Biomedical subjects

Winston D Byblow

Publications and source records attributed to Winston D Byblow.

At least 19 recordsLinked to original sources

PubMed2007

Functional potential in chronic stroke patients depends on corticospinal tract integrity.

Determining whether a person with stroke has reached their full potential for recovery is difficult. While techniques such as transcranial magnetic stimulation (TMS) and MRI have some prognostic value, their role in rehabilitation is undefined. This study used TMS and MRI to determine which factors predict functional potential, defined as an individual's capacity for further functional improvement at least 6 months following stroke. We studied 21 chronic stroke patients with upper limb impairment. The functional integrity of the corticospinal tracts (CSTs) was assessed using TMS and functional MRI. The presence or absence of motor-evoked responses (MEPs) to TMS in the affected upper limb, and the lateralization of cortical activity during affected hand use were determined. The structural integrity of the CST was assessed using MRI, and diffusion tensor imaging was used to measure the asymmetry in fractional anisotropy (FA) of the internal capsules. A multiple linear regression analysis was performed, to predict both clinical score at inception and change in clinical score for 17 patients who completed a 30 day programme of motor practice with the affected upper limb. The main findings were that in patients with MEPs, meaningful gains were still possible 3 years after stroke, although the capacity for improvement declined with time. In patients without MEPs, functional potential declines with increasing CST disruption, with no meaningful gains possible if FA asymmetry exceeds a value of 0.25. This study is the first to demonstrate the complementary nature of TMS and MRI techniques in predicting functional potential in chronic stroke patients. An algorithm is proposed for the selection of individualized rehabilitation strategies, based on the prediction of functional potential. These strategies could include neuromodulation using a range of emerging techniques, to prime the motor system for a plastic response to rehabilitation.

Adult↗

PubMed2006

Decreased desychronisation during self-paced movements in frequency bands involving sensorimotor integration and motor functioning in Parkinson's disease.

This study examined sensorimotor integration and motor functioning in seven patients with Parkinson's disease (PD) who had mild symptoms, and seven age-matched controls. Neuro-oscillations were recorded by high-density 128-channel electroencephalography (EEG). Participants were required to perform two tasks: simple tapping of the index finger and thumb and a complex Luria finger apposition task. Both tasks were performed unimanually and bimanually. There were no significant group differences in the task-related power (TRPow) within alpha 1 (mu1) or in beta 1 frequencies (beta1). In contrast, there were significant group differences in the alpha 2 (mu2) and beta 2 frequencies (beta2). Patients had less desychronisation than controls at the electrodes covering the central regions of the scalp. Alpha 2 and beta 2 frequencies have been associated with task-specific sensorimotor integration and motor function, respectively. This activity difference in patients with Parkinson's disease may be due to deficits in sensorimotor integration.

Aged↗

PubMed2006

Kinesthetic but not visual imagery assists in normalizing the CNV in Parkinson's disease.

OBJECTIVE: This study investigated whether kinesthetic and/or visual imagery could alter the contingent negative variation (CNV) for patients with Parkinson's disease (PD). METHODS: The CNV was recorded in six patients with PD and seven controls before and after a 10min block of imagery. There were two types of imagery employed: kinesthetic and visual, which were evaluated on separate days. RESULTS: The global field power (GFP) of the late CNV did not change after the visual imagery for either group, nor was there a significant difference between the groups. In contrast, kinesthetic imagery resulted in significant group differences pre-, versus post-imagery GFPs, which was not present prior to performing the kinesthetic imagery task. In patients with PD, the CNV amplitudes post-, relative to pre-kinesthetic imagery, increased over the dorsolateral prefrontal regions and decreased in the ipsilateral parietal regions. There were no such changes in controls. CONCLUSIONS: A 10-min session of kinesthetic imagery enhanced the GFP amplitude of the late CNV for patients but not for controls. SIGNIFICANCE: While the study needs to be replicated with a greater number of participants, the results suggest that kinesthetic imagery may be a promising tool for investigations into motor changes, and may potentially be employed therapeutically, in patients with Parkinson's disease.

Aged↗

PubMed2006

Lateralization of unimanual and bimanual motor imagery.

Most studies of motor imagery have examined motor cortex function during imagery of dominant hand movement. The aim of this study was to examine the modulation of excitability in the dominant and non-dominant corticomotor pathways during kinesthetic motor imagery of unimanual and bimanual movement. Transcranial magnetic stimulation (TMS) was applied over the contralateral motor cortex (M1) to elicit motor-evoked potentials (MEPs) in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles of each hand, in two separate sessions. Transcutaneous electrical stimuli were also delivered to the median nerve at each wrist, to elicit F-waves from APB. Fifteen right-handed volunteers imagined unimanual and bimanual phasic thumb movements, paced with a 1-Hz auditory metronome. Stimuli were delivered at rest, and either 50 ms before (ON phase), or 450 ms after (OFF phase), the metronome beeps. Significant MEP amplitude facilitation occurred only in right APB, during the ON phase of motor imagery of the right hand and both hands. Significant temporal modulation of right APB MEP amplitude was observed during motor imagery of right, left and bimanual performance. F-wave persistence and amplitude were unaffected by imagery. These results demonstrate that the motor imagery is lateralized to the left (dominant) hemisphere, which is engaged by imagery of each hand separately, and bimanual imagery. This finding has implications for the use of motor imagery in rehabilitation.

Adult↗

PubMed2006

Intracortical inhibition during volitional inhibition of prepared action.

Volitional inhibition is the voluntary prevention of a prepared movement. Here we ask whether primary motor cortex (M1) is a site of convergence of cortical activity associated with movement preparation and volitional inhibition. Volitional inhibition was studied by presenting a stop signal before execution of an anticipated response that requires a key lift to intercept a revolving dial. Motor evoked potentials (MEPs) were elicited in intrinsic hand muscles by transcranial magnetic stimulation (TMS) to assess corticomotor excitability and short interval intracortical inhibition (sICI) during task performance. The closer the stop cue was presented to the anticipated response, the harder it was for subjects to inhibit their response. Corticomotor pathway excitability was temporally modulated during volitional inhibition. Using subthreshold TMS, corticomotor excitability was reduced for Stop trials relative to Go trials from 140 ms after the cue. sICI was significantly greater for Stop trials compared with Go trials at a time that preceded the onset of muscle activity associated with the anticipated response. These results provide evidence that volitional inhibition is exerted at a cortical level and that inhibitory networks within M1 contribute to volitional inhibition of prepared action.

Adult↗

PubMed2006

Corticomotor excitability during a choice-hand reaction time task.

Fourteen neurologically healthy, right-handed subjects performed a choice-hand reaction time (RT) task, which involved wrist flexion or extension of either the left or right hand to one of three fixed target locations corresponding to 45 degrees flexion, 20 degrees flexion, or 20 degrees extension from the starting position. In each trial, a pre-cue provided information regarding the forthcoming target location. The hand was specified by the imperative signal. Focal transcranial magnetic stimulation (TMS) was delivered over the hand motor area of either the right or left hemisphere at set times during the foreperiod, and at random intervals during the RT interval defined by electromyography onset. As expected, an increase in corticomotor excitability was observed in the agonist of the responding hand over the RT interval. When the cue appeared at a location that required flexion with either hand, an increase in excitability was observed following stimulation over the hemisphere ipsilateral to the responding hand, indicating activation of the homologous muscle. However, when the cue appeared at a location at which the response would require flexion with one hand and extension with the other, the modulation of excitability was also based on the direction of the response. This direction-specific effect was only observed for TMS delivered to the left hemisphere during the left-hand movement, and suggested goal-based preparation in the left hemisphere independent of whether the actual movement is made with the right or left hand. These results indicate that both the homologous-muscle and the directional-specific constraints affect the corticomotor excitability of the non-responding hand.

Adult↗

PubMed2006

The yips in golf: multimodal evidence for two subtypes.

PURPOSE: To determine whether a model of two subtypes of yips is supported by evidence from a range of physiological, behavioral, and psychological measures. METHODS: Fifteen golfers who experience yips symptoms while putting (mean age 58.1 yr, SD 13.6 yr), and nine golfers with no yips symptoms (mean age 39.6 yr, SD 19.3 yr) were recruited. Participants completed a golf history questionnaire to determine their playing experience and the nature of any yips symptoms experienced. In experiment 1, participants performed a putting task while electromyographic data were recorded from the forearm flexors and extensors and biceps brachii, bilaterally. The task was performed in two sessions, under low-pressure and high-pressure experimental conditions. The high-pressure condition was intended to increase anxiety through the use of a monetary incentive, video-taping of performance, and the presence of a confederate who provided negative feedback. Participants' state of anxiety was assessed using a questionnaire before each of the experimental sessions. In experiment 2, participants completed a task that required the inhibition of an anticipated response. Their accuracy and ability to inhibit their response was determined. RESULTS: The golfers who experienced yips could be categorized according to whether they reported mainly movement-related symptoms (Type I) or anxiety-related symptoms (Type II). The Type I group exhibited greater muscle activity during putting and greater errors and less inhibition of the anticipated response task. The Type II group exhibited greater changes in cognitive anxiety and normal performance of the anticipated response task. CONCLUSION: This study provides evidence in support of two yips subtypes. Type I is related to impaired movement initiation and execution, whereas Type II is related to performance anxiety.

Adolescent↗

PubMed2005

Modulation of short-latency intracortical inhibition in human primary motor cortex during synchronised versus syncopated finger movements.

Rhythmic movements are inherently more stable and easier to perform when they are synchronised with a periodic stimulus, as opposed to syncopated between the beats of a pacing stimulus. Although this behavioural phenomenon is well documented, its neurophysiological basis is poorly understood. In a first experiment, we demonstrated that all healthy subjects (N=8) performing index finger abduction in time with an auditory metronome exhibited transitions from syncopation to synchronisation when the metronome tempo was scaled from 0.8 to 2.0 Hz. Subjects' mean transition frequency was 1.7+/-0.2 Hz. In a second experiment, we used paired-pulse transcranial magnetic stimulation to examine short-latency intracortical inhibition (sICI) directed towards the first dorsal interosseous (FDI) muscle in healthy subjects (N=9) who made synchronised and syncopated phasic finger movements in time with metronome pacing of 1.0 Hz. Despite the equivalence between the patterns in terms of task performance and corticospinal excitability of FDI at this movement frequency, there was significantly greater sICI during syncopation than during synchronisation. From this result, we infer that the stability of movement patterns may be contingent upon excitability of inhibitory networks within primary motor cortex.

Adult↗

PubMed2005

Kinesthetic, but not visual, motor imagery modulates corticomotor excitability.

The hypothesis that motor imagery and actual movement involve overlapping neural structures in the central nervous system is supported by multiple lines of evidence. The aim of this study was to examine the modulation of corticomotor excitability during two types of strategies for motor imagery: Kinesthetic Motor Imagery (KMI) and Visual Motor Imagery (VMI) in a phasic thumb movement task. Transcranial magnetic stimulation (TMS) was applied over the contralateral motor cortex (M1) to elicit motor evoked potentials (MEPs) in the dominant abductor pollicis brevis (APB) and abductor digiti minimi (ADM). In a separate experiment, transcutaneous electrical stimuli were delivered to the median nerve at the dominant wrist, to elicit F-waves from APB. Imagined task performance was paced with a 1 Hz auditory metronome, and stimuli were delivered either 50 ms before (ON phase), or 450 ms after (OFF phase), the metronome beeps. Recordings were also made during two control conditions: Rest, and a Visual Static Imagery (VSI) condition. Significant MEP amplitude facilitation occurred only in APB, and only during the ON phase of KMI. F-wave persistence and amplitude were unaffected by imagery. These results demonstrate that kinesthetic, but not visual, motor imagery modulates corticomotor excitability, primarily at the supraspinal level. These findings have implications for the definition of motor imagery, and for its therapeutic applications.

Adult↗

PubMed2005

Amplitude of muscle stretch modulates corticomotor gain during passive movement.

Previous studies have shown that the excitability of corticomotor projections to forearm muscles exhibit phasic modulation during passive movement (flexion-extension) about the wrist joint. We examined the stimulus-response properties of flexor carpi radialis (FCR) and extensor carpi radialis (ECR) to transcranial magnetic stimulation (TMS) applied over the contralateral motor cortex while the wrist was moved passively at two different sinusoidal frequency-amplitude relationships. Movement velocity (and therefore, the rate of change in muscle length) at the time of stimulation was held constant. Motor evoked potential (MEP) amplitudes were facilitated during passive muscle shortening and suppressed during passive muscle lengthening with suppression being more evident at higher stimulation intensities. For both FCR and ECR, during the shortening phase, responses were facilitated during the large amplitude movement relative to the small amplitude movement. It is suggested that the altered gain may be related to the thixotropic properties of muscle.

Adult↗

PubMed2005

Task-dependent modulation of silent period duration in focal hand dystonia.

Focal hand dystonia (FHD) is a movement disorder that is also associated with impaired sensory function and sensorimotor integration. The aim of this study was to assess the modulation of inhibitory function in the motor cortex during the performance of four motor tasks (isometric pinch grip, writing, texture discrimination, and a phasic control task) in 8 FHD and 8 control subjects. The affected hands of the FHD subjects and the dominant hands of the control subjects were tested. Inhibitory function was assessed using transcranial magnetic stimulation to evoke a silent period in the ongoing electromyographic activity of the target muscle (first dorsal interosseous). There was no difference between FHD subjects and control subjects in silent period duration, which was significantly longer during the phasic texture discrimination and phasic control task than during the isometric pinch or writing. This finding suggests that the phasic nature of the task may increase cortical inhibitory function, rather than the sensory discrimination task itself. The accuracy of texture discrimination was significantly lower in FHD subjects than in control subjects. Sensory discrimination tasks do not appear to directly modulate the inhibitory processes responsible for the duration of the silent period.

Adult↗

PubMed2004

An interhemispheric asymmetry in motor cortex disinhibition during bimanual movement.

The release of short interval intracortical inhibition (SICI) induced by passive bimanual movement was assessed in dominant and non-dominant primary motor cortices (M1). Dual-pulse focal transcranial magnetic stimulation (TMS) was delivered over M1 while the limbs were at rest, and during the mid-flexion phase of contralateral rhythmical wrist flexion-extension. Test and conditioned responses were recorded from flexor carpi radialis (FCR) when the wrist was passively moving alone, during bimanual mirror symmetric passive synchronous movement, and during bimanual passive asynchronous movement. Tonic inhibition was released to a greater extent in the non-dominant M1 than in the dominant M1 during synchronous mirror symmetric movement. This interhemispheric asymmetry was not evident during asynchronous movement. The findings support the idea that the dominant M1 has the capacity to disinhibit homologous representations in the contralateral M1 during synchronous movement, but the non-dominant M1 does not reciprocate to the same extent.

Aged↗

PubMed2004

Impaired inhibition of a pre-planned response in focal hand dystonia.

The hypothesis that focal hand dystonia (FHD) is associated with impaired inhibitory function is supported by a broad base of evidence from studies of neurophysiological function. The purpose of this study was to investigate the inhibition of a pre-planned response in FHD and control subjects. Nine FHD subjects and 11 control subjects performed an anticipated response task, which required them to lift their index finger from a keyboard button to stop the sweep of an indicator at a specified point on a sweep-dial. The affected hands of the FHD subjects were tested, as were the dominant hands of the control subjects. Electromyographic (EMG) data were recorded from the long finger extensors of the tested arm. On 90 out of 220 trials, the sweep indicator would stop prior to the specified point, and subjects were instructed to continue holding the key down when this occurred. The sweep indicator stopped 10 times at each of nine different points around the dial in a randomised order. The accuracy of subjects' performance when stopping the sweep indicator at the specified point, and the proportion of 'stop' trials where they successfully inhibited this pre-planned response, were recorded. The sweep indicator stop time at which each subject had a 50% probability of successfully inhibiting their response (R50) was calculated, as was the probability of extensor EMG (burst) activity occurring during a successfully inhibited response. For FHD subjects, it was found that R50 was significantly lower, and the probability of an extensor EMG burst occurring during a successfully inhibited response was significantly higher, compared to control subjects. These results are discussed with respect to the 'horse-race' model for the inhibition of pre-planned responses.

Adult↗

PubMed2004

Impaired modulation of intracortical inhibition in focal hand dystonia.

Previous studies have shown that intracortical inhibition (ICI) plays an important role in shaping the output from primary motor cortex, and that ICI may be impaired in people with Focal Hand Dystonia (FHD). This study explored the muscle-specificity and temporal modulation of ICI during the performance of a phasic index finger flexion task. Eight control subjects and seven with FHD were asked to rest their dominant hand upon a computer mouse, and depress the mouse button using their index finger in time with a 1 Hz auditory metronome, while keeping the rest of their hand as relaxed as possible. Responses to single and paired-pulse transcranial magnetic stimulation were recorded from the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) muscles while subjects were at rest and during 'on' and 'off' phases of the task. For control subjects during the movement (i). FDI motor evoked potential (MEP) amplitude and pretrigger EMG increased, and ICI decreased, as expected, and (ii). there was no significant facilitation of MEP amplitude or pretrigger EMG for APB, which was associated with a significant increase in ICI during the movement. This may have helped prevent the unwanted activation of this muscle. While FHD subjects demonstrated the same patterns of modulation of both MEP amplitude and pretrigger EMG for both FDI and APB, their levels of ICI were not modulated by task performance. This was despite no difference between subject groups in the level of ICI observed at rest. These findings suggest that FHD is associated with impaired modulation of ICI during performance of a precise manual task, which may contribute to a lack of specificity in the output from M1 and the development of dystonic symptoms.

Adaptation, Physiological↗

PubMed2004

Modulation of corticospinal excitability and intracortical inhibition during motor imagery is task-dependent.

Previous studies have clearly shown that motor imagery modulates corticospinal excitability. However, there is no clear evidence for the modulation of intracortical inhibition (ICI) during imagined task performance. The aim of this study was to use transcranial magnetic stimulation (TMS) to assess changes in corticospinal excitability and ICI during the imagined performance of two types of task. In Experiment 1, eight subjects performed phasic depression of a computer mouse button using the dominant index finger in time with a 1 Hz auditory metronome. Single and paired pulse magnetic stimuli were delivered at rest, and during the 'on' and 'off' phases of actual and imagined task performance. Motor evoked potentials (MEPs) were recorded from FDI and APB. In Experiment 2, eight subjects performed phasic isometric abduction of the dominant thumb in time with a 1 Hz auditory metronome. As before, single and paired pulse magnetic stimuli were delivered at rest, and during the 'on' and 'off' phases of actual and imagined task performance. In both experiments, the conditioning stimulus intensity was set to produce 50% inhibition at rest, to enable both increases and decreases in ICI during task performance to be detected. No significant temporal or spatial modulation of MEP amplitude or ICI was observed in Experiment 1. In contrast, MEP amplitude was significantly greater, and ICI significantly lower during the 'on' phase of imagined task performance in Experiment 2. These results are most likely related to the higher levels of target muscle activation required during actual task performance and the greater anatomical distance between target and control muscles in Experiment 2. These task characteristics may influence the observed degree of corticospinal excitability and ICI modulation.

Acoustic Stimulation↗

PubMed2004

Elevated threshold for intracortical inhibition in focal hand dystonia.

Differences between control and focal hand dystonia (FHD) subject groups in short interval intracortical inhibition (SICI) as determined by paired transcranial magnetic stimulation (TMS) can be difficult to demonstrate, due to interindividual differences. The purpose of this study was to compare two TMS methods for assessing SICI in 8 control and 7 FHD subjects. Electromyographic (EMG) data were recorded from the first dorsal interosseous (FDI) muscle of the dominant hands of the control subjects and affected hands of the FHD subjects. The first method used a conventional approach of setting conditioning stimulus intensity to 80% of rest threshold (RTh) and test stimulus intensity to 120% RTh. Three interstimulus intervals (ISIs) were used: 2 msec, 3 msec, and the ISI between 2 and 3 msec that produced optimal SICI. The second method was novel in that test stimulus intensity was set to 150% active threshold (ATh), and conditioning stimulus intensity was varied between 50% and 100% ATh. The latter was determined at the threshold for SICI and expressed as a ratio of ATh. There was no difference between the subject groups in the degree of SICI produced using the first method, at the three ISIs studied. However, using the second method, the SICI threshold:ATh ratio was found to be significantly higher for FHD subjects. This finding suggests that determining the SICI threshold:ATh ratio may be a more sensitive measure of intracortical inhibitory function than more conventional methods.

Adult↗

PubMed2004

Modulation of human cervical premotoneurons during bilateral voluntary contraction of upper-limb muscles.

A greater proportion of the voluntary command to the affected upper limb of well-recovered stroke patients descends via the putative C3/4 propriospinal system compared with the unaffected limb or the limbs of control subjects. We have examined whether there are differences in the pattern and extent of the modulation in intact subjects when the upper-limb muscles are bilaterally activated compared with unilateral activation. Motor evoked potentials (MEPs) recorded from flexor carpi radialis (FCR) in response to transcranial magnetic stimulation (TMS) were assessed for an effect of cocontraction with biceps brachii (BB) and subthreshold electrical conditioning of the musculocutaneous (MC) nerve. No between-hand differences were revealed, but there was less facilitation during bilateral than unilateral contraction. The findings suggest that the C3/4 propriospinal system is more active during unilateral muscle contraction and less active during bilateral contraction of upper-limb muscles. Therefore, bimanual rehabilitation strategies for patients with upper-limb hemiparesis should be developed with caution.

Adult↗

PubMed2004

The effects of repetitive proprioceptive stimulation on corticomotor representation in intact and hemiplegic individuals.

OBJECTIVE: To determine the effects of a passive wrist movement intervention on cortical representation of forearm musculature. METHODS: Transcranial magnetic stimulation was used to map cortical representation of a forearm flexor muscle in healthy individuals and in individuals following stroke before and immediately after a 30 min session of passive wrist movement. RESULTS: In the healthy individuals, no changes in map area or map centre of gravity were noted after the intervention; however, map volume increased significantly across all subjects. In the stroke patient group there were no significant changes in any parameters following the intervention. CONCLUSIONS: It is speculated that the enlargement in map volume following the passive movement intervention arose through a heightened synaptic efficacy of the corticospinal pathway in response to the increase in afferent information. Short-term proprioceptive stimulation can induce alterations in corticomotor excitability in the target musculature. SIGNIFICANCE: These findings provide a potential neural substrate to account for alterations in motor and sensory function in stroke patients in response to long-term passive movement interventions.

Aged↗