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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
PubMed2001

Brain plasticity: 'visual' acuity of blind persons via the tongue.

The 'visual' acuity of blind persons perceiving information through a newly developed human-machine interface, with an array of electrical stimulators on the tongue, has been quantified using a standard Ophthalmological test (Snellen Tumbling E). Acuity without training averaged 20/860. This doubled with 9 h of training. The interface may lead to practical devices for persons with sensory loss such as blindness, and offers a means of exploring late brain plasticity.

Adult↗
PubMed2001

Theoretical and practical considerations in the restoration of function after stroke.

Recovery of function after stroke appears to include elements of both restoration and compensation. The brain is highly plastic, which allows reorganization after damage. Stroke produces permanent damage to the brain, so recovery must be based on activity in surviving cells that are either adjacent, contralateral, or in a different region. Furthermore, representation of a particular function in the brain is usually not limited to a single brain region. Multiple representation provides the opportunity for brain reorganization; functions are assumed by surviving brain structures. Compensation can be the initial response in the recovery phase and may persist through later phases because of the new habits formed (as the restraint therapy studies of Taub and others would suggest), because the damage to the brain is extensive and hinders restoration, because of secondary pathology, such as tendon shortening and muscle wasting, that does not allow brain reorganization to be translated into functional recovery, or because of inadequate (especially late) rehabilitation.

Journal Article↗
PubMed2000

The cost of an action potential.

Neuronal modules, or 'cell-assemblies', comprising millions of mutually interconnected cells have been postulated to form the basis of many functions of the brain, such as mood, sleep, hunger, vigilance, and more. Depending on the extent of the module, neurocommunication in cell-assemblies might exceed metabolic resources. A medium-size (10000 neurons) module would require at least 10 J per l of brain, based on a calculated cost of an isolated action potential (AP) of 10(11)-10(12) molecules of ATP per cm(2) of cell membrane, with an absolute minimum of 10(6) ATP at a node of Ranvier. The figure matches the cost of depolarizing the unmyelinated axon of the large monopolar cell in the blowfly retina. A circuit model of the cell membrane, based on abrupt changes of Na(+) and K(+) conductances, is used to emulate the AP and to assess the resulting ionic unbalance. The cost of an AP is equated to the metabolic energy necessary to fuel ATP-based pumps that restore intracellular K(+). The high metabolic demand of a cell-assembly suggests that less expensive means of neurocommunication may be involved, such as non-synaptic diffusion neurotransmission (NDN), which would comply with a proposed law of conservation of space and energy in the brain.

Action Potentials↗
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↗