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Biomedical subjects

M J Aminoff

Publications and source records attributed to M J Aminoff.

At least 37 records · Page 2Linked to original sources
PubMed1997

Changes of forearm EMG and cerebral evoked potentials following sudden muscle stretch during isometric contractions in patients with Parkinson's disease.

Various investigators have reported that the late reflex EMG activity following muscle stretch is increased in patients with Parkinson's disease. To explore the basis of this increased activity, we have now recorded the late EMG responses together with associated cerebral responses following muscle stretch in parkinsonian patients. Nine patients and eight controls participated in two sets of experiments in which they grasped a handle attached to a torque motor and maintained the wrist isometrically against a constant flexor force. The force was changed unpredictably (first set) or predictably (second set of experiments), causing a stretch of wrist extensors or flexors. Cerebral responses and muscle responses from the forearm were recorded and averaged separately depending upon condition. The late muscle responses to unpredictable muscle stretch were enhanced in parkinsonian patients while the cerebral responses were attenuated when compared to controls. The alteration of the electrocerebral response began approx. 25 ms prior to the late M2 muscle response. Both controls and patients showed a markedly attenuated cerebral response when the muscle stretch was predictable. These results indicate that the electrocerebral response to muscle stretch is altered prior to the onset of M2 in patients with Parkinson's disease, and suggest that these cerebral events reflect components of a long-latency transcerebral reflex pathway that is affected in this disorder.

Brain↗
PubMed1997

Sensory perception in Parkinson disease.

OBJECTIVE: To determine whether there is a complex sensory disturbance that may be contributing to the motor deficit in patients with Parkinson disease. DESIGN: Comparison of performance by patients and healthy, age- and sex-matched subjects in tests of various sensory functions. SETTING: The Center for Human Performance and Testing at a university hospital and research center. PARTICIPANTS: Ten subjects with Parkinson disease and 10 control subjects matched for age and sex. MAIN OUTCOME MEASURE: Performance on 4 subjects of the Sensory Integration and Praxis Test: finger identification, graphesthesia, localization of tactile stimuli, and kinesthesia. RESULTS: Data were analyzed using paired t tests for ratio data and the paired Wilcoxon test for ordinal data. Patients with Parkinson disease performed significantly worse (P = .001) than the control patients on the test of kinesthesia. There were no significant differences between the 2 groups on the other subtests. CONCLUSIONS: Without visual guidance, patients with Parkinson disease had more difficulty in perceiving the extent of a movement made to a target away from the body, a task requiring reliance on proprioceptive feedback. Parkinsonian patients had no more difficulty than controls in making movements to a target on the surface of the body when they could use tactile sensations. Movement difficulties in patients with Parkinson disease may relate in part to a decrease in proprioception. Activities that enhance kinesthetic awareness may be an important adjunct to the treatment of these patients.

Humans↗
PubMed1997

Magnetoencephalography in partial epilepsy: clinical yield and localization accuracy.

The goals of this study were to determine (1) the yield of magnetoencephalography (MEG) according to epilepsy type, (2) if MEG spike sources colocalize with focal epileptogenic pathology, and (3) if MEG can identify the epileptogenic zone when scalp ictal electroencephalogram (EEG) or magnetic resonance imaging (MRI) fail to localize it. Twenty-two patients with mesial temporal (10 patients), neocortical temporal (3 patients), and extratemporal lobe epilepsy (9 patients) were studied. A 37-channel biomagnetometer was used for simultaneously recording MEG with EEG. During the typical 2-3-hour MEG recording session, interictal epileptiform activity was observed in 16 of 22 patients. MEG localization yield was greater in patients with neocortical epilepsy (92%) than in those with mesial temporal lobe epilepsy (50%). In 5 of 6 patients with focal epileptogenic pathology, MEG spike sources were colocalized with the lesions. In 11 of 12 patients with nonlocalizing (ambiguous abnormalities or normal) MRI, MEG spike sources were localized in the region of the epileptogenic zone as ultimately defined by all clinical and EEG information (including intracranial EEG). In conclusion, MEG can reliably localize sources of spike discharges in patients with temporal and extratemporal lobe epilepsy. MEG sometimes provides noninvasive localization data that are not otherwise available with MRI or conventional scalp ictal EEG.

Adolescent↗
PubMed1997

Proton MR spectroscopic imaging of the striatum in Parkinson's disease.

Assess the feasibility of proton MR spectroscopic imaging (1H-MRSI) of the striatum (putamen and caudate nucleus) in patients with Parkinson's disease and evaluate striatal neuronal density. Proton MRSI of the striatum and thalamus with 2 cc spatial resolution was performed in 10 patients with Parkinson's disease, 1 patient with atypical parkinsonism, and 13 control subjects. Single voxel proton MR spectra with signals from choline metabolites (Cho), creatine metabolites (Cr), and the putative neuronal marker, N-acetyl-aspartate (NAA), were obtained from the putamen and thalamus, but not the caudate nucleus, of patients with parkinsonism and control subjects. Metabolite rations in controls and patients were: in putamen NAA/Cho 1.70 +/- 0.25 vrs 1.74 +/- 0.32, NAA/Cr 2.80 +/- 0.79 vrs 2.36 +/- 0.42, Cho/Cr 1.63 +/- 0.25 vrs 1.39 +/- 0.3; in thalamus, NAA/Cho 1.78 +/- 0.15 vrs 1.62 +/- 0.22, NAA/Cr 2.78 +/- 0.34 vrs 2.64 +/- 0.41, Cho/Cr 1.57 +/- 0.25 vrs 1.65 +/- 0.28. There were no statistically significant differences between patients and controls. The putaminal NAA/Cho ratio of the single subject with atypical parkinsonism was lower than that of 9 of the 10 patients with classic Parkinson's disease and 11 of the 13 control subjects. Likewise, the putaminal NAA/Cr ratio in the single subject with atypical parkinsonism was lower than that of 7of the patients with guided selection of spectra from very small brain volumes, is a technique that can be used to evaluate neuronal density in individual subcortical gray nuclei in the brains of patients with parkinsonism. Using this technique, we have shown that Parkinson's disease produces no change in relative levels of the neuronal marker, NAA, in the putamen.

Adult↗
PubMed1997

The decision to make a movement: neurophysiological insights.

It is unclear how the brain enables a subject to discriminate between two or more sensory stimuli and to respond appropriately to them. This process must include the ability to detect and identify the stimuli, and to select and initiate an appropriate motor response. With the advent of improved computer technology, this behavior can now be studied in the laboratory, not only by monitoring the input to (stimulus) and output from the brain (response), but also by measuring the associated electrical activity of the brain in order to gain an understanding of how this task is accomplished. In this paper we discuss our work in this area and its relevance to understanding the neural organization of the decision to make a movement in response to a sensory stimulus.

Animals↗
PubMed1997

New pharmacotherapy for Parkinson's disease.

OBJECTIVE: To summarize the development, pharmacology, pharmacokinetics, efficacy, and safety of five investigational antiparkinsonian drugs that are in or have recently completed Phase III trials: three dopamine agonists, pramipexole, ropinirole, and cabergoline; and two catechol-O-methyltransferase (COMT) inhibitors, entacapone and tolcapone. The pathophysiology and the role of dopamine in Parkinson's disease are also reviewed. DATA SOURCES: A MEDLINE search of relevant English-language literature, clinical studies, abstracts, and review articles pertaining to Parkinson's disease was conducted. Manual searches of 1996/1997 meeting abstracts published by the American Academy of Neurology and the Movement Disorders Society were also performed. Manufacturers provided unpublished Phase III trial efficacy and pharmacokinetic data. STUDY SELECTION AND DATA EXTRACTION: Clinical trial investigations selected for inclusion were limited to human subjects. Interim analyses after 6 months for long-term clinical studies in progress were included. Pharmacokinetic data from animals were cited if human data were unavailable. Statistical analyses for all studies were evaluated. DATA SYNTHESIS: By selectivity targeting D2 receptors, the newer dopamine agonists (i.e., cabergoline, pramipexole, ropinirole) may delay the introduction of levodopa and thus the occurrence of levodopa-induced dyskinesias. In addition, they are efficacious as adjunctive therapies in patients with advanced Parkinson's disease. Unlike the currently available dopamine agonists, pramipexole and ropinirole are non-ergot derivatives and do not cause skin inflammation, paresthesias, pulmonary infiltrates, or pleural effusion. The COMT inhibitors, tolcapone and entacapone, improve the pharmacokinetics of levodopa by preventing its peripheral catabolism and increasing the concentration of brain dopamine; thus, these agents may reduce the incidence of "wearing-off" effects associated with the short half-life of levodopa and the progression of Parkinson's disease. CONCLUSIONS: Interim 6-month analyses of pramipexole, ropinirole, and cabergoline for symptomatic treatment of early Parkinson's disease have shown these drugs to be efficacious and relatively well-tolerated when used as monotherapy. Their role in delaying the development of motor fluctuations and delaying the addition of levodopa is the subject of long-term clinical studies. In advanced stages of Parkinson's disease, these medications were also efficacious; however, the main adverse effects included dyskinesias, somnolence, and hallucinations. The COMT inhibitors, entacapone and tolcapone, have also demonstrated efficacy in improving on-time in patients with stable disease. Tolcapone has also demonstrated efficacy in patients with motor fluctuations. Both drugs are relatively well-tolerated, with the exception of dyskinesias that require reduction of the levodopa dosage and occasional diarrhea.

Benzophenones↗
PubMed1996

Historical perspective Brown-Sequard and his work on the spinal cord.

Charles Edouard Brown-Sequard was born in Mauritius in 1817, graduated as a physician in Paris in 1846, was a founder-physician of the National Hospital (for Neurology and Neurosurgery) in England, and held the Chair of Physiology and Pathology of the Nervous System at Harvard College before succeeding Claude Bernard as professor of medicine at the College de France in Paris, where he remained until his death in 1894. Erratic and unpredictable, he spent much of his life in traveling between Europe and the United States, married three times, fathered three children, authored almost 600 scientific publications, and was the founder-editor of three journals. Widely regarded as a founder of modern endocrinology, his work on tissue extracts toward the end of his career brought scorn and derision from colleagues and much of the lay public, but was the foundation of modern hormone replacement therapy. Brown-Sequard made many contributions to neurology, but is best known for his work on the sensory pathways in the spinal cord. He initially showed that these pathways are not confined to the posterior columns and that certain sensory fibers decussate soon after their entry into the spinal cord, and he subsequently described the clinical features of the syndrome now named after him. In his later life, he modified his views to suggest that dynamic spinal mechanisms are responsible at least in part for the sensory changes resulting from spinal cord lesions, stressing that any deficit is not simply the result of the interruption of a hard-wired system. The clinical implications of these views are profound, but this aspect of his work has been virtually ignored until very recently.

Europe↗
PubMed1996

Response times and handedness in simple reaction-time tasks.

The anticipatory (preparatory) cerebral events in simple reaction-time tasks may depend on the ability of a subject to predict accurately the time of occurrence of the stimulus requiring a particular response. In order to examine this hypothesis, we recorded cerebral and muscle responses in two different conditions, each involving three simple reaction-time tasks. Auditory tones were presented either regularly (i.e., predictably) or irregularly and subjects were required to respond to each tone with left hand, right hand or both hands in different runs. Responses were simultaneously averaged both backward and forward from the response (response-synchronized) and forward from the stimulus (stimulus-synchronized). Response-synchronized cerebral potentials to the regular tones were characterized by a slow negative shift, the bereitschaftspotential (BP), that began prior to stimulus onset and whose terminal phase was characterized by a small, higher frequency, negative shift (HFNS). By contrast, response-synchronized cerebral potentials to the irregular tones for both groups did not contain a BP, but a more conspicuous HFNS that began after stimulus onset. Both the response time and the latency of the N1 sensory-related component of the cerebral evoked potential recorded in the stimulus-synchronized averages (which aligns with HFNS) were delayed in the irregular condition. These findings suggest that, for both right- and left-handed subjects, the BP is not required for voluntary movement, and that anticipatory cerebral activity, as reflected by the BP, represents not only a preparation to make a particular response but also a preparation to process the stimulus.

Adult↗
PubMed1996

Comparison of late components in simultaneously recorded event-related electrical potentials and event-related magnetic fields.

We have attempted to define the late components of the event-related magnetic field (ERF) and to relate them to the late components of the event-related electrical potential (ERP). Simultaneous multichannel electroencephalogram (EEG) and magnetoencephalogram (MEG) were recorded in 13 subjects during an auditory oddball paradigm in two series of experiments. EEG responses to frequent tones consisted of the N1 and P2 components of the auditory vertex potential. Responses to rare tones consisted of N1, apparent P2, N2 and P3 components. All EEG components were best seen in the midline and were highly reproducible for all subjects. MEG responses to frequent tones consisted of N1m and P2m components that were highly reproducible only when recorded over the temporal region. By contrast, the ERF to rare tones was less well defined and only the N1m component could be identified satisfactorily. There was little consistent activity in the MEG at the time of occurrence of the N2 and P3 components of the ERP.

Acoustic Stimulation↗
PubMed1996

Brown-Séquard and his syndrome.

The contributions of Charles Edouard Brown-Séquard (1817-1894) to the advancement of medical science included his emphasis on functional processes in the integrative action of the nervous system, his discovery of the vasomotor nerves, his experimental demonstration that the adrenal glands are esential to life, and his pioneering work on hormone replacement therapy. He is best remembered, however, for his work in delineating the sensory pathways in the spinal cord. His later work on the sensory function of the cord emphasized dynamic spinal mechanisms that may well have major implications for the rehabilitation of patients with cord injuries.

History, 19th Century↗
PubMed1996

Response compatibility and the relationship between event-related potentials and the timing of a motor response.

1. Earlier studies have shown that changes in the difficulty of sensory discrimination in a choice reaction time task result in a prolongation of the peak latency for several components of the long-latency event-related potential (ERP). With the use of the technique of response-locked averaging, we have previously shown that manipulation of the difficulty of sensory discrimination also affects response execution as assessed by the interval between the ERP and onset of the response. In the present paper we examine the hypothesis that changing the compatibility of the responses may also affect the difficulty of the discrimination, as well as the execution of the response, as assessed by the interval between stimulus onset and the ERP. Such an effect of response compatibility would provide further evidence for the close integration of motor and sensory processes in the performance of choice reaction time tasks. 2. We continuously recorded the electroencephalogram (EEG) from the scalp and the electromyogram (EMG) from the responding muscles in both compatible and noncompatible visual choice reaction time tasks. In the compatible task subjects responded to a lateralized visual stimulus with the hand ipsilateral to the stimulus, whereas in the noncompatible task they responded with the contralateral hand. EEG and EMG responses were analyzed and averaged off-line, aligning the waveforms by either stimulus onset (stimulus-synchronized averages) or response onset (response-synchronized averages), and averaged separately for both correct and incorrect response outcomes. 3. Response times were significantly faster for frequent stimuli than rare stimuli and were significantly faster to rare stimuli in the compatible than the noncompatible condition. In responses to the frequent stimuli (where both hands were required to respond), the right hand was slightly but consistently faster than the left hand. The right hand also accounted for 83% of the errors made. 4. Stimulus-synchronized and response-synchronized ERPs to either frequent or rare stimuli had a similar appearance for correct responses in both the compatible and noncompatible conditions. The coupling of the response to the ERP for the rare stimuli, however, was different for the two conditions: the response occurred later relative to the ERP components in the response-synchronized average in the noncompatible condition compared with the compatible condition. By contrast, the coupling of the ERPs to the onset of the stimulus was the same in the two conditions. 5. Stimulus-synchronized averages for error responses in which the rare tone was mistaken for a frequent tone showed early sensory processing (as judged by the ERPs) that was similar to that of correct responses to the rare stimuli. After the apparent positive (P2) component of the cerebral response, however, the processing differed, with a superimposed broad negativity possibly reflecting awareness by the subject that a mistake had been made. By contrast, the response-synchronized averages for these error trials appeared like those to frequent stimuli, with the response being coupled to the P2 component of the cerebral response. 6. These results suggest that response compatibility affects response selection processes but does not alter sensory discrimination. However, despite the similarly tight coupling of the response to the ERP in both the compatible and noncompatible conditions, the response occurred later relative to the ERPs in the noncompatible condition. This suggests that different components of the ERP are responsible for triggering the response in different circumstances. Our observations on the error trials suggests that the decision to respond (on these trials) is based on the occurrence of cerebral events that are evoked by either rare or frequent stimuli, whereas this decision (on correct response trials) is based on cerebral events elicited only by the rare stimuli.

Adult↗
PubMed1996

Reduced corticomotoneuronal excitatory postsynaptic potentials (EPSPs) with normal Ia afferent EPSPs in amyotrophic lateral sclerosis.

We studied excitatory postsynaptic potentials (EPSPs) arising in single spinal motoneurons (composite EPSPs) induced by Ia afferent and magnetic cortical stimulation in 28 normal subjects ranging in age from 24 to 84 years and 28 patients with amyotrophic lateral sclerosis (ALS) aged 34 to 82 years. The subjects voluntarily recruited single motor units of the first dorsal interosseous muscle. Using peristimulus time histograms, we determined changes in the firing probability of the first dorsal interosseous motor units and measured the magnitude of the EPSP. An early period of increased firing probability (primary peak) occurred at approximately 30 msec after la afferent and 25 msec after cortical stimulation, reflecting underlying EPSPs arising in spinal motoneurons induced by either projection. The latency of the primary peaks for both Ia afferent and cortical stimulation was mildly prolonged in ALS, suggesting a loss of the fastest-conducting spinal motoneurons. Patients with ALS had la afferent-driven EPSPs whose amplitude and rise time were equivalent to those of normal subjects. However, the ratio of cortical to la afferent-driven composite EPSPs in ALS was significantly lower than that for normal subjects. Fourteen of 28 ALS motor units had cortically driven EPSPs that were small or large only because of a prolonged rise time. The findings suggest that in ALS, corticomotoneuronal attrition or dispersion of the descending volley occurs in the presence of normally functioning spinal motoneurons to which they project.

Adolescent↗
PubMed1995

The frontal N30 component of the median-derived SEP in patients with predominantly unilateral Parkinson's disease.

There are conflicting reports concerning attenuation of the frontal N30 component of the median-derived somatosensory evoked potential in patients with Parkinson's disease (PD). We found that the mean N30 latency (28.03 +/- 2.50 msec) and amplitude (2.30 +/- 1.58 microV) obtained with stimulation of the affected arm of 10 patients with predominantly unilateral PD were not significantly different from those obtained from the unaffected arm (mean latency, 28.14 +/- 2.47 msec; mean amplitude, 2.43 +/- 1.65 microV) or from 10 age-matched controls (mean latency, 29.01 +/- 1.88 msec; mean amplitude, 1.92 +/- 0.64 microV). Three patients had an N30 of abnormal amplitude; in two, responses were absent with stimulation of either side, and in one there was a response asymmetry exceeding the normal range, with the smaller response elicited from the affected arm. Thus, only one of 10 patients had a diminished N30 consistent with the clinical findings. We conclude that the N30 is unlikely to be clinically useful in the assessment of patients with PD.

Aged↗