Alan Sunderland

fMRI signal decreases in ipsilateral primary motor cortex during unilateral hand movements are related to duration and side of movement.

Interactions between the primary motor cortices of each hemisphere during unilateral hand movements appear to be inhibitory, although there is evidence that the strengths of these interactions are asymmetrical. In the present study, functional magnetic resonance imaging (fMRI) was used to investigate the effects of motor task duration and hand used on unilateral movement-related BOLD signal increases and decreases in the hand region of primary motor cortex (M1) of each hemisphere in six right-handed volunteers. Significant task-related BOLD signal decreases were observed in ipsilateral M1 during single and brief bursts of unilateral movements for both hands. However, these negative-to-baseline responses were found to intensify with increasing movement duration in parallel with greater task-related increases in contralateral M1. Movement-related BOLD signal decreases in ipsilateral M1 were also stronger for the right, dominant hand than for the left hand in our right-handed subjects. These findings would be consistent with the existence of interhemispheric interactions between M1 of each hemisphere, whereby increased neuronal activation in M1 of one hemisphere induces reduced neuronal activity in M1 of the opposite hemisphere. The observation of a hemispheric asymmetry in inhibition between M1 of each hemisphere agrees well with previous neuroimaging and electrophysiological data. These findings are discussed in the context of current understanding of the physiological origins of negative-to-baseline BOLD responses.

Recovery of Ipsilateral Dexterity After Stroke

UNLABELLED BACKGROUND AND PURPOSE; Previous work indicated that patients within 1 month of parietal or posterior frontal damage are often abnormally slow or clumsy when using the ipsilateral hand for dexterity tasks. This article reports a 6-month follow-up study to assess recovery and the impact on functional outcome. METHODS Twenty-four patients (80%) were available for follow-up. They used the ipsilateral hand on a dexterity test that simulated everyday hand function. Weakness and ideomotor apraxia were also assessed. Performance was compared with that of healthy age-matched control subjects using the same hand. Rating scales for self-care and dexterity in everyday life were completed by patients and carers. RESULTS Significant recovery had occurred on all measures, but patients with left hemisphere damage remained impaired on the dexterity test, with 7 patients (58%) scoring below the normal range. Five of these were apraxic. Reports of everyday functioning did not reflect this impairment, but there were inconsistencies in these reports, which raised doubts as to their accuracy. CONCLUSIONS Ipsilateral dexterity shows recovery during the first 6 months, but there may be persistent impairment related to apraxia after left hemisphere stroke. It appears that the impact of this on functional outcome is typically small compared with the large effect of severity of contralateral paresis. It may be a significant factor in some cases, however, and direct observation of everyday functioning would be needed to clarify more subtle effects on outcome.

Neuroplasticity, learning and recovery after stroke: A critical evaluation of constraint-induced therapy

Constraint-induced movement therapy (CIMT) has been hailed as a radical new approach to stroke rehabilitation. The guiding theory is that impairment of hand function is exacerbated by learned non-use and that this in turn leads to a loss of cortical representation of the upper limb. It is claimed that these processes can be reversed by two weeks of constraint of the unaffected limb combined with intensive practice in use of the paretic hand, and numerous small-scale studies have suggested that CIMT can lead to large improvements in function more than a year after stroke. However, the theory of learned non-use is open to question and there is uncertainty about the nature of the improvements induced by CIMT. The greatest effect seems to be increased spontaneous use of the hand, either through reduction of learned non-use or by overcoming the sense of effort during movement. There is also evidence of some improvement on dexterity tests but no studies have analysed in detail whether this reflects reduction of basic motor impairment or learning of compensatory movement strategies. The current weight of evidence is in favour of compensatory learning. Cortical changes detected by transcranial magnetic stimulation (TMS) or functional imaging may reflect this compensatory motor skill learning rather than restoration of representations lost due to the infarct or non-use of the limb. If future studies confirm this then the clinical implication is that direct teaching of unimanual or bimanual compensatory strategies might be a more productive approach than constraint.

A Pilot Study of Event-Related Functional Magnetic Resonance Imaging of Monitored Wrist Movements in Patients With Partial Recovery

Background and Purpose— Previous functional imaging studies of motor recovery after stroke have investigated cerebral activation during periods of repetitive, often complex, movement. This article reports the use of an event-related approach to study activation associated with isolated simple movements (wrist extension). This allows investigation of the pattern of the motor response and corresponding brain activation on a trial-by-trial basis. Patients with partial recovery can be assessed, and allowance can be made for abnormalities in the shape of hemodynamic responses. Methods— Functional MRI at 3 T was performed during a series of isolated, near-isometric wrist extension movements. A visual tracking procedure was used to elicit forces of 10% and 20% of maximum voluntary contraction. Force output from both wrists was monitored continuously. A voxel-wise procedure was used to fit the optimum hemodynamic response functions in each case. Results— Three chronic stage patients with partial recovery were successfully scanned and compared with 8 healthy controls. The patients showed well-lateralized motor responses but inaccurate control of force. During movement of the paretic wrist, we observed excessive activation of the ipsilateral primary motor cortex and increased relative activation of the supplementary motor area compared with movement of the nonparetic side. In the primary motor area, hemodynamic responses peaked more quickly on the ipsilateral side in 2 patients for movements of the paretic hand, whereas controls showed the opposite trend. Conclusions— An event-related approach can be used to study the relationship between motor responses and cerebral activation in patients with partial recovery. These preliminary findings suggest that excessive activation in ipsilateral motor cortex and secondary motor areas remains evident under these tightly controlled conditions and cannot be ascribed to mirror movements or abnormalities in the timing of the blood oxygen level–dependent (BOLD) response. However, close monitoring of motor responses also makes evident continuing impairment in motor skill, which makes comparison with activation in normal controls difficult.

Effects of Conventional Physical Therapy and Functional Strength Training on Upper Limb Motor Recovery After Stroke: A Randomized Phase II Study

Background. Functional training and muscle strength training may improve upper limb motor recovery after stroke. Combining these as functional strength training (FST) might enhance the benefit, but it is unclear whether this is better than conventional physical therapy (CPT). Comparing FST with CPT is not straightforward. Objective. This study aimed at assessing the feasibility of conducting a phase III trial comparing CPT with FST for upper limb recovery. Methods. Randomized, observer-blind, phase II trial. Subjects had upper limb weakness within 3 months of anterior circulation infarction. Subjects were randomized to CPT (no extra therapy), CPT + CPT, and CPT + FST. Intervention lasted 6 weeks. Primary outcome measure was the Action Research Arm Test (ARAT). Measurements were taken before treatment began, after 6 weeks of intervention, and 12 weeks thereafter. Attrition rate was calculated and differences between groups were interpreted using descriptive statistics. ARAT data were used to inform a power calculation. Results. Thirty subjects were recruited (8% of people screened). Attrition rate was 6.7% at outcome and 40% at follow-up. At outcome the CPT + FST group showed the largest increase in ARAT score and this was above the clinically important level of 5.7 points. Median (interquartile range) increases were 11.5 (21.0) for CPT; 8.0 (13.3) for CPT + CPT; and 19.5 (22.0) for CPT + FST. The estimated sample size for an adequately powered subsequent phase III trial was 279 subjects at outcome. Conclusion. Further work toward a phase III clinical trial appears justifiable.

Ideomotor apraxia and functional ability.

The impact of ideomotor apraxia (IMA) on functional ability has been a relatively neglected topic in research. This has been due to the continued focus on performance on gesture imitation and pantomime of tool-use, together with widespread acceptance of anecdotal evidence that IMA has no effect when directly manipulating objects. An increasing number of studies have shown that IMA does in fact result in increased clumsiness when handling objects and may contribute to disability in everyday life. However the effect seems relatively mild compared to the stark abnormalities on gesture imitation and pantomime. The conventional explanation for this is that the cues provided by naturalistic contexts improve retrieval of action representations, but an alternative account concerns task-specific cognitive demands. Performance on simple prehensile tasks can be successfully guided by physical affordances whereas motor tasks may be failed if they require the support of memory or problem solving ability. A central deficit in IMA may be impaired postural representation causing inability to solve the problem of how to manipulate objects where neither affordance nor memory can dictate action. However, this account still fails to explain fully the patterns of error seen on complex naturalistic tasks such as dressing. Future research needs to further our understanding of how IMA maps on to disability, which will have implications for theory building and for therapeutic intervention.

Validity of a Virtual Environment for Stroke Rehabilitation

Background and Purpose— Virtual environments for use in stroke rehabilitation are in development, but there has been little evaluation of their suitability for this purpose. We evaluated a virtual environment developed for the rehabilitation of the task of making a hot drink. Methods— Fifty stroke patients undergoing rehabilitation in a UK hospital stroke unit were involved. The performance of stroke rehabilitation patients when making a hot drink had the neurological impairments associated with performance of this task, and the errors observed were compared for standardized task performance in the real world and in a virtual environment. Neurological impairments were measured using standardized assessments. Errors in task performance were assessed rating video recordings and classified into error types. Results— Real-world and virtual environment performance scores were not strongly associated (&rgr;=0.30; P<0.05). Performance scores in both settings were associated with age, Barthel ADL score, Mini Mental State Examination score, and tests of visuospatial function. Real-world performance only was associated with arm function and sequencing ability. Virtual environment performance only was associated with language function and praxis. Participants made different errors during task performance in the real world and in the virtual environment. Conclusions— Although this virtual environment was usable by stroke rehabilitation patients, it posed a different rehabilitation challenge from the task it was intended to simulate, and so it might not be as effective as intended as a rehabilitation tool. Other virtual environments for stroke rehabilitation in development require similar evaluation.

Ideomotor apraxia, visuomotor control and the explicit representation of posture.

Ideomotor apraxia is normally viewed as a disorder of the representation or execution of action. However, the evidence from gesture imitation is that apraxic patients are unable to reproduce the final posture of a gesture but may not show abnormality in movement kinematics. This supports a hypothesis that impaired gesture imitation is due to a deficit in a conceptual representation of body posture rather than indicating a disorder specific to action control. The present study evaluated whether other aspects of apraxic behaviour might also be most consistent with a deficit in the representation of posture. Patients with left hemisphere damage and apraxia on gesture imitation had difficulty in reproducing a series of actions due to failure to adopt the required configuration of the hand whereas there was no consistent reduction in speed of response once the actions had been learned. They also tended to use an abnormal, clumsy grasp when using a spoon but this dissociated from accurate performance on other tests of manual dexterity where there was less scope for variation in configuration of the hand. These data suggest that the most common deficit in ideomotor apraxia is impaired ability to perform tasks where the goal is to reproduce or adopt complex hand configurations and that impaired execution of some types of action is secondary to this problem. This is consistent with a role for the human left parietal lobe in providing an explicit representation of posture which is used to guide some actions and to supplement a more primitive system of direct visuomotor control.

Action errors and dressing disability after stroke: An ecological approach to neuropsychological assessment and intervention

A combination of detailed observation of dressing behaviour and neuropsychological assessment was used to identify the cognitive barriers to independent dressing in a series of eight stroke patients. For those with right hemisphere damage, dressing was disrupted by visuospatial problems or poor sustained attention. Those with left hemisphere damage and ideomotor apraxia were unable to learn the correct procedure to compensate for hemiparesis when dressing. The value of a therapeutic approach based on these observations was assessed in a single-blind randomised multiple-baseline experiment. A baseline phase of conventional dressing therapy which takes no account of individual patterns of cognitive impairment was contrasted with an approach which was formulated for each case. A permutation test demonstrated that there was a significant treatment effect for the right hemisphere cases but there was no therapy-related improvement for those with left or bilateral damage and apraxia. Observation of a naturalistic but controlled task (dressing with a standard item of clothing) appears to allow greater insight into the impact of specific neuropsychological deficits than has been found for more complex naturalistic tasks. The benefits of this ecological approach over conventional approaches to dressing therapy need to be evaluated further in a randomised clinical trial.

Cerebral activation during a simple force production task: changes in the time course of the haemodynamic response.

An event-related paradigm was used to investigate the fMRI signal from the primary motor cortex (M1) and the supplementary motor area (SMA) during isolated isometric wrist extension at five different force levels. There was only a weak trend towards increased area of activation with increased force output, but there was a force-related increase in percentage change of signal within voxels in M1 (Kendall Tc = 0.48, p < 0.01), which may indicate control of force output by variation of neural firing rate. In SMA there was a correlation between peak force output and time-to-peak of the haemodynamic response in SMA (Kendall Tc = 0.74, p < 0.0001). This unexpected finding of a task-related change in the shape of the haemodynamic response within a single brain area requires further investigation. It may indicate a slower rise time at lower perfusion rates, or may be the result of inhibitory processes in motor control.