A case of severe dysexecutive syndrome consecutive to chronic bilateral pallidal stimulation

In treatment for severe Parkinson's disease (PD), a recent procedure was developed which consists of implanting electrodes in the internal Globus Pallidus (GPi) for chronic electrical stimulation. The consequences on cognitive function of such an intervention are quite variable. Although most group studies observed no significant post-operative change, individual cases of post-operative cognitive impairment were reported. The present study reports the case of a PD patient who underwent bilateral implantation of deep brain stimulation electrodes in the GPi and who, after surgery, suffered from a severe dysexecutive syndrome. An extensive neuropsychological examination showed a selective negative effect of pallidal stimulation on tests assessing executive function. When the stimulation was turned off, the impairment was partly reversible. This observation emphasizes the role of the GPi in executive function.

Neuropsychological abnormalities in first degree relatives of patients with familial Parkinson's disease

OBJECTIVE

To investigate the cognitive profile of first degree relatives of patients with familial Parkinson's disease to determine whether these subjects presented signs of neuropsychological dysfunction compared with healthy controls. Results of recent genetic and neuroimaging studies suggest a genetic contribution to the aetiology of Parkinson's disease and underline the interest in identifying preclinical signs of the disease.

METHODS

A battery of tests evaluating executive function was administered to 41 first degree relatives of patients with well documented familial Parkinson's disease and 39 healthy controls. A factorial discriminant analysis allowed isolation of a subgroup of 15 first degree relatives who could be considered as impaired compared with the healthy controls. Among these 15 "deviant" relatives, nine performed globally worse than the control subjects on all tasks. The six other subjects had mean or even high scores on all task variables, except on those highly correlated with the discriminant score of the factorial discriminant analysis.

RESULTS AND CONCLUSION

Among the first degree relatives of patients with familial Parkinson's disease, some manifested executive dysfunction comparable with that typically associated with the disease. Such impairment could represent a preclinical form of Parkinson's disease.

Impairment of the supervisory attentional system in early untreated patients with Parkinson's disease

The aim of this study was to specify the frontal type dysfunction widely reported in Parkinson's disease (PD) early in the course of the disease and before dopaminergic therapy. Seventeen "de novo" PD patients and 17 healthy control subjects performed modified versions of the Stroop word-color test and the Brown Peterson paradigm. A dissociation between results on the two tasks was observed in PD patients. They had difficulties in inhibiting a strong habitual response and establishing a new, better adapted pattern of response; but they performed as well as controls in a dual-task paradigm requiring correct allocation of the processing resources of working memory. Early in the course of the disease, untreated PD patients suffer from dysfunction of the supervisory attentional system. However, the present findings suggest that this system is not a single unit but rather could be composed of multiple subsystems whose sensitivity depends on the origin of frontal dysfunction. Indeed, only a few of these subsystems seemed to be impaired in de novo PD patients. It can be hypothesized that those involved in the phenomena of adaptation and consolidation of currently appropriate responses depend on the dorsolateral prefrontal loop, which is affected by the dopaminergic innervation of the caudate nucleus.

Comparison of the effects of zolpidem and flunitrazepam on sleep structure and daytime cognitive functions. A study of untreated unsomniacs

The effects of zolpidem 10 mg, flunitrazepam 1 mg, and placebo, administrated at bedtime, were studied in 12 healthy male insomniac patients. The assessments included polygraphic sleep recordings during the night and a battery of cognitive tests (sign crossing test, dichotic listening test, digit span test, visual recognition test and free recall test during four times during the following day. Compared with placebo, both active drugs improved sleep parameters. However, with zolpidem, the results were not statistically different from placebo. Zolpidem dit not alter sleep architecture in contrast to flunitrazepam, which significantly increased stage 2 and decreased slow wave sleep and REM sleep. No significant interaction was found between time of day for the evaluation of cognitive function. Flunitrazepam significantly impaired attention and memory compared with zolpidem and placebo, while zolpidem did not differ from placebo. These results indicate that zolpidem 10 mg preserved sleep structure and daytime cognitive functions in contrast to flunitrazepam.

Attention impairment in recently diagnosed multiple sclerosis

Patients with multiple sclerosis (MS) experience cognitive disorders which can occur early in the course of the disease. The present study tried to investigate attention abilities of MS patients at the early stage of the disease. Three attention modalities (sustained, simple and complex focused attention) were evaluated. The results show that MS patients at the early stage of the disease presented attentional dysfunction only when the cognitive load of the attention task was high and when controlled information processing was required. This suggests that MS patients probably suffer from a processing resources deficit without modification of the attentional mechanisms.

Event-related desynchronization (ERD) patterns during memory processes: effects of aging and task difficulty

Event-related desynchronization (ERD) was studied in 10 young (mean age = 19.1) and 10 older (mean age = 62.8) subjects during two recognition tasks: verbal and visuo-spatial. The difficulty of these tasks varied according to the difficulty to distinguish between targets and distractors. EEGs recorded from 29 electrodes were used to compute ERDs from 14 source derivations in 125 msec intervals. Thereafter, they were displayed as spatio-temporal maps. The results show that desynchronization was more widespread in the visuo-spatial compared to the verbal task. This was observed in the two age groups, although it was more pronounced in the young subjects. The effect of task complexity was also influenced by the kind of material to be remembered: more differences between the two levels of difficulty were observed during the verbal task. The results revealed significant influences of the task and time variables on the ERD patterns. A distinct time course of the desynchronization phenomenon was observed to be related to the kind of recognition task. Age and task complexity interacted with the other variables.

Spatiotemporal study of Bereitschaftspotential and event-related desynchronization during voluntary movement in Parkinson's disease

Bereitschaftspotential (BP) and Event-Related Desynchronization (ERD) were simultaneously recorded during a voluntary wrist flexion in 10 patients with Parkinson's disease (PD) treated with L-Dopa therapy and 10 control subjects. BP and ERD were analyzed 2 s before and 0.5 s after the movement, during two successive left and right experimental conditions. ERD (9-11 Hz) was computed from 11 source derivations (frontocentral, central, parietocentral). The BP was averaged from these 11 electrodes. For the BP, no spatiotemporal difference was found between the two groups. BP began bilaterally over the 3 groups of electrodes, 1250 ms before movement onset for the right flexion and 1500 ms for the left flexion. A contralateral predominance appeared 500 ms before movement onset over the central area. ERD began in the control group 1750 ms before movement over the contralateral central area, and then appeared bilaterally after its execution. In the PD group, the ERD appeared with a shorter latency than in the control group, 1250 ms (left flexion) and 1000 ms (right flexion) before movement onset; diffusion over the ipsilateral side was found 500 ms before movement onset. ERD also involved the frontocentral area and could be interpreted as a compensatory activity of the supplementary motor area. These findings suggest that with Parkinsonian and control subjects, ERD gives additional and maybe more information than the BP about changes of cortical activity during the motor preparation period. In the PD group the delay of ERD appearance seems to confirm that the programming of movement would be affected, thus explaining partially akinesia.

Event-related desynchronization (ERD) patterns during verbal memory tasks: effect of age

Event-related desynchronization (ERD) was studied in 10 young (mean age = 19.1) and 10 older (mean age = 62.8) subjects during a verbal recognition task. The attention load of the task varied according to the difficulty of discriminating between targets and distractors. EEG recorded from 29 electrodes was used to compute ERD from 14 source derivations in 125 ms intervals. Thereafter, it was displayed as spatiotemporal maps. The results show that attention influences the characteristics of EEG desynchronization. In young subjects, ERD is more pronounced and more widespread when the attentional load is high. In the elderly, differences between the two attention conditions are less marked. ANOVA reveals main effects of attention and time. The significant 'attention x time x age group' interaction confirms the presence of different brain activation patterns in the two age groups in relation to attention load.

[Topographical study of event-related desynchronization: value in the psychophysiologic approach to cognitive processes]

The interest of the event-related desynchronization study has already been evidenced, for example in the study of the cerebral activation modifications consecutive to cognitive processes. We observed here the evolution of this index during a recognition task where the material to memorize varied. Ten young subjects had to learn and then recognize a list of words or forms. The desynchronization of the alpha rhythm consecutive to each stimulus was recorded at 14 localizations on the scalp. We observed that the time evolution of the event-related desynchronization was different in each task. In the visual task, the phenomenon began sooner and was longer lasting. As long as the cortical area were concerned, any dominance nor interhemispheric difference were observed. During the visuospatial recognition task, the event-related desynchronization was however more widespread.

[Spatiotemporal study of event-related desynchronization during self-paced movement]

The desynchronization of Alpha band components during a self-paced movement of the thumb was studied in 7 subjects. The EEG was recorded from 23 electrodes located on the frontocentral, central, and parietocentral regions, referred to the right mastoïde, 4 s before and 2 s after movement onset. The data were then transformed to obtain 11 source derivations. The temporal evolution of the power of the signal within the Alpha band, every 250 ms, associated to the non parametric statistic test of Wilcoxon, authentifies the event-related desynchronization (ERD). The spatiotemporal analysis of ERD underlines on the central regions, two principal locations of ERD: one controlateral to the movement, starting more than 1 s before the movement; the other, ipsilateral, shorter, during the movement. However, no significance desynchronization was underlined on the vertex. The ANOVA used to analyse these results confirms the principal location of ERD on the central region, and seems to indicate a right lateralisation during the right or the left movement.

Effect of aging on the spatio-temporal pattern of event-related desynchronization during a voluntary movement

Event-related desynchronization (ERD) of alpha components was studied in young and elderly subjects during planning of voluntary movement. ERD was quantified from 11 source derivations covering regions of the scalp corresponding to the supplementary motor area, the left and right primary sensorimotor areas, the vertex, and the medial posterior parietal cortex. Spatio-temporal display of ERD showed a very different pattern in elderly subjects, with mainly a spatial diffusion of ERD over the parietal and frontal regions. On the contrary, ERD in young subjects was limited to the central regions. ERD was also more lasting in elderly subjects. Changes of the ERD pattern in elderly subjects could indicate a change of cortical activation during voluntary movement. The data also confirm that ERD study is a useful electrophysiological exploration to observe the changes of cortical activation during cerebral aging.

P300 component of the event-related potentials (ERP) during an attention task: effects of age, stimulus modality and event probability

The effects of age, stimulus modality and event probability on event-related potentials (ERP) were studied in 12 young and 12 elderly healthy subjects. The ERP were recorded from 15 electrodes referred to linked ears. Results showed that both amplitude and latency of the P300 component are affected by aging. Study of the latency of the earlier ERP components in the two age groups revealed that the P300 delay was not imputable to a delay of the earlier components. P300 amplitude and latency were also affected by event probability and stimulus modality: infrequent stimulus involved higher and later P300, but this effect was more pronounced in the young than in the old group; higher and later P300 were also recorded during the visual task compared to the auditory. Topographical repartition of the brain wave revealed a predominance of the central sites (Fz, Cz, Pz). The findings are discussed in relation to the sensitivity of the ERP assessment procedures in age related modifications of information processing.

Evaluation of event-related desynchronization (ERD) during a recognition task: effect of attention

Event-related desynchronization (ERD) was studied in 10 subjects during a verbal recognition task. The attentional load of the task varied according to the difficulty to discriminate targets and distractors. The EEG recorded from 29 electrodes was used to compute ERD from 14 source derivations in 125 msec intervals and displayed as spatio-temporal maps. The results show that large brain areas of both hemispheres are significantly activated when the attentional load is high. This cerebral activation pattern is less pronounced when the load is low. ANOVA reveals main effects of attention and time and a significant interaction between attention and time.

Sleep, brain activation and cognition

Some data have shown the presence of time-of-day effects in learning processes. We explore here whether the same phenomenon occurs during the night and how it relates to REM sleep. In an initial approach to the question, this paper points out the relationships between: 1) REM sleep and brain activation, and 2) REM sleep and information processing. The data are discussed in terms of a REM sleep implication on information processing and we examine the possibility of modifying this processing by acting on REM sleep.

REM sleep modifications following a Morse code learning session in humans

Various experimental data indicate that rapid eye movement (REM) sleep is involved in learning processes. In animals, any complex task in a learning environment leads to an increase of the consecutive total REM sleep time, especially just before learning completion. In humans, the oculomotor activity during REM sleep seems to constitute an interesting marker of learning performance. In this work, we focus on the qualitative analysis of REM sleep characteristics after a Morse code learning session. Eight male subjects were polygraphically recorded during three consecutive nights. A computer aided teaching session was performed just before bedrest onset of the experimental night. The learning performance (percentage of saving) was checked on awakening. The Morse code learning led to some modifications in REM sleep components, particularly increases of REM sleep time and number of REM episodes. We did not observe any significant modification in the total number of REMs in the experimental night. However, the correlative analysis between learning performance and sleep parameters indicates a superior r for the oculomotor activity than for the tonic components. This is consistent with the information processing hypothesis in which the temporal distribution of REMs reflects the subject's ability to increase the signal-noise ratio from environmental information intake.

Enhancement of memory by auditory stimulation during postlearning REM sleep in humans

REM sleep involvement in memory processes was demonstrated in animals and humans: 1) REM sleep deprivation impairs the memory fixation, 2) learning sessions are followed by modifications of REM sleep characteristics. Moreover, sleep patterns can be modified by applying auditory stimulations during REM sleep. We show that REM actual auditory stimulations significantly improve the retention of a Morse code learning task. These results are discussed in terms of brain activation.