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Biomedical subjects

F Morrell

Publications and source records attributed to F Morrell.

At least 55 records · Page 3Linked to original sources
PubMed1984

Hemispheric asymmetry of visual evoked potentials in patients with well-defined occipital lesions.

Visual evoked potentials were examined in 3 patients who had well defined unilateral occipital lobectomy. In an attempt to resolve discrepancies in the interpretation of hemispheric asymmetries in evoked potentials, recordings were obtained from a wide array of electrodes with multiple montages during full-field and hemi-field stimulation with checkerboard pattern reversal and during full-field flash stimulation. The discrepancies appear to be due primarily to differences in electrode montages used in recording. The use of a midfrontal reference electrode reliably produces a paradoxical EP lateralization: abnormal EPs are recorded over the intact occipital lobe and normal EPs are recorded over the ablated occipital lobe. These findings are fully consistent with the interpretation of Barrett et al. (1976) that the generator of the P100 has an equivalent dipole located in the calcarine cortex on the posteromedial surface of the contralateral hemisphere. Our findings support the use of the Queen Square montage (Halliday et al. 1977). The use of electrodes at O1 and O2 referred to the ipsilateral earlobe yields inconsistent lateralization and should be discouraged. The lateralization of EP abnormalities did not differ for flash and pattern reversal, although the asymmetries were sometimes more prominent with pattern reversal.

Brain↗
PubMed1984

Pentoxifylline reverses age-related deficits in spatial memory.

Pentoxifylline, a phosphodiesterase inhibitor, produces a marked reversal of an age-dependent spatial memory deficit in Fischer 344 strain male rats. Performance of 26-month-old animals treated chronically with pentoxifylline approached that of 3-month-old controls. The effect was not dependent upon concurrent administration of the acetylcholine precursor choline chloride. It is concluded that the pentoxifylline-induced reversal of the age-dependent memory decline is not dependent on any presumed facilitation of acetylation and utilization of exogenously supplied transmitter substrate.

Aging↗
PubMed1984

Age-dependent deficits in spatial memory are related to impaired hippocampal kindling.

Fischer 344 rats, 3 and 26 months of age, were first tested in an eight-arm spatial maze to assess memory function behaviorally. The same animals were then subjected to hippocampal kindling to examine alterations in neuronal plasticity as a function of aging. The results indicated that spatial memory was poorer and hippocampal kindling slower in aged rats than in young ones. Furthermore, there was a striking positive relation between performance in the eight-arm spatial maze and speed of kindling. This finding suggests that age-related deficits in spatial memory and hippocampal kindling reflect decreased efficacy of synaptic transmission in a common neuroanatomical substrate.

Aging↗
PubMed1984

Application of phase spectral analysis for brain stem auditory evoked potential detection in normal subjects and patients with posterior fossa tumors.

A statistical test of the brain stem auditory-evoked potential (BAEP) detection is presented. The data were collected by averaging groups of 200 sweeps in order to obtain a set of group averages. The synchrony measure (SM), which represents the degree of reproducibility for group averages, is used as a statistical measure and is calculated from the phase variance for selected Fourier components of the group averages. The sensitivity of the test was demonstrated on 375 normal BAEPs with different stimulus intensities (45, 60, 75 dB SL) from both the ipsilateral and contralateral recordings, and on 82 BAEP recordings in the absence of stimulus. In all 375 cases of normal BAEPs the SM exceeds the threshold level while in the absence of stimulation the SM was below the threshold level. The clinical usefulness of the test was demonstrated on 22 patients with tumors of the posterior fossa. The absence of the BAEP was detected in 21 patients. In 12 out of 13 patients with lateralized tumors (acoustic neuromas), absence of the BAEP was noted for stimulation of the affected ear.

Adolescent↗
PubMed1983

Conditioning of single units in visual association cortex: cell-specific behavior within a small population.

These experiments examine the interrelationships between the activity of adjacent neurons during learning. Does learning depend on coherent behavior in a population of neurons or does it depend on particular neurons engaging in a particular activity at specific times? A second purpose was to examine specificity in response modification as a function of reinforcement contingency. Cells from visual association cortex of locally anesthetized, paralyzed cats and rabbits were studied with extracellular microelectrodes capable of recording single and multiunit activity, as well as local field potentials. Multiunit records were fractionated by amplitude "windows" discrimination. Pavlovian discriminative conditioning procedures were used to evaluate selective plasticity. Cells that were activated by at least two different visual stimuli were selected. Only one of the effective stimuli was paired with foot-shock (reinforcement). Of the 180 cells or cell clusters studied, 27% exhibited conditioned modification to the reinforced stimulus (CS+) and 19% changed their response pattern to the unreinforced stimulus (CS-). None of the well isolated cells showed conditioning to both CS+ and CS-. Thus, cellular plasticity was specific to reinforcement contingency. These results provide a first demonstration of reinforcement-dependent functional distinctiveness at the neuronal level. Some cells showed no alteration of response pattern despite a most prolonged conditioning procedure. Neighboring cells, responsive to the same stimuli, revealed increases or decreases in firing rate, selective changes in the latency or amplitude of single response peaks, or the appearance of one or more new peaks as a function of conditioning. Rarely did adjacent cells show the same type of alteration when alteration occurred; there was no general tendency toward coherent firing patterns as conditioning proceeded.

Animals↗
PubMed1982

Transient global amnesia after cerebral angiography. Report of seven cases.

Because of a case of typical transient global amnesia following cerebral angiography, the records of all patients undergoing cerebral angiography during a seven-year period were reviewed. Six other cases were discovered. All patients had either transfemoral catheter or brachial angiograms performed immediately before the development of amnesia. Spasm of a vertebral artery was noted in one case. None had clinically obvious seizures. All recovered within 24 hours. This only recently reported complication of cerebral angiography is consistent with a vascular etiology of the syndrome of transient global amnesia when not associated with angiography, although a direct toxic effect of the contrast material cannot be excluded.

Acute Disease↗
PubMed1982

Methohexital anesthesia in the surgical treatment of uncontrollable epilepsy.

Twenty-five patients (aged 3 to 39 years) were anesthetized with methohexital for electrocorticographic mapping and resection of epileptogenic foci. These patients have been compared with 11 patients (aged 11 to 40 years) who had the same surgical procedure performed while they were awake because their epileptogenic foci were near the speech or motor areas. All patients received morphine and droperidol to produce analgesia and sedation, and a field block was established with local anesthetics. In the 25 patients, general anesthesia was induced with methohexital, 1.5 mg/kg. and maintained with a 0.1% infusion. After intubation, ventilation to a PaCO2 of 30 mm Hg was maintained with O2/air. A resectable abnormal electroencephalogram focus was localized in every case. All but two of the patients awoke promptly in the operating room, allowing extubation and participation in neurologic assessment. None remembered the procedure. The incidence of improvement of seizures in patients given methohexital was similar to that in patients who had surgery while awake. Unlike many general anesthetics that depress epileptogenic activity, methohexital activates seizure activity and can therefore be used for the dual purpose of producing general anesthesia and enhancing electrocorticographic delineation of epileptogenic foci.

Adolescent↗
PubMed1979

Conditioned inhibition: selective response of single units.

Single cell activity and local field potentials in parastriate cortex of cats and rabbits were studied during a Pavlovian discrimination procedure. Cell activity was selectively modified; conditioned changes occurred in response either to the reinforced stimulus or to the unreinforced one, but not to both. Cells exhibiting conditioned alteration in response to the unreinforced stimulus are thought to participate in specialized circuits mediating conditioned inhibition.

Action Potentials↗
PubMed1979

The BAER profile: a method for reporting electrophysiologic brainstem examinations in clinical practice.

We present a method for graphically reporting the results of brainstem auditory evoked response examinations on the basis of multiple parameters. The method is based on a transform that normalizes the many latency and amplitude measures obtained from the averaged evoked responses of normal subjects tested under standardized conditions. Among the advantages of the method are the simplicity of its use, the identification of disease profiles, and the isolation of relevant parameters for research and diagnosis.

Adult↗
PubMed1976

Kindling in the frog: development of spontaneous epileptiform activity.

The present report is the first demonstration of the kindling phenomenon in a non-mammalian, poikilothermic species. Brief (2 sec) localized electrical stimulation was delivered to the hippocampal cortex of one hemisphere of the partially paralyzed bullfrog, Rana catesbeiana, at current levels just sufficient to elicit brief after-discharge (AD) on first application. Succeeding stimulations, once per hour, gave rise to more and more prolonged AD involving first the side stimulated (1 degree focus) and secondly the opposite hemisphere (2 degree focus). In addition to these stimulus-dependent alterations, after several hours spontaneous, paroxysmal discharges occurred in interstimulus intervals. They appeared first in the stimulated hemisphere, then as evoked spikes in the secondary hemisphere, and finally independently on the two sides. The waveshape of the spontaneous epileptiform potentials exhibited an extraordinary constancy from complex to complex which was specific to each animal. Such wave-shape coherence implies a constancy to both the anatomical substrate and the sequency of synaptic engagement each time spontaneous paroxysmal activity invades the network. The model is especially suitable for analysis of temperature-dependent biochemical events responsible for this functional transformation.

Animals↗
PubMed1976

Correlation between diffuse EEG abnormalities and cerebral atrophy in senile dementia.

Thirty-five elderly patients were investigated because of clinical signs of dementia. The presence or diffuse cerebral atrophy, and its severity, were determined by the use of computed tomography (CT scan). All of the patients were also examined by electroencephalography (EEG), and the presence of diffuse abnormalities, especially diffuse slowing, was noted. Specifically, patients with normal or near-normal EEGs were compared with those with severe diffuse slowing. No correlation between the presence or severity of diffuse EEG abnormalities and the degree of cerebral atrophy as measured by CT scan was found. Though the EEG is clearly identifying physiological dysfunction of nerve cells in demented patients it does not appear to be reliable tool for the prediction of diffuse cerebral atrophy in this population.

Age Factors↗
PubMed1975

Secondary epileptogenesis in frog forebrain: effect of inhibition of protein synthesis.

Secondary epileptogenesis was induced in the hippocampal cortex of the paralyzed bullfrog by means of localized, unilateral, intermittent electrical stimulation (kindling). Stimuli were designed to yield a brief but definite after-discharge. In control animals a progressive increase in after-discharge duration occurred at the 1 degree (stimulated) site and then at the 2 degrees site (contralateral hippocampus). Spontaneous epileptiform potentials (SEP's) occurred between stimuli, eventually independently on both sides. Cycloheximide (50 mg/kg) caused 88-99% reduction in protein synthesis, measured by 14C-leucine incorporation into brain protein. Cycloheximide-treated animals revealed no evidence of progressive prolongation of after-discharge duration when subjected to the kindling procedure (p = 0.1205 X 10(-7)). SEP's were reduced in the cycloheximide-treated animals, and confined to 1 degree hemisphere (p = 0.6 X 10(-10)). Since cycloheximide did not disturb normal electrogenesis or disrupt the after-discharges, this experiment distinguishes processes dependent upon electrical events from those requiring macromolecular synthesis. Protein synthesis seems critical to the emergence of spontaneous and autonomous epileptiform behavior of neural aggregates.

Animals↗