Mirror Symmetric Bimanual Movement Priming Can Increase Corticomotor Excitability and Enhance Motor Learning

Repetitive mirror symmetric bilateral upper limb may be a suitable priming technique for upper limb rehabilitation after stroke. Here we demonstrate neurophysiological and behavioural after-effects in healthy participants after priming with 20 minutes of repetitive active-passive bimanual wrist flexion and extension in a mirror symmetric pattern with respect to the body midline (MIR) compared to an control priming condition with alternating flexion-extension (ALT). Transcranial magnetic stimulation (TMS) indicated that corticomotor excitability (CME) of the passive hemisphere remained elevated compared to baseline for at least 30 minutes after MIR but not ALT, evidenced by an increase in the size of motor evoked potentials in ECR and FCR. Short and long-latency intracortical inhibition (SICI, LICI), short afferent inhibition (SAI) and interhemispheric inhibition (IHI) were also examined using pairs of stimuli. LICI differed between patterns, with less LICI after MIR compared with ALT, and an effect of pattern on IHI, with reduced IHI in passive FCR 15 minutes after MIR compared with ALT and baseline. There was no effect of pattern on SAI or FCR H-reflex. Similarly, SICI remained unchanged after 20 minutes of MIR. We then had participants complete a timed manual dexterity motor learning task with the passive hand during, immediately after, and 24 hours after MIR or control priming. The rate of task completion was faster with MIR priming compared to control conditions. Finally, ECR and FCR MEPs were examined within a pre-movement facilitation paradigm of wrist extension before and after MIR. ECR, but not FCR, MEPs were consistently facilitated before and after MIR, demonstrating no degradation of selective muscle activation. In summary, mirror symmetric active-passive bimanual movement increases CME and can enhance motor learning without degradation of muscle selectivity. These findings rationalise the use of mirror symmetric bimanual movement as a priming modality in post-stroke upper limb rehabilitation

Influence of combined afferent stimulation and task-specific training following stroke: A pilot randomized controlled trial

© 2007 American Society of NeurorehabilitationBackground. Reorganization of the human motor cortex can be induced by specific patterns of peripheral afferent stimulation. The potential for afferent stimulation to facilitate the functional recovery associated with conventional rehabilitative techniques has not previously been investigated. Objective. The authors sought to determine whether combining appropriate afferent stimulation with task-specific training resulted in greater improvements than training alone in patients with impaired upper limb function in the subacute phase following stroke. Method. Twenty patients with hemiparesis due to stroke were allocated randomly to either a stimulation or control group. All received 9 sessions of task-specific physiotherapy training over 3 weeks. Prior to each training session, associative electrical stimulation of the motor point of 2 hand muscles was given in the stimulation group, whereas the control group received sham stimulation. Changes in dexterity were assessed using a grip-lift task, and standard measures of upper-limb function were made before and following the intervention. Corticospinal excitability was examined using transcranial magnetic stimulation. Results. Both groups showed comparable improvements in functional measures of upper-limb function. Of the 20 patients, only 14 could perform the grip-lift task, which is an objective measure of dexterity. Patients in the stimulation group From the Research Centre for Human Movement Control, School of exhibited significantly greater improvements in this task than the control group. There was no significant change in corticospinal excitability in either group. Conclusion. This pilot study provides preliminary data suggesting that targeted afferent stimulation may facilitate the response to conventional rehabilitation in patients with hemiparesis due to stroke, but these results need to be confirmed in a larger scale study.Michelle N. McDonnell, Susan L. Hillier, Timothy S. Miles, Philip D. Thompson, and Michael C. Riddin

The influence of correlated afferent input on motor cortical representations in humans

Animal models reveal that correlated afferent inputs are a powerful driver of sensorimotor cortex reorganisation. Recently we developed a stimulation paradigm, which evokes convergent afferent input from two hand muscles and induces reorganisation within human motor cortex. Here we investigated whether this reorganisation is characterised by expansion and greater overlap of muscle representation zones, as reported in animal models. Using transcranial magnetic stimulation, we mapped the motor representation of the right first dorsal interosseous (FDI), abductor digiti minimi (ADM) and abductor pollicis brevis (APB) in 24 healthy subjects before and after 1 h of (1) associative stimulation to FDI and ADM motor points, (2) associative stimulation to digits II and V (3) a control condition employing non-correlated stimulation of FDI and ADM motor points. Motor point associative stimulation induced a significant increase in the number of active sites in all three muscles and volume in FDI and ADM. Additionally, the centre of gravity of the FDI and ADM maps shifted closer together. Similar changes were not observed following digital associative stimulation or motor point non-associative stimulation. These novel findings provide evidence that convergent input induces reorganisation of the human motor cortex characterised by expansion and greater overlap of representational zones.S. M. Schabrun and M. C. Riddin

Corticospinal responses to sustained locomotor exercises: moving beyond single-joint studies of central fatigue

There is substantial evidence that fatiguing exercise is accompanied by changes within the central nervous system that reduce the force that can be produced by working muscles. Here we review studies that used non-invasive neurophysiological techniques to show that sustained single-joint contractions have the capacity to increase corticospinal responsiveness and reduce motoneuronal responsiveness. We contrast these findings with new evidence from our laboratory regarding corticospinal responsiveness during sustained cycling exercise. There seems to be a similar increase in responsiveness of the intracortical inhibitory interneurons during sustained locomotor and single-joint exercise which might be due to acute exercise responses that are common to fatiguing exercise of any nature, such as local accumulation of fatigue metabolites. In contrast, the pattern of changes in corticospinal responsiveness is fundamentally different between the two modes of exercise which might be due to greater systemic fatigue responses to locomotor exercises