Gerald Leisman

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.

A force/displacement analysis of muscle testing.

Manual muscle testing procedures are the subject of a force and displacement analysis. Equipment was fabricated, tested, and employed to gather force, displacement, and time data for the purpose of examining muscle-test parameters as used by clinicians in applied kinesiology. Simple mathematical procedures are used to process the data to find potential patterns of force and displacement which would correspond to the testing of strong and weak muscles of healthy subjects. Particular attention is paid to the leading edge of the force pulses, as most clinicians report they derive most of their assessment from the initial thrust imparted on the patients limb. An analysis of the simple linear regression of the slope (distance vs force) of the leading edge of a force pulse indicates that a significantly large slope is indicative of weak muscles (as perceived by the clinician), and a small slope is indicative of strong muscles. Threshold criteria for slopes are specified to create a model that may discriminate between strong and weak muscles. The model is accurate 98% of the time compared to judgments of clinicians with more than 5 years of experience but is considerably lower for clinicians with less than five years of experience (64%). this accuracy rate indicates that the model is reliable in predicting the clinicians perception of muscle strength and it also indicates that the testing procedure for muscle strength used by experienced clinicians in applied kinesiology are reliable. The experiment lays the groundwork for studies of the objectivity of muscle-strength assessment in applied kinesiology.

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.

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.

A continuum model of activity waves in layered neuronal networks: a neuropsychology of brainstem seizures.

We model and brainstem as two layers of respectively purely excitatory and purely inhibitory cells, with instantaneous synaptic interactions within a layer, but with a variable time delay between the layers. For appropriate values of the connection parameters, this configuration provides an attentional mechanism. As the inhibitory delay increases, input signals are, at first, increasingly amplified and confined spatially. At larger delays, the amplified activity propagates into other regions allowing for spatial summation. The temporal frequency of the amplified activity decreases with increasing delay, but its spatial frequency remains relatively constant. As the delay increases through a critical region, a new regime is reached in which highly amplified activity occurs simultaneously over large areas. This regime exhibits many properties of seizure activity.

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 ocular-motor differences between subjects, which is consistent with the previous study in which no differences in saccadic control are demonstrated between groups of subjects.

Conditioning variables in attentional handicaps

Abstract The relationship between attention and the process of conditioning was investigated in spastic-hemiplegic subjects suffering from attentional handicaps. Observations were made on the effects of retinally stabilized images on the course of alpha blocking responses to tone before, during and after the pairing with light stimulation. Changes in the subjective attention state over time were rated by the use of a self-assessment checklist on both control (indirectly photically stimulated) and directly photically stimulated groups. Stabilized retinal image procedures appeared to have a significant effect when the tone was paired with a light stimulus during conditioning and to a lesser extent during extinction. A significant increase was noted in the duration of the alpha blocking response during conditioning amongst the directly photically stimulated hemiplegic subjects. The stabilized retinal image techniques seem to have aided the hemiplegic subjects in acting selectively to augment the components of the conditioned response which develops after repeated pairings.

A continuum model of activity waves in layered neuronal networks: computer models of brain-stem seizures

A model of dysfunctional brain-stem activity as nonlinear homogeneous disturbances in a structure consisting of excitatory and inhibitory layers is presented. Cortical EEG traces are identified with the time derivative of the active fraction of excitatory cells. Increase in the time delay between the layers causes the onset of periodic nonlinear oscillations. Change in the biochemical state can cause rapid oscillations similar to seizures.<<ETX>>

Assessment of visual field impairment by objective technique.

An objective psychophysical technique for investigating visual fields by averaged scalp potentials evoked by pattern gratings of alternating contrast and by sinusoidally modulated flickering light is applied to a child with a right homonomous hemianopsia. This technique illustrates a value in obtaining clinical data on visual fields in situations where subjective perimetry is difficult to administer or where conservative diagnostic methods do not yield evidence of pathology.

Neuropsychological Systems Deficits and the Isomorphism of Control

The papers that follow are based on a symposium presented at the Twelfth European Conference of the International Neuropsychological Society held in Antwerp, Belgium between 5-8th July 1989. The symposium, using closed head injury as a vehicle, attempted to overview approaches to the study of systems function and dysfunction. Rather than concentrate on skill and subtest deficit, the papers addressed diffuse, systemic, subcortical effects and disruption of lower integration centers. They addressed the utility of neural network models to develop theory to explain deficits in behavioral integrating systems; the role of systems approaches in better understanding the overlapping clinical subsets of migraine and seizure disorders; the provision of visual examples of lateralized systemic changes associated with closed head injury through infrared thermology and the presentation of an application of biomathematical systems modeling with potent applications for diagnosis and rehabilitation. Finally the papers were discussed in terms of the clinical and philosophical issues.