I.M. Donaldson

Fractionation of visuoperceptual dysfunction in Parkinson's disease

There is considerable evidence that visuoperceptual function is impaired in Parkinsons disease although this view remains contentious. The issue is confounded by studies which have demonstrated impairment of visual sensation, in particular high-contrast visual acuity, in Parkinsons disease. We have measured the visuoperceptual performance of 16 patients with mild to moderate Parkinsons disease, both on and off drugs, and 16 age and sex matched control subjects on non-motor tests of visual resolution, static perception, and dynamic perception. Performance on the perceptual tasks was measured in terms of perceptual resolutions and was found impaired in the parkinsonian group. After removal of the contribution of poorer visual resolution, the overall visual perception remained impaired, although to a relatively subtle degree, such that the difference between the two groups on its static and dynamic components did not reach significance.

Tics and developmental stuttering

BACKGROUND Developmental stuttering affects 1% of the population but its cause remains unclear. Recent PET studies of metabolism in the central nervous system suggest that it may be related to dysfunction in the basal ganglia or its connections with regions of the cortex associated with speech and motor control. OBJECTIVE To determine the presence and characteristics of involuntary movements (IMs) in people who stutter and to investigate the hypothesis that these movements may be of a very similar nature to the IMs seen in patients with movement disorders due to basal ganglia dysfunction. METHODS Sixteen adults with developmental stuttering and 16 controls matched for sex and age were audio-videotaped while freely speaking 300 words in conversation and reading aloud 300 words. The audio data was inspected for dysfluencies and the video data was scrutinised for the presence and characteristics of IMs. RESULTS Subjects who stuttered produced more IMs than controls during free speech (354 vs 187, p<0.05) and reading (297 vs 47, p<0.001). Most of the IMs in both groups were tics, with a greater number of both simple and complex motor tics (CMTs) in subjects who stuttered. CMTs were more frequent than simple motor tics in those who stuttered, but not in controls. The combination of repetitive eye blink followed by prolonged eye closure was found exclusively in the stuttering group, as were simple tics consisting of eyebrow raise or jaw movement. Dystonia in the form of blepharospasm was identified in a small number of subjects who stuttered. Choreic movements were not associated with stuttering. CONCLUSIONS Developmental stuttering is associated with the presence of IMs that are predominantly simple and CMTs. This association suggests that tics and stuttering may share a common pathophysiology and supports the view that, in common with tics, stuttering may reflect dysfunction in the basal ganglia or its immediate connections.

Measurement of sensory-motor integrated function in neurological disorders: Three computerised tracking tasks

Tâche poursuite aleatoire, tâche poursuite a pas et tâche poursuite mixte sont les 3 systemes informatiques etudies

Real-time detection of epileptiform activity in the EEG: a blinded clinical trial.

The aim of this study was to determine the performance of a PC-based system for real-time detection and topographical mapping of epileptiform activity (EA) in the EEG during routine clinical recordings. The system incorporates a mimetic stage to locate candidate spikes (including sharp-waves) followed by two expert-system-based stages, which utilize spatial and wide-temporal contextual information in deciding whether candidate events are epileptiform or not. The data comprised 521 consecutive routine clinical EEG recordings (173 hours). Performance was evaluated by comparison with three independent electroencephalographers (EEGers-I). A second group of two EEGers (EEGers-II) separately interpreted the spike topographical maps and, for EEGs categorized as containing only questionable EA by the detection system, reviewed 6 sec segments of raw EEG centered on each questionable event. Thirty-eight of the EEGs were considered to contain definite EA by at least two of EEGers-I. The false detection rate of the system was 0.41 per hour. The system was found to have a sensitivity of 76% and a selectivity of 41% for EEGs containing definite EA. However, it only missed detection of EA in 5% of the recordings. EEGers-II agreed with EEGers-I on the distribution (generalized, lateralized, focal, multifocal) of EA in 79% of cases. This is by far the largest clinical evaluation of computerized spike detection reported in the literature and the only one to apply this in routine clinical recordings. The false detection rate is the lowest ever reported, suggesting that this multi-stage rule-based system is a powerful and practical tool in clinical electroencephalography and long-term EEG monitoring.

Measurement and Analysis of Single and Multiple Finger Tapping in Normal and Parkinsonian Subjects

A four-finger tapping sensor and associated software have been developed for the investigation of timing and rhythm performance and mechanisms in normal subjects and their disruption in neurological disorders. The tapping sensor comprises four electronic touch pads and pacing lights. A personal computer (PC) is used to control visual and auditory pacing, record the time and pad of each tap, and carry out several performance analyses including graphing, phase-space plots, calculation of spectra and autocorrelations, filtering and descriptive statistical analysis. A study was conducted to investigate disruptions of timing and rhythm in subjects with Parkinsons disease (PD). Seven Parkinsonian and ten control subjects undertook paced and unpaced finger tapping tests. The hastening phenomenon-tapping asynchronously at a speed faster than the pacing-was seen with similar occurrence in both normal and PD subjects and appears to be due to perceptual difficulties. No evidence was seen of an increased variability of tapping at particular frequencies, contrary to previous reports. Festinated tapping, in which subjects cycled between acceleration to near-maximum speed and abrupt slowing down, was seen only in PD subjects. As noneof these subjects showed significant hastening, it appears that hastening and festination are unrelated phenomena. Inspection of variations of finger tapping intervals gave no evidence for the presence of deterministic chaos in the control of rhythmic tapping. In speed tests performed with and without a weight attached to the finger, it was found that, for reasons which remain unclear, normal subjects increased their maximum tapping speed with the weight attached.

Dysfluency and involuntary movements : A new look at developmental stuttering

Studies using modern imaging techniques suggest that, in developmental stuttering, there is dysfunction within the cortical and subcortical areas of the motor control system wider than that pertaining to speech motor control alone. If this is the case, one might expect motor deficits extending beyond and unrelated to the production of speech in people who stutter. This study explored this proposal by investigating the presence and characteristics of involuntary movements accompanying stuttering. Sixteen adults with developmental stuttering and 16 controls matched for age and sex were audio-videotaped during 5 minutes of conversational speech and reading a passage of 350 words. Audio-data were examined for dysfluencies. Movements of the face, head and upper body considered involuntary and not part of normal facial expression or gesture and not part of the mechanics of speech were identified and described from muted video-data. Subjects who stuttered had a higher proportion of classic (within-word) dysfluencies accompanied by involuntary movements (IMs) than controls during speech (24.4% vs. 4.5%, p=.054) and reading (28.6% vs. 4.9%, p equals;. 033). There was no difference in proportion of classic dysfluencies accompanied by IMs between speech and reading for either group. IMs were also seen in both groups during fluent speech, with a similar incidence during free speech (3.9% vs. 3.0%, NS) but a greater incidence in the subjects who stuttered during reading (2.4% vs. 0.8%, p equals;. 03). In contrast, there was no difference between the two groups for IMs accompanying normal (between-word) dysfluencies. This suggests that classic and normal dysfluency and their accompanying IMs have different etiologies. The notion that stuttering and IMs are due to altered function in a motor control system wider than that of speech motor control alone is supported by a higher incidence of IMs in people who stutter during both classic dysfluencies and fluent speech.

Impairment and recovery profiles of sensory-motor function following stroke: Single-case graphical analysis techniques

Graphical analysis procedures have been developed to improve interpretation of sensory-motor tests from individual subjects following acute brain damage. The procedures have been applied to 11 unilateral stroke patients assessed serially over 12 months on a computerized quantitative sensory-motor test battery of which grip strength, arm speed, and tracking have been chosen for illustrative purposes. The results indicate that four graphs are necessary to fully demonstrate neurologic impairment and recovery of each sensory-motor function, although fewer graphs would be satisfactory in some applications. Such analyses have proven valuable in the display of serial performance of individual patients but demonstration of impairment and recovery is much more difficult than for group analyses.

A technique for removal of the visuoperceptual component from tracking performance and its application to Parkinson's disease

Although it is well established that subjects with Parkinsons disease perform poorly on complex sensory-motor tasks, the extent to which this is due to visuoperceptual deficits is unclear. The authors measured the performance of 16 patients with Parkinsons disease, both on and off drugs, and 16 age and sex matched control subjects on preview and nonpreview tracking tasks and a nonmotor test of dynamic visuoperception. Order effects were controlled for by a randomized cross-over design. Performance on the perceptual task was measured in terms of perceptual resolution and was found impaired in the Parkinsonian group. The contribution of visuoperceptual function to tracking performance was removed using the concept of a visuoperceptual buffer-zone. The mean tracking error remained impaired on all tracking tasks and demonstrated that limitations in visuoperceptual function play only a minor role in the tracking errors in both Parkinsonian and control subjects. It is clear that the technique for determining the visuoperceptual component of performance on complex sensory-motor tasks has considerable scope for application in studies of a variety of brain disorders.

Tracking tasks and the study of predictive motor planning in Parkinson's disease

The authors have studied the performances of 16 subjects with PD (Parkinsons disease) and 16 matched control subjects on a range of computerized tracking tasks (preview and nonpreview forms of sine, random, and step inputs, plus a random-step combination) and related tests. Predictive motor planning was studied by way of three types of advance information which may be available on a targets path: memory (periodicity), form (speed/acceleration characteristics), and preview. PD subjects were impaired with respect to preview only. This deficit could, however, be a consequence of impaired visuospatial perception rather than being a true motor planning deficit. Hence, no evidence was found for impaired sensory-motor performance that could be unequivocally attributed to a deficit in predictive motor planning.<<ETX>>

The Use Of Multi-channel Information In The Detection Of Epileptiform Activity In The EEG

A PC-based system has been developed to automatically detect epileptiform events in the inter-ictal EEG. The system consists of three stages : data collection, data reduction and confirmation and classification of epileptiform events. A basic multi-channel capability has been introduced into the data reduction stage (in the form of a two threshold system) to increase the proportion of epileptiform transients detected. The classification of epileptiform events as definite or probable overcomes, to an extent, the problem of maintaining high detection rates while eliminating false detections. The system has been evaluated on the EEGs of 8 patients with 54-70% of epileptiform events being detected as definite (i.e no false detections), and 60-100% as either definite or probable events at the expense of introducing up to 15 false detections per hour. Current work aimed at taking temporal, as well as spatial, information into account should realize still higher detection rates.