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Biomedical subjects

F H Duffy

Publications and source records attributed to F H Duffy.

At least 73 records · Page 4Linked to original sources
PubMed1983

Animal models of strabismic amblyopia: comparative behavioral studies.

Visual acuity and visuo-motor behavior were assessed in various models of experimental amblyopia in cats (n = 15). Three models of strabismic amblyopia were studied: surgical esotropia by sectioning one lateral rectus muscle; comitant optical strabismus by rearing cats with goggles which placed a stationary wedge prism before one eye; and incomitant optical strabismus by rearing cats with goggles which placed a rotatable wedge prism before one eye. These cats were compared with normal and monocularly deprived cats. Clear amblyopic deficits were found in monocularly deprived, esotropic and rotating prism cats. The amblyopic deficits were graded among these preparations, being most severe in monocularly deprived cats and least severe in esotropic cats. The degree of behavioral amblyopia in these preparations was correlated with the extent of physiological abnormalities in visual cortex and the lateral geniculate nucleus. Fixed optical strabismus did not result in behavioral deficits and does not appear to be a good model of strabismic amblyopia. Variable optical strabismus, on the other hand, produced clear deficits in one eye, both behaviorally and physiologically, without impaired ocular motility.

Amblyopia↗
PubMed1982

Animal models of strabismic amblyopia: physiological studies of visual cortex and the lateral geniculate nucleus.

Receptive field properties of visual cortical and lateral geniculate cells were studied in 4 models of amblyopia in the cat: monocular deprivation (MD cats), surgical esotropia (esotropic cats), optically induced concomitant strabismus (stationary prism cats) and optically induced incomitant strabismus (rotating prism cats). Comparison observations were made in normal cats. Recordings in visual cortex indicated a reduction in responsiveness to the treated eye in MD and rotating prism cats. Esotropic and stationary prism cats showed mainly a loss of binocular cells. Recordings in the lateral geniculate nucleus indicated a reduction in the spatial resolving capacity of X-cells driven by the treated eye in MD, esotropic and rotating prism cats. The magnitude of this effect was comparable in all of these preparations. Stationary prism cats showed comparable spatial resolving capacities in X-cells driven by either eye. Y-cells were unaffected in any preparation except MD where there were reduced frequencies of Y-cells driven by the treated eye. These results indicate that: (1) interocular differences in spatial patterns without form deprivation are sufficient to produce a loss of responsiveness to one eye in visual cortex; (2) incomitant disparities are necessary to produce the physiological correlates of amblyopia in cats; and (3) deficits in spatial resolution in geniculate neurons are comparable in magnitude in various amblyopic preparations.

Amblyopia↗
PubMed1981

Comparison of the effects of dark rearing and binocular suture on development and plasticity of cat visual cortex.

Comparisons were made between the effects of binocular suture and dark rearing in terms of: (1) the state of visual cortical physiology after prolonged deprivation; and (2) the nature of physiological recovery seen when monocular vision was experienced after prolonged deprivation. These comparisons were based on the ocular dominance distribution and receptive field tuning characteristics of visual cortical cells. After prolonged dark rearing, most visual cortical cells were binocularly activated and had non-specific receptive field properties. Monocular vision after dark rearing produced dramatic changes: the majority of cells were responsive only to the open eye and these cells typically displayed orientation and direction selectivity. Prolonged binocular suture, on the other hand, resulted in a high incidence of unresponsive cells and cells with unmappable receptive fields, and a low proportion of binocularly responsive cells. Monocular vision experienced after binocular suture resulted in only slight physiological changes, and there was no evidence for selective development of connections from the open eye. These results indicate that dark rearing and binocular suture have different effects on the development of cat visual cortical cells. Diffuse visual stimulation through the sutured lids (binocular suture) appears to produce permanent developmental effects on cortical physiology, whereas complete deprivation (dark rearing) leaves cortex in a state which can be modified by subsequent visual experience.

Animals↗
PubMed1981

Role of intracortical inhibition in deprivation amblyopia: reversal by microiontophoretic bicuculline.

The GABA antagonist, bicuculline, was microiontophoretically applied to 31 cells in the visual cortices of 4 cats monocularly deprived of vision from birth to time of study at age 5 months. Bicuculline restored input from the deprived eye to 42% of cells studied. Elevation of background firing rates by glutamate failed to restore deprived eye input. We suggest that intracortical inhibition plays an important role in maintaining the physiological abnormalities produced in visual cortex by monocular deprivation.

Animals↗
PubMed1981

Significance probability mapping: an aid in the topographic analysis of brain electrical activity.

We illustrate the application of significance probability mapping (SPM) to the analysis of topographic maps of spectral analyzed EEG and visual evoked potential (VEP) activity from patients with brain tumors, boys with dyslexia, and control subjects. When the VEP topographic plots of tumor patients were displayed as number of standard deviations from a reference mean, more subjects were correctly identified than by inspection of the underlying raw data. When topographic plots of EEG alpha activity obtained while listening to speech or music were compared by t statistic to plots of resting alpha activity, regions of cortex presumably activated by speech or music were delineated. DIfferent regions were defined in dyslexic boys and controls. We propose that SPM will prove valuable in the regional localization of normal and abnormal functions in other clinical situations.

Alpha Rhythm↗
PubMed1981

The effects of dark-rearing on the development and plasticity of the lateral geniculate nucleus.

During a prolonged period of dark-rearing, lateral geniculate X-cells developed normal spatial resolving capacities and otherwise normal receptive field properties. Y-cells were reduced in frequency. Neither of these developmental processes were altered by subsequent monocular vision. In visual cortex, on the other hand, both the development of normal receptive field properties and the susceptibility to monocular deprivation were delayed by dark-rearing.

Animals↗
PubMed1980

Dyslexia: regional differences in brain electrical activity by topographic mapping.

Electroencephalographic (EEG) and evoked potential data were recorded during behavioral testing from 8 dyslexic and 10 normal boys aged 9 to 11 years. Topographic mapping of their brain electrical activity revealed four discrete regions of difference between the two groups involving both hemispheres, left more than right. Aberrant dyslexic physiology was not restricted to a single locus but was found in much of the cortical region ordinarily involved in reading and speech. Prominent group differences were observed in the bifrontal area in addition to the more expected left temporal and left posterior quadrant regions. Although activation tests produced more prominent group difference, dyslexics differed from normal subjects at rest as well. EEG alpha activity was increased for the dyslexics, suggesting relative cortical inactivity in that group.

Alpha Rhythm↗
PubMed1980

Dyslexia: automated diagnosis by computerized classification of brain electrical activity.

We describe a method for the diagnosis of dyslexia based upon a study of electroencephalographic and evoked potential data recorded from 13 normal and 11 dyslexic boys. Measurements were made from topographic maps of brain electrical activity recorded during resting and activated testing conditions. Using a statistically based technique, we developed rules for classification that successfully diagnosed 80 to 90% of subjects not used in the initial rule development. The nature of the most useful measurements suggests that aberrant neurophysiology in dyslexia involves both hemispheres and is present at rest as well as during complex testing. The method has promise for future diagnosis and research.

Alpha Rhythm↗
PubMed1979

Neuronal supersensitivity to acetylcholine induced by kindling in the rat hippocampus.

Kindling is an experimental model of epilepsy in which periodic brain stimulation induces the progressive development of electrical and behavioral seizures. A kindling-induced electrical seizure (afterdischarge) in the rat hippocampus produces prolonged neuronal supersensitivity to microiontophoretically applied acetylcholine after a latency of 40 to 60 minutes. Neuronal acetylcholine supersensitivity is correlated with the further progression of kindling. A larger hippocampal after-discharge is elicited by a subsequent kindling stimulus delivered in the presence of acetylcholine supersensitivity, but not by one delivered before the onset of the supersensitivity. The results suggest that alteration of synaptic sensitivity to acetylcholine may contribute to kindling and epileptogenesis.

Acetylcholine↗
PubMed1979

Brain electrical activity mapping (BEAM): a method for extending the clinical utility of EEG and evoked potential data.

The difficulties inherent in extracting clinically useful information by visual inspection alone from the massive amounts of data contained in multichannel polygraphic recordings have placed limits on the accuracy and range of utility of electroencephalography and evoked potentials. A method for condensing and summarizing the spatiotemporal information contained in recordings from multiple scalp electrodes is described. Data dimensionality is reduced and visibility increased by computer-controlled topographic mapping and display of data as color television images. Examples are given in which such brain electrical activity mapping (BEAM) (1) localizes tumors in patients with normal or nondiagnostic EEGs, (2) adds additional information to that visible on computerized axial tomography, and (3) demonstrates electrophysiological abnormalities in patients with functional lesions but normal CT scans. A sensitivity to the functional component of a neurological lesion suggests that BEAM may provide complementary information to the anatomical definition provided by the CT scan.

Adolescent↗
PubMed1978

Paroxysmal beta activity in the pediatric electroencephalogram.

A total of 5,401 electroencephalograms performed in the Seizure Unit at Children's Hospital Medical Center over a 12-month period were analyzed for the presence of paroxysmal beta activity. Nine examples were found in patients under the age of 10 years, each of whom had a clinical seizure disorder. Seven patients showed abnormalities such as tumor, cerebral dysgenesis, or hydrocephalus on CAT scans or skull roentgenograms. Paroxysmal beta activity should be considered a manifestation of a seizure disorder. Furthermore, the finding of paroxysmal beta activity on an electroencephalogram in the young child should lead to further evaluation for a possible structural lesion.

Beta Rhythm↗
PubMed1978

The pharmacology of amblyopia.

Physiologic and anatomic evidence has suggested an anatomic disconnection between the deprived eye and visual cortical neurons in cats made amblyopic by monocular deprivation. Clinical and visual-evoked response data suggest, however, that inhibition may play a major role in amblyopia. Accordingly, we intravenously administered anti-inhibitory compounds (bicuculline, ammonium ion, naloxone) to amblyopic cats and demonstrated a substantial restoration of binocular input to the visual cortex. Such pharmacologic reversal suggests that amblyopia is not an anatomically fixed lesion.

Adult↗