Recovery functions of somatosensory evoked potentials in parkinsonian patients

Brain Networks Involved in Sensory Perception in Parkinson's Disease: A Scoping Review

Parkinson's Disease (PD) has historically been considered a disorder of motor dysfunction. However, a growing number of studies have demonstrated sensory abnormalities in PD across the modalities of proprioceptive, tactile, visual, auditory and temporal perception. A better understanding of these may inform future drug and neuromodulation therapy. We analysed these studies using a scoping review. In total, 101 studies comprising 2853 human participants (88 studies) and 125 animals (13 studies), published between 1982 and 2022, were included. These highlighted the importance of the basal ganglia in sensory perception across all modalities, with an additional role for the integration of multiple simultaneous sensation types. Numerous studies concluded that sensory abnormalities in PD result from increased noise in the basal ganglia and increased neuronal receptive field size. There is evidence that sensory changes in PD and impaired sensorimotor integration may contribute to motor abnormalities.

The Suppressive Effect of the Motor System on the Sensory System in Patients With Tourette Syndrome

Objective: Tourette syndrome (TS) is a complicated sensorimotor disorder. Some patients with TS relieve their involuntary premonitory urges via tics. However, the effect of the motor system on the sensory system has not yet been elucidated. The purpose of the present study was to investigate changes in the excitability of the sensory cortex following repetitive transcranial magnetic stimulation (rTMS) of the motor cortex in patients with TS.

Methods: Twenty-nine patients with TS and 20 healthy, age-matched controls were enrolled in this study. All subjects were divided into four groups: patients with rTMS, patients with sham-rTMS, controls with rTMS, and controls with sham-rTMS. The clinical severity of tics was evaluated using the Yale Global Tic Severity Scale. Single somatosensory evoked potentials (SEPs) and paired SEPs were recorded by stimulating the median nerve at the wrist of all subjects. The resting motor threshold (RMT) was tested in each subject in the rTMS group. Afterwards, all four groups were administered rTMS (1 Hz, 90% RMT) or sham-rTMS for 200 s, followed by a 15-min rest. Finally, single SEPs and paired SEPs were repeated for each subject.

Results: No significant differences in RMT, the amplitudes of single SEPs, or the suppression of paired SEPs were observed between patients with TS and controls at baseline. After rTMS, a significant suppression of the peak-to-peak amplitude of the N20–P25 responses of single SEPs was observed in both controls (p = 0.049) and patients (p < 0.0001). The suppression of the N20–P25 peak-to-peak amplitude was more significant in patients than in controls (p = 0.039). A significant difference in the suppression of paired SEPs after rTMS was not observed between groups.

Conclusions: The more significant suppression of N20–P25 components of single SEPs with normal suppressed paired SEPs in patients with TS after 1-Hz rTMS of the motor cortex suggests that the suppressive effect of the motor system on the sensory system might originate from the motor-sensory cortical circuits rather than the sensory system itself.

Influence of parameter settings on paired-pulse-suppression in somatosensory evoked potentials: a systematic analysis

OBJECTIVE

Paired-pulse somatosensory evoked potentials (SEPs) are a common tool to investigate excitability in the human somatosensory cortex. Comparing literature about paired-pulse SEP, there is no standard set of stimulation parameters, while little is known about the influence of stimulation parameters on paired-pulse suppression.

METHODS

We analyzed changes of paired-pulse ratios by varying repetition rates from 1 to 9Hz, and using stimulus intensities of 250% of the sensory threshold and 100%, 120%, and 140% of the motor threshold, which are most frequently used in studies using paired-pulse SEPs.

RESULTS

We found a significant effect of repetition rate on paired-pulse suppression with increasing paired-pulse ratios from 1 to 9Hz, which is mainly caused by a change of single pulse amplitudes. We found no difference in paired-pulse suppression at the tested stimulation intensities.

CONCLUSIONS

The extent of paired-pulse ratios across different studies should be interpreted with caution due to the high dependence on repetition rate, while the results at the commonly used stimulus intensities are comparable.

SIGNIFICANCE

For an optimized parameter setting with sufficient paired-pulse suppression, we suggest a stimulation rate of 1 or 3Hz and a stimulation intensity of 250% of sensory threshold or slightly above motor threshold.

Abnormal recovery function of somatosensory evoked potentials in patients with primary insomnia

Neurobiological correlates underlying insomnia are poorly understood. The hyperarousal of the central nervous system indicates that cortical excitability may be abnormal in patients with insomnia. The purpose of the present study was to investigate changes in cortical excitability by examining the recovery function of median nerve somatosensory evoked potentials (SEPs) in patients with primary insomia (PI). We studied the recovery function of median nerve SEPs in 12 medication-naive PI patients and in 12 age- and sex-matched healthy subjects. SEPs in response to single stimulus and paired stimuli at interstimulus intervals (ISIs) of 20, 60, 100 and 150 ms were recorded. The recovery function of the cortical components of frontal P20 and parietal N20 showed significantly reduced suppression in PI patients as compared to healthy controls. In conclusion, this is the first study investigating changes in cortical excitability in PI patients by examining the recovery function of median nerve SEPs. The present study suggests that cortical excitability is increased in PI patients. Dysfunction of inhibitory GABAergic interneurons of the cerebral cortex might contribute to the increased cortical excitability in PI patients.

Paired-pulse inhibition in the auditory cortex in Parkinson's disease and its dependence on clinical characteristics of the patients

We aimed to determine the value of the paired-pulse inhibition (PPI) in the auditory cortex in patients with Parkinson's disease (PD) and analyze its dependence on clinical characteristics of the patients. The central (Cz) auditory evoked potentials were recorded in 58 patients with PD and 22 age-matched healthy subjects. PPI of the N1/P2 component was significantly (P < .001) reduced for interstimulus intervals 500, 700, and 900 ms in patients with PD compared to control subjects. The value of PPI correlated negatively with the age of the PD patients (P < .05), age of disease onset (P < .05), body bradykinesia score (P < .01), and positively with the Mini Mental State Examination (MMSE) cognitive score (P < .01). Negative correlation between value of PPI and the age of the healthy subjects (P < .05) was also observed. Thus, results show that cortical inhibitory processes are deficient in PD patients and that the brain's ability to carry out the postexcitatory inhibition is age-dependent.

Sensory integration in writer's cramp: comparison with controls and evaluation of botulinum toxin effect

OBJECTIVE

Abnormal temporal and spatial sensory integration have been described in mixed groups of dystonic patients. We tested somatosensory integration and the effect of botulinum toxin (BoNT) in patients with writer's cramp (WC).

METHODS

Median and ulnar SEPs were recorded in 29 WC patients and in 10 controls. We performed: individual and simultaneous stimulation of median and ulnar nerves (MU) and paired stimulation of median nerve at interstimulus-interval (ISI) of 40 and 100 ms. All the trials were repeated after blinded randomized treatment with placebo or BoNT-A.

RESULTS

We found no differences between patients and controls in standard SEPs. Spatial (except for N9) and temporal suppression after ISI 40 were present in both groups for all the waves; after ISI 100, suppression was present only for N70. There were no differences between patients and controls. After BoNT-A treatment, no changes were observed.

CONCLUSIONS

In contrast with previous findings in heterogeneous dystonic groups, and although some studies suggest impairment of spatial and temporal sensory discrimination in patients with focal dystonia, in our large cohort of patients with WC we found no evidence of abnormal somatosensory integration investigated by means of SEPs and no changes in somatosensory variables after BoNT-A treatment.

SIGNIFICANCE

Our findings may suggest pathophysiological differences between focal and generalized dystonia, and may also point to an inferior sensitivity of SEPs in detecting abnormalities in sensory discrimination as compared to methods based on subjective discrimination.

Sustained increase of somatosensory cortex excitability by tactile coactivation studied by paired median nerve stimulation in humans correlates with perceptual gain

Cortical excitability can be reliably assessed by means of paired-pulse stimulation techniques. Recent studies demonstrated particularly for motor and visual cortex that cortical excitability is systematically altered following the induction of learning processes or during the development of pathological symptoms. A recent tactile coactivation protocol developed by Godde and coworkers showed that improvement of tactile performance in humans can be achieved also without training through passive stimulation on a time scale of a few hours. Tactile coactivation evokes plastic changes in somatosensory cortical areas as measured by blood oxygenation level-dependent (BOLD) activation in fMRI or SEP-dipole localization, which correlated with the individual gain in performance. To demonstrate changes in excitability of somatosensory cortex after tactile coactivation, we combined assessment of tactile performance with recordings of paired-pulse SEPs after electrical median nerve stimulation of both the right coactivated and left control hand at ISIs of 30 and 100 ms before, 3 h after and 24 h after tactile coactivation. Amplitudes and latencies of the first and second cortical N20/P25 response components were calculated. For the coactivated hand, we found significantly lowered discrimination thresholds and significantly reduced paired-pulse ratios (second N20/P25 response/first N20/P25 response) at an ISI of 30 ms after tactile coactivation indicating enhanced cortical excitability. No changes in paired-pulse behaviour were observed for ISIs of 100 ms. Both psychophysical and cortical effects recovered to baseline 24 h after tactile coactivation. The individual increase of excitability correlated with the individual gain in discrimination performance. For the left control hand we found no effects of tactile coactivation on paired-pulse behaviour and discrimination threshold. Our results indicate that changes in cortical excitability are modified by tactile coactivation and were scaled with the degree of improvement of the individual perceptual learning. Conceivably, changes of cortical excitability seem to constitute an additional important marker and mechanism underlying plastic reorganization.

Recovery function of and effects of hyperventilation on somatosensory evoked high-frequency oscillation in Parkinson's disease and myoclonus epilepsy

To evaluate recovery function of and effects of hyperventilation (HV) on high-frequency oscillations (HFOs) of median nerve somatosensory evoked potential (SEP), we recorded SEPs in 8 Parkinson's disease (PD) patients with enlarged HFOs, 4 myoclonus epilepsy (ME) patients and 10 healthy volunteers (N). SEP was recorded from the hand sensory area contralateral to the median nerve stimulated at the wrist. Responses were amplified with filters set at 0.5 and 3000 Hz. HFOs were obtained by digitally filtering raw SEPs from 500 to 1000 Hz. We measured amplitudes of the N20 onset-peak (N20o-p), N20 peak-P25 peak (N20p-P25p), P25 peak-N33 peak (P25p-N33p), the early (1st-2nd) and late (3rd) HFOs. For the recovery function study, paired-pulse stimuli at various interstimulus intervals (20, 50, 100, 150, 200 and 300 ms) were given. To investigate effects of HV, amplitudes of several components of SEPs recorded after HV were compared with those before HV. In PD and ME, the N20o-p recovery curve showed significantly less suppression as compared with those of N. The P25p-N33p recovery curve of ME showed longer suppression than those of N and PD. There were no significant differences in the early or late HFOs recovery curves among three groups. At the dysinhibited state after HV, the late HFO was reduced in association with a significant enlargement of the N20p-P25p amplitude in normal subjects. This suggests that the late HFOs should reflect bursts of inhibitory interneurons. In the ME patients, the early HFOs significantly decreased by HV. The pattern in ME patients may be explained by a kind of compensation for already enhanced SEPs (giant SEP) in the dysinhibited situation. We conclude that (1) Giant HFOs are normally regulated by inhibitory neuronal systems involving in paired stimulation SEP. (2) The late HFOs must reflect bursts of GABAergic inhibitory interneurons.

Somatosensory evoked potential recovery in kii amyotrophic lateral sclerosis/parkinsonism-dementia complex (kii AlS/PDC)

OBJECTIVE

To evaluate the recovery function of the sensory cortex in patients with Kii amyotrophic lateral sclerosis/parkinsonism-dementia complex (Kii ALS/PDC) using somatosensory evoked potentials (SEPs) elicited by paired stimuli of the median nerve at the wrist.

METHODS

Five patients with Kii ALS/PDC were compared with 5 patients with classical ALS, 5 with Parkinson's disease (PD), and 7 healthy normal volunteers. SEPs were recorded from the hand sensory area contralateral to the side of stimulation. Recovery functions of N20-P25 and P25-N33 components were evaluated by comparing the second SEPs elicited by paired pulse stimuli at various interstimulus intervals (ISIs, 20-300 ms) with the SEPs elicited by single stimuli.

RESULTS

Conventional SEPs to a single stimulus had a normal latency and size in all patients. The recovery function of the N20-P25 and P25-N33 components showed significantly less suppression at short ISIs without any facilitation at long ISIs in Kii ALS/PDC patients than in normal subjects, classical ALS or PD patients.

CONCLUSIONS

In Kii ALS/PDC, the sensory cortex is disinhibited or hyperexcitable. These abnormalities may reflect cortical pathology in the sensory cortex and may be partly due to a secondary effect on the sensory cortex from the primary parkinsonian pathological changes.

Effect of chronic pallidal deep brain stimulation on off period dystonia and sensory symptoms in advanced Parkinson's disease

OBJECTIVE

To investigate the efficacy of chronic pallidal deep brain stimulation (DBS) on off period dystonia, cramps, and sensory symptoms in advanced Parkinson's disease (PD).

METHODS

16 patients (6 women, 10 men; mean age at surgery 65 years) suffering from advanced PD were followed up prospectively for one year after implantation of a monopolar electrode in the posteroventral lateral globus pallidus internus. Unilateral DBS was performed in 9 patients. 10 patients had bilateral procedures (contemporaneous bilateral surgery in 7 and staged bilateral surgery in 3 instances). The decision whether to perform unilateral or bilateral surgery depended on the clinical presentation of the patient. Patients were formally assessed preoperatively, at 3-5 days, 3 months, and 12 months after surgery.

RESULTS

In patients who underwent unilateral surgery, pain was present in 7 (78%), off dystonia in 5 (56%), cramps in 6 (67%), and dysaesthesia in 4 (44%). In patients who underwent bilateral surgery, pain was present in 7 (70%), off dystonia in 6 (60%), cramps in 7 (70%), and dysaesthesia in 4 (40%). With unilateral DBS, contralateral off period dystonia was improved by 100% at 1 year postoperatively, pain by 74%, cramps by 88%, and dysaesthesia by 100%. There was less pronounced amelioration of ipsilateral off period dystonia and sensory symptoms. With bilateral DBS, total scores for dystonia were improved by 86%, for pain by 90%, for cramps by 90%, and for dysaesthesia by 88%. The benefit appeared early at the first evaluation 3-5 days after surgery and was stable throughout the follow up period.

CONCLUSIONS

Pallidal DBS yields major improvement of off period dystonia, cramps, and sensory symptoms in patients with advanced PD.

Somatosensory disinhibition in dystonia

Despite the fact that somatosensory processing is inherently dependent on inhibitory functions, only excitatory aspects of the somatosensory feedback have so far been assessed in dystonic patients. We studied the recovery functions of spinal N13, brainstem P14, parietal N20, P27, and frontal N30 somatosensory evoked potentials (SEPs) after paired median nerve stimulation in 10 patients with dystonia and in 10 normal subjects. The recovery functions were assessed (conditioning stimulus: S1; test stimulus: S2) at interstimuls intervals (ISIs) of 5, 20, and 40 ms. SEPs evoked by S2 were calculated by subtracting the SEPs of the S1 only response from the SEPs of the response to the paired stimuli (S1 + S2), and their amplitudes were compared with those of the control response (S1) at each ISI considered. This ratio, (S2/S1)*100, investigates changes in the excitability of the somatosensory system. No significant difference was found in SEP amplitudes for single stimulus (S1) between dystonic patients and normal subjects. The (S2/S1)*100 ratio at the ISI of 5 ms did not significantly differ between dystonic patients and normal subjects, but at ISIs of 20 and 40 ms, this ratio was significantly higher in patients than in normals for spinal N13 and cortical N20, P27, N30 SEPs. These findings suggest that in dystonia there is an impaired inhibition at spinal and cortical levels of the somatosensory system which would lead to an abnormal sensory assistance to the ongoing motor programs, ultimately resulting in the motor abnormalities present in this disease.

Two evoked responses with different recovery functions in the primary somatosensory cortex in humans

OBJECTIVES

We investigated the recovery function of somatosensory evoked magnetic cortical fields (SEFs) to confirm the temporal aspects of the somatosensory process in humans.

METHODS

SEFs were recorded following median nerve electrical stimulation in 6 healthy subjects. Double stimulation, with interstimulus intervals (ISIs) from 3 to 100 ms, was applied, and the SEF components for the second stimulation were analyzed. In a supplementary experiment, responses to single stimulations of various intensities from the sensory threshold to the motor threshold were studied.

RESULTS

The first SEF component (1M) diminished when the ISI was less than 10 ms, while the second component (2M) remained even when the ISI was 3 ms. The two components showed a very similar attenuation with decrease of stimulus intensity. There was no significant difference in dipole location between 1M and 2M in the primary somatosensory cortex (SI).

CONCLUSIONS

The results suggested that at least two independent pathways with different recovery functions exist in a similar area in the SI.

Somatosensory evoked potential recovery in myotonic dystrophy

OBJECTIVE

To evaluate recovery functions of the sensory cortex using somatosensory evoked potentials (SEPs) elicited by paired stimuli of the median nerve in patients with myotonic dystrophy (MD).

SUBJECTS/METHODS

Twelve MD patients were enrolled in the present investigation. Five patients with facioscapulohumeral muscular dystrophy (FSH) and 12 healthy volunteers were studied as control groups. SEP was recorded from the hand sensory area contralateral to the median nerve stimulated at the wrist. Single pulse or paired-pulse stimuli at various interstimulus intervals (ISIs) (10, 20, 40, 60, 80, 100, 150, 200 and 300 ms) were given. Recovery functions of N9, N20onset-N20peak, N20-P25 and P25-N33 components were studied.

RESULTS

Conventional SEPs to a single stimulus were normal in the latency and amplitude in all the patients. Recovery functions of both N9 and N20o-N20p components were normal in the patients. In contrast, in MD patients, disinhibited or hyperexcitable recovery pattern was observed in recovery curves of the N20-P25 or P25-N33 components, whereas those were normal in FSH patients.

CONCLUSIONS

Disinhibited cortical excitability (or hyperexcitability) is present in the sensory cortex in patients with myotonic dystrophy. This may reflect cortical pathology or functional alteration of the sensory cortex in MD.

Somatosensory evoked potentials in progressive supranuclear palsy

We report median and digital nerve somatosensory evoked potentials (SEPs) in 14 patients with probable progressive supranuclear palsy (PSP) along with transcortical long-loop reflexes, motor evoked potentials, and auditory startle responses. Enlarged cortical responses were found in 14 median and 13 digital nerve SEP studies, while long-loop reflexes were increased in only one patient. All motor evoked potential studies were normal. Auditory startle responses were either absent or reduced in 11 patients. The observed neurophysiological abnormalities may reflect cortical hyperexcitability but are distinct from those in other disorders associated with giant SEPs, such as progressive myoclonus epilepsy. A number of groups reported widespread cortical changes in addition to the characteristic subcortical neurofibrillary degeneration in post-mortem confirmed PSP. However, clinical features reflecting cortical dysfunction such as ideomotor apraxia and cortical sensory loss are uncommon in classical PSP. Furthermore, frontal lobe dementia which is frequently present in PSP patients, is thought to be of subcortical origin resulting from striato-frontal deafferentation. We propose that cortical neurofibrillary pathology may lead to subclinical intracortical disinhibition accounting for the enlarged cortical SEPs in PSP.

Sensory processing in Parkinson's and Huntington's disease: investigations with 3D H(2)(15)O-PET

There is conjoining experimental and clinical evidence supporting a fundamental role of the basal ganglia as a sensory analyser engaged in central somatosensory control. This study was aimed at investigating the functional anatomy of sensory processing in two clinical conditions characterized by basal ganglia dysfunction, i.e. Parkinson's and Huntington's disease. Based on previously recorded data of somatosensory evoked potentials, we expected deficient sensory-evoked activation in cortical areas that receive modulatory somatosensory input via the basal ganglia. Eight Parkinson's disease patients, eight Huntington's disease patients and eight healthy controls underwent repetitive H(2)(15)O-PET activation scans during two experimental conditions in random order: (i) continuous unilateral high-frequency vibratory stimulation applied to the immobilized metacarpal joint of the index finger and (ii) rest (no vibratory stimulus). In the control cohort, the activation pattern was lateralized to the side opposite to stimulus presentation, including cortical [primary sensory cortex (S1); secondary sensory cortex (S2)] and subcortical (globus pallidus, ventrolateral thalamus) regional cerebral blood flow (rCBF) increases (P < 0.001). Between-group comparisons (P < 0.01) of vibration-induced rCBF changes between patients and controls revealed differences in central sensory processing: (i) in Parkinson's disease, decreased activation of contralateral sensorimotor (S1/M1) and lateral premotor cortex, contralateral S2, contralateral posterior cingulate, bilateral prefrontal cortex (Brodmann area 10) and contralateral basal ganglia; (ii) in Huntington's disease, decreased activation of contralateral S2, parietal areas 39 and 40, and lingual gyrus, bilateral prefrontal cortex (Brodmann areas 8, 9, 10 and 44), S1 (trend only) and contralateral basal ganglia; (iii) in both clinical conditions relative enhanced activation of ipsilateral sensory cortical areas, notably caudal S1, S2 and insular cortex. Our data show that Parkinson's disease and Huntington's disease, beyond well-established deficits in central motor control, are characterized by abnormal cortical and subcortical activation on passive sensory stimulation. Furthermore, the finding that activation increases in ipsilateral sensory cortical areas may be interpreted as an indication of either altered central focusing and gating of sensory impulses, or enhanced compensatory recruitment of associative sensory areas in the presence of basal ganglia dysfunction. Altered sensory processing is thought to contribute to pertinent motor deficits in both conditions.

N30 somatosensory evoked potentials in patients with unilateral Parkinson's disease

The N30 component of the somatosensory evoked responses (SEP) was reported as absent or abnormally low in various basal ganglia disorders, including Parkinson's disease (PD), but its relationship to the more affected side in asymmetric disease has not been assessed systematically. In 14 patients with unilateral PD and 10 controls, SEP were performed by stimulating each upper limb and recording from the parietal and frontal contralateral cortex. N30 was symmetric in 4 patients and 4 controls; it was asymmetric in 2 controls and in 8 patients (in 4 the responses were of lower amplitude over the affected hemisphere); no response was elicited in 2 patients and 4 controls. In all patients SEP were recorded off medication; in 9 of them the test was repeated following administration of L-dopa and did not show any significant changes. In conclusion, the N30 was asymmetric in a similar proportion of PD patients and controls. No correlation was found between the affected side and N30 latencies or amplitudes; no change was seen following L-dopa administration as well. The motor deficits and SEP abnormalities in PD probably reflect pathologies in different anatomical structures or functional circuits.

Somatosensory evoked potential recovery (SEP-R) in various neurological disorders

Recovery functions of somatosensory evoked potentials were studied by the paired stimulation technique in 61 patients with various neurological disorders. A less suppressive or hyperexcitable phase at short intervals, which had been shown in myoclonic patients, was seen in 22 patients. This abnormality was observed even in patients without myoclonus or involuntary movements, which suggests that this phenomenon is not mainly due to some dysfunction causing myoclonus or movement disorders. Less suppression at short intervals was observed for both N20-P25 and P25-N33 components in most of them. Less suppressive recovery of the N20-P25 component with normal recovery of the P25-N33 component was shown only in 3 patients with subcortical lesions with relative sparing of the cortical elements (Binswanger's subcortical encephalopathy). We conclude that less suppressive recovery of only the N20-P25 component suggests the presence of subcortical lesions.

Recovery functions of early cortical median nerve SSEP components: normative data

The recovery functions of parietal P14-N20, N20-P27 and frontal P22-N30 amplitudes were assessed in 17 healthy controls aged 20-50 years by means of the paired stimulus technique. One unpaired and 4 paired stimuli with interstimulus intervals (ISIs) of 25, 50, 75 and 100 msec were cyclically presented in a single run. Responses to the unpaired stimulus were subtracted off-line from paired stimulus responses. The highest suppression was reached at shorter ISIs for components with shorter latencies. The mean suppression of P22-N30 was influenced by the subject's age, being greater in younger subjects. Normative data are reported.

Somatosensory evoked potentials at rest and during movement in Parkinson's disease: evidence for a specific apomorphine effect on the frontal N30 wave

Studies attempting to relate the abnormalities of the frontal N30 components of the somatosensory evoked potentials (SEPs) to motor symptoms in Parkinson's disease (PD) have shown contradictory results. We recorded the frontal and parietal SEPs to median nerve stimulation in 2 groups of PD patients: a group of 17 patients presenting the wearing-off phenomenon, and a group of 10 untreated PD patients. The results were compared with a group of 13 healthy volunteers of the same age and with a group of 10 non-parkinsonian patients. All parkinsonian and non-parkinsonian patients were studied before ("off" condition) and after a subcutaneous injection of apomorphine ("on" condition). The gating effects of a voluntary movement (clenching of the hand) on the SEPs were also studied for the wearing-off group of PD patients (in states off and on) in comparison with the healthy subjects. At rest and in the off condition the amplitude of the frontal N30 was significantly reduced in the 2 groups of PD patients. We demonstrate that the movement gating ability of the PD patient is preserved in spite of the reduced amplitude of the frontal N30. This result suggests that the specific change in the frontal N30 in PD is not the consequence of a continuous gating of the sensory inflow by a motor corollary discharge. Clinical motor improvement induced by apomorphine was associated with a significant enhancement of the frontal N30 wave. In contrast, the subcortical P14 and N18 waves and the cortical N20, P22, P27 and N45 were not statistically modified by the drug. Apomorphine infusion did not change the absolute reduced voltage of the N30 reached during the movement gating. While the frontal N30 component of the non-parkinsonian patients was significantly lower in comparison to healthy subjects, this wave did not change after the apomorphine administration. In the wearing-off PD patient group the frontal N30 increment was positively correlated with the number of off hours per day. This specific apomorphine sensitivity of the frontal N30 was interpreted as a physiological index of the dopaminergic modulatory control exerted on the neuronal structures implicated in the generation of the frontal N30.

Pre- and postcentral cortical somatosensory evoked potentials in hemiparkinsonism

We recorded cortical frontal, central, and parietal somatosensory evoked potentials (SEPs) in 9 patients with hemiparkinsonism and in a group of 25 healthy volunteers. No differences were observed in the SEPs recorded after stimulation of the asymptomatic and symptomatic sides in the patients. Likewise, comparison with the healthy controls did not reveal significant group differences or abnormal waveforms in the patients. Even frontal N30 deflection, which has been reported to be diminished in Parkinson's disease (PD), was normal and symmetric in the patients. Therefore, no evidence was found for altered sensory input to the motor or premotor and supplementary motor cortices in PD.

Suppression of magnetic mu rhythm during parkinsonian tremor

We recorded spontaneous magnetoencephalographic (MEG) activity and somatosensory-evoked fields (SEFs) with a 24-channel planar SQUIDgradiometer in five patients with hemiparkinsonism. The SEFs of the patients were within normal limits. During tremorless periods, the spontaneous activity over the somatomotor cortex had a frequency peak at approximately 10 Hz in all five patients and another at approximately 20 Hz in three. Tremor dampened the 10-Hz activity in all patients; in three the effect was bilateral. Tremor did not increase MEG activity at the tremor frequency. The suppression of the mu rhythm by the parkinsonian tremor resembled that occurring during voluntary movements in healthy subjects.