Penelope A. McNulty

Wii-based movement therapy to promote improved upper extremity function post-stroke: a pilot study.

BACKGROUND Virtual-reality is increasingly used to improve rehabilitation outcomes. The Nintendo Wii offers an in-expensive alternative to more complex systems. OBJECTIVE To investigate the efficacy of Wii-based therapy for post-stroke rehabilitation. METHODS Seven patients (5 men, 2 women, aged 42-83 years; 1-38 months post-stroke, mean 15.3 months) and 5 healthy controls (3 men, 2 women, aged 41-71 years) undertook 1 h of therapy on 10 consecutive weekdays. Patients progressively increased home practice to 3 h per day. RESULTS Functional ability improved for every patient. The mean performance time significantly decreased per Wolf Motor Function Test task, from 3.2 to 2.8 s, and Fugl-Meyer Assessment scores increased from 42.3 to 47.3. Upper extremity range-of-motion increased by 20.1º and 14.33º for passive and active movements, respectively. Mean Motor Activity Log (Quality of Movement scale) scores increased from 63.2 to 87.5, reflecting a transfer of functional recovery to everyday activities. Balance and dexterity did not improve significantly. No significant change was seen in any of these measures for healthy controls, despite improved skill levels for Wii games. CONCLUSION An intensive 2-week protocol resulted in significant and clinically relevant improvements in functional motor ability post-stroke. These gains translated to improvement in activities of daily living.

Evidence for strong synaptic coupling between single tactile afferents and motoneurones supplying the human hand.

1 Electrical stimulation of digital nerves elicits short‐latency excitatory and inhibitory spinal reflex responses in ongoing EMG in muscles acting on the fingers and thumb. Similar responses are elicited by stimulating a population of muscle spindles but not when a single muscle spindle is activated. The current study investigated whether short‐latency EMG responses could be evoked from the discharge of a single cutaneous afferent. 2 Thirty‐three tactile afferents were recorded via tungsten microelectrodes in the median nerve of awake humans. Spike‐triggered averaging revealed EMG events time‐locked to the afferent discharge. The afferents were activated by an external probe and the EMG was elicited by a weak voluntary contraction. 3 Eleven cutaneous afferents (33 %) showed a short‐latency response in the ongoing EMG. Overt increases or decreases in EMG were observed for seven afferents (onset latency 20.0‐41.1 11hms1h). For four slowly adapting (SA) type II afferents, EMG showed a periodicity that was correlated to the afferent interspike interval (r= 0.99). 4 The EMG associated with two rapidly adapting (FA) type I afferents (29 %) showed a short‐latency excitation while five showed neither excitation nor inhibition. Seven SA II afferents (39 %) showed excitation and 11 no response; and none of the six SA I afferents showed any response. 5 We conclude that, unlike muscle spindle afferents, the input from a single cutaneous afferent is strong enough to drive, via interneurones, motoneurones supplying muscles acting on the digits. The potent short‐latency response we found supports the important role of cutaneous mechanoreceptors in fine motor control of the human hand.

Cortically evoked neural volleys to the human hand are increased during ischaemic block of the forearm

Reorganisation of the motor cortex may occur after limb amputation or spinal cord injury. In humans, transcranial magnetic stimulation (TMS) shows expansion of motor cortical representations of muscles proximal to the injury. Similarly, ischaemic block of the hand can increase acutely the representation of the biceps muscle, measured by increased biceps motor potentials evoked by TMS. It is thought that this increase occurs at the expense of the cortical representation of the paralysed and deafferented hand muscles but this has never been investigated. To study what changes occur in the cortical representation of the hand muscles during ischaemic block, a tungsten microelectrode was inserted into the ulnar or median nerve above the elbow and the size of the neural potential elicited by TMS in fascicles supplying the hand was measured in seven subjects. Prior to ischaemia, TMS evoked EMG responses in the intrinsic hand muscles. In the nerve, a brief motor potential preceded the response in the muscle and was followed by a contraction‐induced sensory potential. During 40 min of ischaemia produced by a blood pressure cuff inflated around the forearm to 210 mmHg, the EMG response to TMS and the sensory potential from the hand were progressively blocked. However, the motor neural evoked potential showed a significant increase in amplitude during the ischaemic period (30.5 %, P= 0.005). The increase in the neural potential suggests that output to the hand evoked from the cortex by TMS was not decreased by ischaemic block. Thus, we conclude that the increased response of biceps to TMS during distal ischaemia is not accompanied by a corresponding decrease in the motor cortical representation of the hand.

Changes in measures of motor axon excitability with age

OBJECTIVE Threshold tracking is a novel technique that permits examination of the excitability of human axons in vivo. Protocols have been validated for sensory and motor axons, but there are limited data on the changes in the excitability of motor axons with age. This study aimed to determine such changes from the third to the eighth decades. METHODS Sixty healthy subjects aged 22-79, 10 per decade, were studied using the TRONDXM4 protocol of the QTRAC threshold-tracking program to assess motor axon function. The median nerve was stimulated at the wrist and the compound muscle action potential was recorded from the thenar muscles. RESULTS There was an increase in threshold in elderly subjects, associated with a decrease in slope of the stimulus-response curves. Strength-duration time constant and threshold electrotonus to depolarising and hyperpolarising currents of up to 40% did not change significantly with aging. The current-threshold relationship was similar across all decades for subthreshold depolarising currents, but the slope of the current-threshold relationship was significantly steeper the older the subjects for hyperpolarising currents, particularly those greater than 40% of threshold. There was also a significant decrease in supernormality in the recovery cycle with increasing age. CONCLUSIONS The threshold of axons increases with age and the extent of supernormality decreases. There may also be greater inward rectification in motor axons, perhaps due to greater activity of I(H), the hyperpolarisation-activated conductance, though this is only significant with hyperpolarising currents greater than 40% of the threshold current. SIGNIFICANCE Many indices of axonal excitability, such as strength-duration time constant, the relative refractory period, late subnormality, threshold electrotonus and the depolarising side of the current-threshold relationship, do not change significantly with age. For other indices, age-related changes may be due to a combination of non-neural factors that alter current access to the node of Ranvier, changes in the axon and its myelination and, possibly, changes in channel activity and/or changes in extracellular [K(+)](o).

Modulation of ongoing EMG by different classes of low threshold mechanoreceptors in the human hand

1 We have previously demonstrated that the input from single FA I and SA II cutaneous mechanoreceptors in the glabrous skin of the human hand is sufficiently strong to modulate ongoing EMG of muscles acting on the digits. Some unresolved issues have now been addressed. 2 Single cutaneous (n= 60)), joint (n= 2)) and muscle spindle (n= 34)) afferents were recorded via tungsten microelectrodes inserted into the median and ulnar nerves at the wrist. Spike‐triggered averaging was used to investigate synaptic coupling between these afferents and muscles acting on the digits. The activity of 37% of FA I (7/19), 20% of FA II (1/5) and 52% of SA II afferents (11/21) evoked a reflex response. The discharge from muscle spindles, 15 SA I and two joint afferents did not modulate EMG activity. 3 Two types of reflex responses were encountered: a single excitatory response produced by irregularly firing afferents, or a cyclic modulation evoked by regularly discharging afferents. Rhythmic stimulation of one FA I afferent generated regularly occurring bursts which corresponded to the associated cyclic EMG response. 4 Selectively triggering from the first or last spike of each burst of one FA I afferent altered the averaged EMG profile, suggesting that afferent input modulates the associated EMG and not vice versa. 5 The discharge from single FA I, FA II and SA II afferents can modify ongoing voluntary EMG in muscles of the human hand, presumably via a spinally mediated oligosynaptic pathway. Conversely, we saw no evidence of such modulation by SA I, muscle spindle or joint afferents.

Selective Activation of Human Finger Muscles after Stroke or Amputation

Individuated finger movements of the human hand require selective activation of particular sets of muscles. Such selective activation is controlled primarily by the motor cortex via the corticospinal tract. Is this selectivity therefore lost when lesions damage the corticospinal tract? Or when the motor cortex reorganizes after amputation? We studied finger movements in normal human subjects and in patients who had recovered substantially from pure motor hemiparesis caused by lacunar strokes, which damage the corticospinal tract without affecting other pathways. Even after substantial recovery from these strokes, individuation of finger movements remained reduced-both for flexion/extension and for adduction/ abduction motion of the fingers. Stroke subjects regained the ability to move the instructed digit through a normal range, but unintentional motion of other digits was increased. This increase did not result from a change in the passive biomechanical coupling of the fingers. Rather, voluntary contractions of muscles that move the intended digit were accompanied by inappropriate contractions in muscles acting on additional digits. These observations suggest that the normal corticospinal system produces individuated finger movements not only by selectively activating certain muscles, but also by suppressing activation of other muscles during voluntary effort to move a given digit. In a separate experiment, reversible amputation of the hand was produced in normal subjects by ischemic nerve block at the wrist. Motor output to the intrinsic muscles and sensory input both become blocked under these conditions, effectively amputating the hand from the nervous system. But the long extrinsic muscles that flex and extend the digits remain normally innervated, and thus flexion forces still can be generated at the fingertips. During reversible amputation of the hand produced by ischemic nerve block, the ability of subjects to activate subdivisions of extrinsic muscles and to exert flexion force at individual fingertips continued to show essentially normal selectivity. Voluntary activation of the remaining muscles thus continues to be selective after amputation, in spite of both the loss of sensory input from the amputated hand, and reorganization within the primary motor cortex. During cortical reorganization after amputation, then, voluntary patterns of motor output intended for finger muscles may not be lost. We therefore examined activity in the stump muscles of above-elbow amputees, who have no remaining hand muscles. Different movements of the phantom hand were accompanied by different patterns of EMG in remaining proximal muscles, distinct from the EMG patterns associated with movement of the phantom elbow. We infer that voluntary motor output patterns that normally control finger movements after amputation may become diverted to remaining proximal muscles.

Comparison of contractile properties of single motor units in human intrinsic and extrinsic finger muscles

1 The purpose of the present study was to compare the contractile properties of single motor units in the intrinsic (short) and extrinsic (long) finger muscles in awake human subjects using intraneural motor axon stimulation. 2 Twitch properties were measured for 17 intrinsic and 11 extrinsic motor units by selective stimulation of a single motor axon in the ulnar or the median nerve. Force was measured from the appropriate digit, just distal to the muscles point of insertion and single unit EMG was recorded with surface electrodes. Force‐frequency relationships (2‐100 Hz) were established for 16 of these units (7 intrinsic, 9 extrinsic). Across the 16 motor units for which force‐frequency data were obtained, twitch contraction time (63.7 ± 6.0 ms, mean ±s.e.m.) was inversely correlated with the frequency required to generate half‐maximum tetanic force (12.0 ± 1.1 Hz). 3 We found no systematic differences between the contractile properties of intrinsic and extrinsic motor units. There was no evidence of a bimodal distribution into large/small or fast/slow units based on maximum force or contraction times, although both fast and slow motor units were encountered. 4 The peak slope of the sigmoidal force‐frequency relationship for intrinsic motor units (9.1 and 4.4‐12.9 mN Hz−1, median and interquartile range) was significantly higher than that for extrinsic motor units (2.9 and 2.3‐3.1 mN Hz−1; P= 0.028), i.e. greater force steps were produced by the intrinsic motor units for a given change in stimulation frequency. This difference suggests that motor units in the intrinsic muscles of the hand are more sensitive to modulating force output by changes in motoneurone firing rates than are those in the extrinsic muscles. This reflects the important role of the intrinsic hand muscles in the fine manipulation of objects.

The magnitude and rate of reduction in strength, dexterity and sensation in the human hand vary with ageing

Cutaneous sensation and motor performance of the hand decline with age. It is not known if motor performance declines are influenced by reductions in cutaneous sensation, or if motor performance deteriorates at a consistent rate across motor tasks. Handgrip strength, finger-tapping frequency and grooved-pegboard performance were assessed for both hands of 70 subjects (20-88 years), 10 per decade. Motor declines were compared to reductions in perceptual cutaneous sensation tested at 10 hand sites using calibrated von Frey filaments. Motor performance decreased with age for all motor tasks (p<0.001). Handgrip strength (mean±SEM) decreased from 42.6±9.5 kg (in the 30s), to 23.7±7.6 kg (80s) or 44%; finger-tapping frequency from 6.4±0.8 Hz to 4.2±0.9 Hz, 34%; and grooved-pegboard (median [IQR]) increased from 59 s [57-66 s] to 111.5 s [101-125 s], 47%. The onset of the deterioration in motor performance varied with sex and task. Cutaneous sensation also decreased with age, measured as increased von Frey thresholds of 0.04 g [0.02-0.07] to 0.16 g [0.04-0.4] (p<0.001) between the 20s and the 80s, or 73%. Cutaneous sensation varied with sex, side-tested and site. Reductions in grip-based tasks were associated with sensory declines in the palm, but elsewhere there was little correlation among motor tasks and cutaneous sensation in the hand. Grooved-pegboard performance was the best predictor of age-related declines in motor performance regardless of sex or side-tested. Our results suggest age-related declines in motor function cannot be inferred from, or provide information about, changes in cutaneous sensation.

Threshold behaviour of human axons explored using subthreshold perturbations to membrane potential.

The present study explores the threshold behaviour of human axons and the mechanisms contributing to this behaviour. The changes in excitability of cutaneous afferents in the median nerve at the wrist were recorded to a long‐lasting subthreshold conditioning stimulus, with a waveform designed to maximize the contribution of currents active in the just‐subthreshold region. The conditioning stimulus produced a decrease in threshold that developed over 3–5 ms following the end of the depolarization and then decayed slowly, in a pattern similar to the recovery of axonal excitability following a discharge. To ensure that the conditioning stimulus did not activate low‐threshold axons, similar recordings were then made from single motor axons in the ulnar nerve at the elbow. The findings were comparable, and behaviour with the same pattern and time course could be reproduced by subthreshold stimuli in a model of the human axon. In motor axons, subthreshold depolarizing stimuli, 1 ms long, produced a similar increase in excitability, but the late hyperpolarizing deflection was less prominent. This behaviour was again reproduced by the model axon and could be explained by the passive properties of the nodal membrane and conventional Na+ and K+ currents. The modelling studies emphasized the importance of leak current through the Barrett–Barrett resistance, even in the subthreshold region, and suggested a significant contribution of K+ currents to the threshold behaviour of axons. While the gating of slow K+ channels is slow, the resultant current may not be slow if there are substantial changes in membrane potential. By extrapolation, we suggest that, when human axons discharge, nodal slow K+ currents will be activated sufficiently early to contribute to the early changes in excitability following the action potential.

Two Common Tests of Dexterity Can Stratify Upper Limb Motor Function After Stroke

Background. Neurological deficits after a stroke are commonly classified according to motor function for clinical decision making regarding discharge and rehabilitation. Participants in clinical stroke studies are also stratified by motor function to avoid a sampling bias. Objective. This post hoc analysis examined a suite of upper limb functional assessment tools to test the hypothesis that motor function of survivors of stroke can be stratified using 2 simple tests of manual dexterity despite the heterogeneity of the population. Methods. The functional ability of the more affected hand and arm was assessed for 67 hemiparetic patients, aged 18 to 83 years (mean ± standard deviation, 59.8 ± 14.0 years), at 1 to 264 months after a stroke (23.6 ± 39.6 months) using the Wolf Motor Function Test (WMFT), upper limb motor Fugl-Meyer Assessment (F-M), Box and Block Test (BBT), grooved pegboard test, and wrist range of motion. We tested the strength of our proposed stratification scheme with a hypothesis-driven hierarchical cluster analysis using standardized raw scores and dichotomous BBT and grooved pegboard test values. Results. The most salient discriminator between low and higher motor function was the ability to move >1 block on the BBT. Within the higher function group, the ability to place all 25 pegs on the grooved pegboard test discriminated between moderate and high motor function. The derived scheme was congruent with clinical observations. The WMFT timed tasks, F-M scores, and range of motion did not discriminate functional groups. Conclusions. Two simple unambiguous and objective tests of gross (BBT) and fine (grooved pegboard test) manual dexterity discriminated 3 groups of motor function ability for a heterogeneous group of patients after stroke.