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Biomedical subjects

G Leisman

Publications and source records attributed to G Leisman.

At least 37 records · Page 2Linked to original sources
PubMed1990

Biomechanics of head injury.

The enormous incidence of closed head injury has resulted in employing the field of biomechanics as a means of predicting the site of a lesion, discovering, and understanding the forces acting during cranial impact. This paper indicates that the possibilities associated with trauma-induced lesions include: the establishment of large pressure gradients associated with damage resulting from absolute motion of the brain and its displacement relative to the skull; flexion-extension of the upper cervical cord; skull deformation and/or rotational acceleration. Analytical representations, inanimate and cadaver models and, experimental paradigms are presented and their behavioral implications discussed.

Animals↗
PubMed1990

Limb segment information transmission capacity infers integrity of spinal transmission tracts and cortical visual-motor control.

Limb segment movement times have been investigated previously in relation to Fitts' Index of Difficulty (ID = log22A/W) over various movement distances (Leisman, 1987; 1989a). Results supported Fitts' theory that different limb segments show different maximum information processing rates. The results indicated that visually-mediated discrete correction control processes are used. In the presently reported experiments, normal human subjects performed movements with left or right arms. Visual-motor control was inter- or intrahemispheric. Direction of movement was adductive or abductive. It was hypothesized that abductive movements are controlled by the contralateral hemisphere while adductive movements are controlled by either hemisphere. It was also hypothesized that abductive movements are related to the lateral system which projects to the contralateral side of the spinal cord. The control of adductive movements is related to the medial system which projects bilaterally to the spinal cord.

Arm↗
PubMed1989

Somatosensory evoked potential changes during muscle testing.

Fifteen naive subjects with no known neurological problems were tested by means of manual muscle testing to determine two "strong" and one "weak" muscle on a limb contralateral to the stimulated side. Somatosensory evoked potentials (SEP) were then recorded from contralateral median nerve stimulation while a naive tester tested the three previously identified muscles. In all subjects the baseline (no muscle test) and control "strong" muscle test recordings were comparable while the recording from the "weak" muscle test showed increased amplitudes in contralateral layer components. These findings suggest a neurologic basis for manual muscle testing.

Adult↗
PubMed1989

Cybernetic model of psychophysiological pathways: I. Control functions.

Electrophysiological events carry information, but the signals are not specific for a given bit of information. Therefore, the nervous system is required to extract the information from a multitude of signals. The process of information recognition is achieved by a superization process, i.e., by means of transition from many lower-order signals to a superior-order signal. In this way, a gradual recognition of the respective signal's emitting sources is realized. The recognition is performed with the aid of certain logical circuits representing models of different sources written in the structure of the neuronal network. In this manner, the nervous system passes step by step from control by means of signals to control by means of information. The superior structures can thereby exert much more subtle control and supervise the inferior structures that work by signals. However, because this control cannot refine all the general information of the inferior structures, psychophysiological dysfunction may occur. The nature of the superization process from signals to information is examined in this paper.

Cybernetics↗
PubMed1989

Cybernetic model of psychophysiologic pathways: II. Consciousness of tension and kinesthesia.

This paper describes a series of experiments directed toward the following questions: a) do signals from musculotendinous receptors reach consciousness?, and b) does feed-forward information of muscular force and expected extent of voluntary movement exist? To answer these questions, data from voluntary compression of springs and strain-gauge have been analyzed in healthy young subjects. By successive elimination of information from other sources, it was possible to verify that receptors in muscles and tendons do signal movement magnitude and muscular tension to the cerebral cortex, and that this information does reach consciousness. There also exists a feed-forward mechanism signalling parameters of voluntary contraction. However, it is unclear whether peripheral, subcortical or intracortical loops are directly involved.

Biofeedback, Psychology↗
PubMed1989

Cybernetic model of psychophysiologic pathways: III. Clinical impairment of tension and kinesthesia.

It is unclear whether peripheral, subcortical or intracortical loops are directly involved between receptors in muscles and tendons and the cerebral cortex in signaling movement magnitude and muscular tension information. Previous experiments have indicated that this information does reach consciousness. Data from voluntary compression of springs and strain-gauge were analyzed in patients with unilateral focal lesions of the cerebral hemispheres. It was found that the perception of signals of muscular tension is abolished by lesions of the contralateral cortex near the central sulcus. It was concluded that the possibility exists of separate cortical projection areas for kinesthetic signals from muscles and from joints.

Brain Diseases↗
PubMed1989

Limb segment information transmission capacity.

Movement time for finger, wrist, and whole arm motions were investigated in relation to Fitts' Index of Difficulty (ID = log2 2A/W) over movement distances of 0.25 to 30.5 cm. Results supported Fitts' original theory that various limb segments may show different maximum information processing rates. Short-distance finger and wrist motions showed much higher rates than longer distance arm motions. Examination of motion trajectories qualitatively supported a descriptive model whereby a visually mediated discrete correction control process is used. However, evidence of severe nonlinearities in the measured humam movement responses did not support the use of linear control models in explaining the empirical validity of Fitts' law in predicting human motor performance.

Adult↗
PubMed1981

Co-evolution of luminous bacteria and their eukaryotic hosts.

Several species of three genera of luminous bacteria from marine and soil environments are known to form specific symbioses with fish, squid, urochordates, and nematodes. These bacteria contain a unique and easily detectable enzyme, bacterial luciferase, which allows the detection of the bacteria even when they cannot be cultured from animal tissue. The bacteria-animal associations vary; they range from transient, nonspecific gut symbionts in many fishes to highly specific, nonculturable, intracellular symbionts in pyrosomes. The study of these microbe-animal symbioses may allow understanding of the alterations that occur in the partners during the establishment of intracellular organelles. These studies are incomplete, in particular the level of partner integration, the nature of the metabolic exchange, the mechanism of transmission of symbionts to offspring, and the identification of the cellular inclusions as modified bacteria are not always known. However, the outline of what is likely to be a continuous evolutionary sequence of luminous bacterial symbionts with their various animal hosts is becoming clear. As more of these symbioses are studied, we anticipate that new systems will be found that represent states between those described here, and that the luminous bacteria will provide a living model for the gradual evolution from free-living microbes in intracellular organelles.

Bacteria↗
PubMed1981

Computerized localization of sources of evoked potentials in the assessment of visual field impairment.

Objective computer-based techniques are described along with their underlying theoretical rationale for investigating visual field disorders. The paper concerns methods for the collection and analysis of evoked potentials and provides a description of methods for obtaining information about the conduction pathways of the visual system for clinical, neurological and neuropsychological applications.

Brain Diseases↗
PubMed1980

Aetiological factors in dyslexia: IV. Cerebral hemispheres are functionally equivalent.

Left parieto-occipital EEG leads record a frequency spectrum in dyslexics which is consistently different from normals, indicating differences in the functional organization of these areas. EEG coherence values indicate normals to have greater sharing between hemispheres at symmetrical locations. Dyslexics demonstrate greater sharing within hemisphere. A parallel study indicated that CT scans of dyslexics parieto-occipital regions demonstrates reversal or lack of cerebral asymmetry.

Brain↗
PubMed1978

Aetiological factors in dyslexia: I saccadic eye movement control.

A study was performed to examine the character of saccadic eye movement in dyslexic and normal children and normal adults. No significant differences were noted between 20 normal and 20 dyslexic children, but significant differences were noted between both groups of children and the adult population. Results were explained as reflecting no measured difference in duration/amplitude and velocity/amplitude functions in dyslexic and normal children, thereby indicating no differences in their saccadic eye-movement control functions. Observed differences between normal adult and child populations are explained.

Adolescent↗
PubMed1978

Aetiological factors in dyslexia: II. ocular-motor programming.

A study is presented in which the preprogramming of saccadic eye movements is examined in normal (16 boys, 4 girls) and dyslexic subjects (19 boys, 1 girl), as well as the patterning of occular-motor differences between subjects, which is consistent with the previous study in which no differences in saccadic control are demonstrated between groups of subjects.

Child↗
PubMed1977

Return sweep latency in reading with a paralyzed eye.

The study concerned the distribution of directional control of eye movement in reading. With the paralysis of the right eye, progressive movements of the left eye were possible, but regressive movements were cancelled, being observed as drift. Base-out prism placed over the non-paralyzed eye allowed for the re-establishment of regressive movements. The results for this subject were explained on the basis of a large retinal error marker having been established. With the paralysis of one eye, base-out prisms reduce that error.

Eye Movements↗
PubMed1977

Ocular-motor effects on the human electroencephalogram.

In response to the findings that gross vertical and horizontal eye deviation can be associated with facilitation of the human EEG alpha rhythm, an hypothesis is suggested that the deviation of gaze which exceeds a critical angle and results in a loss of subjective ocular stability is related to the occurrence of the paradoxical alpha effect.

Adult↗
PubMed1977

Ocular-motor function and information processing: implications for the reading process.

This paper discusses the dichotomy between continually moving eyes and the lack of blurred visual experience. A discontinuous model of visual perception is proposed, with the discontinuities being phase and temporally related to saccadic eye movements. It is further proposed that deviant duration and angular velocity characteristics of saccades in patients with hypertonic motor impairment relate to information processing defects. Stabilized retinal image procedures, which control for the effects of eye movements, significantly increase the ability of these patients actively to recall information presented for periods of less than three sec. A model of the reading process is presented based on these findings that addresses itself to the specific components of an interactions between eye movement, information transmission and information processing.

Alpha Rhythm↗