Background Gait impairment in Parkinson's disease reduces mobility and increases fall risk, particularly during cognitive multi-tasking. Studies suggest that bilateral subthalamic deep brain stimulation, a common surgical therapy, degrades motor performance under cognitive dual-task conditions, compared to unilateral stimulation. Objective To measure the impact of bilateral versus unilateral subthalamic deep brain stimulation on walking kinematics with and without cognitive dual-tasking. Methods Gait kinematics of seventeen patients with advanced Parkinson's disease who had undergone bilateral subthalamic deep brain stimulation were examined off medication under three stimulation states (bilateral, unilateral left, unilateral right) with and without a cognitive challenge, using an instrumented walkway system. Results Consistent with earlier studies, gait performance declined for all six measured parameters under cognitive dual-task conditions, independent of stimulation state. However, bilateral stimulation produced greater improvements in step length and double-limb support time than unilateral stimulation, and achieved similar performance for other gait parameters. Conclusions Contrary to expectations from earlier studies of dual-task motor performance, bilateral subthalamic deep brain stimulation may assist in maintaining temporal and spatial gait performance under cognitive dual-task conditions.

Age-related changes in proprioceptive ability and their contributions to postural instability have been well documented. In contrast, and despite the known importance of proprioceptive feedback in the control of coordinated arm and hand movement, studies focusing on upper limb proprioception in older populations are few and equivocal in their findings. This study focused on kinesthetic awareness about the wrist joint in healthy young and older adults. Passive movement detection thresholds (PMDTs) were twice as high in older compared to young participants. In contrast to previous findings demonstrating asymmetries in static position sense, PMDT did not differ between the dominant and non-dominant wrist joints nor did direction of joint displacement affect PMDT as has been reported for the lower limb. Preliminary analysis indicated that PMDT was significantly higher in older adults categorized as sedentary while active older adults were able to detect passive movement as well as young adults. These findings demonstrate that upper limb kinesthesia is impaired in older adults although the degree of impairment may be influenced by one's level of physical activity.

Objective: To study the effects of a 6-week home-based training program on hand sensorimotor function in older adults. Design: Single cohort, repeated measures. Setting: Not provided. Participants: 7 right-hand dominant healthy older adults, 80±5 years of age. Intervention: All participants performed a series of hand activities for 30 to 40 minutes a day, 7 days a week, for 6 weeks. The home program was comprised of motor and sensory tasks such as stringing beads, picking up small objects with chopsticks and/or a pincer grasp, rotating golf balls in the palm, and grasp force control with a medicine dropper. Sensorimotor measures included the ability to reproduce a perceived pinch force with 1 or both hands. Additional clinical measures included sensory discrimination using a gratings technique (JVP domes), pinch and grasp strength, and manual dexterity (Purdue pegboard). All measures were obtained at baseline, week 3, and week 6 of the intervention. Main Outcome Measures: Dependent measures included pinch force matching error at 20% maximum voluntary contraction, maximum pinch force, and grasp strength, Purdue pegboard scores, sensory discrimination thresholds, and self-reported function with activities of daily living (ADLs). Results: The ability to reproduce a perceived target pinch force using the dominant hand improved by 60% in week 3 compared with baseline (P=.015), with no further mean improvement seen in week 6. The nondominant hand improved by 45% in week 3 and by 60% in week 6. No significant changes in clinical measures of muscle strength, motor dexterity, and sensory discrimination were observed. All subjects reported improved hand ADL function. Conclusions: Improved pinch force control using a matching paradigm was observed following a 3- to 6-week program. Given the importance of force control during ADLs, a sensorimotor home program may be effective in maintaining hand function in older populations.

The ability to accurately control grasp force and limb position, critical in performing daily living tasks, is thought to rely heavily on somatosensory feedback. While age-related changes in upper limb motor function are well established, much less is known regarding changes in proprioceptive ability across the lifespan. This study examines the effects of age, task and hand preference on the performance of two sensorimotor tasks: perception of wrist movement and force grasp matching. Ten young adults (mean age = 21+/- 1.9 years) and ten elderly (mean age = 78 +/- 6.4 years) who were all healthy, right handed individuals participated in this study. Perception of wrist movement was examined in the absence of vision using a manipulandum and a servo-motor to passively displace the wrist at 0.5 deg/s into either flexion or extension. Participants indicated perception of movement by pressing a button with the opposite hand. The degree of wrist displacement at the time of movement perception was used to determine the movement threshold. Instrumented grasp devices were used to measure grasp force while participants performed three force matching tasks at 20% of their perceived maximum grasp force of the reference limb. In the Ipsilateral (IR) and Contralateral Remembered (CR) conditions, participants matched the reference force with the same hand or opposite hand using memory-based information. In the Contralateral Concurrent (CC) condition, participants matched the reference force with the opposite hand while the reference force was maintained. Mean movement threshold was significantly greater (p<0.001) in the elderly group (2.4 deg) compared to the young (1.2 deg). No asymmetries were seen between the right and left hands or between flexion and extension direction in either group. Force matching error across all conditions (IR, CR, CC) was worse in elderly than young (p<0.001). In the elderly group, right compared to left hand matching was worse (p=0.05). These differences were most pronounced in the contralateral conditions where matching was performed by the opposite hand (CC: p=0.007 and CR: p=0.05). This study demonstrates that perception of upper limb movement and grasp force declines with age. Right-left differences in force matching ability, particularly in tasks requiring interhemispheric transfer of force information, support age-related asymmetries in callosal function (Jeeves and Moes 1996).