Jeffery J. Summers

Ability to modulate walking cadence remains intact in Parkinson's disease.

Gait hypokinesia (slowness) is a characteristic feature of Parkinsons disease. It is not clear, however, whether the slowness is due to a problem in regulation of the timing of consecutive steps or the control of stride size. Examination of cadence control for slow to medium walking speeds has shown an increase in step frequency that was a compensation for reduced stride length. In this investigation the ability of Parkinsonian patients to modulate their cadence (steps per minute) at the fast walking speeds exhibited by age and height matched controls was examined. The findings indicated that cadence control remains unaffected throughout its entire range in Parkinsons disease and that gait hypokinesia is directly attributable to an inability to internally generate sufficiently large steps.

On the selection of signals

In a previous paper, it was argued that alertness, selectivity (set), and processing capacity (consciousness) could be identified and studied as separate components of attention. The current paper develops this theme by showing that alertness does not affect the buildup of information within the memory system but only the rate at which a later system responds to that information. Thus, in standard reaction-time tasks, increased alertness produces a reduction in reaction ’time but no decrease in errors. In contrast, providing a model of the signal the S is to process improved both speed and accuracy. The,. presence of a model of what the S is to process varies the vertex neural response to that specific signal as compared to a mismatching signal in the first 200–300 msec after its presentation. Three accounts of this effect are: speeded processing of a matching stimulus, habituation of the electrical response to a matching stimulus, and prolonged or enhanced processing of a mismatch. Evidence favors the first of these explanations, but the other two cannot be dismissed as possible contributors to this effect.

Bilateral movement training and stroke rehabilitation: A systematic review and meta-analysis

OBJECTIVE AND DESIGN Bilateral movement training is being increasingly used as a post-stroke motor rehabilitation protocol. The contemporary emphasis on evidence-based medicine warrants a prospective meta-analysis to determine the overall effectiveness of rehabilitating with bilateral movements. METHODS After searching reference lists of bilateral motor recovery articles as well as PubMed and Cochrane databases, 11 stroke rehabilitation studies qualified for this systematic review. An essential requirement for inclusion was that the bilateral training protocols involved either functional tasks or repetitive arm movements. Each study had one of three common arm and hand functional outcome measures: Fugl-Meyer, Box and Block, and kinematic performance. RESULTS The fixed effects model primary meta-analysis revealed an overall effect size (ES=0.732, S.D.=0.13). These findings indicate that bilateral movement training was beneficial for improving motor recovery post-stroke. Moreover, a fail-safe analysis indicated that 48 null effects would be necessary to lower the mean effect size to an insignificant level. CONCLUSION These meta-analysis findings indicate that bilateral movements alone or in combination with auxiliary sensory feedback are effective stroke rehabilitation protocols during the sub-acute and chronic phases of recovery.

The Structure of Motor Programs

Publisher Summary This chapter focuses on the memorial representation of sequencing. The movements anticipate or coincide with the events in the environment that they are intended to deal with, and they appear coordinated with each other. In other words, the sequence of movements becomes stored in the memory system so that it can be executed without constant correction by reference to the environment. The chapter reviews the nature of the memory structure that underlies skill. Some evidence is described that led to a particular theory of sequence representation, namely, motor program theory. Essentially motor program theory posits that the sequencing of a skill is represented centrally and does not require peripheral feedback from prior movements to elicit succeeding movements. Evidence for motor programs in humans is less adequate than for animals because of the difficulty of manipulating kinesthetic sensations without permanent neural damage. An approach for studying kinesthetic loss in humans is to observe people who have had dorsal roots cut to control pain or relieve spasticity.

Bilateral and unilateral movement training on upper limb function in chronic stroke patients: A TMS study

The use of activity-dependent interventions has shown some success in promoting recovery of upper limb function in chronic stroke patients. This study compared the neurophysiological and behavioural changes associated with two such rehabilitation protocols: unilateral and bilateral movement training. Twelve chronic stroke patients were randomly assigned to the two training protocols involving six daily practice sessions. Each session consisted of 50 trials of a dowel placement task performed either with both impaired and unimpaired arm moving synchronously (bilateral training group) or with only the impaired arm moving (unilateral training). Kinematic measurements of upper limb movements were made in four unilateral test trials performed prior to and following each practice session. Functional assessments of the impaired upper limb and neurophysiological assessments, using transcranial magnetic stimulation (TMS), of the affected and non-affected cortical hemispheres were made prior to and following the intervention sessions. Individuals receiving bilateral training showed a reduction in movement time of the impaired limb and increased upper limb functional ability compared to individuals receiving unilateral training. In some patients changes to upper limb function were associated with changes to the cortical representation of a target muscle in the non-affected hemisphere. Overall, these findings suggest that a short-term bilateral training intervention may be effective in facilitating upper limb motor function in chronic stroke patients.

Bilateral movement training and stroke motor recovery progress: a structured review and meta-analysis.

The purpose was to conduct a structured review and meta-analysis to determine the cumulative effect of bilateral arm training on motor capabilities post stroke. Forty-eight stroke studies were selected from three databases with 25 comparisons qualifying for inclusion in our meta-analysis. We identified and coded four types of bilateral arm interventions with 366 stroke patients. A random effects model using the standardized mean difference technique determined a large and significant effect size (0.734; SE=0.125), high fail-safe N (532), and medium variability in the studies (I(2)=63%). Moderator variable analysis on the type of bilateral training revealed two large and significant effects: (a) BATRAC (0.842; SE=0.155) and (b) coupled bilateral and EMG-triggered neuromuscular stimulation (1.142; SE=0.176). These novel findings provide strong evidence supporting bilateral arm training with the caveat that two coupled protocols, rhythmic alternating movements and active stimulation, are most effective.

The Dynamics of Bimanual Circle Drawing

A bimanual circle drawing task was employed to elucidate the dynamics of intralimb and interlimb coordination. Right-handed subjects were required to produce circles with both hands in either a symmetrical (mirror) mode (i.e. one hand moving clockwise, the other counter-clockwise) or in an asymmetrical mode (i.e. both hands moving clockwise or counter-clockwise). The frequency of movement was scaled by an auditory metronome from 1.50 Hz to 3.25 Hz in8 (8-sec) steps. In the asymmetrical mode, distortions ofthe movement trajectories, transient departures from the target pattern of coordination, and phase wandering were evident as movement frequency was increased. These features suggested loss of stability. Deviations from circular trajectories were most prominent for movements of the left hand. Transient departures from the required mode of coordination were also largely precipitated by the left hand. The results are discussed with reference to manual asymmetries and mechanisms of interlimb and intersegmental coordination.

Mirror movements in normal adult subjects

Intensity of mirror movements occurring under specific task conditions in normal adults was investigated using a finger flexion task. Subjects were asked to sustain target pressures using different fingers. Greater pressures of mirror movement were recorded when the weaker, small finger of either hand performed the task. The target pressure which subjects were asked to sustain did not influence the amount of mirror movement exhibited by either males or females, even though higher target forces required a significantly greater percentage of total finger strength. On average, males exhibited the same quantity of mirror movements as female subjects, despite the force requirements of the task representing for them a significantly smaller percentage of total finger strength. Moreover, when the right hand performed the experimental tasks, less mirror movement was exhibited than when the left hand was active. Thus, the left hand showed stronger mirror movements. The findings were consistent with previous research using children as subjects, although the nonsignificant effects of gender and pressure were unexpected and need to be examined further. It appears that, while the force requirement of the task does influence the magnitude of mirror movement, it is not the principle determinant.

Production of polyrhythms.

Previous research has shown that there are strong constraints on the concurrent performance of nonharmonically related motor sequences such as polyrhythms. A model of polyrhythm production is proposed that involves a hierarchical timing system. The model assumes a single mechanism (a counter) for the timing and serial ordering of responses. Predictions derived from the model were tested in an experiment in which skilled (musically trained) and unskilled Ss attempted to reproduce polyrhythms of varying complexity. The results agreed with the models predictions and showed that Ss adopted a hierarchical form of integrated motor organization in which movements of the slow hand were subordinate to movements of the fast hand. This strategy was consistent across S groups, polyrhythms, and hand arrangements.

Simulating a neural cross-talk model for between-hand interference during bimanual circle drawing.

Abstract. Studies on drawing circles with both hands in the horizontal plane have shown that this task is easy to perform across a wide range of movement frequencies under the symmetrical mode of coordination, whereas under the asymmetrical mode (both limbs moving clockwise or counterclockwise) increases in movement frequency have a disruptive effect on trajectory control and hand coordination. To account for these interference effects, we propose a simplified computer model for bimanual circle drawing based on the assumptions that (1) circular trajectories are generated from two orthogonal oscillations coupled with a phase delay, (2) the trajectories are organized on two levels, “intention” and “motor execution”, and (3) the motor systems controlling each hand are prone to neural cross-talk. The neural cross-talk consists in dispatching some fraction of any force command sent to one limb as a mirror image to the other limb. Assuming predominating coupling influences from the dominant to the nondominant limb, the simulations successfully reproduced the main characteristics of performance during asymmetrical bimanual circle drawing with increasing movement frequencies, including disruption of the circular form drawn with the nondominant hand, increasing dephasing of the hand movements, increasing variability of the phase difference, and occasional reversals of the movement direction in the nondominant limb. The implications of these results for current theories of bimanual coordination are discussed.