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Biomedical subjects

H J Freund

Publications and source records attributed to H J Freund.

At least 145 records · Page 8Linked to original sources
PubMed1987

Differential effects of cortical lesions in humans.

The best-known example of motor deficits after cortical lesions is contralateral paresis and spasticity after damage to the precentral motor strip. After recovery the residual motor functions can be used in a purposive and skillful manner. In patients with lesions of the supplementary motor area (SMA) and cingulate gyrus transient akinesia and mutism have been described. Lesions restricted to more lateral parts of the premotor field interfere with proximal muscle function and interlimb coordination, whereas distal motor activity and bimanual coordination are unimpaired. In contrast, hand function in patients with parietal lesions is severely disturbed. This dysfunction includes deficits such as ataxia, dysmetria and postural instability that are typically observed in deafferented patients. Severe disturbances of the purposive behaviour of the hand during exploratory finger movements and manipulation of objects are seen in patients with posterior parietal lesions. Observations in human patients are compatible with the hypothesis that lesions of the frontal agranular motor fields interfere with the control of postural and force control whereas parietal lesions are associated with motor programme disorders affecting the use of the hand or the eye as a sense organ or affecting more complex motor behaviour.

Apraxias↗
PubMed1987

Neuromuscular, autonomic and central cholinergic hyperactivity associated with thymoma and acetylcholine receptor-binding antibody.

Two cases of a neuromuscular hyperactivity syndrome associated with a proliferative thymoma and high serum titres of acetylcholine receptor (AChR) antibody with no signs of myasthenia are reported. The clinical and electrodiagnostic findings indicated generalized cholinergic hyperactivity at the neuromuscular junction and in the autonomic and central nervous system, resulting in generalized myokymia, excessive sweating and intermittent psychotic behaviour. The association with thymoma and raised AChR antibody suggests that this syndrome represents a unique type of autoimmune disease, in which antibodies against the AChR facilitate rather than inhibit cholinergic action. This conclusion is supported by the remission of symptoms after thymectomy and with immunosuppressive therapy in one case.

Adult↗
PubMed1987

Stability of frequency during long-term recordings of hand tremor.

During recording of physiological postural hand tremor over a period of 60 min tremor peak frequency (PF) did not change in 14 normal subjects as long as the mechanical conditions were not changed. In contrast, tremor amplitude and synchronization of the corresponding EMG varied considerably. Any alteration in hand mechanics such as changing hand position or adding masses led to changes of PF according to the alteration in mechanical resonant properties. The results show that PF of physiological postural hand tremor is mainly determined by mechanical factors. There is no evidence for a systematic decrease of PF (Stiles et al. 1976) or for the emergence of a formerly described (Lippold 1981) 4-6 Hz tremor component with prolonged maintenance of posture. In the pathological tremor forms of Parkinson's disease or essential tremor PF also remained unchanged during prolonged maintenance of posture.

Adolescent↗
PubMed1987

Impairment of rapid movement in Huntington's disease.

Patients with Huntington's disease (HD) and relatives at risk were examined with respect to their capacity to produce rapid voluntary motor activity. For this purpose, the fastest possible self-paced single isometric forefinger extensions and the fastest alternating forefinger movements were tested. In addition to these fastest voluntary performances, the time course of spontaneous hyperkinetic finger movements and the peak frequency of finger and hand tremor were analysed as a measure of the temporal characteristics of involuntary movements. Comparison of these parameters in HD patients and individuals at risk with age and sex-matched normal controls revealed a significant slowing of all types of contractions or movements in the majority (up to 95%) of the patients and in up to 40% of the relatives at risk. Reaction times were only slightly prolonged, and the abnormalities of the movement parameters showed no correlation with detailed psychometric data. Hence it is unlikely that the disturbance in the execution of rapid motor acts is due to dementia. Tremor was also slower than normal and the hyperkinesias were still slower than the fastest voluntary contractions. It appears from this study that slowness of motor performance is not only evident in Parkinson's disease but may represent a more general dysfunction in basal ganglia disease.

Adult↗
PubMed1987

Differential effects of changes in mechanical limb properties on physiological and pathological tremor.

The effect of changes in mechanical limb properties on the peak frequency of different tremor forms was analysed. Wrist tremor was recorded by an accelerometer fixed to the dorsum of the hand and demodulated surface EMG was recorded from the wrist extensors, while the extended hand was loaded with successively heavier weights. Physiological tremor was characterised by flat EMG spectra and a gradual decrease in tremor peak frequency with increasing load, as would be expected from the properties of a passive spring-mass-system. Also the peak frequency of activated physiological tremor characterised by increased synchronisation between motor units decreased in frequency with increasing loads. EMG spectra showed clear peaks of activity at the various mechanically determined tremor frequencies. In contrast, in two pathological tremor forms, the postural tremor in Parkinsonian patients and essential tremor, peak frequency tended to remain stable irrespective of changes in load. The method therefore allows a simple distinction between physiological and these two pathological tremors.

Adolescent↗
PubMed1987

Comparative characteristics of predictive eye-hand tracking.

Eye and arm-hand movements were recorded in human subjects under three conditions. In the first a spot of light moved 30 deg back and forth sinusoidally at different frequencies. Limits of ocular pursuit were about 60 deg/sec at a frequency of about 1 Hz. In the second condition the arm and hand pointed a lever at the spot of light and pursued the moving visual target together with the eyes. The maximum velocity and frequency of ocular pursuit increased by about 20-30% with the addition of arm-hand movements. The arm and hand could move the lever faster than the eyes could pursue, but phase relations with regard to position between arm-hand movements and the visual target deteriorated at about 2 Hz when the eyes were unable to pursue the target. In the third condition the arm and hand drove the lever in self-paced movements, and the eyes pursued a target at the end of the lever. Maximum eye velocity increased slightly in two of three subjects in this condition, but no eye movements were made above 2.2 Hz. In contrast, self-paced arm and hand movements were made at frequencies up to 5 Hz and velocities of 400 deg/sec. The data are consistent with previous studies that indicate that the limits of ocular pursuit can be extended when eye movements are coupled to efferent signals and/or proprioceptive input from the skeletal motor system. The data also support previous findings of a dual-mode control system for the skeletal musculature during repetitive movements (Freund 1986).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

The muscle activity spectrum: spectral analysis of muscle force as an estimator of overall motor unit activity.

Starting from the observation that the part above 6 Hz of the power spectrum of force tremor during isometric contractions can be related to the unfused twitches of motor units firing asynchronously, an attempt was made to study the usefulness of force tremor spectral analysis as a global descriptor of motoneurone pool activity. To compensate for the mechanical low-pass filter characteristic of skeletal muscle which leads to increased damping of mechanical ripples at higher frequencies, a numerical compensation rule was derived from data obtained by electrical microstimulation of small ensembles of motor units (MUs). Hidden line plots of consecutive partially overlapping spectra allowed visualization of changes in spectral composition during ongoing muscle activity. The resulting muscle activity spectra (MAS) showed broad peaks according to the range of onset firing rates in normal subjects. These tended to shift to higher frequencies with increasing force. Under conditions with increased synchronization of the MUs these broad peaks were replaced by sharp peaks corresponding to the burst repetition rate. Patients with different motor dysfunctions were selected to illustrate how alterations of MU activity are reflected in the MAS. Decreased or increased firing rates were observed as well as abnormal states of synchronization. It is concluded that the MAS provides useful information about some aspects of the discharge characteristics of ensembles of MUs and therefore represents a method to monitor some qualitative 'image' of the MU activities within a muscle.

Adolescent↗
PubMed1986

[Dependence of the action potential amplitude of motor units on the recruitment threshold: implications for electromyography].

The relationship between the action potential amplitude and the threshold force of recruitment of 275 motor units (MU) recorded from the first dorsal interosseus muscle of 15 healthy subjects was analysed. The number of newly recruited MU decreased exponentially with increasing muscular force. Action potential amplitudes showed a highly significant positive linear correlation with threshold force of recruitment. This relationship is in accordance with the size principle of MU recruitment. Applying the rank correlation method, 88.6 +/- 2.0% (mean +/- standard deviation) of paired comparisons between all MU of one subject followed the normal activation sequence of MU with an increasing action potential amplitude. It is shown that small variations of the distance between the leading-off surface of the electrode and the MU recorded do not affect these findings. These results demonstrate that the force at which a MU is recruited is the most important factor influencing MU action potential amplitude in normal subjects. So far this fact has not been adequately appreciated in clinical electromyography although it is of significance for the assessment of pathological conditions.

Action Potentials↗
PubMed1985

Lesions of premotor cortex in man.

Moderate unilateral weakness of shoulder and hip muscles and limb-kinetic apraxia were observed in 11 patients with frontal lobe lesions on the side opposite to the neurological deficits. On the CT scans, the posterior border of the lesions lay anterior to the precentral gyrus, thus involving the premotor cortex but not the primary motor cortex. In 9 cases, the lesions were caused by a brain infarct, in 2 cases by a tumour. In 1 patient the lesion was purely subcortical. Whereas the paresis affected all hip muscles, in the shoulder mainly those movements associated with abduction and elevation of the arm were disturbed. The EMG showed considerable delays for the preactivation of proximal arm muscles during rapid arm movements, thus interfering with the normal proximal-distal sequencing of muscle action. Limb-kinetic apraxia only became apparent during tasks requiring certain coordinations between both arms or legs. Bimanual interaction was normal. Two patients with proximal hemiparesis and small lesions in the precentral gyrus which have been examined for comparison showed no limb-kinetic apraxia and different distributions of the paretic shoulder girdle muscles. In view of the long-standing controversies as to the functional role of the premotor cortex and the question of specific deficits after lesions of this area, the relevant literature is reviewed.

Adult↗
PubMed1983

Ultrasonic compound scans from brain specimens.

This paper demonstrates the high quality of ultrasonograms obtained from brain specimens by compound scanning when the angular range of insonation is extended to 360 degrees. The technique employs linear photographic superposition and a commercial real time scanner as basic instrument. Comparative anatomical cross-sections showed that the major normal structures and pathological processes like hemorrhage, tumors, infarctions and edema are displayed. The image quality indicates the potential of this approach when applied to organs accessible to this type of scanning procedure.

Brain↗
PubMed1980

Cerebellar dyssynergia in humans--a quantitative analysis.

Patients with cerebellar lesions and limb ataxia performed two types of continuous tracking tasks involving flexion and extension of the index finger. In both tasks, patients were provided cutaneous and proprioceptive cues, but visual feedback was given in the first task (visual tracking) and not in the second (arbitrarily termed proprioceptive tracking). Raw records and Fourier-analyzed power spectra were compared with results in normal controls. Harmonic distortion was determined for each task. In all patients, as well as normal subjects, tracking performance was markedly improved and harmonic distortion substantially reduced during proprioceptive tracking. This surprising finding may result from a much shorter feedback loop for proprioceptive stimuli compared to visual stimuli. The tracking records, power spectra analysis, and determination of harmonic distortion provide both qualitative and quantitative data in patients with dyssynergia.

Cerebellar Ataxia↗
PubMed1978

The relationship between speed and amplitude of the fastest voluntary contractions of human arm muscles.

The relationship between the speed of the fastest possible voluntary contractions and their amplitude was examined for several hand- and forearm muscles under isometric and isotonic conditions. The consistent finding was the amplitude dependence of the speed of the fastest voluntary efforts: the larger the amplitude, the faster the contraction. The increase of the rate of rise of isometric tension or of the velocity of isotonic movements with rising amplitude was linear. The slope of this relationship was the same for three different hand- and forearm muscles examined. The duration of the contractions measured from onset to peak was approximately constant for all amplitudes. The duration of the EMG-burst recorded from the contracting muscle was similar as the time from onset to peak of the contraction. These results show that the skeleto-motor speed control system operates by adjusting the velocity of a contraction to its amplitude in such a way that the contraction time remains approximately constant. It is suggested that this type of speed control is a necessary requirement for the synchrony of synergistic muscle contractions.

Adult↗
PubMed1978

Neuronal mechanisms underlying physiological tremor.

1. Tremor force was recorded during stationary isometric contractions of intrinsic hand muscles of normal subjects. Subjects maintained a steady force level between their thumb and forefinger for 30 s. The force level varied from weak (0.2 kg) to strong contractions (7 kg). These experimental conditions were the same as those in two preceding studies, where single motor-unit activity (14) and the correlation between the discharges of two simultaneously recorded motor units and physiological tremor (11) have been investigated. 2. Two alterations of the power spectra were observed at successively stronger contractions: increase of tremor amplitude and changes in the shape of the power spectrum. At all force levels, the power spectra of tremor force show the well-known decay of tremor amplitude from the lower to the higher frequencies with a local peak at 6--10 Hz. This peak does not show a significant change with respect to frequency when the force level is varied. It is shifted toward lower frequencies in a pathological condition (Parkinsonism) where the recruitment firing rates of the motor units are significantly lower than in the normal. 3. Higher frequencies (greater than 20 Hz) are barely present in the power spectrum during the very weak contractions. They become significant as the contractions become stronger. 4. The steep decay of the power spectrum toward higher frequencies has a similar slope (--43 dB/decade) as the reduction in amplitude of the unfused part of the muscle contractions with increasing stimulus rates (--38 dB/decade). The cutoff of the power spectrum above 25 Hz parallels the achievement of total fusion of muscle twitches above this rate. 5. The results are consistent with the hypothesis that the power spectrum over the range of 6--25 Hz is mainly caused by the unfused parts of the twitch contractions of motor units firing between recruitment (6--8/s) and total fusion of the twitches (25--30/s). The decline of the power spectrum toward higher frequencies can be explained by mechanical damping, which results from increasing fusion of the twitch contractions. The low-frequency part of the power spectrum is assumed to be the result of the slow force deviations produced by changes in the net output of the motoneuron pool. 6. These assumptions were supported by additional animal experiments where the number and rate of force-producing elements could be controlled. Bundles of ventral root filaments innervating cat soleus and gastrocnemius muscles were stimulated synchronously and asynchronously at a number of different rates. The force output of the strain gauge was recorded, filtered, and analyzed in the same way as the human force records. 7. Stimualtion of one nerve bundle at one fixed frequency led to a sharp peak in the power spectrum at that frequency plus peaks of decreasing height representing the harmonics of the stimulation frequency. The height of the peaks decreased at --37 dB/decade. 8...

Animals↗