P. J. Delwaide

Potentiation instead of habituation characterizes visual evoked potentials in migraine patients between attacks.

We have studied habituation of the pattern‐reversal visual evoked potential (VEP) in healthy volunteers (n = 16) and in patients suffering from migraine without (n = 27) or with aura (n = 9). Five blocks of 50 responses at a stimulation rate of 3.1 Hz were sequentially averaged and analyzed separately for latencies, peak‐to‐peak amplitudes of N1‐P1 and P1‐N2, and the area under the N2 component Latencies of N1, P1, or N2 components were not significantly different between the sequential trial blocks, or between groups. Mean amplitudes of N1‐P1 and P1‐N2 in the first and subsequent blocks of SO responses were not statistically different among groups. In healthy subjects, there was a decrement of N1‐P1 and P1‐N2 amplitudes and N2 area on successive averagings. This habituation was maximal in the third and fourth blocks, but tended to disappear in the fifth block. In marked contrast to healthy subjects, migraine patients were characterized by a transient amplitude increment (i.e. potentiation) of VEP components which reached its maximum in the second to fourth blocks. Amplitude changes in sequential blocks were not dependent on attention and differed significantly between healthy subjects and migraineurs, but not between migraine with and without aura. Taken together with previous studies showing deficient habituation of contingent negative variation in migraine, these results indicate a dysfunction of central information processing which might have behavioral and pathogenic correlates.

Exteroceptive suppression of temporalis muscle activity in chronic headache

Early (ES1) and late (ES2) exteroceptive suppression periods elicited by electrical stimulation of the labial commissure during teeth-clenching were recorded over the temporalis muscle in 45 headache patients (25 tension headaches and 20 migraines) and 22 controls. Mean duration of ES2 for single shocks was significantly reduced in tension headache when compared with migraine or controls. At a stimulation rate of 2 Hz, ES2 was abolished in 40% of tension headache sufferers, but in none of the migraineurs. EMG analysis of temporalis late exteroceptive suppression might be a helpful diagnostic tool in functional headaches. Reduction of ES2 suggests that there is deficient activation or excessive inhibition of pontobulbar inhibitory interneurons which receive a strong input from limbic structures. ES2 might thus represent an interface between psychogenic and myogenic factors putatively involved in the pathogenesis of tension headache.

Can Motor Recovery in Stroke Patients Be Predicted by Early Transcranial Magnetic Stimulation

BACKGROUND AND PURPOSE We used transcranial magnetic stimulation of the motor cortex to evaluate the functional state of corticospinal pathways innervating the first dorsal interosseous muscle of the hand in 26 patients suffering from a first-ever ischemic stroke in the middle cerebral artery territory. METHODS All patients had complete hand palsy and were tested within the first 24 hours from stroke onset. Patients were also tested clinically with the MRC, Rankin, and National Institutes of Health (NIH) stroke scales at day 1 and with MRC and NIH scales and the Barthel Index at day 14. Electrophysiological testing was repeated at day 14. Patients were divided into three subgroups according to the amplitude of the maximal response (motor evoked potential [MEP]) evoked at day 1. RESULTS After 2 weeks, all 6 patients with initial MEPs > 5% maximum motor response (Mmax) showed some first dorsal interosseous muscle motor function recovery, whereas 19 of 20 patients with initially absent or small (< 5% Mmax) MEPs were left with complete hand palsy. There were strong positive correlations between MEP amplitude at day 1 and MRC and Barthel Index scores at day 14. However, measurement of central motor conduction time proved to be of little prognostic value. CONCLUSIONS We conclude that early-performed transcranial magnetic stimulation is a valuable prognostic tool for motor recovery from stroke and that relatively preserved MEP amplitude shortly after stroke is a better prognostic factor than normal central motor conduction time.

Absence of Response to Early Transcranial Magnetic Stimulation in Ischemic Stroke Patients Prognostic Value for Hand Motor Recovery

BACKGROUND AND PURPOSE Transcranial magnetic stimulation (TMS) has been proposed as a prognostic tool in stroke patients. Most of the previous studies agree in considering the presence of motor-evoked potentials (MEPs) in the first days after a stroke as an indicator of good outcome. In the present study, we have assessed the prognostic value of the absence of response to early TMS on hand motor recovery in stroke patients with complete hand palsy at onset due to ischemia in the area of the middle cerebral artery. METHODS Fifteen patients submitted to TMS within 48 hours of stroke onset (defined as day 1) and again after 1 year. They were also evaluated clinically on day 1 by a scale derived from the Medical Research Council (MRC) and by the National Institutes of Health (NIH) stroke scale; they were reevaluated by the same scales and by Barthel Index on day 365. RESULTS On day 1, all the patients had complete hand palsy and no response to TMS; their NIH scores showed great variability. After 1 year, 6 of 15 patients regained small and prolonged MEPs, together with a very poor and not functionally useful motor recovery. NIH scores were significantly improved. Barthel Index scores showed large interindividual differences and were not correlated with MRC scores. CONCLUSIONS We conclude that in patients with complete hand palsy, the absence of response to TMS in the first hours is predictive of absent or very poor, not useful, hand motor recovery.

Reinforcement of reciprocal inhibition by contralateral movements in man

A reduction of flexor carpi radialis H reflex size was produced by submotor threshold stimulation of the radial nerve. This reduction reflects reciprocal inhibition exerted by the inhibitory IA interneuron. The effects of contralateral movements on IA reciprocal inhibition were studied in eight normal subjects. Active contralateral arm movement appeared to significantly increase the degree of reciprocal inhibition without affecting the unconditioned reflex. A minor enhancement of reciprocal inhibition was also noted after passive mobilization. Results are discussed in terms of contralateral segmental afferent fibers influencing IA interneuronal excitability. They strongly suggest that contralateral muscular IA afferents may reinforce reciprocal inhibition in man.

Percutaneous magnetic stimulation of the motor cortex in migraine.

We have used transcranial magnetic stimulation of the motor cortex interictally in 12 patients with unilateral classic migraine with sensorimotor auras and 10 patients with common migraine and unilateral headache. In classic migraine, the threshold of activation of the FDI muscle by the cortical stimulus was significantly increased on the side of the auras, when compared to the unaffected side (P less than 0.01) and to normal subjects (P less than 0.01). The amplitude of EMG responses was also reduced in FDI on the affected side when compared to normals (P less than 0.02). Responses obtained in common migraine patients were normal on both sides. We suggest that some permanent subclinical dysfunction of the motor cortex might play a role in the pathogenesis of attacks of classic migraine with sensorimotor auras.

Double‐blind randomized controlled study of phosphatidylserine in senile demented patients

A double‐blind randomized controlled study was conducted in 42 hospitalized demented patients to evaluate the therapeutical effect of phosphatidylserine (BS‐PS). Half of the patients received 3x100 mg of this product, and the other half a placebo of the same appearance. After a wash‐out period, prescription lasted for six weeks. To evaluate the patients, two distinct rating scales were used: the Crichton Scale and an original one (Peri Scale) designed in our geriatric unit (see Appendix). A circle crossing test was added. Out of the 35 patients who completed the trial, 18 had received placebo and 17 BC‐PS. The results indicated a trend toward improvement in the BC‐PS treated patients and an analysis of covariance showed a significant (p<0.05) treatment effect on the Peri Scale. The results at the end of the treatment period were compared with those obtained three weeks later. Here again there was a statistically significant difference in the Peri Scale results, indicating that modifications are drug‐related. The behavioral improvement shown in this study is in agreement with experimental studies on aged animals.

Motor cortex inhibition is not impaired in patients with Alzheimer's disease: evidence from paired transcranial magnetic stimulation

Motor cortex excitability was studied by transcranial magnetic stimulation (TMS) in 17 patients with Alzheimers disease (AD). Resting and active thresholds for TMS were significantly reduced in AD patients compared to young and aged healthy subjects. The maximum amplitude of the motor response evoked by TMS was also significantly increased in AD patients. We have tested if these changes are related to a modification of the short-lasting intracortical inhibition of the motor cortex by paired conditioning-test TMS. We found no significant differences between AD patients and aged healthy subjects even if there is a slight but significant difference between aged and young normal subjects. We conclude that the modification of excitability of the motor cortex does not result from an impaired intracortical inhibition.

Age-related changes in fastest and slowest conducting axons of thenar motor units

Single thenar motor unit F waves (FMUPs) were collected from 23 healthy volunteers (age range 21–91 years, mean 46 ± 20 SD). In each subject, 10 distinct FMUPs were recorded, using surface stimulating and recording electrodes, and the conduction velocity (CV) of each motor unit was calculated. The distribution of CVs (overall range 42–66 m/s; individual FMUP CV dispersion range 6–27% of the maximal FMUP CV) was close to those previously reported whatever the technique used. With age, a progressive CV reduction was observed, and maximal FMUP CV was significantly correlated with age (r = −0.58, P < 0.01), whereas no statistically significant correlation was found between minimal FMUP CV and age (r = −0.27, ns). Individual FMUP CV dispersion presented a statistically significant decrease with age (r = −0.46, P < 0.05). Furthermore, thenar motor unit number (MUNE), estimated by the adapted multiple point stimulation method, decreased progressively with age and was statistically correlated with maximal FMUP CV (r = 0.59, P < 0.01), whereas there was no correlation with minimal FMUP CV (r = 0.34, ns). Thus, we propose that motor unit loss is progressive with age throughout life, affecting particularly the largest and fastest conducting motor units. Preferential involvement of these fibers could be responsible for the age‐related changes in motor nerve CV.

Projections from basal ganglia to tegmentum: a subcortical route for explaining the pathophysiology of Parkinson's disease signs?

Abstract Functional changes in the organisation of neuronal circuitries are generally used to explain parkinsonian motor symptoms and levodopa-induced dyskinesias. Based on information from histology and neurophysiological microrecordings of specific basal ganglia nuclei, the most widely accepted scheme is based on a central loop which starts in the cerebral cortex, makes multiple relays in the basal ganglia, and returns to the cerebral cortex. Transcranial magnetic stimulation studies, however, reveal no significant differences in the excitability of the motor cortex between normal subjects and patients with Parkinson’s disease. Furthermore, electrophysiological and audiospinal facilitation studies indicate that the activity of reticular nuclei is altered in Parkinson’s disease. It therefore appears that a circuit with the cortex as the only recipient of basal ganglia output is an oversimplification. This paper explores the relationships between various basal ganglia nuclei and proposes a subcortical pathway via which modifications in the basal ganglia may influence motor function.