Frank H. Duffy

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.

A three-center, randomized, controlled trial of individualized developmental care for very low birth weight preterm infants: medical, neurodevelopmental, parenting, and caregiving effects.

ABSTRACT. Medical, neurodevelopmental, and parenting effects of individualized developmental care were investigated in a three-center, randomized, controlled trial. A total of 92 preterm infants, weighing less than 1250 g and aged less than 28 weeks, participated. Outcome measures included medical, neurodevelopmental and family function. Quality of care was also assessed. Multivariate analysis of variance investigated group, site, and interaction effects; correlation analysis identified individual variable contributions to significant effects. The results consistently favored the experimental groups. The following contributed to the group effects: shorter duration of parenteral feeding, transition to full oral feeding, intensive care, and hospialization; lower incidence of necrotizing enterocolitis; reduced discharge ages and hospital charges; improved weight, length, and head circumferences; enhanced autonomic, motor, state, attention, and self-regulatory functioning; reduced need for facilitation; and lowered family stress and enhanced appreciation of the infant. Quality of care was measurably improved. Very low birth weight infants and their parents, across diverse settings, may benefit from individualized developmental care.

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.

Altered topography of EEG spectral content in schizophrenia

EEG data were recorded in resting and in specific test conditions designed to activate different regions of the brain in a group (n = 10) of chronic schizophrenics and matched controls. EEG spectral energy was computed using the Fast Fourier Transform and numerical matrices representing the topographic distribution of spectral energy in a specified band were constructed and displayed as color images. Significance Probability Mapping was employed to identify regions of maximal group difference; it was found that the schizophrenic group showed increased low frequency energy (0-7 c/sec) in the frontal regions and increased fast activity (12-32 c/sec) in post-central areas and the left anterior temporal area. The different psychological test conditions were associated with different patterns of energy distribution. The consistency of our findings with other investigations suggests that topographic mapping of brain EEG spectral activity may play a useful role in the functional understanding of schizophrenia.

Correlations between abnormal auditory P300 topography and positive symptoms in schizophrenia: A preliminary report

P300 component amplitude in the left temporal scalp region, shown in three previous studies to differentiate normals from schizophrenics, was found to be significantly correlated with the Thought Disorder Index (TDI) and the Scale for the Assessment of Positive Symptoms (SAPS). These correlations occurred primarily in the P300 waveform derived from the Goodin paradigm. These findings suggest a brain processing disturbance in positive symptom schizophrenia that may be reflected by electrophysiological abnormalities detectable in the temporal scalp region.

Human cerebral potentials associated with REM sleep rapid eye movements: links to PGO waves and waking potentials

Eye movement triggered averaging and topographic display techniques indicate the presence of parieto-occipital potentials that precede the rapid eye movements of human REM sleep. Since these potentials have strong similarities with PGO waves in animals, including lateralization according to eye movement (EM) direction, and with waking EM-antecedent potentials in man, this suggests that PGO-like activity both exists in man, and may be functionally related to EM-antecedent potentials in waking. The ability to detect such central potentials opens the possibility of studying REM sleep central physiological structure in a variety of normal and pathological conditions in humans.

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 source analysis of epileptiform activity using a 1 mm anisotropic hexahedra finite element head model

The major goal of the evaluation in presurgical epilepsy diagnosis for medically intractable patients is the precise reconstruction of the epileptogenic foci, preferably with non-invasive methods. This paper evaluates whether surface electroencephalography (EEG) source analysis based on a 1 mm anisotropic finite element (FE) head model can provide additional guidance for presurgical epilepsy diagnosis and whether it is practically feasible in daily routine. A 1 mm hexahedra FE volume conductor model of the patients head with special focus on accurately modeling the compartments skull, cerebrospinal fluid (CSF) and the anisotropic conducting brain tissues was constructed using non-linearly co-registered T1-, T2- and diffusion-tensor-magnetic resonance imaging data. The electrodes of intra-cranial EEG (iEEG) measurements were extracted from a co-registered computed tomography image. Goal function scan (GFS), minimum norm least squares (MNLS), standardized low resolution electromagnetic tomography (sLORETA) and spatio-temporal current dipole modeling inverse methods were then applied to the peak of the averaged ictal discharges EEG data. MNLS and sLORETA pointed to a single center of activity. Moving and rotating single dipole fits resulted in an explained variance of more than 97%. The non-invasive EEG source analysis methods localized at the border of the lesion and at the border of the iEEG electrodes which mainly received ictal discharges. Source orientation was towards the epileptogenic tissue. For the reconstructed superficial source, brain conductivity anisotropy and the lesion conductivity had only a minor influence, whereas a correct modeling of the highly conducting CSF compartment and the anisotropic skull was found to be important. The proposed FE forward modeling approach strongly simplifies meshing and reduces run-time (37 ms for one forward computation in the model with 3.1 million unknowns), corroborating the practical feasibility of the approach.