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Biomedical subjects

J A Mortimer

Publications and source records attributed to J A Mortimer.

69 records · Page 4Linked to original sources
PubMed1982

Relationship of motor symptoms to intellectual deficits in Parkinson disease.

We studied 60 patients with idiopathic Parkinson disease with motor and neuropsychologic tests to ascertain whether the severity of motor symptoms was associated with the degree of neuropsychologic deficity. Significant correlations were found between the severity of brady kinesia and impaired performance on tests assessing visual-spatial reasoning and psychomotor speed. More severe tremor was associated with better performance on a spatial orientation memory test. There relationships remained when age, age at onset, and self-rated depression were controlled. The findings suggested that cognitive impairment may result from the same subcortical lesions that cause motor symptoms.

Cognition Disorders↗
PubMed1981

Changes in short and long latency stretch responses during the transition from posture to movement.

Experiments were performed in 18 normal subjects to estimate the time course of changes in the gains of pathways mediating short- and long-latency responses to muscle stretch during the transition from a maintained posture against a steady load to a rapid ballistic movement. Subjects were instructed to rapidly flex or extend their forearm in response to a tone from an initial position of 90 degree of elbow flexion. Torque pulses stretching the biceps muscle were applied to the forearm at 8 different times before and after the signal to initiate the movement, and the gains of short- and long-latency pathways were estimated from averages of rectified biceps EMG activity for 20 trials at each time interval between the onsets of the tone and torque pulse. The findings demonstrate that changes in the magnitude of long-latency responses (M2, M3) occur during the period between the onset of the auditory signal and the voluntary motor response. However, the magnitude of the short-latency response (M1) remains unchanged until after the onset of voluntary motor activity. The differences in the timing of short- and long-latency stretch responses suggests that activity in long-latency pathways may play an important preparatory role in facilitating the transition from posture to movement.

Adult↗
PubMed1977

Failure of L-dopa to relieve activated rigidity in Parkinson's disease.

Rigidity in Parkinson patients can be easily quantitated by determining net work required to passively flex and extend the forearm through an arc of 100 degrees. Rigidity thus measured can be subdivided into two very distinct types, resting and activated. Resting rigidity, measured while the patient is relaxed, responds to all effective therapeutic agents and correlates closely to degree of clinical improvement. Activated rigidity, measured during voluntary activity, is not relieved by any presently available medical treatment. It remains unchanged at pre-therapy levels even in patients who may temporarily appear to have dramatic improvement in clinical symptomatology. Longitudinal measurements made in hundreds of parkinson patients over intervals ranging from 5 to 15 years show continuing high levels of activated rigidity through the entire period of study. In marked contrast to our wide experience with parkinson patients is a single, well documented case of Wilson's disease who appears to have recovered completely both by clinical examination and by all of our machine measurements. This patient had high levels of extrapyramidal deficit, repeatedly measured over a period of four months when penicillamine therapy was being investigated. He then suddenly reverted to normal and returned to full time employment. High values of resting rigidity activated rigidity, akinesia and resting tremor all reverted to normal and have remained normal for the past 6 years. The implication of this study is that L-dopa and related treatments only mask the symptomatology of Parkinson's disease and are not retarding the underlying pathological process. Penicillamine, on the other hand, probably does relieve the destructive process in Wilson's disease and may in early cases, permanently relieve the extrapyramidal dysfunction.

Adult↗
PubMed1975

Cerebellar responses to teleceptive stimuli in alert monkeys.

Discharges of single Purkinje cells in the intermediate and lateral zones of the cerebellar cortex and of neurons in the interpositus and dentate nuclei were recorded in alert monkeys during the presentation of intense auditory and visual stimuli. Concomitant monitoring of the electromyogram (EMG) demonstrated that these stimuli evoked characteristic startle responses in most instances. Firing patterns of cerebellar nuclear cells to auditory stimuli could be categorized into four types, the most common of which consisted of a short-latency acceleration of discharge, followed by a decrease in activity, and in most cells by a later period of facilitation. Simple spike discharge patterns of Purkinje cells consisted largely of prolonged increases or decreases in firing rate, although more complex patterns were seen. In almost 50% of the Purkinje cells tested, complex spikes were evoked by the auditory stimuli. Comparison of simple spike responses of Purkinje cells and of the discharges of cerebellar nuclear cells to auditory and visual inputs revealed that, except for a longer latency, the discharge pattern evoked by flash stimuli was identical to that evoked by sound in all instances. By contrast, in about one-third of the Purkinje cells with related complex spike discharge, complex spikes were evoked by stimuli of only a single modality. Comparison of the times of changes in nuclear and Purkinje cell activity suggests that the initial change in nuclear cell discharge was due to an increase in mossy fiber activity, while the subsequent decrease resulted from Purkinje cell inhibition evoked by mossy and climbing fiber inputs. The absence of increases in nuclear cell discharge at the time of most decreases in Purkinje activity indicates that removal of Purkinje inhibition does not have a major effect on the discharge rates of individual nuclear cells. The data also suggest that excitation of nuclear cells via climbing fiber collaterals played only a minor role in influencing their discharge. Since most EMG changes occurred after or at about the same time as the initial changes in cerebellar discharge, it is unlikely that the initial changes in cerebellar activity were a result of feedback from contracting muscles. It is proposed that the similar discharge patterns of cerebellar neurons to auditory and visual input results from a convergence of these inputs on a structure which projects to the cerebellum as mossy fibers.

Acoustic Stimulation↗
PubMed1975

A hybrid compartmental model for the alligator Purkinje cell. I: Preferred somatopetal conduction of dendritic spikes and soma-axon interaction.

A compartmental hardware model of an alligator Purkinje cell is described, consisting of a branched dendritic tree with four zones of spike generation and electrically excitable soma and initial-segment regions. Passive properties of the model compartments are represented by a cable analog circuit. Simulated action potentials, generated by a combination of depolarizing and hyperpolarizing conductance changes, are triggered in active compartments when the simulated membrane potential passes through preset thresholds. These were set at values corresponding to 28mV depolarization in the dendrites, 22 mV in the soma, and 7 mV in the initial-segment compartment. Synaptic inputs consisting of brief (0.35 msec) rectangular conductance changes give rise to exponentially decaying postsynaptic potentials in the input compartment which are electrotonically spread to other compartments. Orthodromic activation of the model neuron by computer-generated random pulse trains generates a simple spike discharge in the initial-segment compartment without evoking complex spikes. Synchronized excitatory input to the same compartments, however, does evoke a complex spike response in the soma and initial segment, coupled with dendritic spikes. Following antidromic activation of the model neuron, dendritic spikes are not generated, demonstrating a tendency in the dendritic tree for preferential conduction of spikes toward the soma. Investigation of some of the factors underlying this tendency suggests that variations in voltage attenuation due to dendritic geometry, convergence of electrotonically spread dendritic spikes, and the relative durations of dendritic and somatic action potentials may contribute to it. The presence of a threshold gradient in the dendritic tree, proposed by Llinás and his coworkers, was not found to be necessary to explain this tendency toward somatopetal conduction, although it cannot be excluded by the model. Examination of the role of the conically shaped initial-segment region suggests that this zone may provide a low-pass filter for signals conducted electrotonically from the axon to the soma, blocking repolarization of the soma during the complex spike burst generated in the axon.

Action Potentials↗
PubMedDate not supplied

Rate of cognitive decline in Alzheimer's disease is associated with EEG alpha power.

Fifteen patients with Alzheimer's disease who were initially mildly or moderately impaired were followed for up to 4 years. Scores of the Mini-Mental State Examination (MMSE) were regressed on time of examination (measured at 6-month intervals) to estimate cognitive progression rates in individual patients. A quantitative electroencephalographic (EEG) examination was administered to each patient. Log-absolute EEG power in the alpha bandwidth (8-12 Hz) was found to be correlated with the computed rate of MMSE decline. This association was present for electrode sites across all regions of the scalp and remained significant when the effects of current cognitive severity were partialled out. These data suggest that a quantitative EEG measure (absolute alpha power) is related to the rate of cognitive decline in patients with Alzheimer's disease.

Alpha Rhythm↗
PubMedDate not supplied

Premovement silence of EMG activity prior to movement in Parkinson patients.

Premovement silence (PMS) of tonic agonist electromyographic activity (EMG) preceding a maximum effort elbow extension was studied in eight bradykinetic Parkinson patients. The occurrence and duration of PMS have been shown to be significantly correlated with peak acceleration of movement in normal subjects. To determine if inability to silence the EMG prior to the initial agonist burst may contribute to bradykinesia of Parkinson's disease, patients maintained elbow extension against a tonic load on triceps, and in response to a tone performed a maximum effort elbow extension. All eight patients showed some trials (mean = 30%) with PMS. However, neither the incidence of PMS nor its duration were significantly correlated with mean peak acceleration. A significant correlation was found between the incidence of abnormal initial agonist bursts, called "segmented bursts," and mean peak acceleration. We conclude that ability to silence the agonist muscle prior to movement is not strongly associated with bradykinesia in Parkinson's disease.

Aged↗
PubMedDate not supplied

Cognitive Performance Test: a new approach to functional assessment in Alzheimer's disease.

A new performance-based assessment instrument for evaluating function in patients with Alzheimer's disease (AD), the Cognitive Performance Test (CPT), is described. This instrument, based on Allen Cognitive Disability Theory, uses six common activities of daily living (ADL) tasks, for which the information-processing requirements can be systematically varied to assess ordinal levels of functional capacity. Seventy-seven patients with mild to moderate Alzheimer's disease (AD) and 15 neurologically normal elderly controls were administered the CPT. Subsets of the AD patients were assessed again at 4 weeks and 1, 2, and 3 years following the initial evaluation. Internal consistency of the CPT estimated by alpha was .84. Intraclass correlation for interrater reliability was .91 and for test-retest reliability at 4 weeks, .89. CPT scores were significantly correlated with Mini-Mental State Examination scores (r = .67) and two measures of caregiver-rated ADL (Instrumental Activities of Daily Living, r = .64; Physical Self-Maintenance Scale, r = .49). Significant declines in CPT scores were seen on 1-, 2-, and 3-year follow-ups. Initial CPT scores predicted risk of institutionalization over a 4-year follow-up period.

Activities of Daily Living↗