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Biomedical subjects

J L Bradshaw

Publications and source records attributed to J L Bradshaw.

At least 19 recordsLinked to original sources
PubMed2003

Hypometric primary saccades and increased variability in visually-guided saccades in Huntington's disease.

Eye movement abnormalities can be distinctive and suggestive of a specific pathophysiology. To further investigate the deficits in the control of saccades in patients with Huntington's disease (HD), we investigated the ability of 11 HD patients and 11 matched controls to perform visually-guided saccades. We adopted reflexive saccade tasks involving predictable and unpredictable sequences, at different amplitudes of target step (10 degrees, 20 degrees, 30 degrees, 40 degrees ), as well as voluntary self-paced saccades. Prolongation of initiation was observed in the HD group as the target amplitude of predictable saccades increased. During the self-paced saccade task, the HD patients had increased intersaccadic intervals, performed fewer saccades in the allocated time and displayed an increased temporal variability in comparison to the controls. Furthermore, hypometric primary saccades, and an increased number of corrective saccades, were observed during both reflexive and voluntary saccades in the HD group. The delayed initiation of large saccades, deficits in voluntary, self-paced saccades, impaired saccadic accuracy and increased corrective saccades in HD, were interpreted in light of other ocular motor and limb studies, and appear to be due to damage to the fronto-striatal loop, including the supplementary eye fields, as well as possible brainstem and cerebellar involvement.

Adult↗
PubMed2002

Attentional asymmetries following ECT in patients with major depression.

Neuropsychological abnormalities of lateralization have been reported after right unilateral electroconvulsive therapy (ECT), that may reflect temporary disruption of the treated hemisphere. A visuospatial task sensitive to lateralization of spatial attention was administered in a test-retest design to patients with unipolar major depression and a group of age and gender matched controls. The patient group underwent right unilateral ECT between the two test sessions. The patient and control groups did not differ significantly at the initial baseline testing. After ECT, the patient group showed a significant shift of attentional bias toward the left, while the control group showed no significant shift in the second session relative to the first. The results suggest that approximately 1 h after termination of ictus there is a leftward attentional bias, possibly reflecting a change in right hemisphere cerebral activity.

Adult↗
PubMed2002

Abnormal line bisection judgements in children with Tourette's syndrome.

Tourette's syndrome (TS) has been associated with loss of normal basal ganglia asymmetry, as well as loss of normal functional asymmetry, including the leftward bias on traditional visuospatial tasks such as line bisection and turning bias tests. The aim of the present study was to examine the lateralisation of visuospatial attention in TS. We examined the effect of an irrelevant moving-dot background on line bisection judgements. Nine children with a DSM IV diagnosis of TS participated, in addition to 9 healthy controls, individually matched for age, sex and IQ. Horizontal lines of varying length were presented on a computer screen with either a blank background, or a moving, random-dot field. The dots moved either leftward or rightward across the screen at 40 or 80 mm/s, and participants were instructed to ignore these distracting stimuli when judging the lines. TS children were found to be abnormally right-biased in line bisection in a similar fashion to unmedicated ADHD children who, in a previous study, showed a similar small, yet significant, right-bias in line bisection. Matched controls showed a small, nonsignificant left bias, consistent with past research. Unlike previous findings with hemineglect patients, the irrelevant moving background had no effect on bisection performance for TS children or healthy controls. The present findings suggest a deficit in visuospatial attention consistent with the emerging picture of a lateralised dysfunction of frontostriatal circuitry in TS.

Adolescent↗
PubMed2002

Mental rotation in unipolar major depression.

Mental rotation (MR) performance may be used as an index of mental slowing or bradyphrenia, and may reflect, in particular, speed of motor preparation. MR was employed with a sample of both melancholic (n=8) and non-melancholic (n=9) unipolar depressed patients and healthy controls (n=10) to determine if motor slowing associated with depression might be reflected in slowed motor preparation (as reflected in slope of the MR function) independent of actual motor slowing (overall response time). Both melancholic and non-melancholic patients showed a generalised slowing relative to controls, perhaps reflecting bradykinesia and akinesia. This effect was significantly greater in the melancholic group than in the non-melancholic group. Relative to both the controls and the non-melancholic groups, the melancholic patients showed a progressive slowing with increasing angle of orientation indicating a specific slowing of MR. This deficit suggests a role of slowed motor planning in the psychomotor retardation of patients with melancholic depression.

Adult↗
PubMed2001

Unconscious priming eliminates automatic binding of colour and alphanumeric form in synaesthesia.

Synaesthesia is an unusual perceptual phenomenon in which events in one sensory modality induce vivid sensations in another. Individuals may 'taste' shapes, 'hear' colours, or 'feel' sounds. Synaesthesia was first described over a century ago, but little is known about its underlying causes or its effects on cognition. Most reports have been anecdotal or have focused on isolated unusual cases. Here we report an investigation of 15 individuals with colour-graphemic synaesthesia, each of whom experiences idiosyncratic but highly consistent colours for letters and digits. Using a colour-form interference paradigm, we show that induced synaesthetic experiences cannot be consciously suppressed even when detrimental to task performance. In contrast, if letters and digits are presented briefly and masked, so that they are processed but unavailable for overt report, the synaesthesia is eliminated. These results show that synaesthetic experiences can be prevented despite substantial processing of the sensory stimuli that otherwise trigger them. We conclude that automatic binding of colour and alphanumeric form in synaesthesia arises after initial processes of letter and digit recognition are complete.

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

Bimanual coordination in chronic schizophrenia.

Anomalies of movement are observed both clinically and experimentally in schizophrenia. While the basal ganglia have been implicated in its pathogenesis, the nature of such involvement is equivocal. The basal ganglia may be involved in bimanual coordination through their input to the supplementary motor area (SMA). While a neglected area of study in schizophrenia, a bimanual movement task may provide a means of assessing the functional integrity of the motor circuit. Twelve patients with chronic schizophrenia and 12 matched control participants performed a bimanual movement task on a set of vertically mounted cranks at different speeds (1 and 2 Hz) and phase relationships. Participants performed in-phase movements (hands separated by 0 degrees ) and out-of-phase movements (hands separated by 180 degrees ) at both speeds with an external cue on or off. All participants performed the in-phase movements well, irrespective of speed or cueing conditions. Patients with schizophrenia were unable to perform the out-of-phase movements, particularly at the faster speed, reverting instead to the in-phase movement. There was no effect of external cueing on any of the movement conditions. These results suggest a specific problem of bimanual coordination indicative of SMA dysfunction per se and/or faulty callosal integration. A disturbance in the ability to switch attention during the out-of-phase task may also be involved.

Adult↗
PubMed2001

Movement-related potentials in Huntington's disease: movement preparation and execution.

Movement-related potentials (MRPs) reflect increasing cortical activity related to the preparation and execution of voluntary movement. Execution and preparatory components may be separated by comparing MRPs recorded from actual and imagined movement. Imagined movement initiates preparatory processes, but not motor execution activity. MRPs are maximal over the supplementary motor area (SMA), an area of the cortex involved in the planning and preparation of movement. The SMA receives input from the basal ganglia, which are affected in Huntington's disease (HD), a hyperkinetic movement disorder. In order to further elucidate the effects of the disorder upon the cortical activity relating to movement, MRPs were recorded from ten HD patients, and ten age-matched controls, whilst they performed and imagined performing a sequential button-pressing task. HD patients produced MRPs of significantly reduced size both for performed and imagined movement. The component relating to movement execution was obtained by subtracting the MRP for imagined movement from the MRP for performed movement, and was found to be normal in HD. The movement preparation component was found by subtracting the MRP found for a control condition of watching the visual cues from the MRP for imagined movement. This preparation component in HD was reduced in early slope, peak amplitude, and post-peak slope. This study therefore reported abnormal MRPs in HD, particularly in terms of the components relating to movement preparation, and this finding may further explain the movement deficits reported in the disease.

Adult↗
PubMed2001

Focal dystonia: current theories.

Dystonia is a syndrome characterised by abnormal involuntary sustained muscle contractions that often result in twisted and abnormal positions. Focal dystonia affects only a single body part with symptoms varying from permanent (e.g., torticollis) to task-specific (e.g., musician's cramp). The exact causes of focal dystonia have yet to be determined. Possible causative factors have been identified at all levels along the sensorimotor pathway, including anatomical constraints of the hand (musicians), abnormal co-contractions of the muscles due to reciprocal inhibition in the spinal cord, subcortical and cortical remapping, deficiencies in sensorimotor integration and perceptual deficits. A review of the current literature on these topics is provided with a special focus on musicians with focal dystonia. Also reviewed are current treatments of focal dystonia in musicians. On the basis of the currently available evidence, certain risk factors are identified for the development of task-specific focal dystonia, including number of practice hours, personality, genetic predisposition, performance factors and sensory effects. In addition, it is highlighted that dystonic movements occur predominantly in the context of perceptual-motor tasks involving emotions. When emotional and motor traces have become associated, they are difficult to change; it is suggested that this mechanism plays an important role in the preservation of dystonic symptoms.

Adult↗
PubMed2001

A kinematic analysis of distractor interference effects during visually guided action in spatial neglect.

Patients with left spatial neglect following right hemisphere damage may show anomalies in ipsilesional-limb movements directed to targets on their affected side, in addition to their characteristic perceptual deficits. In this study we examined the extent to which visually guided movements made by neglect patients are susceptible to interference from concurrent visual distractors on the contralesional or ipsilesional side of a designated target. Eleven right hemisphere patients with visual neglect, plus 11 matched healthy controls, performed a double-step movement task upon a digitizing tablet, using their ipsilesional hand to respond. On each double-step trial the first component of the movement was cued to a common central target, whereas the second component was cued unpredictably to a target on either the contralesional or ipsilesional side. On separate trials lateral targets either appeared alone or together with a concurrent distractor in an homologous location in the opposite hemispace. In addition to being significantly slower and more error prone than controls, neglect patients also exhibited a number of interference effects from ipsilesional distractors. They often failed to move to left targets in the presence of a right-sided distractor, or else they moved to the distractor itself rather than to a contralesional target. The initial accelerative phase of their movements to contralesional targets tended to be interrupted prematurely, and they spent significantly more time in the terminal guidance phase of movements to contralesional targets in the presence of an ipsilesional distractor. In contrast, contralesional distractors had little effect on patients' movements to ipsilesional targets. We conclude that right hemisphere damage induces a competitive bias that favors actions to ipsilesional targets. This bias affects multiple stages of processing within the visuomotor system, from initial programming through to the final stages of terminal guidance.

Adult↗
PubMed2001

Movement preparation in high-functioning autism and Asperger disorder: a serial choice reaction time task involving motor reprogramming.

Autism and Asperger disorder have long been associated with movement abnormalities, although the neurobehavioural details of these abnormalities remain poorly defined. Clumsiness has traditionally been associated with Asperger disorder but not autism, although this is controversial. Others have suggested that both groups demonstrate a similar global motor delay. In this study we aimed to determine whether movement preparation or movement execution was atypical in these disorders and to describe any differences between autism and Asperger disorder. A simple motor reprogramming task was employed. The results indicated that individuals with autism and Asperger disorder have atypical movement preparation with an intact ability to execute movement. An atypical deficit in motor preparation was found in Asperger disorder, whereas movement preparation was characterized by a "lack of anticipation" in autism. The differences in movement preparation profiles in these disorders were suggested to reflect differential involvement of the fronto-striatal region, in particular the supplementary motor area and anterior cingulate.

Adolescent↗
PubMed2001

A deficit in shifting attention present in high-functioning autism but not Asperger's disorder.

The aim of this study was to examine executive functioning, in particular, attentional set-shifting deficits in high-functioning autism (n = 12) and Asperger's disorder (n = 12). A large or global digit composed of smaller or local digits was presented during each trial. The participants indicated the presence of 1s or 2s by pressing the appropriate button. These targets could appear globally or locally Relative to IQ, sex and age matched controls, reaction time to global targets in individuals with autism was retarded when the previous target appeared locally. This deficiency in shifting from local to global processing, however, was not observed in individuals with Asperger's disorder. The theoretical and neurobiological significance of this dissociation in executive functioning in these clinically related disorders was explored.

Adolescent↗
PubMed2000

The neurodevelopmental frontostriatal disorders: evolutionary adaptiveness and anomalous lateralization.

The frontostriatal system (dorsolateral prefrontal cortex, lateral orbitofrontal cortex, anterior cingulate, supplementary motor area, and associated basal-ganglia structures) is subject to a range of neurodevelopmental disorders: Tourette's syndrome (TS), obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), schizophrenia (SCZ), autism, and probably depression. The system is responsible for our adaptive responses (initiation, execution, or withholding) to environmental situations, and the above disorders, involving effectively excessive release or withholding of various types of response, are all a consequence of changes in specific frontostriatal regions. The disorders all have a genetic component, and their persistence in the genome indicates that their clinical manifestations may also be associated, perhaps in low levels in close relatives, with certain adaptive advantages in given situations. Thus autism is associated with computational careers, depression with literary creativity, SCZ with lateral thinking and the Odyssean personality, ADHD with an Ice-Age readiness to respond, OCD with a focused range of interests, and TS with competitive sports and jazz improvisation. The disorders are all highly comorbid, and which one predominantly manifests may depend on how the frontostriatal system happens to be compromised as a result of inherited genetic predispositions and environmental contingency. We review the adaptive nature of the various subclinical manifestations and the evidence for concomitant phenomena (possibly epiphenomena): alterations in structural, functional, and behavioral lateralization in each syndrome. Indeed it is not clear that altered lateralization in frontostriatal disorders of a neurodevelopmental origin generally has any adaptive significance; it may often simply serve as a marker for altered regulatory function of the frontostriatal system, alterations which in low genetic dosage or penetrance continue to play an adaptive role in clinically unaffected close relatives of probands, but which, in high dosage or penetrance in the probands themselves, are generally deleterious.

Adaptation, Physiological↗
PubMed2000

Volume perception in parkinsonian speech.

This study contrasted the volume level of speech production with perceived volume. Fifteen idiopathic patients with Parkinson's disease who have hypophonic dysarthria and 15 healthy age- and sex-matched control subjects participated in this study. Testing took place in a sound-proof room. Ability to regulate volume was tested at three instructional levels of loudness: participants were given no instructions regarding volume (to elicit normal default volume) or were asked to read loudly or quietly. Two types of volume-perception judgments were made. First, an estimate of one's own volume, immediately after speaking (that is, immediate perception), and secondly, an estimation of reading volume after hearing one's own voice played back (that is, playback perception). These perceptual ratings were compared with actual speech volume produced in reading and conversation tasks. It was found that there was less of a difference between patients' production and perception of speech volume compared with that of the control subjects. While patients spoke more quietly than control subjects, they nevertheless perceived (immediate and playback perception) their own speech to be louder than did the control subjects. Patients overestimated the volume of their speech during both reading and conversation. The findings raise the question as to whether impaired speech production is driven by a basic perceptual fault or whether perception is abnormal as a consequence of impaired mechanisms involved in the generation of quiet speech.

Aged↗
PubMed2000

Movement sequencing in children with Tourette's syndrome and attention deficit hyperactivity disorder.

Little research has been conducted to examine sequential motor functioning of children with Tourette's syndrome (TS) and attention deficit hyperactivity disorder (ADHD). Movement sequencing performance for a group of 12 children with TS and 24 children with ADHD children (12 taking and 12 not taking stimulant medication) and matched control subjects was examined using a serial choice reaction time button-pressing procedure. Aspects of movement preparation and execution were measured for 10 sequential two-way choice points along a response board that extinguished the illuminated target buttons at certain specific times contingent on the previous button press or release. The level of advance information was systematically reduced to provide three levels of reduction of advance information, including no reduction, moderate reduction, and high reduction. Children with TS and ADHD (unmedicated) showed larger increases in down time, reflecting aspects of movement preparation, for the highest level of reduction of advance information than did their respective control groups. These deficits are suggestive of underlying frontostriatal dysfunction. Furthermore, the normalization of performance for children with ADHD taking stimulant medication assists in the confirmation of the validity of such a clinical diagnosis and seems to add to the clinical efficacy of this form of treatment, which has previously been associated with improvements for predominantly attentional and inhibitory symptoms of ADHD.

Analysis of Variance↗
PubMed2000

Bimanual co-ordination in Huntington's disease.

The ability of Huntington's disease patients to co-ordinate their two hands with and without external cueing was investigated. Twelve Huntington's disease patients and sex- and age-matched controls performed a bimanual cranking task at two speeds (0.5 Hz, 1.5 Hz) and phase relationships (in-phase, anti-phase), with and without an external metronome cue. Data were sampled at 200 Hz, and raw displacement data for each hand, mean and standard deviation measures of the relative positions of the two hands and their velocities were then calculated. All participants could perform the in-phase movement, at both speeds; however. the Huntington's disease patients were more variable and less accurate than the control participants, particularly at the fast speed. While controls could perform the anti-phase movement, in which rotation of the cranks differed by 180 degrees at both speeds, Huntington's disease patients were unable to do so at either speed, reverting to the in-phase movement at the slow speed. An external metronome cue did not improve the performance of the Huntington's disease patients, which differentiated this group from patients suffering from Parkinson's disease. The Huntington's disease patients' inability to perform the anti-phase movement may be due to damage to the basal ganglia and its output regions.

Adult↗
PubMed2000

Parkinsonian motor characteristics in unipolar major depression.

Clinical observation points to similarities between psychomotor retardation in major depression and bradykinesia in Parkinson's disease (PD). While common elements of neuropathology have been proposed to account for this, experimental investigations of this possible link have been few and inconclusive. The present study attempts to determine whether patients with depression display the characteristically Parkinsonian reliance on external cues; and if so, whether this is common to both melancholic and non-melancholic patients. Twenty three patients with unipolar major depression (11 melancholic and 12 non-melancholic) and 24 age-matched healthy controls performed a serial choice reaction time task known to be sensitive to Parkinsonian movement deficits. The melancholic patients showed a Parkinsonian pattern of impairment on the task, exhibiting a particular difficulty when initiating movements in the absence of external cues. This was largely alleviated when a moderate amount of external cueing was provided. At a high level of advance information, melancholic patients were again slow relative to controls. A base-line measure of bradykinesia and a derived measure of dependence upon external cues both correlated significantly with CORE (measure of psychomotor disturbance) ratings. The non-melancholic patients did not show any measurable motor impairment. This cue-dependent deficit may be due to an underlying basal ganglia dysfunction similar to that involved in PD, i.e. a failure of internal cueing. Difficulty with a high level of external cueing might reflect bradyphrenia or a prefrontal motor deficit of ability to plan multiple upcoming movements simultaneously. The results suggest that depression subtypes involve differing patterns of fronto-striatal impairment.

Cues↗