ORCID Profile
0000-0001-9911-8743
Current Organisations
Flinders Medical Centre
,
University of South Australia
,
Flinders University
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Publisher: Wiley
Date: 27-12-1993
Publisher: Elsevier BV
Date: 03-1996
Publisher: Portland Press Ltd.
Date: 08-07-1999
DOI: 10.1042/BJ3410401
Publisher: Humana Press
Date: 1995
Publisher: Elsevier BV
Date: 09-2020
Publisher: American Chemical Society (ACS)
Date: 10-1993
DOI: 10.1021/JM00072A027
Publisher: American Chemical Society (ACS)
Date: 05-1994
DOI: 10.1021/JO00088A003
Publisher: Wiley
Date: 13-03-2007
DOI: 10.1002/MDS.21416
Publisher: Elsevier
Date: 2016
Publisher: Elsevier BV
Date: 05-2019
DOI: 10.1016/J.CLINPH.2019.02.005
Abstract: The study aim was to determine if use of illicit hetamines or ecstasy is associated with abnormal excitability of the corticomotoneuronal pathway and manipulation of novel objects with the hand. Three groups of adults aged 18-50 years were investigated: in iduals with a history of illicit hetamine use, in iduals with a history of ecstasy use but minimal use of other stimulants, and non-drug users. Transcranial magnetic stimulation was delivered to the motor cortex and the electromyographic response (motor evoked potential MEP) was recorded from a contralateral hand muscle. Participants also gripped and lifted a novel experimental object consisting of two strain gauges and an accelerometer. Resting MEP litude was larger in the hetamine group (6M, 6F) than the non-drug and ecstasy groups (p < 0.005) in males but not females. Overestimation of grip force during manipulation of a novel object was observed in the hetamine group (p = 0.020) but not the ecstasy group. History of illicit hetamine use, in particular meth hetamine, is associated with abnormal motor cortical and/or corticomotoneuronal excitability in males and abnormal manipulation of novel objects in both males and females. Abnormal excitability and hand function is evident months to years after cessation of illicit hetamine use.
Publisher: American Chemical Society (ACS)
Date: 06-1993
DOI: 10.1021/JA00064A002
Publisher: Elsevier BV
Date: 07-1992
Publisher: Wiley
Date: 10-11-2022
DOI: 10.1002/JNR.25145
Abstract: Substantia nigra (SN) hyperechogenicity, viewed with transcranial ultrasound, is a risk marker for Parkinson's disease. We hypothesized that SN hyperechogenicity in healthy adults aged 50–70 years is associated with reduced short‐interval intracortical inhibition in primary motor cortex, and that the reduced intracortical inhibition is associated with neurochemical markers of activity in the pre‐supplementary motor area (pre‐SMA). Short‐interval intracortical inhibition and intracortical facilitation in primary motor cortex was assessed with paired‐pulse transcranial magnetic stimulation in 23 healthy adults with normal ( n = 14 61 ± 7 yrs) or abnormally enlarged (hyperechogenic n = 9 60 ± 6 yrs) area of SN echogenicity. Thirteen of these participants (7 SN− and 6 SN+) also underwent brain magnetic resonance spectroscopy to investigate pre‐SMA neurochemistry. There was no relationship between area of SN echogenicity and short‐interval intracortical inhibition in the ipsilateral primary motor cortex. There was a significant positive relationship, however, between area of echogenicity in the right SN and the magnitude of intracortical facilitation in the right (ipsilateral) primary motor cortex ( p = .005 multivariate regression), evidenced by the litude of the conditioned motor evoked potential (MEP) at the 10–12 ms interstimulus interval. This relationship was not present on the left side. Pre‐SMA glutamate did not predict primary motor cortex inhibition or facilitation. The results suggest that SN hyperechogenicity in healthy older adults may be associated with changes in excitability of motor cortical circuitry. The results advance understanding of brain changes in healthy older adults at risk of Parkinson's disease.
Publisher: Portland Press Ltd.
Date: 11-1993
DOI: 10.1042/BJ2950904
Publisher: Springer Science and Business Media LLC
Date: 03-05-2014
DOI: 10.1007/S00702-014-1218-Y
Abstract: Abnormal substantia nigra morphology in healthy in iduals, viewed with transcranial ultrasound, is a significant risk factor for Parkinson's disease. However, little is known about the functional consequences of this abnormality (termed 'hyperechogenicity') on movement. The aim of the current study was to investigate hand function in healthy older adults with (SN+) and without (SN-) substantia nigra hyperechogenicity during object manipulation. We hypothesised that SN+ subjects would exhibit increased grip force and a slower rate of force application compared to SN- subjects. Twenty-six healthy older adults (8 SN+ aged 58 ± 8 years, 18 SN- aged 57 ± 6 years) were asked to grip and lift a light-weight object with the dominant hand. Horizontal grip force, vertical lift force, acceleration, and first dorsal interosseus EMG were recorded during three trials. During the first trial, SN+ subjects exhibited a longer period between grip onset and lift onset (i.e. preload duration 0.27 ± 0.25 s) than SN- subjects (0.13 ± 0.08 s P = 0.046). They also exerted a greater downward force prior to lift off (-0.54 ± 0.42 N vs. -0.21 ± 0.12 N P = 0.005) and used a greater grip force to lift the object (19.5 ± 7.0 N vs. 14.0 ± 4.3 N P = 0.022) than SN- subjects. No between group differences were observed in subsequent trials. SN+ subjects exhibit impaired planning for manipulation of new objects. SN+ in iduals over-estimate the grip force required, despite a longer contact period prior to lifting the object. The pattern of impairment observed in SN+ subjects shares similarities with de novo Parkinson's disease patients.
Publisher: American Chemical Society (ACS)
Date: 03-1994
DOI: 10.1021/JM00032A022
Publisher: BMJ
Date: 22-10-2011
Abstract: To assess the efficacy of bilateral pedunculopontine nucleus (PPN) deep brain stimulation (DBS) as a treatment for primary progressive freezing of gait (PPFG). A patient with PPFG underwent bilateral PPN-DBS and was followed clinically for over 14 months. The PPFG patient exhibited a robust improvement in gait and posture following PPN-DBS. When PPN stimulation was deactivated, postural stability and gait skills declined to pre-DBS levels, and fluoro-2-deoxy-d-glucose positron emission tomography revealed hypoactive cerebellar and brainstem regions, which significantly normalised when PPN stimulation was reactivated. This case demonstrates that the advantages of PPN-DBS may not be limited to addressing freezing of gait (FOG) in idiopathic Parkinson's disease. The PPN may also be an effective DBS target to address other forms of central gait failure.
Publisher: Elsevier BV
Date: 10-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 1994
DOI: 10.1039/C39940000599
Publisher: Portland Press Ltd.
Date: 15-09-1996
DOI: 10.1042/BJ3180871
Publisher: Royal Society of Chemistry (RSC)
Date: 1994
DOI: 10.1039/C39940001301
Publisher: Wiley
Date: 28-09-2011
DOI: 10.1002/MDS.23866
Publisher: Elsevier BV
Date: 10-0002
Publisher: No publisher found
Date: 2006
Publisher: Elsevier BV
Date: 09-2017
DOI: 10.1016/J.DRUGALCDEP.2017.05.017
Abstract: Despite evidence that cannabinoid receptors are located in movement-related brain regions (e.g., basal ganglia, cerebral cortex, and cerebellum), and that chronic cannabis use is associated with structural and functional brain changes, little is known about the long-term effect of cannabis use on human movement. The aim of the current study was to investigate balance and walking gait in adults with a history of cannabis use. We hypothesised that cannabis use is associated with subtle changes in gait and balance that are insufficient in magnitude for detection in a clinical setting. Cannabis users (n=22, 24±6years) and non-drug using controls (n=22, 25±8years) completed screening tests, a gait and balance test (with a motion capture system and in-built force platforms), and a clinical neurological examination of movement. Compared to controls, cannabis users exhibited significantly greater peak angular velocity of the knee (396±30 versus 426±50°/second, P=0.039), greater peak elbow flexion (53±12 versus 57±7°, P=0.038) and elbow range of motion (33±13 versus 36±10°, P=0.044), and reduced shoulder flexion (41±19 versus 26±16°, P=0.007) during walking gait. However, balance and neurological parameters did not significantly differ between the groups. The results suggest that history of cannabis use is associated with long-lasting changes in open-chain elements of walking gait, but the magnitude of change is not clinically detectable. Further research is required to investigate if the subtle gait changes observed in this population become more apparent with aging and increased cannabis use.
Publisher: Portland Press Ltd.
Date: 02-1996
DOI: 10.1042/BST024058S
Publisher: American Medical Association (AMA)
Date: 13-03-1996
Publisher: Elsevier BV
Date: 04-2015
DOI: 10.1016/J.CLINPH.2014.07.010
Abstract: Restless legs syndrome, now called Willis-Ekbom Disease (RLS/WED), is a sensorimotor-related sleep disorder. Little is known of the effect of RLS/WED on motor function. The current study investigated upper limb function in RLS/WED patients. We hypothesised that RLS/WED patients exhibit subtle changes in tremor litude but normal dexterity and movement speed and rhythmicity compared to healthy controls. RLS/WED patients (n=17, 59 ± 7 years) with moderate disease and healthy controls (n=17, 58 ± 6 years) completed screening tests and five tasks including object manipulation, maximal pinch grip, flexion and extension of the index finger (tremor assessment), maximal finger tapping (movement speed and rhythmicity assessment), and the grooved pegboard test. Force, acceleration, and/or first dorsal interosseus EMG were recorded during four of the tasks. Task performance did not differ between groups. Learning was evident on tasks with repeated trials and the magnitude of learning did not differ between groups. Hand function, tremor, and task learning were unaffected in RLS/WED patients. Patients manipulated objects in a normal manner and exhibited normal movement speed, rhythmicity, and tremor. Further research is needed to assess other types of movement in RLS/WED patients to gain insight into the motor circuitry affected and the underlying pathophysiology.
Publisher: Humana Press
Date: 2005
Publisher: Elsevier BV
Date: 10-2021
Publisher: Springer Science and Business Media LLC
Date: 31-10-2015
Publisher: Wiley
Date: 04-2013
DOI: 10.1002/ANA.23829
Publisher: Elsevier BV
Date: 04-2016
DOI: 10.1016/J.PARKRELDIS.2016.02.019
Abstract: The sonographic appearance of the substantia nigra is abnormally bright and enlarged (hyperechogenic) in young adults with a history of illicit stimulant use. The abnormality is a risk factor for Parkinson's disease. The aim of the current study was to identify the type of illicit stimulant drug associated with substantia nigra hyperechogenicity and to determine if in iduals with a history of illicit stimulant use exhibit clinical signs of parkinsonism. We hypothesised that use of hetamines (primarily meth hetamine) is associated with substantia nigra hyperechogenicity and clinical signs of parkinsonism. The area of echogenic signal in the substantia nigra was measured in abstinent human hetamine users (n = 27 33 ± 8 years) and in three control groups comprising a) 'ecstasy' users (n = 19 23 ± 3 years), b) cannabis users (n = 30 26 ± 8 years), and c) non-drug users (n = 37 25 ± 7 years). A subset of subjects (n = 55) also underwent a neurological examination comprising the third and fifth part of the Unified Parkinson's Disease Rating Scale. Area of substantia nigra echogenicity was significantly larger in the hetamine group (0.276 ± 0.080 cm(2)) than in the control groups (0.200 ± 0.075, 0.190 ± 0.049, 0.191 ± 0.055 cm(2), respectively P < 0.002). The score on the clinical rating scale was also significantly higher in the hetamine group (8.4 ± 8.1) than in pooled controls (3.3 ± 2.8 P = 0.002). Illicit use of hetamines is associated with abnormal substantia nigra morphology and subtle clinical signs of parkinsonism. The results support epidemiological findings linking use of hetamines, particularly meth hetamine, with increased risk of developing Parkinson's disease later in life.
Publisher: Humana Press
Date: 1999
Publisher: Portland Press Ltd.
Date: 15-08-1993
DOI: 10.1042/BJ2940191
Publisher: Elsevier BV
Date: 04-1997
Publisher: Elsevier BV
Date: 09-1996
Publisher: Elsevier BV
Date: 08-1993
Publisher: Portland Press Ltd.
Date: 08-1995
DOI: 10.1042/BST023420S
Publisher: Wiley
Date: 07-1994
Publisher: Public Library of Science (PLoS)
Date: 29-12-2014
Publisher: AMPCo
Date: 12-2001
Publisher: Elsevier BV
Date: 06-1995
Publisher: Elsevier BV
Date: 12-2019
DOI: 10.1016/J.DRUGALCDEP.2019.107595
Abstract: Illicit stimulant use is associated with long-lasting changes in movement and movement-related brain regions. The aim of our study was to investigate the prevalence of movement dysfunction in this population. We hypothesized that prevalence of self-reported movement dysfunction is higher among stimulant users than non-stimulant users. Three groups of adults completed a survey containing questions about demographics, health, drug use, and movement. The groups consisted of ecstasy users with no history of meth hetamine use (ecstasy group, n = 190, 20 ± 3 yrs.), meth hetamine users (meth hetamine group, n = 331, 23 ± 5 yrs.), and non-stimulant users (control group, n = 228, 25 ± 8 yrs.). Movement data was analyzed with logistic regression. In the unadjusted logistic regression model, group had a significant effect on fine hand control, tremor, and voice/speech questions, but not on other movement domain questions. The prevalence of tremor and abnormal fine hand control was significantly higher in the ecstasy and meth hetamine groups than in the control group (p < 0.018), and changes in voice/speech was more prevalent in the ecstasy group than in the control group (p = 0.015). Age and use of cannabis and hallucinogens were confounding variables. However, inspection of chi-square tables suggests that the effect of these parameters on the movement data is likely to be minor. The prevalence of self-reported tremor and changes in fine hand control and voice/speech is significantly higher in stimulant users than in non-stimulant users. Inclusion of these common and noticeable changes in body function may aid public health c aigns that target prevention or harm minimization.
Publisher: Wiley
Date: 27-01-1997
No related grants have been discovered for Robert A. Wilcox.