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Biomedical subjects

W Freedman

Publications and source records attributed to W Freedman.

At least 19 recordsLinked to original sources
PubMed1991

Progression of exencephaly to anencephaly in the human fetus--an ultrasound perspective.

Exencephaly as a precursor of anencephaly is well delineated in animal studies. In humans, a similar though unproven embryologic sequence is postulated. In the case reported, serial ultrasound studies allowed us to identify a 16-week human exencephalic fetus and observe the cephalic changes during its progression to a classic anencephalic appearance.

Adult↗
PubMed1990

Cross-modal functions in alcoholism and aging.

Two experiments were performed to measure separate aspects of cross-modal functions in normal and alcoholic research participants: matching, and utilization of concepts. In Experiment 1, cross-modal equivalence-matching was measured, i.e. the ability to select in a second modality (e.g. vision), the same stimulus that was first presented in a different modality (e.g. touch). Experiment 2 measured cross-modal transfer of information about stimulus dimensions, i.e. the ability to recognize and use the concepts of texture and form, based upon prior experience solving tactual problems, to solve visual problems. Fifty-five normal and alcoholic research participants comprised the following five groups: 13 young normals (YN) and 10 young alcoholics (YA), 28-48 years of age; 13 older normals (ON) and 14 older alcoholics (OA), 50-71 years of age; and 5 alcoholic Korsakoff patients (K), 55-68 years of age. Separate subgroups of 9 age-matched ONs and 9 OAs were devised for purposes of statistical analyses of data involving the 5 Ks. Results of the experiments indicated that aging is associated with decline in tactual discrimination ability. Further, cross-modal functions appear to be compromised by alcoholic Korsakoff's disease, and--to a lesser extent--by the combined effects of alcoholism and normal chronological aging. Brain mechanisms important for normal cross-modal functions are discussed.

Adult↗
PubMed1990

Comparison of vestibulo-ocular reflex (VOR) modification methods in cats.

The vestibulo-ocular reflex (VOR) has been measured and optically modified in several animal species. The VOR gain can be increased optokinetically by rotating the animal's visual surround opposite to the animal's direction of rotation or a VOR increase can result from the use of magnifying lenses. We describe here a comparison of three methods for producing VOR increases in cats: (i) optokinetic drum; (ii) a pair of 2.2 x telescopic lenses; (iii) Fresnel lens goggles. The animals were put through several preliminary calibrations followed by a sequence of VOR modification periods alternating with 10 testing periods. The results of the comparison in 4 cats show that the Fresnel lens system produces a greater and more stable VOR gain increase than the other two methods.

Animals↗
PubMed1988

Vestibulo-ocular reflex adaptation in cats before and after depletion of norepinephrine.

The vestibulo-ocular reflex (VOR) operates to stabilize the eyes in space during movements of the head. The system has been described as having a gain of approximately -1 since stimulation of the semi-circular canals brought about by head movements will have the effect of causing the eyes to rotate an equal amount in the opposite direction. Change in the gain of the VOR has been put forth as a model to study plasticity in the central nervous system. Since numerous studies have implicated norepinephrine (NE) in neuroplasticity and modifiability of neural circuits, we attempted to determine the effect of NE depletion (via 6-hydroxydopamine (6-OHDA) intra-cisternal injection) on the modifiability of the VOR. We have found that cats increase the gain of their VOR over a four hour period when rotated in the horizontal plane in a manner equal but opposite to the rotation of a surrounding opto-kinetic drum. The entire group of animals manifests a statistically significant decrement in their ability to increase VOR gain when central stores of norepinephrine are depleted via intra-cisternal injection of 6-OHDA. Individual animals manifest a wide variety of gain changes (0.98 to 1.62). We have found that there were two groups of cats--high and low gain modifiers. The greatest reduction in VOR gain increase after NE depletion was observed in the high gain modifiers. No difference was observed in the low gain modifiers. These same animals tested for VOR modification after amphetamine injection, produced similar results. Alertness during the VOR modification task, as estimated by saccadic eye movement counts, was unchanged after NE depletion NE levels, measured by HPLC-EC, after depletion were reduced to the greatest extent in the cerebellum. There was also a substantial reduction of NE in the visual cortex with less of a reduction in the brain stem.

Adaptation, Physiological↗
PubMed1987

Selection of movement patterns during functional tasks in humans.

These experiments examine the role of vision and step height in the selection of a simple binary choice of movement pattern by human subjects. The subjects selected a heel strike movement pattern (HS) (as used during level surface locomotion) or a toe strike movement pattern (TS) (as used during stair descent). The functional task involved descending a step of adjustable height followed by level surface walking under vision and nonvision conditions. Triceps surae and tibialis anterior electromyographic (EMG) activity, ankle angle position, and vertical force were examined. As step height was increased, there was an indistinct threshold at which subjects switched from landing with a HS movement pattern to a TS movement pattern. The tibialis anterior and triceps surae precontact EMG burst and subsequent ankle movement for HS and TS trials appear to be part of preprogrammed movement patterns, which are presumably of central origin. The particular mixture of voluntary, stereotypic, and reflex actions for any specified movement is based on the intent or functional outcome desired. The switching to the TS movement pattern as step height increased presumably results in the most efficient and stable movement.

Journal Article↗
PubMed1985

Effect of myoelectric signal processing on the relationship between muscle force and processed EMG.

The relationship between the force generated by an isometrically contracting muscle and the associated myoelectric signal has been the subject of extensive investigation in the past and conflicting results were reported regarding this relationship. The objective of the present study was to investigate some of the sources that may lead to such conflicting results. Two possible sources were examined. The first was the variability in the force-EMG relationship resulting from processing the EMG signal with different EMG signal processing techniques and the second was the variability in the force-EMG relation obtained from repeated muscle contractions. The results of the study indicate that slight variations in the force-EMG relationships can be attributed to the selection of different processing techniques. However, the variability in the force-EMG relation, obtained by using different EMG signal processors, was found to be significantly smaller than the variability in this relationship obtained from repeated muscle contractions.

Adult↗
PubMed1984

Passive and active components of the internal moment developed about the ankle joint during human ambulation.

The internal moment developed about a joint during a functional activity is the result of contraction of muscles and the visco-elastic properties of the joint and its surrounding soft tissues. In this study, the contribution of each one of these mechanisms to the total internal moment developed about the ankle joint during human level walking was assessed. The results indicate that during normal level walking the internal moment about the ankle is mainly due to contraction of muscles surrounding the joint. The contribution of the passive component was found to be negligible. These results, however, were found to be different for the pathological case tested. The results indicated that in a subject with a mild equinus ankle deformity, a substantial portion (21%) of the total internal moment was contributed by the passive resistance of the joint and its surrounding structures.

Adult↗
PubMed1982

The role of sensory conflict on stair descent performance in humans.

Electromyographic (EMG) activity produced in the triceps surae (TS) and subsequent landing were examined under various visual conditions during stair descent with the following results: The amount of precontact TS EMG was reduced during each visual perturbation. Perturbations corresponded to no knowledge or visualization of stairs (B), no stair visualization during descent (A) and vertical movement of the surround during descent (M). Erroneous visual information was primarily responsible for altered EMG activity. The only known difference between the M data sets was that the surround moved up (U) or down (D) as the subject descended. However, TS EMG characteristics were different under these two conditions. Specific visual information appeared necessary for vision to override the other sensory systems. There was no difference in EMG when the room moved up (U) compared to the room not moving (NM). However, EMG activity was significantly different when the room moved down (D) compared to the room not moving (NM). The relationship between TS EMG activity and subsequent landing appeared related to landing strategy. Although the EMG was reduced during both the B and M test conditions compared to the control, the landing was "softer" for B and harder for M. The pre-contact EMG is apparently part of a preprogrammed movement pattern which can be modified by sensory information during task execution. Future studies should examine the neuronal mechanisms which provide the visual system access to the center controlling lower limb muscle activity during dynamic movement.

Adolescent↗
PubMed1976

EMG patterns and forces developed during step-down.

These experiments describe electromyographic activity and forces developed during step-down from several heights. The external environment of the experimental subjects was varied by blindfold or Achilles' tendon vibration during descent. EMG activity of the step-down limb, vertical force of impact and knee angle were measured. The results show that the triceps surae muscle contracts prior to the time of impact of the foot with the substrate if information about the step height is supplied to the subject and if the sensory system is not disturbed by vibration. In the presence of vibration or if the step height is unknown, the triceps surae does not contract prior to foot contact. This produces a large force transient which must be absorbed by the skeletal structure, rather than being damped by a lengthening contraction of the triceps surae. The data suggest that the forces developed during ordinary step-down may be the cause of bone and injury in people with impaired vision or in patients with damaged nervous systems who exhibit large responses to vibration.

Biomechanical Phenomena↗
PubMed1975

Inhibition of electromyographic activity in human triceps surae muscles during sinusoidal rotation of the foot.

Torque and electromyographic (EMG) responses to sinusoidal rotations of the foot were measured. The frequency range of the movements was 0.5 Hz to 15 Hz at amplitudes ranging between 1 and 10 degrees. At frequencies above 7 Hz, the EMG activity did not follow individual foot rotation cycles. The EMG activity was inhibited whenever the peak torque was large with respect to the first cycle peak torque. Dantrolene sodium reduced the torque developed in triceps surae, allowing the EMG activity to follow individual stretch cycles. As the drug was metabolized, the EMG activity returned to the character seen in the pre-drug control--that is, inhibition on alternate stretch cycles. It is concluded that the EMG inhibition phenomenon can be attributed in part to force receptors in muscle but that these receptors are not the sole contributors to the inhibition.

Adult↗
PubMedDate not supplied

Nonstationary properties of postural sway.

Postural sway during quite stance is usually assumed to be a stationary stochastic process. We tested this assumption by investigating the time invariance of the average value and variance of the postural sway of three subjects. The sway was measured with a force plate under three conditions: subject standing on two feet with eyes open; subject standing on two feet with eyes closed; and subject standing on one foot with eyes open. Data were collected in 1 min runs. More than 50 min of data were collected for each subject under each test condition. The data were averaged across all runs for each subject and condition. Trends were found to be present in the data. In addition, there were initial transient increases in the second-order moments about the trends. The transient changes in first- and second-order moments usually disappeared during the first 20 s. In light of these findings, we can reject the hypothesis that postural sway is a stationary process. The results imply that the usual methods to parameterize postural sway have to be either changed or reinterpreted.

Adult↗