James L. Burchfiel

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.

Somatosensory System: Organizational Hierarchy from Single Units in Monkey Area 5

The receptive fields of single cells in area 5 of monkey parietal cortex were studied by extracellular recording. Cells were driven primarily by gentle manipulation of multiple joints residing on one or more limbs. Both excitatory and inhibitory convergence were demonstrated. It is postulated that the multijoint receptive fields of area 5 are the result of convergence from single-joint cells of the primary receiving area. An analogy is drawn between the modification of information in the visual and somatosensory systems.

Long-term effects of an organophosphate upon the human electroencephalogram.

Abstract The brain electrical activity of workers exposed to the organophosphate compound (OP), sarin, was compared to that of control subjects. Exposed workers had a history of one or more documented accidental exposures to toxic levels of sarin. However, no exposed subject had exposure within 1 year of his examination. The comparison included standard clinical electroencephalograms (EEGs), computer-derived EEG spectral analysis, and standard overnight sleep EEGs. It was not possible to diagnose subjects individually by expert visual inspection of their EEGs. However, statistically significant between-group differences for both the visually inspected and computer-derived data were reported by both univariate and multivariate statistical methods. Different EEG changes revealed by visual inspection and computer-derived spectral analysis appear to reflect the differing sensitivites of these two analytic techniques. Statistically significant group differences included increased beta activity, increased delta and theta slowing, decreased alpha activity, and increased amounts of rapid eye movement sleep in the exposed population. It is suggested that the above findings represent an unexpected persistence of known short-term OP actions. It is also suggested that these results, when taken along with the reported long-term behavioral effects of OP exposure, provide parallel evidence that OP exposure can produce long-term changes in brain function.

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.

Persistent effects of sarin and dieldrin upon the primate electroencephalogram.

Abstract Rhesus monkeys were injected with the organophosphate sarin or the chlorinated hydrocarbon dieldrin according to one of two schedules: (1) a single “large dose” (5 μg/kg of sarin or 4 mg/kg of dieldrin, iv) which produced overt signs of toxicity, or (2) a series of 10 “small doses” (1 μg/kg of sarin or 1 mg/kg of dieldrin, im, given 1 week apart) which did not produce any major clinical signs. Electroencephalograms (EEG) were recorded from chronically implanted electrodes according to the following schedule: (1) three recording sessions prior to drug administration, (2) one at 24 hr post-drug, and (3) another three at 1 yr post-drug. Each recording session consisted of runs in the following states: (1) awake and alert in a lighted environment, (2) awake and alert in total darkness, and (3) drowsy. A series of control monkeys received equal treatment but were given only drug diluent. Fast-Fourier transforms were performed on the EEGs with a PDP-12 computer to yield voltage vs frequency spectra. Results of statistical analysis of EEG spectra showed the following: For both sarin and dieldrin the single large-dose administration produced significant increases in the relative amount of beta voltage (15–50 Hz) which persisted for 1 yr. For sarin the predominant effect was in the EEG derivation from the temporal cortex, and for dieldrin from the frontal cortex. For both drugs, the beta increase was most prominent in the states of awake in darkness and drowsy. These results indicate that a single symptomatic exposure or a series of subclinical exposures to sarin or dieldrin can alter the frequency spectrum of the spontaneous EEG for up to 1 yr.

EEG Background as Predictor of Electrographic Seizures in High‐Risk Neonates

Summary: Purpose: Experience with continuous EEG monitoring in 29 consecutive infants at risk of neonatal seizures demonstrated that background abnormalities on the initial EEG were strongly associated with electrographic seizures in the subsequent 18–24 h. To test this association prospectively, we examined the relationship between EEG background and the presence of electrographic seizures in the next 22 at‐risk infants monitored for seizures.

Eye movement-related inhibition of primate visual neurons

The influence of saccadic eye movements (EM) upon spontaneous neuronal activity was studied in the lateral geniculate nucleus (LGN) and striate visual cortex (VC) of encéphale isolé monkeys. EM were spontaneous and occurred in total darkness to eliminate the effects of retinal image displacement. The activity of LGN cells was not altered in association with EM. In contrast, 76% of cells studied in VC displayed a period of inhibition related to spontaneous EM in total darkness. EM-related inhibition of VC neurons was directionally specific; for each cell there was one quadrant of EM direction for which inhibition was most prominent. The majority of VC neurons showed inhibition in relation to EM directed into only one quadrant of the visual field. Reliable detection of EM-related inhibition required the formation of average histograms of neuronal firing time-locked to EM. For individual EM (even of optimum direction), a consistent degree of inhibition was not seen. The time course of EM-related inhibition of VC neurons is consistent with that reported for saccadic suppression. These results support the concept of a central mechanism (corollary discharge) acting at the cortical level being of significance in saccadic suppression.

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.

Differential effects of perinatal hypoxia and anoxia on long term seizure susceptibility in the rat

We have previously demonstrated that hypoxia is acutely epileptogenic in the immature rat but not in the adult. The window during which hypoxia induces seizures in the rat ranges from postnatal day (P) 5-17, with the most severe seizures occurring at P10-12. Perinatal hypoxia resulted in significantly more acute seizure activity than perinatal anoxia. The present study evaluates the long term effects of perinatal hypoxia versus anoxia. Animals were exposed to hypoxia (3%O2) or anoxia (0%O2) at P10 and challenged later in adulthood (P55-60) with administration of pentylenetetrazol (PTZ) (45 mg/kg subcutaneously). Compared to normal littermate controls, the animals which had been exposed to perinatal hypoxia had a significantly higher frequency of generalized convulsions (GC) and a significantly shorter latency to the first myoclonic jerk (MJ) after PTZ. In contrast, perinatal anoxia did not alter long term seizure susceptibility. These results are discussed in context of previous studies which have shown variable long term effects using different models of perinatal hypoxia and/or ischemia.

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.