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Biomedical subjects

P Bach-y-Rita

Publications and source records attributed to P Bach-y-Rita.

At least 19 recordsLinked to original sources
PubMed1999

Theoretical aspects of sensory substitution and of neurotransmission-related reorganization in spinal cord injury.

Spinal cord rehabilitation has progressed enormously since World War II, and persons with spinal cord injuries now have long life expectancies. Research has recently concentrated on improvement of the quality of life, and on neural mechanisms of recovery. This article will explore some aspects of both of these areas. In the first section, the potential applications of sensory substitution systems for such functions as sex sensation and sensation from feet and from robotic hands will be examined. In the second section, the potential role of nonsynaptic diffusion neurotransmission (NDN) in neural reorganization after spinal cord injury will be considered. This article includes portions of previous publications and reports.

Animals↗
PubMed1998

Form perception with a 49-point electrotactile stimulus array on the tongue: a technical note.

Form perception with the tongue was studied with a 49-point electrotactile array. Five sighted adult human subjects (3M/2F) each received 4 blocks of 12 tactile patterns, approximations of circles, squares, and vertex-up equilateral triangles, sized to 4x4, 5x5, 6x6, and 7x7 electrode arrays. Perception with electrical stimulation of the tongue is better than with fingertip electrotactile stimulation, and the tongue requires 3% (5-15 V) of the voltage. The mean current for tongue subjects was 1.612 mA. Tongue shape recognition performance across all sizes was 79.8%. The approximate dimensions of the electrotactile array and the dimensions of compartments built into dental retainers have been determined. The goal is to develop a practical, cosmetically acceptable, wireless system for blind persons, with a miniature TV camera, microelectronics, and FM transmitter built into a pair of glasses, and the electrotactile array in a dental orthodontic retainer.

Adult↗
PubMed1997

Brain cell microenvironment effects on neuron excitability and basal metabolism.

In a model of neurons in a brain cell assembly, changes in volume of the extracellular space affect neuronal excitability and basal metabolism. A widely applicable coefficient of excitability with respect to a variation of the volume fraction has been determined. Calculations suggest that chloride increases membrane stability by indirectly promoting an acceleration of the metabolic pumping rate as a response to a diminished extracellular volume fraction. Volume fraction changes induced by cell swelling in a compact and highly tortuous microenvironment may play a role in epilepsy and, following brain damage, in cell death and recovery.

Basal Metabolism↗
PubMed1996

Nerve length and volume in synaptic vs diffusion neurotransmission: a model.

Non-synaptic diffusion neurotransmission (NDN) may be an important factor in brain space and energy conservation, especially within cell assemblies and for mass sustained functions. We have illustrated the extreme cases of total synaptic and total ND neurotransmission for the purpose of noting the differences between the two. For these modeling studies, in which we assume assemblies of 1000 to 100 000 cells supplied by at least one fiber and a single synapse from each of the other cells, each cell assembly would have approximately 200 m to 8000 km of nerve fibers more than when innervated by diffusion. For coeruleo-cortical synaptic innervation, linking each to a common origin (the locus coeruelus), the fiber lengths are 38 cm (1000 cells) to 170 m (100,000 cells). It is likely , however, that neuronal arrays include both 'wireless' (NDN) as well as synaptic intercellular communication systems.

Brain↗
PubMed1994

The brain beyond the synapse: a review.

Several topics in contemporary neuroscience are treated in historical perspective. These include the localizationist-connectionist model of brain function and its influence on experimental neuroscience and clinical management of brain damaged persons; brain plasticity; the accumulating evidence for non-synaptic diffusion neurotransmission (NDN) as a major mechanism of information transmission in the brain; and the co-existence of plasticity and localization as well as of synaptic and non-synaptic mechanisms. The status of theory in the neurosciences is examined.

Animals↗
PubMed1993

Nonsynaptic diffusion neurotransmission (NDN) in the brain.

The synapse has dominated the conceptual model of neurotransmission; other mechanisms, such as neuromodulation, have been considered to support and complement synaptic transmission. In this commentary, the conceptual framework considers synaptic transmission as one of several mechanisms of neurotransmission. One of these is nonsynaptic diffusion neurotransmission (NDN), which includes both the diffusion of neurotransmitters and other neuroactive substances through the extracellular fluid to reach extrasynaptic receptors, and the diffusion of substances such as nitric oxide through both the extracellular fluid and cellular membranes to act within the cell. The possible roles of NDN in mass, sustained functions such as mood, sleep and brain "tone", as well as in various other functions, such as in long term potentiation, at the retinal, lateral geniculate nucleus and visual cortex levels of the visual system, in recovery from brain damage and in neuropharmacology, are explored.

Animals↗
PubMed1993

Spinal shock: possible role of receptor plasticity and non synaptic transmission.

Spinal shock remains an enigma. To date there has been no convincing explanation of the recovery of reflexes following their complete abolition. Volume transmission includes both the activation of extrasynaptic receptors, and activity induced by substances diffusing into synaptic clefts via the extracellular fluid. A brief review of non synaptic transmission is given, and a review of spinal shock. We suggest that the recovery of reflexes in spinal shock may be related to the up regulation of receptors, resulting in increased sensitivity to neurotransmitters and other neuroactive substances released at the surviving synapses, or elsewhere, and transported in the extracellular fluid. Further understanding of spinal shock would give both practical help for the patient and have academic implications for the scientific basis of neurological rehabilitation.

Animals↗
PubMed1993

Neurotransmission in the brain by diffusion through the extracellular fluid: a review.

Synaptic or 'hard wired' neurotransmission in the brain, subject to modulation by a class of substances called modulators, has been the dominant model of brain function. However, increasing evidence for alternate non-synaptic neurotransmission mechanisms is forcing consideration of a more inclusive model. Evidence is presented for such neurotransmitter systems that require diffusion through the extracellular fluid. Old and new findings have been interpreted within a conceptual framework that is not centered on the synaptic model, but instead considers a continuum of neurotransmitter actions.

Animals↗
PubMed1993

Stroke rehabilitation in Stockholm. Basis for late intervention in patients living at home.

In order to identify the basis of late-therapy intervention in patients with stroke, we studied a population-based sample of 20 patients. The requests were that they should be living at home 1-3 years after being hospitalized, and that they had declared themselves in need of rehabilitation services. The assessment of abilities and activities of the patients was related to the model of human occupation developed by Kielhofner and co-workers. Most individuals reported a change in activity and interest patterns after stroke, and high motivation in current activities. The cognitive functions were within normal limits for all tested patients. However, the motor abilities and verbal performances were frequently affected and varied considerably. About 3/4 of the patients were not motivated to change their level of dependence in personal and instrumental ADL. Social and leisure activities outside the home were identified as the most promising goals for community-based rehabilitation programmes. Focusing on such activities, potential improvement in quality of life for this population could be achieved by individually-planned rehabilitation programmes using non-professional collaborators and patient organizations.

Activities of Daily Living↗
PubMed1993

Stroke rehabilitation: identification of target groups and planning data.

In order to ascertain the need for late stroke rehabilitation in South-West Stockholm (SWS) and explore the conditions for experimental stroke outcome research, we followed a population-based, systematic sample of incident stroke patients, hospitalized during the period 1987-1988, using computer files and a telephone interview. The annual incidence of first-ever or recurrent transitory ischaemic attack (TIA) or acute stroke during the period was 2.83 per 1000. In December 1989, approximately 3% of these incident patients declared subjective residual dysfunction, were living at home and were considered potential candidates for rehabilitation. The estimated prevalence of home-bound individuals with residual dysfunction due to stroke was 0.74 per 1000 (95% CI 0.51-1.04). The average duration of hospitalization for these patients was 95.2 days. Approximately 3/4 of them were interested in further conventional rehabilitation. The group not interested in this therapy were mainly females and were older. They scored lower in personal ADL and mental activity, but similarly in motor function. We concluded that the prevalence need for rehabilitation after stroke in the SWS community amounted to at least 1/1000. Early rehabilitation in the community, linked to post-acute stroke care with reduction of hospital stay would be functionally and socially advantageous and cost-effective for more than 25% of the incident stroke cases. Stroke rehabilitation and clinical follow-up are closely related processes that should be evaluated simultaneously.

Activities of Daily Living↗
PubMed1993

Comparative efficiency of volume and synaptic transmission in the coerulean system: relevance to neurologic rehabilitation.

Over the past few years evidence has accumulated which confirms earlier beliefs that punctate synaptic transmission (wiring transmission) is not the only means by which "informational substances" affect cerebral neurons. This paper considers the relative efficiency of "volume" and "wiring" transmission in controlling large populations of neurons taking as a specific example the mammalian coerulean system. Making reasonable quantitative assumptions it is shown that volume transmission is a more efficient means of controlling "mass" functions than a wiring mode. Implications for the reorganisation of function following brain damage are noted.

Animals↗
PubMed1992

Evaluation of stroke rehabilitation by randomized controlled studies: a review.

In all, 22 reports of 20 randomized, controlled rehabilitation studies were evaluated. In 18 of these, the design of the trial was parallel, with a cross-over format being employed in the remaining 2 instances. Seven studies related to intensive rehabilitation during the early post-acute period. In six others, specific techniques--sometimes associated with traditional physiotherapy procedures--were compared: biofeedback, perceptual retraining, and amphetamine treatment. Eight experiments evaluated speech therapy in aphasia. Frequently, methodological considerations limited the interpretation of the results. The review showed that: 1) as regards activities of daily life and motor function, differences as between rehabilitation in stroke units on the one hand and non-rehabilitation or rehabilitation in medical wards on the other, were detected in relatively few quality studies and remained particularly inconclusive insofar as life in the home environment was concerned; 2) rehabilitation for aphasia and perceptual dysfunction proved effective for at least several months after acute stroke; 3) in general, examination of the reports cited revealed no differences in the effects of biofeedback and perceptual retraining vs conventional physiotherapy; 4) rehabilitation, whether administered by specialists or amateur caregivers purpose-trained by specialists, proved equally effective for aphasia. These conclusions constitute a valuable basis for the development and evaluation of modern rehabilitation programs for stroke patients.

Activities of Daily Living↗
PubMed1991

Electrotactile and vibrotactile displays for sensory substitution systems.

Sensory substitution systems provide their users with environmental information through a human sensory channel (eye, ear, or skin) different from that normally used, or with the information processed in some useful way. We review the methods used to present visual, auditory, and modified tactile information to the skin. First, we discuss present and potential future applications of sensory substitution, including tactile vision substitution (TVS), tactile auditory substitution, and remote tactile sensing or feedback (teletouch). Next, we review the relevant sensory physiology of the skin, including both the mechanisms of normal touch and the mechanisms and sensations associated with electrical stimulation of the skin using surface electrodes (electrotactile (also called electrocutaneous) stimulation). We briefly summarize the information-processing ability of the tactile sense and its relevance to sensory substitution. Finally, we discuss the limitations of current tactile display technologies and suggest areas requiring further research for sensory substitution systems to become more practical.

Artificial Intelligence↗