Biomedical subjects
Publications and source records attributed to M J Aminoff.
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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.
We have previously found that the late reflex electromyographic (EMG) responses to muscle stretch are simultaneously present in both the stretched muscle and its antagonist, suggesting that it may be involved in the control of limb stiffness rather than in a servo-mechanism that returns the limb to an initial or intended position. Nevertheless, in these earlier experiments the size of the late EMG activity was always greater in the stretched muscle than its antagonist, suggesting also a possible servo-role for these responses. To clarify this, we have now recorded the late EMG activity simultaneously from both the right extensor and flexor carpi radialis muscles in ten subjects under four experimental conditions. These conditions differed in which muscle was activated voluntarily prior to the stretch stimulus and in which muscle was stretched by the perturbing force. In all cases subjects were asked to maintain the limb in a fixed position and oppose any displacement that occurred. The amount of integrated EMG activity for both the M2 and M3 components of the late response was greater in the agonist muscle (i.e., the muscle actually stretched by the perturbing force) than the antagonist. The ratio of agonist to antagonist activity, however, was significantly larger for the M2 than for the M3 component. These results suggest that both the M2 and M3 components of the late EMG response have a dual functional role, being involved both in a servo-mechanism and in the control of limb stiffness. Each component, however, seems to have a distinctive role.(ABSTRACT TRUNCATED AT 250 WORDS)
The recording of visual evoked potentials (VEPs) is an important means of obtaining reproducible, quantitative data on the function of the anterior visual pathways. In this review, the technical aspects of recording VEPs are briefly discussed, components of the VEPs are described, and the clinical uses of VEPs are considered. It is concluded that VEPs are useful in providing information concerning the functional integrity of the anterior visual pathways. They are especially useful in evaluating patients with visual symptoms but no objective findings on examination and in patients without visual symptoms but with diseases that are known to involve the visual pathways commonly and subclinically. Lastly, the utility and limitations of VEPs in various neurological disorders are summarized, bearing in mind the widespread availability of advanced neuroimaging techniques.
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Pharmacotherapy with levodopa for Parkinson's disease provides symptomatic benefit, but fluctuations in (or loss of) response may eventually occur. Dopamine agonists are also helpful and, when taken with low doses of levodopa, often provide sustained benefit with fewer side effects; novel agonists and new methods for their administration are therefore under study. Other therapeutic strategies are being explored, including the use of type B monoamine oxidase inhibitors to reduce the metabolic breakdown of dopamine, catechol-O-methyltransferase inhibitors to retard the breakdown of levodopa, norepinephrine precursors to compensate for deficiency of this neurotransmitter, glutamate antagonists to counteract the effects of the subthalamic nucleus, and various neurotrophic factors to influence dopaminergic nigrostriatal cells. Surgical procedures involving pallidotomy are sometimes helpful. Those involving cerebral transplantation of adrenal medullary or fetal mesencephalic tissue have yielded mixed results; benefits may relate to the presence of growth factors in the transplanted tissue. The transplantation of genetically engineered cell lines will probably become the optimal transplantation procedure. The cause of Parkinson's disease may relate to oxidant stress and the generation of free radicals. It is not clear whether treatment with selegiline hydrochloride (a type B monoamine oxidase inhibitor) delays the progression of Parkinson's disease, because the drug also exerts a mild symptomatic effect. Daily treatment with vitamin E (a scavenger of free radicals) does not influence disease progression, perhaps because of limited penetration into the brain.
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1. Previous studies have shown that the long latency event-related potentials (ERPs) reflect certain aspects of the sensory discrimination process, although the coupling of these ERPs to the actual discrimination is variable. Indeed, we have previously shown that during a two-choice reaction time task the discrimination is accomplished as a two-stage process, with the more frequently occurring stimulus discriminated at an earlier point than the rarer stimulus. The present paper examines the hypothesis that, in a three-choice reaction time task, the discrimination is similarly organized, i.e., is accomplished with the use of a three-stage process. 2. In the present experiments, we continuously recorded the electrocerebral activity (EEG) from the scalp and the electromyogram (EMG) from the responding muscles in a three-choice reaction time task in 10 strictly right-handed subjects. EEG and EMG responses were subsequently analyzed off-line by aligning them by the onset of either the stimulus (stimulus-synchronized) or the response (response-synchronized) for both correct and incorrect responses. 3. Subjects could be classified as "fast" or "slow" responders based on the mean response-latency to the most frequently occurring of the three tones (Frequent tone). Fast responders to the Frequent tone were also fast responders to the more frequent of the rare tones (the Rare-1 tone). By contrast, the response latency to the Frequent tone did not predict the speed of response to the most rare tone (the Rare-2 tone). 4. In the response-synchronized averages well-formed premovement potentials were present for the correct responses to all three tones. In the case of the Frequent tone, these potentials were symmetrical over the two cerebral hemispheres (as expected because both hands responded to this tone). They began > or = 200 ms before the average onset of the stimulus, suggesting that the preparation to respond preceded the stimulus. In the case of the two rare tones, the amplitudes of these premovement potentials were asymmetrical over the two hemispheres. For the Rare-1 tone, these potentials were lateralized to the hemisphere contralateral to the hand moved. For the Rare-2 tone, however, these premovement potentials were initially lateralized to the ipsilateral hemisphere, indicating that, even when subjects were able to respond rapidly and correctly to this tone, they were anticipating a need to respond with the incorrect hand (in anticipation of the more frequent Rare-1 tone).(ABSTRACT TRUNCATED AT 400 WORDS)
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We investigated the relationship between sensory discrimination and the selection of appropriate responses in subjects performing two different reaction-time tasks, in which three auditory stimuli were presented in random order and with a different likelihood of occurrence. Subjects anticipated the need to make different responses based on the likelihood that a particular stimulus would occur on a particular trial. This was determined by the occurrence and distribution of premovement potentials prior to the stimulus, which were consistent with preparation to respond to the most frequently occurring stimulus. These anticipatory cerebral events, however, could be altered after recognition that this frequent stimulus had not occurred. Thus, after the occurrence of a stimulus other than the anticipated frequent tone, the scalp distribution of cerebral potentials changed in a manner suggesting that the next most frequently occurring stimulus was anticipated. Nonetheless, subjects were able to respond to the least probable stimulus both accurately and rapidly despite a failure to anticipate it correctly, as judged by the cerebral "lateralized readiness potential." These results indicate that stimulus evaluation and response selection are integrated and dynamic cerebral processes, and raise doubt about the functional significance of the so-called premovement readiness potential.
The present paper examines the hypothesis that the long latency EMG activity produced by muscle stretch is the result of long loop reflex pathways involved in the control of limb stiffness. We recorded the cerebral responses and late EMG activity in agonist and antagonist muscles following sudden stretch of the wrist extensor muscles under 4 experimental conditions in 11 subjects. In each experiment subjects held their right wrist extended isometrically against a constant force of 2.3 N and a trial was begun with a step increase in the force from 2.3 N to 18.4 N, to stretch the extensor muscle. In the first and second experiments the force change occurred unpredictably and subjects had to either oppose the perturbation (Unpredictable Oppose) or relax the forearm muscles once the increase in force was detected (Unpredictable Let-Go). In the third and fourth experiments the force change occurred predictably when subjects pressed a thumb switch with the left hand to cause it. As before, subjects were instructed to either oppose the perturbation (Predictable Oppose) or relax the forearm muscles (Predictable Let-Go). Responses were recorded from the flexor and extensor carpi radialis muscles and from the scalp. When the perturbing force occurred unpredictably, early latency EMG activity (the MI response) was seen in the stretched extensor muscle, and longer latency EMG activity was seen simultaneously in both extensor and flexor muscles. When the force change occurred predictably the late EMG activity was considerably attenuated, especially in the Predictable Let-Go condition. Cerebral responses similarly depended upon the predictability of the perturbation.(ABSTRACT TRUNCATED AT 250 WORDS)
The effectiveness of botulinum toxin injections in 11 patients with hemifacial spasm was investigated in a prospective placebo-controlled blinded study. The patients were treated with four sets of injections to various facial muscles, selected by clinical evaluation. Three injections were with graded doses of toxin and one was with placebo. The order of injections was random and unknown to the patients. Results were scored both subjectively by patient assessment of symptoms and objectively by blinded review of videotapes made one month after each injection. Subjective improvement occurred after 79% of injections with botulinum toxin, regardless of dose of toxin. Only 1 patient improved after placebo. Objective improvement was seen after 84% of injections with botulinum toxin. No patient showed objective improvement after placebo injection. The most frequent side effect was facial weakness, seen after 97% of injections of botulinum toxin. Facial bruising (20%), diplopia (13%), ptosis (7%), and various other mild side effects were seen less frequently. Botulinum toxin appears to be an effective and safe method of therapy for hemifacial spasm.
The effect of different high-pass filters on long-latency auditory evoked potentials was investigated in 25 subjects, 15 of whom were asymptomatic individuals seropositive for the human immunodeficiency virus (HIV) and 10 of whom were normal control subjects without known risk factors for HIV infection. High-pass filtering was done simultaneously at 0.25 Hz and 1.0 Hz, and cerebral responses to rare (2,000 Hz) and frequent (1,000 Hz) tones were recorded from Fpz, Cz, and Pz electrode placements and averaged separately. Using either filter, well-formed and reproducible responses were obtained, although the latencies of the N1, P2, N2, and P3 components of the response were slightly shorter when a 1.0 Hz filter was used. In addition, the appearance of the late response was modified in a manner suggesting that components of the ERP considerably slower than P3 were being attenuated by a 1.0-Hz filter. Although it could be argued that this makes the use of a 1.0-Hz filter setting preferable in the clinical setting, the variability and reproducibility of the ERP were comparable when either high-pass filter was used, and both resulted in similar findings in the HIV-infected individuals compared to normals.
Event-related potentials depend on the context of the target stimulus and relate to the cognitive aspects of discriminating target from nontarget stimuli. For clinical purposes, they are elicited most commonly by auditory stimuli. They are influenced by advancing age and by alterations in mental function. They have been used to distinguish dementia from pseudodementia. More specifically, the P3 component of these potentials has a high sensitivity and specificity to dementia, and a prolongation in P3 latency is therefore helpful in establishing the diagnosis of dementia with confidence. Serial studies can provide a means of following changes in cognitive function over time. It may also be possible to distinguish between different types of dementia by the pattern of electrophysiologic abnormalities and in particular by which components of the event-related potentials are delayed.
We retrospectively evaluated the clinical and EEG features of status epilepticus (SE) in 47 comatose adult patients in whom SE was suspected clinically or because the EEG revealed repetitive electrographic seizures or continuous spike-and-wave activity. Three groups of patients were identified. Group-1 patients (n = 33) had SE both clinically and on EEG. They usually had subtle, clonic movements restricted to the eyes, face, and upper extremities, and the EEG most commonly showed repetitive electrographic seizures or continuous spike-and-wave activity. Group-2 patients (n = 9) also had subtle motor manifestations of seizures, but the EEG was not that of SE, consisting of either irregular slowing with frequent spikes and sharp waves, an irregular mixed-frequency background with episodic accentuation, or diffuse slowing; one patient also had an intermittent burst-suppression pattern. The five patients in Group 3 lacked any clinical signs of seizures, but the EEG showed repetitive electrographic seizures or continuous spike-and-wave activity. There were no significant differences between groups in etiology of SE, response to therapy, or outcome, and there was no obvious relationship between the EEG findings and duration of SE. We conclude that recognition of SE in comatose patients may require both clinical and EEG evaluation since either approach by itself may fail to establish the diagnosis. Furthermore, the EEG findings in established SE do not necessarily progress through the series of defined stages suggested by some authors.
We investigated the effectiveness of botulinum toxin in 17 patients with limb dystonias (10 with occupational cramps, three with idiopathic dystonia unrelated to activity, and two each with post-stroke and parkinsonian dystonia) in a placebo-controlled, blinded study. We identified affected muscles clinically and by recording the EMG from implanted wire electrodes at rest and during performance of tasks that precipitated abnormal postures. There were three injections given with graded doses of toxin (average doses, 5 to 10, 10 to 20, and 20 to 40 units per muscle) and one with placebo, in random order. Subjective improvement occurred after 53% of injections of botulinum toxin, and this was substantial in 24%. Only one patient (7%) improved after placebo injection. Subjective improvement occurred in 82% of patients with at least one dose of toxin, lasting for 1 to 4 months. Response rates were similar between clinical groups. Objective evaluation failed to demonstrate significant improvement following treatment with toxin compared with placebo. The major side effect was transient focal weakness after 53% of injections of toxin.
Dysautonomic symptoms are associated with many disorders of the central nervous system, in some of which the autonomic dysfunction is particularly conspicuous or the major cause of disability. New neuroimaging procedures and microneurographic techniques have helped to clarify the underlying pathophysiology and to distinguish or, classify disorders that are clinically similar. Recent studies also suggest that the autonomic nervous system is involved more frequently or extensively than previously thought in certain neurological conditions such as multiple sclerosis or human immunodeficiency virus (HIV) infection, and have helped to define the nature of its involvement in other disorders.