipsilateral Effect on Rigidity And Bradykinesia in Parkinson Disease

BACKGROUND Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves motor function in Parkinson disease (PD). However, little is known about the quantitative effects on motor behavior of unilateral STN DBS. METHODS In 52 PD subjects with STN DBS, we quantified in a double-blinded manner rigidity (n=42), bradykinesia (n=38), and gait speed (n=45). Subjects were tested in four DBS conditions: both on, left on, right on and both off. A force transducer was used to measure rigidity across the elbow, and gyroscopes were used to measure angular velocity of hand rotations for bradykinesia. About half of the subjects were rated using the Unified Parkinson Disease Rating Scale (part III) motor scores for arm rigidity and repetitive hand rotation simultaneously during the kinematic measurements. Subjects were timed walking 25 feet. RESULTS All subjects had significant improvement with bilateral STN DBS. Contralateral, ipsilateral and bilateral stimulation significantly reduced rigidity and bradykinesia. Bilateral stimulation improved rigidity more than unilateral stimulation of either side, but there was no significant difference between ipsilateral and contralateral stimulation. Although bilateral stimulation also increased hand rotation velocity more than unilateral stimulation of either side, contralateral stimulation increased hand rotation significantly more than ipsilateral stimulation. All stimulation conditions improved walking time but bilateral stimulation provided the greatest improvement. CONCLUSIONS Unilateral STN DBS decreased rigidity and bradykinesia contralaterally as well ipsilaterally. As expected, bilateral DBS improved gait more than unilateral DBS.

Effect of stimulation frequency on tremor suppression in essential tremor

We sought to determine the effect of deep brain stimulation (DBS) frequency on tremor suppression in essential tremor (ET) patients with deep brain stimulators implanted in the ventral intermediate nucleus (VIM) of the thalamus. A uniaxial accelerometer was used to measure tremor in the right upper extremity of subjects with a diagnosis of ET who had DBS electrodes implanted in the left VIM. The root‐mean‐square acceleration was used as the index of tremor magnitude and normalized to the OFF DBS condition. There was a highly significant inverse sigmoidal relationship between stimulation frequency and normalized tremor acceleration (X2/DoF = 0.42, r2 = 0.997). Tremor acceleration had a nearly linear response to stimulation frequencies between 45 and 100 Hz with little additional benefit above 100 Hz. These findings have two important implications. Clinically, frequency of thalamic stimulation is an important variable for optimal tremor control with maximal benefit achieved with 100 to 130 Hz in most patients. Second, thalamic DBS provides tremor benefit in a graded manner and is not an all‐or‐nothing phenomenon.

Effects of Medication on Turning Deficits in Individuals with Parkinson's Disease

Background and Purpose: People with Parkinsons disease often have difficulty executing turns. To date, most studies of turning have examined subjects ON their anti-Parkinson medications. No studies have examined what specific aspects of turning are modified or remain unchanged when medication is administered. The purpose of this study was to determine how anti-Parkinson medications affect temporal and spatial features of turning performance in individuals with Parkinsons disease. Methods: We examined turning kinematics in 10 people with Parkinsons disease who were assessed both OFF and ON medication. For both conditions, participants were evaluated with the Unified Parkinsons Disease Rating Scale motor subscale, rated how well their medication was working on a visual analog scale, and performed straight-line walking and 180-degree in-place turns. We determined the average walking velocity, time and number of steps to execute turns, sequence of yaw rotation onsets of the head, trunk, and pelvis during turns, and amplitudes of yaw rotation of the head, trunk, and pelvis during turns. Results: Medication significantly improved the Unified Parkinsons Disease Rating Scale scores (P = 0.02), visual analog scale ratings (P = 0.03), and walking velocity (P = 0.02). Although improvements in turning were not statistically significant, medication did reduce the time and number of steps required to turn, slightly increased the amplitudes of yaw rotation of the various segments, and increased the rotation of the head relative to the other segments. Medication did not improve the timing of segment rotations, which showed en bloc turn initiation in both the OFF and ON medication conditions. Discussion and Conclusion: These results suggest that only certain aspects of turning may be responsive to anti-Parkinson medications. As such, additional rehabilitative approaches to address turning are needed because turning may not be effectively addressed by pharmacologic approaches. These results should be interpreted cautiously given the small sample size.

Postural tremor suppression is dependent on thalamic stimulation frequency

Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) reduces tremor in people with essential tremor (ET), yet the dependence of tremor suppression on stimulation frequency remains unclear. To address this issue, we tested tremor suppression for three 15‐second measurements during a variety of stimulation frequencies in 11 ET patients treated with VIM DBS. Stimulation frequencies at or above 100 Hz produced maximal benefit; higher frequencies provided no additional benefit. If this short‐term measure predicts long‐term response in routine activities at home, then this stimulation frequency setting will prolong battery half‐life compared to higher frequency settings. These findings suggest that ET patients treated with VIM DBS may receive adequate benefit from stimulation frequencies about 100 Hz and this setting compared to commonly used higher settings will prolong battery life of surgically implanted pulse generators.

Podokinetic after-rotation in Parkinson disease.

Walking on a rotating platform for 15 min causes healthy subjects to involuntarily turn when walking without vision. This adaptive response, called podokinetic after-rotation (PKAR), uses the same kinematic patterns as voluntary turning suggesting that PKAR and voluntary turning share common mechanisms. The purpose of this study is to determine whether people with Parkinson disease (PD), a condition that produces substantial disability from turning difficulties, can adapt to the rotating platform. Initial testing of people with PD revealed that most were unable to step on the rotating platform for 15 continuous minutes. We thus tested a less intense version of the paradigm in eight healthy people. On one day, subjects walked on the platform for 15 continuous minutes; on another day, they walked on the platform for three 5-minute intervals separated by 5-minute rests. After both sessions, subjects rested for 5 min then walked in place for 30 min without vision, while we recorded rotational velocity of PKAR. Continuous and interval protocols effectively elicited robust PKAR. We then tested eight subjects with PD and matched controls using the 5-minute interval protocol and recorded PKAR responses for 10 min. There were no significant differences between the PD and control groups. We conclude that PD subjects can adapt to the rotating platform and develop PKAR from interval training. Future studies are needed to determine whether the rotating platform may act as a rehabilitative tool to reinforce motor patterns for turning and alleviate turning difficulties in people with PD.

Kinematics of podokinetic after-rotation: similarities to voluntary turning and potential clinical implications.

We examined the kinematics of voluntary turning in place at three different speeds and of inadvertent turning in place during attempts to step in place following stepping on a rotating disc (podokinetic after-rotation, PKAR). We hypothesized that voluntary turning in place, like online turning during walking, would be characterized by a top-down sequence of yaw rotations in the direction of the turn, i.e. the head would rotate first, followed by the trunk and then the foot. We also hypothesized that in place PKAR would be characterized by a bottom-up sequence of yaw rotations, i.e. the foot would rotate first, followed by the trunk and the head. The alternative possibility was that PKAR, like voluntary turning, would be initiated by the head and trunk and the foot would rotate last. As expected, voluntary turning in place was characterized by a top-down sequence similar to that noted previously during online turning in the midst of walking. Turning velocity did not alter the sequence of rotations in voluntary turning. In place PKAR was also characterized by a top-down sequence, indicating that PKAR may access the same neural circuits employed during voluntary turning. These data suggest that the rotating treadmill may be a useful training tool for addressing difficulties with turning that are experienced by individuals with Parkinson disease (PD).

Effects of thalamic stimulation frequency on intention and postural tremor

Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) of the thalamus improves essential tremor. Suppression of the amplitude of the postural tremor component with VIM DBS depends on stimulation frequency. The purpose of this study was to determine the effect of DBS frequency on the intention tremor component, that is, tremor that is enhanced by target-directed movement, and to compare it to the effect of DBS frequency on postural tremor in people with essential tremor. We measured tremor frequency and amplitude during trials of postural holding and voluntary reaching between two targets at 10 different stimulation frequency settings between 0 and 185 Hz. Tremor frequency did not change with changes in stimulation frequency. Amplitude suppression of both intention and postural tremor depended on stimulation frequency. Maximal tremor reduction occurred at approximately 130 Hz for both forms of tremor. However, at optimal frequencies, the percent reduction in tremor amplitude relative to the DBS OFF condition was greater for postural than for intention tremor. These results suggest that VIM DBS stimulation frequencies near 130 Hz may provide maximal control of intention and postural tremor. Identification of optimal stimulation settings should consider assessment of intention tremor, not just postural tremor, as intention tremor may not be as well controlled as postural tremor but may be a better gauge for functional benefit.

Perception of Active and Passive Turning in Parkinson Disease

Background. Many individuals with Parkinson disease (PD) experience difficulty with turning, yet little is known about the reasons for this difficulty. Objective. The authors sought to determine whether individuals with PD can use visual, vestibular, and proprioceptive cues to estimate how far they have turned. Methods. Fifteen PD subjects and 11 controls performed active and passive turns to the left and right, with and without vision, with amplitudes of 90, 180, 270, and 360 degrees. For active conditions, subjects were told the direction and amplitude of the desired turn and then attempted to turn in place the specified amount via actively stepping. For passive conditions, subjects were told that the disc they stood on would turn and they were to press a button when they had traveled the specified amplitude. Results. There were no differences between PD and control groups in any of the conditions, suggesting that those with PD effectively used sensory cues available in the different conditions to accurately judge distance turned. The authors found no apparent deficits in the visual, vestibular, or proprioceptive systems or in integration of these senses for performance of the turning task tested. Conclusions. Turning difficulties associated with PD may more likely relate to motor or sensorimotor integration deficits than to pure sensory or sensory integration deficits. Generalizability of the study may be limited by the fact that subjects were tested at a single velocity for passive rotations, were on medication, and had relatively mild PD (primarily H&Y 2).

Enhancement of rigidity in Parkinson's disease with activation

Rigidity, a cardinal symptom of Parkinsons disease (PD), increases with movement of a contralateral limb. It is unclear whether this effect is specific for movement of a contralateral limb. The goal of this study was to test the hypothesis that ipsilateral or contralateral movement would enhance rigidity but that bilateral limb movements would maximally increase rigidity in people with PD. We assessed rigidity in 12 people with PD off meds, 12 matched controls, and 10 young controls, using a Rigidity Analyzer (Neurokinetics, Alberta, Canada). The elbow was passively moved repetitively into flexion and extension by the examiner, while the subjects engaged in different toe tapping conditions: no tapping, ipsilateral tapping, contralateral tapping, and bilateral tapping. Three 50‐second trials were done for each condition and the order of the trials was randomized. A 2‐way repeated measures ANOVA and Holm–Sidak post hoc tests were used to determine differences across conditions and groups. There was a significant effect of group, tapping conditions and an interaction of the two. Post hoc tests revealed that for the PD group, all tapping conditions were significantly different from the no tapping condition but not different from each other. There were no differences across conditions for the controls. We conclude that movement of either the contralateral or ipsilateral lower extremity can increase arm rigidity in people with PD but the effects from left and right are apparently not additive. Further, activation did not enhance muscle tone in controls suggesting that this procedure may help distinguish people with PD from controls.