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Biomedical subjects

A R Wyler

Publications and source records attributed to A R Wyler.

At least 19 recordsLinked to original sources
PubMed1979

Operant control of precentral neurons in monkeys: evidence against open loop control.

Four normal monkeys were operantly conditioned to change the firing pattern of 111 precentral neurons from phasic to tonic using an operant paradigm which quantifies the control of single neurons. Two monkeys then had their contralateral pyramidal tract (PT) sectioned and one monkey had C5-7 ventral rhizotomies. Postlesion data were: (1) contralateral C1-2PT lesions did not encumber the monkeys' control of precentral PTNs: (2) contralateral C5-7 ventral rhizotomies completely abolished accurate control of precentral neurons which received proprioceptive feedback from flaccid arm regions. These results indicate that precentral neurons are operantly controlled through proprioceptive feedback from peripheral mechanoreceptors. The output of the mechanoreceptors is probably dependent upon discrete joint angles and/or muscle tension which is maintained through non-PT pathways. These data do not support the concept that precentral neurons are operantly controlled directly from a central; 'open loop', pathway.

Animals↗
PubMed1979

The influence of attending on seizure activity in epileptic monkeys.

Six studies are presented on the influence of attending upon epileptic activity in the alumina-gel monkey model of focal motor and secondarily generalized tonic--clonic seizures. Seizure frequency and EEG paroxysms are reported during (a) scheduled feeding periods, (b) visual attending, and (c) three different operant tasks, including the conditioning of single neurons. An explanatory hypothesis of the cumulative data is proposed in terms of the different bursting behavior of group 1 (strongly epileptic) and group 2 (weakly epileptic) neurons of the epileptogenic focus. It is suggested that attending, or participation in operant tasks, results in a decrease in bursting of group 2 neurons and a disruption of synchrony between group 1 (pacemaker), group 2, and normal neurons. This desynchronization is said to lower the probability of an ictal event occurring either during or immediately following an operant task. Attending factors may be responsible for some of the conflicting findings in therapeutic studies of epilepsy which have not controlled for this parameter.

Aluminum Hydroxide↗
PubMed1979

EEG operant conditioning for control of epilepsy.

We report the results of 23 severely epileptic patients who were given EEG feedback training. The paradigm reinforced the patients' 18 Hz activity over the scalp approximation of their focus while suppressing temporalis EMG and low frequency EEG activity. In contrast to other studies using EEG feedback, only 43% of patients showed significant changes in seizure occurrence and a lesser number were felt to have benefited clinically. None of our neuropsychological test parameters were helpful in identifying (prospectively or retrospectively) patients most likely to respond to this treatment. Although a few patients were significantly helped by this training, the mechanism for this effect is unclear.

Adolescent↗
PubMed1979

Kindling phenomenon: impairment by auditory stimuli.

By coupling kindling stimuli with tones, it is shown that kindled epileptiform activity is not easily classically conditioned such that it can be evoked by an auditory stimulus. On the contrary, a tone presented 400 msec before and during the kindling stimulus impedes the rate of kindling.

Acoustic Stimulation↗
PubMed1979

Operant control of single neurons in monkey motor cortex.

This article reviews three points. Monkeys may be trained by operant conditioning to control the firing rate and pattern of single neurons in the precentral cortex. Recent data provide an explanation of how this control is mediated and an accounting of various factors that influence it. Using this technique to study cortical physiology, researchers have generated new insights into the pathophysiology and clinical effects of epilepsy.

Animals↗
PubMed1979

Prophylactic phenytoin in severe head injuries.

We are reporting a retrospective study of 62 patients whose head injury was sufficiently severe to cause a high probability of posttraumatic epilepsy. Of 50 patients treated with phenytoin, 10% developed epilepsy of late onset. Twelve patients not treated with phenytoin but who had head injuries of equal magnitude had a 50% incidence of epilepsy. These data from a highly selected group of patients with severe head injuries confirm the bias that treatment with phenytoin decreases the incidence of posttraumatic epilepsy.

Adult↗
PubMed1978

Operant control of pyramidal tract neurons: the role of spinal dorsal columns.

A monkey was trained to control the firing patterns of precentral pyramidal tract neurons. The operant task was for the monkey to produce consecutive interspike intervals (ISI) within a requisite range, or target. The mean time off-target (error) is used to quantify the accuracy of control the monkey could assert over each PTN. Following partial destruction of the dorsal funiculi the number of PTNs driven by peripheral stimuli greatly decreased. Those PTNs which remained responsive to peripheral stimuli were as accurately controlled as those tested before column section, whereas, those PTNs unresponsive to peripheral stimuli were significantly less accurately controlled. The conclusion is that the monkey relies heavily upon proprioceptive feedback to operantly control precentral PTNs.

Acoustic Stimulation↗
PubMed1978

Epileptic and normal neurons in monkey neocortex: a quantitative study of degree of operant control.

The object of this study was to quantify and compare the degree of control monkeys may assert over firing patterns of normal and epileptic neurons. Thirty-seven epileptic and 70 normal neurons were studied in detail. The operant task was for the monkey to generate specified consecutive interspike intervals (ISI). The monkeys demonstrated far greater accuracy in controlling consecutive ISIs of normal neurons and were only able to control the intervals between bursts from epileptic neurons. The data implies that high frequency bursts of action potentials from epileptic neurons are all-or-nothing events initiated by synaptic mechanisms. In addition, some data are from a monkey with epilepsia partialis continua; in comparison to less active foci, this focus was comprised of a higher percentage of 'pacemaker' epileptic neurons.

Animals↗
PubMed1978

Operant conditioning of tonic firing patterns from precentral neurons in monkey neocortex.

This report presents a single neurons operant conditioning paradigm which allows the quantification of operant control between neurons and monkeys. The operant task is for the monkey to change firing patterns of the neuron from phasic to tonic. In 60 neurons conditioned after the protocol had been standardized the following results were obtained. (1) For a fixed interspike interval target range, the time off target may be considered error, and this may be used as a parameter with which to judge operant neuronal control. (2) The degree to which the monkey could control a neuron was not correlative with the neuron's initial firing rate, firing rate variance, or pattern. (3) Neurons coactivated by distal arm muscle groups were, as a group, more highly controlled in comparison to neurons coactivated by proximal muscle groups. (4) Pyramidal tract neurons, as a group, appear more accurately controlled than non-pyramidal tract neurons. (5) The role of proprioception in response acquisition is discussed.

Animals↗
PubMed1978

The effects of chronicity on burst structure in epileptogenic foci.

Pyramidal tract neurons (PTNs) from tungstic acid, cobalt and alumina gel foci in cat were studied for spontaneous and antidromically-evoked firing patterns. Specifically, the structured long-first-interval (LFI) burst was looked for. The LFI burst did occur spontaneously from PTNs in tungstic acid foci but could not be antidromically evoked. The LFI burst did not occur as often as would have bee predicted from cobalt and alumina foci, but, in foci older than 60 days, antidromically-evoked activity could be a burst which was structurally identical to those which occurred spontaneously. This data, in addition to that from acute penicillin foci, would indicate that the ability for single antidromic APs to evoke burst activity in PTNs is a function of the chronicity of the epileptic focus rather than the agent used to produce the focus.

Action Potentials↗
PubMed1978

Effects of chronic epileptic foci on control of pyramidal tract neurons in monkeys.

Five Macaca mulatta monkeys were operantly conditioned to control the firing patterns of single precentral pyramidal tract neurons. The accuracy with which the monkeys could control normal PTNs from within the focus was significantly poorer than PTNs from contralateral, homotopic cortex. In comparison to nonepileptic monkeys, there was no significant difference in the accuracy with which PTNs from cortex contralateral to interictal foci were controlled. By contrast, comparison of the time necessary to gain accurate control over individual PTNs from contralateral cortex showed the epileptic monkeys to be significantly encumbered when compared to nonepileptic monkeys. These data suggest that interictal foci produce "noise" in remote regions of brain that are involved in an operant task requiring a high degree of discrimination.

Aluminum Hydroxide↗
PubMed1978

Epileptogenic agents applied to trigeminal ganglia: absence of neuronal hyperexcitability.

Chronic application of alumina cream to the trigeminal ganglion in 10 cats failed to produce a long-lasting behavioral syndrome of facial dysesthesia. Histologic and electron microscopic analysis demonstrated morphologic similarities between these ganglia and primate neocortical alumina cream epileptic foci. None of 87 ganglia neurons recorded extracellularly exhibited evidence of intrinsic hyperexcitability, i.e., abnormal spontaneous or physiologically evoked activity or any significant differences in threshold of responses to antidromic or orthodromic electrical stimulation, compared to 67 normal ganglion cells. Furthermore, topical application of penicillin to normal ganglia failed to produce abnormal activity in 42 neurons tested. These data suggest that neuronal somata lacking either dendrites or postsynaptic membranes, or both, do not develop abnormal firing behavior when challenged with these two epileptogenic agents.

Aluminum Hydroxide↗