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Biomedical subjects

J G Colebatch

Publications and source records attributed to J G Colebatch.

At least 19 recordsLinked to original sources
PubMed2004

The acoustic startle reflex in ischemic stroke.

The authors recorded the acoustic startle response in 32 patients with stroke, 6 patients with incomplete cervical cord lesions, and 26 controls. Increased startle occurred in about one quarter of both stroke and spinal cord injury patients. The response in biceps demonstrated the greatest deviation from normal, with less marked changes in tibialis anterior. Increased startle in spinal cord injury suggests that changes at the segmental level may contribute. Symptomatic increased startle occurred only in pontine lesions.

Acoustic Stimulation↗
PubMed2003

EMG responses evoked by the termination of galvanic (DC) vestibular stimulation: 'off-responses'.

OBJECTIVE: Vestibular responses in soleus electromyography (EMG) evoked by the sudden onset of galvanic (DC) stimulation ('on-responses') have been described in detail previously. The aim of the present study was to describe responses in soleus triggered by the termination of galvanic stimulation ('off-responses'). METHODS: In 10 healthy human subjects, we studied responses to transmastoid (bilateral) stimuli of 200 ms and 2 s average duration and 3 or 4 mA intensity. We obtained both on- and off-responses using the same raw data. EMG activity was recorded onto tape while current pulses of systematically varying duration were delivered. Averaged on-responses were obtained by triggering from the beginning of the current pulses. Averaged off-responses were obtained by triggering from the termination of the current pulses. RESULTS: Short-latency (SL) and medium latency (ML) off-responses were both obtained in all but one study. The SL and the ML components of the off-responses were present and had similar latencies and amplitudes, but opposite excitability, to the on-responses obtained with the same stimuli. CONCLUSIONS: Off-responses to galvanic vestibular stimulation can be recorded from soleus EMG. Our findings imply that vestibular SL and ML reflex responses in the legs are dependent on the change in the rate of vestibular nerve discharge, not its absolute level. Both on- and off-responses have properties appropriate to a role in maintaining body stability.

Adult↗
PubMed2003

Vestibular activation by bone conducted sound.

OBJECTIVE: To examine the properties and potential clinical uses of myogenic potentials to bone conducted sound. METHODS: Myogenic potentials were recorded from normal volunteers, using bone conducted tone bursts of 7 ms duration and 250-2000 Hz frequencies delivered over the mastoid processes by a B 71 clinical bone vibrator. Biphasic positive-negative (p1n1) responses were recorded from both sternocleidomastoid (SCM) muscles using averaged unrectified EMG. The best location for stimulus delivery, optimum stimulus frequency, stimulus thresholds, and the effect of aging on evoked response amplitudes and thresholds were systematically examined. Subjects with specific lesions were studied. Vestibular evoked myogenic potentials (VEMP) to air conducted 0.1 ms clicks, 7 ms/250-2000 Hz tones, and forehead taps were measured for comparison. RESULTS: Bone conducted sound evoked short latency p1n1 responses in both SCM muscles. Ipsilateral responses occurred earlier and were usually larger. Mean (SD) p1 and n1 latencies were 13.6 (1.8) and 22.3 (1.2) ms ipsilaterally and 14.9 (2.1) and 23.7 (2.7) ms contralaterally. Stimuli of 250 Hz delivered over the mastoid process, posterosuperior to the external acoustic meatus, yielded the largest amplitude responses. Like VEMP in response to air conducted clicks and tones, p1n1 responses were absent ipsilaterally in subjects with selective vestibular neurectomy and preserved in those with severe sensorineural hearing loss. However, p1n1 responses were preserved in conductive hearing loss, whereas VEMP to air conducted sound were abolished or attenuated. Bone conducted response thresholds were 97.5 (3.9) dB SPL/30.5 dB HL, significantly lower than thresholds to air conducted clicks (131.7 (4.9) dB SPL/86.7 dB HL) and tones (114.0 (5.3) dB SPL/106 dB HL). CONCLUSIONS: Bone conducted sound evokes p1n1 responses (bone conducted VEMP) which are a useful measure of vestibular function, especially in the presence of conductive hearing loss. For a given perceptual intensity, bone conducted sound activates the vestibular apparatus more effectively than air conducted sound.

Adult↗
PubMed2002

Movement-related potentials associated with self-paced, cued and imagined arm movements.

Self-paced movements, movement to a cue and imagined movement have all been reported to be preceded by a prolonged negativity on averaged electroencephalograph (EEG) recordings. Considerable evidence supports an important contribution from the supplementary motor area (SMA) to this potential and all three types of movement have been shown to be associated with SMA activation. This study was designed to compare the premovement component of these movement-related potentials (MRPs) in a group of subjects who performed each of these three types of movement. In addition, in view of the greater SMA activation in association with proximal arm movements, we studied movements at multiple joints in the right arm. All the potentials were largest at Cz. Self-paced movements were preceded by a negativity (mean onset 1.2 s prior to electromyographic activity) with two distinct phases - an early slow increase (early BP, Bereitschaftspotential) and a later, steeper phase (NS', negative slope). Proximal movements were associated with a larger peak amplitude (mean peak amplitude for shoulder 11.6 micro V, finger movement 9.0 micro V at Cz, n=14) due to a bigger NS' phase. Movements to a regular cue, but not to a randomly timed cue, were also preceded by a long duration negativity, but the NS' phase began earlier and was less distinct than for self-paced movements (mean peak amplitude for shoulder movement 9.1 micro V, finger 8.2 micro V at Cz, n=12). Imagining the movements to a regular cue was associated with a slow negativity, with no clear NS' phase (mean peak amplitude for shoulder movement 6.5 micro V, finger 6.2 micro V at Cz). Our results indicate that the MRPs prior to the three types of movement have distinct characteristics, most notably for the NS' phase. The MRP associated with movement to a regular cue may be analogous to the S2-related negativity of the contingent negative variation (CNV). We discuss the findings in the light of current evidence from functional imaging as to the cortical areas activated in similar movements.

Adult↗
PubMed2002

Selective effects of ageing on vestibular-dependent lower limb responses following galvanic stimulation.

OBJECTIVES: To examine the influence of ageing on electromyographic (EMG) responses to galvanic vestibular stimulation (GVS) in the lower limbs and to define normal values. METHODS: EMG responses to 4 mA/20 ms transmastoid binaural GVS were recorded from the soleus muscles of 70 healthy adults aged 24-85 years. Short (SL) and medium latency (ML) vestibular-dependent reflex latencies and amplitudes were measured from averaged rectified EMG. Side to side differences were examined in 30 subjects, using monaural stimulation, and expressed as an asymmetry ratio (AR). RESULTS: SL reflexes to transmastoid binaural stimulation were absent in 10 of the 25 subjects over the age of 60. ML responses were present in all subjects. SL reflex amplitudes decreased from 24.4+/-12.4% (mean+/-SD) in the 3rd decade to 7.6+/-6.2% in the 8th and 9th decades. The ML reflex amplitudes showed a tendency to increase with age. The mean AR for SL reflex amplitudes increased from 12.1% in the 3rd decade to 80.7% in the 8th and 9th decades but that for ML amplitudes did not change significantly. The average SL and ML response onset latencies were 56.5+/-7.5 and 97.2+/-9.4 ms. SL onset latencies were significantly delayed with age. Both SL and ML responses were highly reproducible between experiments. CONCLUSIONS: SL and ML responses behave differently in response to age. The decrease in SL reflex amplitudes correlates well with previously described age-related morphological changes. Preservation of the ML reflex may reflect central adaptation to reduced afferent input. SL and ML responses are potentially useful measures of vestibular-spinal function, which may have a role in the assessment of older subjects with dysequilibrium. These reflexes need to be interpreted in the context of age.

Adult↗
PubMed2002

Differential effect of current rise time on short and medium latency vestibulospinal reflexes.

OBJECTIVES: To investigate the effect of varying current rise time on galvanic-evoked short (SL) and medium (ML) latency vestibulospinal reflexes. METHODS: We recorded the soleus EMG of standing subjects in response to 3 mA direct current transmastoid stimulation with a series of current ramps with rise times of 0-300 ms. RESULTS: Longer current rise times significantly delayed the onset of both SL (P<<0.001) and ML (P<<0.001) vestibulospinal responses, by approximately 20 and 39 ms, respectively. The SL response amplitude was reduced with increasing rise time (P<<0.001), whereas the ML response amplitude was relatively unaffected by stimulus rise time. With very slow rise times a prolonged ML response alone was evoked. CONCLUSIONS: Both SL and ML reflexes can be evoked by changes in vestibular activity produced by transmastoid galvanic stimulation with a ramp onset. We found a differential effect of current rise time on SL and ML vestibulospinal reflexes, suggesting different potential functional roles for the two reflexes. SL reflexes can participate in the response to abrupt disturbances only. ML reflexes are evoked by both fast and slow changes in vestibular discharge and may be particularly effective for slowly-changing disturbances.

Adult↗
PubMed2001

Motor imagery in Parkinson's disease: a PET study.

We used positron emission tomography (PET) with 15O-labelled water to record patterns of cerebral activation in six patients with Parkinson's disease (PD), studied when clinically "off" and after turning "on" as a result of dopaminergic stimulation. They were asked to imagine a finger opposition movement performed with their right hand, externally paced at a rate of 1 Hz. Trials alternating between motor imagery and rest were measured. A pilot study of three age-matched controls was also performed. We chose the task as a robust method of activating the supplementary motor area (SMA), defects of which have been reported in PD. The PD patients showed normal degrees of activation of the SMA (proper) when both "off" and "on." Significant activation with imagining movement also occurred in the ipsilateral inferior parietal cortex (both "off" and when "on") and ipsilateral premotor cortex (when "off" only). The patients showed significantly greater activation of the rostral anterior cingulate and significantly less activation of the left lingual gyrus and precuneus when performing the task "on" compared with their performance when "off." PD patients when imagining movement and "off" showed less activation of several sites including the right dorsolateral prefrontal cortex (DLPFC) when compared to the controls performing the same task. No significant differences from controls were present when the patients imagined when "on." Our results are consistent with other studies showing deficits of pre-SMA function in PD with preserved function of the SMA proper. In addition to the areas of reduced activation (anterior cingulate, DLPFC), there were also sites of activation (ipsilateral premotor and inferior parietal cortex) previously reported as locations of compensatory overactivity for PD patients performing similar tasks. Both failure of activation and compensatory changes are likely to contribute to the motor deficit in PD.

Aged↗
PubMed2001

Vestibulospinal reflexes: quantitative effects of sensory feedback and postural task.

Vestibulospinal and vestibulocollic reflexes evoked by galvanic stimulation were studied in 20 normal volunteers. In an initial "baseline" study, subjects stood unsupported on a flat surface and a narrow base with their eyes shut and with their heads rotated to the left. The effects of vision, external support and increasing stance width were examined both individually and in combination. In a second series, the effects of the same factors were examined while subjects stood on a compliant surface. Short latency (SL) and medium latency (ML) vestibulospinal reflex responses were evoked using 4 mA/20 ms galvanic vestibular stimulation (GVS) and measured from the right soleus muscle. Vestibulocollic reflexes to short duration galvanic stimulation (4 mA/2 ms) were also measured under similar conditions. Both SL and ML vestibulospinal reflexes decreased significantly and to a similar degree with vision, external support and increasing stance width on a flat surface. On the compliant surface, stance width did not result in a decrease in the ML reflex. Reflex amplitudes further decreased in a non-linear fashion with each additional sensory modality ("factor") that was made available; the degree of attenuation due to the addition of a second and third factor closely approximated the product of the effect of each factor in isolation. Standing on a compliant surface resulted in enhancement of average SL and ML reflexes under all conditions. Vestibulocollic reflexes in contrast showed no significant modulation with vision, external support and stance width. The dissociation between vestibulocollic and vestibulospinal reflexes indicates that the modulation of vestibulospinal reflexes with task occurs proximal to the primary vestibular afferents. Vestibulospinal reflexes were largest when subjects stood on a narrow base, on a compliant surface, deprived of vision and external support, consistent with the importance of vestibular function under these conditions. Although attenuated, vestibulospinal reflexes were preserved in most subjects even when vision and external support were available and a wider stance width was adopted. The combination of different factors caused a multiplicative attenuation of the initial response.

Adult↗
PubMed2001

Vestibulocollic reflexes: normal values and the effect of age.

OBJECTIVES: To define normal values and examine the influence of ageing on vestibulocollic reflexes (VCR). METHODS: Vestibulocollic responses to 100 dB (normal hearing level; NHL) clicks, forehead taps and galvanic stimulation were measured in 70 healthy adults aged 25-85 years. RESULTS: Click- and galvanic-evoked responses were present bilaterally in all subjects below 60. Average click-evoked response amplitudes decreased with age, with a pronounced decline of 25-30% per decade from the 6th decade. The average click thresholds increased from 85 dB in the third decade to 96.5 dB in the 8th and 9th decades. Average galvanic-evoked VCR amplitudes decreased sharply from the seventh decade. Tap-evoked reflex amplitudes showed a milder decrease. When side to side differences in amplitude were expressed as asymmetry ratios (AR) in subjects below the age of 60, values of up to 35 and 46% were obtained for click amplitudes corrected and uncorrected for background electromyogram (EMG), up to 61% for both corrected and uncorrected tap response amplitudes, and up to 41 and 55% for corrected and uncorrected galvanic-evoked responses. CONCLUSIONS: A normative range of values can be specified for click- and galvanic-evoked VCRs for subjects up to the age of 60. Click- and galvanic-evoked VCR amplitudes decrease rapidly thereafter while tap-evoked responses are less affected. These changes are probably due to morphological changes in the vestibular system occurring with ageing and are more marked than in several previous reports of age-related changes in caloric responses and vestibulo-ocular reflexes.

Acoustic Stimulation↗
PubMed2001

Vestibular evoked potentials.

Loud clicks, short tone bursts, head taps and short duration transmastoid currents are all capable of activating vestibular receptors and evoking reflex changes in tonic electromyogram activity within the sternocleidomastoid muscles. Because they derive from averaged electromyograms, the responses are termed 'vestibular evoked myogenic potentials'. The earliest response ipsilateral to a loud click, p13n23, is dependent upon vestibular activation, specifically saccular afferents. These new techniques are beginning to be applied clinically. An important application is in suspected cases of the Tullio phenomenon, a condition that is characterized by a pathological reduction in click threshold. The techniques have also been applied in the assessment of otolith function, vestibular neuritis, Meniere's disease and vestibular nerve tumours (acoustic neuromas).

Acoustic Stimulation↗
PubMed2001

Characteristics of tone burst-evoked myogenic potentials in the sternocleidomastoid muscles.

HYPOTHESIS: Optimum stimulus parameters for tone burst-evoked myogenic responses can be defined. These optimized responses will be similar to those evoked by clicks in the same subjects. BACKGROUND: Loud tones give rise to myogenic responses in the anterior neck muscles, similar to click-evoked potentials, and are likely to be saccular in origin. METHODS: Tone burst-evoked and click-evoked myogenic potentials were measured from the sternocleidomastoid muscles of 12 normal subjects (6 men, 6 women) during tonic activation. The effects of tone burst frequency and duration were systematically investigated. Thresholds were measured and compared with click thresholds for the same subjects. Patients with specific lesions were studied using both stimuli. RESULTS: Tone burst-evoked responses showed frequency tuning, with the largest reflex amplitudes at either 500 Hz or 1 kHz. As the stimulus duration was increased, using a constant repetition rate, there was an increase in the reflex amplitudes followed by a decline. The overall optimum stimulus duration was 7 milliseconds. The mean tone burst threshold was 114.4-dB sound pressure level. Stimulus thresholds for click-evoked and tone burst-evoked responses were significantly correlated. Tone burst-evoked and click-evoked responses were present after stimulation of the affected ears of subjects with profound sensorineural hearing loss. Four subjects who had previously undergone vestibular neurectomy had an absence of click and tone burst-evoked responses on the side of the lesion, confirming their vestibular dependence. CONCLUSION: Tone burst-evoked myogenic responses are similar to click-evoked responses but require lower absolute stimulus intensities. To be certain of an optimum response, a stimulus duration of 7 milliseconds, an adequate intensity, and frequencies of both 500 Hz and 1 kHz should be used.

Acoustic Stimulation↗
PubMed2000

Vestibular hypersensitivity to sound (Tullio phenomenon): structural and functional assessment.

OBJECTIVES: To establish the role of high-resolution CT imaging and tests of vestibulocollic reflexes in diagnosing and understanding the pathogenesis of the Tullio phenomenon. BACKGROUND: The Tullio phenomenon is a syndrome in which acoustic stimulation produces symptoms and signs of vestibular activation. It has previously been associated with an abnormally low threshold for click-evoked vestibulocollic responses and also with dehiscence of the roof of the anterior (superior) semicircular canal on high-resolution CT scans of the temporal bones. METHODS: High-resolution CT scans of the temporal bones and vestibulocollic responses in sternocleidomastoid to both clicks and transmastoid galvanic stimulation (3 mA/2 msec) were studied in four patients with the Tullio phenomenon (one bilateral). RESULTS: Click-evoked thresholds were low for all affected ears (four at 65 dB nHL, one at 55 dB nHL) and normal (>70 dB nHL) for the three unaffected ears. In contrast, galvanic-evoked vestibulocollic responses were symmetric and of normal size in all patients. The bony roof of the anterior (superior) semicircular canal was thin, possibly absent, on CT of all affected ears and also in two out of three unaffected ears. CONCLUSIONS: The normal galvanic vestibulocollic responses indicate that sound sensitivity in patients with the Tullio phenomenon is likely to occur distal to the vestibular nerve, probably at the level of the receptors. Both click hypersensitivity and dehiscence of the anterior (superior) semicircular canal are associated with the Tullio phenomenon but as the CT scan abnormality can occur in clinically unaffected ears, click testing is important for specific diagnosis. Abnormal sound sensitivity, as demonstrated by click responses, confirms that the radiologic abnormality is function significant.

Adult↗
PubMed1999

Resetting voluntary movement using peripheral nerve stimulation: influence of loading conditions and relative effectiveness.

The effect of peripheral nerve stimulation on voluntary rhythmic flexion-extension movements at the wrist was studied in nine normal volunteers, and the results compared with the effect of cortical stimulation on the same task. In the first part of the study, magnetic stimulation was given over the inner aspect of the right arm at levels which, at rest, resulted in a wrist flexion twitch of at least 10 degrees. We were able to confirm that this form of (peripheral-nerve) stimulation is an effective means of phase-resetting voluntary wrist movements. In addition, and unlike magnetic stimulation applied over the contralateral motor cortex, changes in the standing torque load, against which the subjects moved, had little influence on the effectiveness of this form of stimulation. Similarly, the amplitude and direction of the averaged first post-stimulus position peak ("P1"), previously identified as important determinants of the resetting induced by a cortical stimulus, were largely independent of the loading torque. In a second part to the study, we directly compared, for a constant loading torque, the resetting induced by magnetic cortical stimulation with that following magnetic stimulation of peripheral nerves. The relationship between the amplitude of P1 and the associated resetting index was identical for both forms of stimulation. Our observations indicate that magnetic stimulation of peripheral nerves is an effective means of resetting voluntary movement. It differs from magnetic cortical stimulation in that the effects of peripheral nerve stimulation are little altered by changes in loading torque. When differences in the size of P1 are allowed for, both peripheral nerve and cortical stimulation are equally effective means of resetting voluntary rhythmical movement.

Adult↗
PubMed1998

Vestibulocollic reflexes evoked by short-duration galvanic stimulation in man.

1. Vestibular-dependent responses in leg muscles following transmastoid galvanic stimulation have been well characterized. Here we describe the properties of vestibulocollic responses evoked by transmastoid galvanic stimulation. 2. In twelve healthy human subjects we examined the averaged responses in unrectified sternocleidomastoid (SCM) EMG evoked by transmastoid stimulation using current pulses of 4 mA intensity and 2 ms duration. In ten subjects we also examined the effects of unilateral vestibular stimulation with the indifferent electrode at the vertex. In further experiments we studied the effects of different levels of background muscle activation, head position, current intensity and current duration. We compared these responses with click-evoked vestibulocollic responses in SCM. 3. A clearly defined biphasic response, beginning with a surface positivity, was recorded in the SCM ipsilateral to the side of cathode placement in all subjects. We refer to this as the p13/n23 [g] (galvanic) response, given the close similarity, in terms of waveform and latencies, to the previously described click-evoked p13/n23 vestibulocollic response. The amplitude of this response was linearly related to background muscle activation, current intensity and current duration, but independent of head position. Unilateral galvanic stimulation revealed the p13/n23 [g] response to be solely generated by the cathode. 4. A biphasic response beginning with a surface negativity (n12/p20 [g]) contralateral to the cathode was seen in all subjects and was generated by both the cathode contralaterally and the anode ipsilaterally. 5. Both the p13/n23 [g] and n12/p20 [g] potentials were abolished by selective vestibular nerve section and unaffected by severe sensorineural deafness. 6. We conclude that galvanic stimulation evokes short-latency vestibulocollic reflexes. These vestibulocollic reflexes have properties that are distinct from those described for galvanic-evoked vestibular reflexes in leg muscles, and which may be related to their differing physiological roles.

Acoustic Stimulation↗
PubMed1998

An akinetic-rigid syndrome, depression, and stereotypies in a young man.

A young man is presented who developed an akinetic-rigid syndrome shortly after a minor illness. Rituals and stereoptypies were prominent. At its most severe he was unable to feed himself. There was no response to L-dopa/cardopa treatment. A course of ECT was followed by a marked improvement in his condition. Attempts to stop ECT for more than a week have led to recurrence of his bradykinesia.

Adult↗