J. Colebatch - Academia.edu (original) (raw)

Papers by J. Colebatch

Medical Journal of Australia, 1986

Le diagnostic clinique le plus probable etait une maladie de Pick. Le diagnostic anatomo-patholog... more Le diagnostic clinique le plus probable etait une maladie de Pick. Le diagnostic anatomo-pathologique est une maladie de Crentz-feldt-Jakob

Neurology, 2004

The authors recorded the acoustic startle response in 32 patients with stroke, 6 patients with in... more 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.

Movement Disorders Clinical Practice, 2014

Psychiatric symptoms are historically thought a relative contraindication to DBS for advanced Par... more Psychiatric symptoms are historically thought a relative contraindication to DBS for advanced Parkinson's disease (PD). However, in the case of drug-induced mental illness, DBS may provide an acceptable alternative for the treatment of motor symptoms. This allows reduction of pharmacological dopaminergic therapy that might otherwise cause negative psychiatric consequences. For example, DBS is increasingly used to ameliorate specific complications of PD , such as impulse control disorders. We present a series of 3 cases of young male patients who developed Othello syndrome (OS) during treatment with dopamine agonists. In each case, the OS resolved with withdrawal of the offending drug. Subsequent treatment with bilateral STN DBS improved motor symptoms and allowed reduction in their dopaminergic drug regimen. We therefore propose that drug-induced psychopathology may be an indication (rather than a contraindication) for DBS in selected cases.

Experimental Brain Research, 2012

We investigated the changes in cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic pot... more We investigated the changes in cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic potentials in response to differing stimulus durations. cVEMPs (n = 12 subjects) and oVEMPs (n = 13 subjects) were recorded using air-conducted (AC: 500 Hz) and boneconducted (BC: 500 Hz) tone burst stimuli with durations varying from 2 to 10 ms. BC stimulation was applied both frontally and to the mastoid. AC cVEMPs showed an increase in amplitude with stimuli up to 6-ms duration associated with a prolonged latency, as previously reported. In contrast, AC oVEMP amplitude decreased with increasing stimulus duration. BC stimuli showed no significant increase in amplitude with increasing stimulus duration for either reflex using either location of stimulation. BC cVEMPS following forehead stimulation showed a significant decrease as duration increased, and BC oVEMPs to mastoid stimulation were largest at 2 ms and decreased thereafter. We conclude that an increase in amplitude with increasing stimulus duration, using 500 Hz stimuli, only occurs for AC cVEMPs. There is no definite benefit in using longer stimuli than 2 ms for BC or oVEMP studies. Shorter stimuli also minimise subject exposure to sound and vibration.

Experimental Brain Research, 2004

Weakness is a common symptom of neurological illness, and recovery may occur via restorative or c... more Weakness is a common symptom of neurological illness, and recovery may occur via restorative or compensatory mechanisms. Functional imaging studies have shown varied patterns of activity in motor areas following recovery from stroke. Movement related potentials (MRP) reflect the activity in primary and non-primary motor areas. We recorded MRPs in association with index finger abduction in six normal volunteers before and after induced weakness of a hand muscle and in six stroke patients with subcortical lesions and weakness affecting the arm. In both groups of subjects the greatest change was observed in the motor potential component of the MRP. On average, the motor potential had its greatest amplitude and duration at the time of the greatest weakness and became smaller with recovery. In artificially-induced weakness, the MRP had an earlier onset latency (P=0.042) and a greater early BP component (P=0.05) for the weakened finger. For the stroke subjects overall, the peak and NS' amplitudes were largest for the initial study and declined thereafter. Similar but smaller changes were present for movements of the clinically unaffected side. The increased motor potential is therefore consistent with increased activity in the motor cortex, and this may occur as compensation for weakness in both normals and after stroke.

Experimental Brain Research, 2002

Self-paced movements, movement to a cue and imagined movement have all been reported to be preced... more 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 V, finger movement 9.0 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 V, finger 8.2 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 V, finger 6.2 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.

Clinical Neurophysiology, 2003

Objective: Vestibular responses in soleus electromyography (EMG) evoked by the sudden onset of ga... more 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.

Clinical Neurophysiology, 2004

Objective: Following stroke, the startle reflex, mediated via the reticulospinal tract, is often ... more Objective: Following stroke, the startle reflex, mediated via the reticulospinal tract, is often facilitated. Vestibulospinal reflexes are another bulbospinal reflex, abnormalities of which may contribute to impaired body posture and stance following stroke. We recorded galvanic evoked vestibulospinal and vestibulocollic reflexes to assess whether these showed similar changes to those for startle following stroke affecting the pons and above. Methods: Twenty-four stroke subjects (aged 40-82) were studied in the vestibulospinal part of the study, 21 stroke subjects (aged 40-81 years) were studied in the vestibulocollic part, including 18 studied in both. Transmastoid galvanic (DC) current was used to stimulate the vestibular nerve. Vestibulocollic responses were recorded from the sternocleidomastoid muscles and vestibulospinal responses from over soleus in standing subjects. Results: Vestibulocollic reflex amplitudes and latencies showed no significant differences between the two sides. Similarly short latency (SL) and medium latency (ML) vestibulospinal reflexes did not differ significantly in frequency, latency or amplitude between the affected and unaffected legs. Conclusions: Vestibular reflexes are not facilitated by stroke at or above the pontine level. The exaggeration of startle by stroke may be specific to this reflex.

Clinical Neurophysiology, 2010

Since the first description of sound-evoked short-latency myogenic reflexes recorded from neck mu... more Since the first description of sound-evoked short-latency myogenic reflexes recorded from neck muscles, vestibular evoked myogenic potentials (VEMPs) have become an important part of the neuro-otological test battery. VEMPs provide a means of assessing otolith function: stimulation of the vestibular system with air-conducted sound activates predominantly saccular afferents, while bone-conducted vibration activates a combination of saccular and utricular afferents. The conventional method for recording the VEMP involves measuring electromyographic (EMG) activity from surface electrodes placed over the tonically-activated sternocleidomastoid (SCM) muscles. The "cervical VEMP" (cVEMP) is thus a manifestation of the vestibulo-collic reflex. However, recent research has shown that VEMPs can also be recorded from the extraocular muscles using surface electrodes placed near the eyes. These "ocular VEMPs" (oVEMPs) are a manifestation of the vestibulo-ocular reflex. Here we describe the historical development and neurophysiological properties of the cVEMP and oVEMP and provide recommendations for recording both reflexes. While the cVEMP has documented diagnostic utility in many disorders affecting vestibular function, relatively little is known as yet about the clinical value of the oVEMP. We therefore outline the known cVEMP and oVEMP characteristics in common central and peripheral disorders encountered in neuro-otology clinics.

Acta oto-laryngologica. Supplementum, 1995

A 55 year old female with idiopathic Tullio phenomenon is presented. Binocular, scleral search ey... more A 55 year old female with idiopathic Tullio phenomenon is presented. Binocular, scleral search eye coil recordings demonstrated a predominantly torsional left-beating and vertical down-beating nystagmus in response to sound intensities over 100 dB HL to the left ear, increasing in amplitude and slow phase velocity with sound intensity and removal of visual fixation. The vertical ocular movement was conjugate, i.e. without skew deviation. Neuro-imaging, all other neuro-otological features, including ipsilateral-contralateral stapedius muscle reflexes, and surgical exploration of the middle ear, were normal. Click-evoked vestibulo-collic potentials were normal from the right ear but showed low threshold (70 dB) and increased amplitude from the left. There was no evidence that the Tullio phenomenon in this patient arises from stapes footplate hypermobility. The findings suggest that some cases of the Tullio phenomenon may be due to a hyperexcitability of the normal vestibular response ...

Experimental Brain Research

Journal of Neurophysiology

Our object was to investigate the effect of location and phase on the properties of oVEMPs and cV... more Our object was to investigate the effect of location and phase on the properties of oVEMPs and cVEMPs evoked by two bone conducted (BC) stimuli, 500 Hz and an impulsive stimulus for midline skull sites from Nz to Iz, in normal volunteers. Compressive and rarefactive onset phases were used and the induced linear and rotational accelerations measured. We confirmed our previous finding of marked changes in the polarity of oVEMPs with location. For cVEMPs using the 500Hz stimulus there were few changes with location or phase, but the impulsive stimulus showed clear phase-related changes at several locations, with the shortest latencies occurring with compressive stimuli at AFz and Fz and the largest amplitudes at Iz. For oVEMPs, both stimuli showed clear effects of phase, with the shortest latencies with compressive stimuli at AFz and Fz and with the largest negativity at Oz or Iz. Whereas the effectiveness at Iz is consistent with a role in the linear VOR, the inversion of polarity and...

PloS one, 2018

The provision of written information is a low-cost and readily available intervention that has be... more The provision of written information is a low-cost and readily available intervention that has been found to reduce pain and anxiety in a variety of clinical settings. The current study was undertaken to determine if information provision may improve patients' experience during conventional electrodiagnostic studies. 128 participants were recruited from a tertiary teaching hospital who were referred for electrodiagnostic studies. They were randomized into 2 groups where the intervention group was provided with written information about the electrodiagnostic testing. Patients were invited to complete a questionnaire that included pain and anxiety using a visual analogue scale (VAS) following the testing. All participants underwent nerve conduction studies (NCS) whilst a subset also underwent subsequent needle electromyography (EMG). Those who received information had a statistically significant lower perception of anxiety during NCS, whilst only females who received information h...

Neurology, 2017

To systematically review the evidence and make recommendations with regard to diagnostic utility ... more To systematically review the evidence and make recommendations with regard to diagnostic utility of cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP, respectively). Four questions were asked: Does cVEMP accurately identify superior canal dehiscence syndrome (SCDS)? Does oVEMP accurately identify SCDS? For suspected vestibular symptoms, does cVEMP/oVEMP accurately identify vestibular dysfunction related to the saccule/utricle? For vestibular symptoms, does cVEMP/oVEMP accurately and substantively aid diagnosis of any specific vestibular disorder besides SCDS? The guideline panel identified and classified relevant published studies (January 1980-December 2016) according to the 2004 American Academy of Neurology process. Level C positive: Clinicians may use cVEMP stimulus threshold values to distinguish SCDS from controls (2 Class III studies) (sensitivity 86%-91%, specificity 90%-96%). Corrected cVEMP amplitude may be used to distinguish SCDS from controls (2...

Neuroscience Letters, Feb 1, 2009

Recent work has demonstrated that the human vestibular system displays a remarkable sensitivity t... more Recent work has demonstrated that the human vestibular system displays a remarkable sensitivity to low-frequency vibration. To address the origin of this sensitivity we compared the frequency response properties of vestibular reflexes to 10 ms bursts of air-conducted sound and transmastoid vibration, which are thought to be differentially selective for the saccule and utricle, respectively. Measurements were made using two separate central pathways: vestibular evoked myogenic potentials (VEMPs), which are a manifestation of vestibulo-collic projections, and ocular vestibular evoked myogenic potentials (OVEMPs), which are a manifestation of vestibulo-ocular projections. For both response pathways air-conducted sound and vibration stimuli produced the same patterns of quite different tuning. Sound was characterised by a band-pass tuning with best frequency between 400 and 800 Hz whereas vibration showed a low-pass type response with a largest response at 100 Hz. Our results suggest that the tuning is at least in part due to properties of end-organs themselves, while the 100 Hz best frequency may be a specifically utricular feature.

Clinical Neurophysiology Official Journal of the International Federation of Clinical Neurophysiology, Jan 12, 2011

Experimental Brain Research, 2015

differ from the pattern of automatic postural responses that follow displacements at the level of... more differ from the pattern of automatic postural responses that follow displacements at the level of the ankles, and it is unlikely that proprioceptive afferents excited by ankle movement had a role in the initial responses. Vision and surface properties had only minor effects. Perturbations of the upper trunk evoke stereotyped compensatory postural responses for each direction of perturbation. For posterior perturbations, EMG onset occurs earlier than for voluntary responses.

Physiological reports, 2014

We compared the brain areas that showed significant flow changes induced by selective stimulation... more We compared the brain areas that showed significant flow changes induced by selective stimulation of muscle and cutaneous afferents using fMRI BOLD imaging. Afferents arising from the right hand were studied in eight volunteers with electrical stimulation of the digital nerve of the index finger and over the motor point of the FDI muscle. Both methods evoked areas of significant activation cortically, subcortically, and in the cerebellum. Selective muscle afferent stimulation caused significant activation in motor-related areas. It also caused significantly greater activation within the contralateral precentral gyrus, insula, and within the ipsilateral cerebellum as well as greater areas of reduced blood flow when compared to the cutaneous stimuli. We demonstrated separate precentral and postcentral foci of excitation with muscle afferent stimulation. We conclude, contrary to the findings with evoked potentials, that muscle afferents evoke more widespread cortical, subcortical, and ...