Biomedical subjects

M Jahanshahi

Publications and source records attributed to M Jahanshahi.

At least 37 records · Page 2Linked to original sources

PubMed2000

How does Parkinson's disease affect quality of life? A comparison with quality of life in the general population.

BACKGROUND: Adequate provision of appropriate healthcare resources for patients with chronic neurologic disorders such as Parkinson's disease (PD) requires knowledge of the impact of the illness on their life. Quality of life (QoL) instruments measure the impact of the disease on general well-being that cannot be fully appreciated by clinical rating scales and allow comparisons with other patient groups and the general population. OBJECTIVES: To assess QoL in a population-based sample of patients with PD in different disease stages in comparison with the general population. METHODS: All 124 patients with PD seen in a population-based study on the prevalence of parkinsonism in the London area were asked to complete a QoL battery including the EuroQoL 5D (EQ-5D), the Medical Outcome Study Short Form (SF 36), and the 39-item Parkinson's Disease questionnaire (PDQ-39). An interview and complete neurologic examination, including the Hoehn and Yahr scale, were performed on the same day. The patients' QoL scores were compared with published QoL norms from the United Kingdom population. RESULTS: Quality of life, as measured by the PDQ-39, the EQ-5D, and the physical summary of the SF 36, deteriorated significantly with increasing disease severity. The greatest impairment was seen in the areas related to physical and social functioning, whereas reports of pain and poor emotional adjustment had similar prevalence in patients with PD and the general population. The impairment of QoL was seen in all age groups and was similar for men and women, but the differences between patients with PD and the general population were most marked in the younger patient groups. CONCLUSIONS: Parkinson's disease interferes with various aspects of QoL, particularly those related to physical and social functioning. This information should be taken into account in the clinical management and planning and allocation of healthcare resources to this population.

Adult↗

PubMed2000

The role of the dorsolateral prefrontal cortex in random number generation: a study with positron emission tomography.

Random number generation (RNG) engages a number of executive processes. We used positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in six volunteers who performed RNG and a control counting (COUNT) task at six rates paced by a tone. This provided a systematic variation of difficulty of RNG. Relative to COUNT, RNG was associated with significant activation of the left dorsolateral prefrontal cortex (DLPFC), the anterior cingulate, the superior parietal cortex bilaterally, the right inferior frontal cortex, and the left and right cerebellar hemispheres. Faster rates of RNG were associated with a significant decrease in regional cerebral blood flow (rCBF) in the left and right DLPFC and the right superior parietal cortex. rCBF in the left DLPFC was significantly and negatively associated with count score 1, a measure of habitual counting during RNG. These results are discussed in relation to the network modulation model of RNG developed on the basis of our previous studies using transcranial magnetic stimulation and dual task paradigms. This suggests that during RNG, suppression of habitual counting is achieved through the modulatory (inhibitory) influence of the left DLPFC over a number associative network distributed in the superior temporal cortex. At faster rates of RNG the synchronization demands of paced RNG result in the breakdown of this modulatory influence, which is evident from decreased rCBF in the left DLPFC and increased habitual counting at faster rates.

Adult↗

PubMed2000

Cortical potentials related to the nogo decision.

The go/nogo reaction time task has been frequently used to assess volitional inhibition. Psychophysiological studies of the correlates of the go/nogo decision have almost exclusively been concerned with N2 and P3 potentials of the event-related potentials (ERPs). However, in studies where the EMG onset latency was available, it was obvious that this latency was shorter than or at least equal to the latencies of the studied cerebral potentials. In this study, by concurrent recording of the EEG and EMG activity we aimed to better define the temporal relationship between cortical activity and motor response. Particularly, we wanted to identify the early (i.e. pre EMG-onset) electrophysiological correlates of the nogo decision. We used a modified S1-S2 paradigm that involved a two-stage go/nogo decision. In this task both S1 and S2 were informative and required the subject to make a decision, but the nature of the decision differed. The decision at S1 involved whether to prepare a movement, whereas the decision at S2 involved whether to initiate or inhibit an already prepared response. To better visualise the nogo decision related components of the ERPs, the go ERPs were subtracted from the corresponding nogo ERPs and difference ERPs were formed. Before EMG onset, a small negative component common to both go/nogo difference traces and corresponding roughly with the N1 wave was detected. It is suggested that this early negativity may be a more specific electrophysiological reflection of the nogo decision proper.

Adult↗

PubMed2000

Transcranial magnetic stimulation studies of cognition: an emerging field.

In this short review, we consider the application of transcranial magnetic stimulation (TMS) to the study of cognitive function. Following an introduction to the technique, we consider its possible mechanisms of action. We then review the studies that have applied TMS to the investigation of cognition. In the majority of these investigations, TMS has been applied to disrupt function and demonstrate that a particular cortical area is essential for performance of the task under study. Finally, we highlight pertinent design and procedural issues and consider other types of questions that can be addressed by future TMS studies of cognitive function.

Brain Mapping↗

PubMed2000

The impact of deep brain stimulation on executive function in Parkinson's disease.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the internal segment of the globus pallidus (GPi) improves Parkinson's disease and increases frontal blood flow. We assessed the effects of bilateral DBS on executive function in Parkinson's disease patients, seven with electrodes implanted in the STN and six in the GPi. Patients were assessed off medication with stimulators off, on and off again. The groups showed differential change with stimulation on the Reitan Trail-Making test (TMT B) (STN more improved) and on some measures of random number generation and Wisconsin Card Sorting (STN improved, GPi worse with stimulation). Across the groups, stimulation speeded up responding (Stroop control trial, TMT A) and improved performance on paced serial addition and missing digit tests. Conversely, conditional associative learning became more errorful with stimulation across the two groups. In general, change in performance with stimulation was significant for the STN but not the GPi group. These results support two opposite predictions. In support of current models of Parkinson's disease, 'releasing the brake' on frontal function with DBS improved aspects of executive function. Conversely, disruption of basal ganglia outflow during DBS impaired performance on tests requiring changing behaviour in novel contexts as predicted by Marsden and Obeso in 1994.

Association Learning↗

PubMed2000

Self-initiated versus externally triggered movements. II. The effect of movement predictability on regional cerebral blood flow.

Event-related potential studies in man suggest a role for the supplementary motor area (SMA) in movement preparation, particularly when movements are internally generated. In a previous study combining PET with recording of movement-related cortical potentials, we found similar SMA activation and early pre-movement negativity during self-initiated and predictably paced index finger extensions. Early pre-movement negativity was absent when finger movements were paced by unpredictable cues. We postulated that preparation preceding self-initiated and predictably cued movements was responsible for equivalent levels of SMA activation in these two conditions. To test this, we have performed further studies on six normal volunteers with H2(15)O-PET. Twelve measurements of regional cerebral blood flow were made in each subject under three conditions: rest; self-initiated right index finger extension at a variable rate of once every 2-7 s; and finger extension triggered by pacing tones at unpredictable intervals (at a rate yoked to the self-initiated movements). Activation associated with these conditions was compared using analysis of covariance and t statistics. Compared with rest, unpredictably cued movements activated the contralateral primary sensorimotor cortex, caudal SMA and contralateral putamen. Self-initiated movements additionally activated rostral SMA, adjacent anterior cingulate cortex and bilateral dorsolateral prefrontal cortex (DLPFC). Direct comparison of the two motor tasks confirmed significantly greater activation of these areas and of caudal SMA in the self-initiated condition. These results, combined with our previous data, suggest that rostral SMA plays a primary role in movement preparation while caudal SMA is a motor executive area. In this experiment and in our earlier study, DLPFC was activated only during the self-initiated task, in which decisions were required about the timing of movements.

Adult↗

PubMed2000

Factors that ameliorate or aggravate spasmodic torticollis.

A sample of 72 patients with adult onset torticollis were asked to complete a checklist to indicate how a list of situations and activities affected the severity of their torticollis. Stress and self consciousness were reported as aggravating factors by more than 80% of the sample, whereas walking, fatigue, and carrying objects were noted as exacerbators by over 70% of the patients. For more than 40% of the sample, torticollis improved in the supine position, by relaxation, sleep, and lying on the side. However, the last four factors also worsened the head deviation in 16% to 25% of the patients. Use of a "geste antagoniste" to maintain the head in the body midline, was reported by 64 (88.9%) of the patients, which was still effective in correcting head position in 47%. The sensitivity of torticollis to social and emotional factors can be best explained in terms of a possible link between extrapyramidal and affective disorders through overlapping changes in catecholamine metabolism. The worsening of torticollis with peripheral motor activity (walking, running, writing) or its improvement with changes in body posture or with the geste antagoniste is best viewed in terms of alterations of peripheral proprioceptive feedback or central corollary discharge provoked by the motor output or command.

Adult↗

PubMed2000

The EQ-5D--a generic quality of life measure-is a useful instrument to measure quality of life in patients with Parkinson's disease.

OBJECTIVE: To test the feasibility and validity of the EQ-5D (a widely used generic (disease non-specific) quality of life (QoL) instrument which allows comparisons between different patient groups and the general population) to assess QoL in patients with Parkinson's disease. METHODS: All 124 patients with Parkinson's disease seen in a community based study on the prevalence of parkinsonism were asked to complete a QoL battery comprising the EQ-5D, the medical outcome study short form (SF-36), the PDQ-39, a disease specific instrument to assess QoL in PD, and the Beck depression inventory. A structured questionnaire interview and a complete neurological examination including the Hoehn and Yahr stage of illness scale, the Schwab and England disability scale, the motor section of the unified Parkinson's disease rating scale (UPDRS), and the mini mental state examination (MMSE) were performed on the same day. RESULTS: The response rate was 78% and the completion rate of the EQ-5D among responders was 96%. The EQ-5D summary index correlated strongly with the PDQ-39 (r=-0.75, p<0.0001) as well as the physical score of the SF-36 (r=0.61, p<0.0001). There was a significant correlation of the EQ-5D summary index with disease severity, as measured by the Hoehn and Yahr stage of illness, the Schwab and England disability scale, the motor section of the UPDRS, and the depression score. The EQ-5D summary index also distinguished between patients with and without depression, falls, postural instability, cognitive impairment hallucinations, and those with deterioration of health over the previous year. CONCLUSION: The EQ-5D is a feasible and valid instrument to measure QoL in Parkinson's disease and reflects the severity and complications of the disease.

Activities of Daily Living↗

PubMed2000

What contributes to quality of life in patients with Parkinson's disease?

OBJECTIVE: To identify the factors that determine quality of life (QoL) in patients with idiopathic Parkinson's disease in a population based sample. Quality of life (QoL) is increasingly recognised as a critical measure in health care as it incorporates the patients' own perspective of their health. METHODS: All patients with Parkinson's disease seen in a population based study on the prevalence of parkinsonism were asked to complete a disease-specific QoL questionnaire (PDQ-39) and the Beck depression inventory. A structured questionnaire interview and a complete neurological examination, including the Hoehn and Yahr scale, the Schwab and England disability scale, the motor part of the unified Parkinson's disease rating scale (UPDRS part III), and the mini mental state examination were performed by a neurologist on the same day. RESULTS: The response rate was 78%. The factor most closely associated with QoL was the presence of depression, but disability, as measured by the Schwab and England scale, postural instability, and cognitive impairment additionally contributed to poor QoL. Although the UPDRS part III correlated significantly with QoL scores, it did not contribute substantially to predicting their variance once depression, disability, and postural instability had been taken into account. In addition, patients with akinetic rigid Parkinson's disease had worse QoL scores than those with tremor dominant disease, mainly due to impairment of axial features. CONCLUSION: Depression, disability, postural instability, and cognitive impairment have the greatest influence on QoL in Parkinson's disease. The improvement of these features should therefore become an important target in the treatment of the disease.

Aged↗

PubMed1999

Cortical potentials related to decision-making: comparison of two types of go/no-go decision.

The S1-S2 go/no-go reaction time task has been frequently used to assess volitional inhibition. In this study our aim was to compare the ERPs elicited by S1 and S2 by using a modified S1-S2 paradigm which involved a two-stage go/no-go decision. The go and the no-go S1 ERPs did not differ substantially, and both displayed a prominent negativity with peaks at 260 ms (S1N260) and at 330 ms (S1N330) post-S1. The S1N260 was similar to the N2 from no-go S2 trials. Since after all three types of stimuli, movement is not required and is inappropriate, this negativity may represent the correlate of the voluntary decision to suppress movement. Later, the S1 ERPs were dominated by frontal negativity (S1N330), probably reflecting further processes related to response preparation, while the S2 ERPs displayed a large central and parietal positivity (P3), probably reflecting the processes of evaluation of response accuracy.

Adult↗

PubMed1999

Impact of deep brain stimulation on upper limb akinesia in Parkinson's disease.

Recent pathophysiological models of Parkinson's disease have led to new surgical approaches to treatment including deep brain stimulation (DBS) and lesioning of basal ganglia structures. Various measures of upper limb akinesia were assessed in 6 patients with bilateral DBS of the internal pallidum and 6 with DBS of the subthalamic nucleus. Stimulation improved a number of aspects of motor function, and particularly movement time, and force production. Time to initiate movements, and to perform repetitive movements also improved but less dramatically. Processes indicating preparatory motor processes showed no significant change. Few significant differences were found between the internal pallidum and subthalamic nucleus groups. In general, the effects of DBS closely parallel previous reports of the effects of dopaminergic medication. It is suggested that disrupted pallidal output in Parkinson's disease interferes with the rate, level, and coordination of force production but has little effect on preparatory processes. The similarity of the effects of subthalamic nucleus and internal pallidum stimulation suggests this disrupted outflow is the most important determinant of upper limb akinesia in Parkinson's disease. The effects of DBS were similar to the effects of unilateral pallidal lesions reported elsewhere.

Brain↗

PubMed1999

Movement-related potentials prior to self-initiated movements are impaired in patients with schizophrenia and negative signs.

It has been suggested that certain symptoms of schizophrenia such as poverty of action and speech, and stereotyped action, reflect a dysfunction of "willed" actions while the processes involved in "stimulus-driven" actions remain intact. The aim of this study was to test this hypothesis by measuring movement-related potentials (MRPs) prior to self-initiated and externally triggered movements in three groups of subjects, five patients with a diagnosis of schizophrenia with high ratings of negative signs, six patients with a diagnosis of schizophrenia with high ratings of positive symptoms and six normal controls. Subjects lifted their right index finger at an average rate of once every 3 s in two conditions, either as self-initiated movements, or as a response to a tone while MRPs were recorded from frontal, frontocentral, central and parietal sites. The patients with schizophrenia and high ratings of negative signs had reduced amplitude of MRPs for the late and peak component and reduced slope of the early and late MRPs prior to self-initiated movements. These differences were not found prior to externally triggered movements. The patients with schizophrenia with higher ratings of positive symptoms did not differ significantly from the normal controls in terms of amplitude or slope of MRPs prior to self-initiated or externally triggered movements. These findings support the proposal that patients with schizophrenia, particularly those with negative signs, show impairment of willed actions but are not impaired in externally triggered movements. These deficits in willed actions may be mediated by impaired functioning of the frontostriatal loops.

Adult↗

PubMed1999

The left dorsolateral prefrontal cortex and random generation of responses: studies with transcranial magnetic stimulation.

Evidence from PET studies suggests that the dorsolateral prefrontal cortex (DLPFC) is involved in generation of random responses. We used TMS to examine the specific role of this area in random generation of responses, a task which requires holding information 'on line', suppression of habitual or stereotyped response patterns, intrinsic response generation, monitoring of responses and modification of production strategies. From the results of a previous study of the effects of TMS on random number generation, we proposed a network modulation model, whereby suppression of habitual responses is considered a key process of random response generation and is achieved through the modulatory influence of the left DLPFC over an associative network distributed in the superior temporal cortex. The aim of the present study was to further investigate the generality of this model by examining the effects of short trains of TMS over the left or right DLPFC or medial frontal cortex on random letter generation in healthy participants. TMS over the left DLPFC significantly increased non-randomness relative to control no stimulation trials, which was not obtained with TMS over the right DLPFC or medial frontal cortex. The results suggest the generality of network modulation model of random response generation.

Adult↗

PubMed1999

The effects of posteroventral pallidotomy on the preparation and execution of voluntary hand and arm movements in Parkinson's disease.

We studied the effect of posteroventral pallidotomy on movement preparation and execution in 27 parkinsonian patients using various motor tasks. Patients were evaluated after overnight withdrawal of medication before and 3 months after unilateral pallidotomy. Surgery had no effect on initiation time in unwarned simple and choice reaction time tasks, whereas movement time measured during the same tasks was improved for the contralesional hand. Movement times also improved for isometric and isotonic ballistic movements. In contrast, repetitive, distal and fine movements measured in finger-tapping and pegboard tasks were not improved after pallidotomy. Preparatory processes were investigated using both behavioural and electrophysiological measures. A precued choice reaction time task suggested an enhancement of motor preparation for the contralesional hand. Similarly, movement-related cortical potentials showed an increase in the slope of the late component (NS2) when the patients performed joystick movements with the contralesional hand. However, no significant change was found for the early component (NS1) or when the patient moved the ipsilesional hand. The amplitude of the long-latency stretch reflex of the contralesional hand decreased after surgery. In summary, the data suggest that pallidotomy improved mainly the later stages of movement preparation and the execution of proximal movements with the contralesional limb. These results provide detailed quantitative data on the impact of posteroventral pallidotomy on previously described measures of upper limb akinesia in Parkinson's disease.

Electroencephalography↗

PubMed1999

Sequential bilateral transplantation in Parkinson's disease: effects of the second graft.

Five parkinsonian patients who had received implants of human embryonic mesencephalic tissue unilaterally in the striatum 10-56 months earlier were grafted with tissue from four to eight donors into the putamen (four patients) or the putamen plus the caudate nucleus (one patient) on the other side, and were followed for 18-24 months. After 12-18 months, PET showed a mean 85% increase in 6-L-[18F]fluorodopa uptake in the putamen with the second graft, whereas there was no significant further change in the previously transplanted putamen. Two patients exhibited marked additional improvements after their second graft: 'on-off' fluctuations virtually disappeared, movement speed increased, and L-dopa could be withdrawn in one patient and reduced by 70% in the other. The improvement in one patient was moderate. Two patients with atypical features, who responded poorly to the first graft, worsened following the second transplantation. These findings indicate that sequential transplantation in patients does not compromise the survival and function of either the first or the second graft. Moreover, putamen grafts that restore fluorodopa uptake to normal levels can give improvements of major therapeutic value.

Adult↗

PubMed1999

Parkinson's syndrome after closed head injury: a single case report.

A 36 year old man, who sustained a skull fracture in 1984, was unconscious for 24 hours, and developed signs of Parkinson's syndrome 6 weeks after the injury. When assessed in 1995, neuroimaging disclosed a cerebral infarction due to trauma involving the left caudate and lenticular nucleus. Parkinson's syndrome was predominantly right sided, slowly progressive, and unresponsive to levodopa therapy. Reaction time tests showed slowness of movement initiation and execution with both hands, particularly the right. Recording of movement related cortical potentials suggested bilateral deficits in movement preparation. Neuropsychological assessment disclosed no evidence of major deficits on tests assessing executive function or working memory, with the exception of selective impairments on the Stroop and on a test of self ordered random number sequences. There was evidence of abulia. The results are discussed in relation to previous literature on basal ganglia lesions and the effects of damage to different points of the frontostriatal circuits.

Adult↗

PubMed1999

Impairment of willed actions and use of advance information for movement preparation in schizophrenia.

OBJECTIVES: To assess willed actions in patients with schizophrenia using reaction time (RT) tasks that differ in the degree to which they involve volitionally controlled versus stimulus driven responses. METHODS: Ten patients diagnosed with schizophrenia and 13 normal controls of comparable age were tested. Subjects performed a visual simple RT (SRT), an uncued four choice reaction time (CRT), and a fully cued four choice RT task. A stimulus 1(S1)-stimulus 2(S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 (no warning signal or precue) 200, 800, 1600, or 3200 ms. RESULTS: The patients with schizophrenia had significantly slower RTs and movement times than normal subjects across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, fully cued CRTs were significantly faster than the uncued CRTs. However, the S1-S2 interval had a differential effect on CRTs in the two groups. For the normal subjects fully cued CRTs and SRTs were equivalent when S1-S2 intervals were 800 ms or longer. A similar pattern of effects was not seen in the patients with schizophrenia, for whom the fully cued CRT were unexpectedly equivalent to SRT for the 200 ms interval and expectedly for the 1600 ms S1-S2 interval, but not the 3200 or 800 ms intervals. CONCLUSIONS: Patients with schizophrenia were able to use advance information inherent in SRT or provided by the precue in fully cued CRT to speed up RT relative to uncued CRT. However, in the latter task, in which the volitional demands of preprogramming are higher since a different response has to be prepared on each trial, patients showed some unusual and inconsistent interval effects suggesting instability of attentional set. It is possible that future studies using RT tasks with higher volitional demands in patients with predominance of negative signs may disclose greater deficits in willed action in schizophrenia.

Adult↗

PubMed1999

Concurrent performance of motor tasks and processing capacity in patients with schizophrenia.

Any task is carried out more successfully if we allocate undivided attention to it, but as demands on attentional capacity increase-for example, in concurrent or dual task conditions-performance on attended tasks becomes more impaired. Patients with schizophrenia show impaired performance on tasks requiring high levels of attentional capacity. This study examines performance of 11 patients with schizophrenia and 13 normal controls on two motor tasks (placing pegs in a pegboard and repetitive index finger tapping) under unimanual, bimanual, and dual task conditions. The patients with schizophrenia placed fewer pegs and had reduced tapping speed in unimanual and bimanual conditions. However, the decrement in bimanual performance as a percentage of unimanual performance was not significantly different for the patients and controls on either the pegboard or tapping tasks. By contrast, under dual task conditions, the performance of the patients with schizophrenia in peg placement actually improved relative to the unimanual pegboard task, whereas tapping performance deteriorated compared with the unimanual tapping, a decrement that was significantly greater for the patients. Thus the improvement in the visually guided pegboard task was at the expense of the repetitive tapping task. These results are discussed in terms of an impairment of self initiated movement with general sparing of externally triggered movements in schizophrenia and the role of frontostriatal loops in this process.

Adult↗