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Biomedical subjects

R W Thatcher

Publications and source records attributed to R W Thatcher.

At least 37 records · Page 2Linked to original sources
PubMed1995

Tomographic electroencephalography/magnetoencephalography. Dynamics of human neural network switching.

New developments in multimodal registration of electroencephalography (EEG), magnetic resonance imaging (MRI), and positron emission tomography (PET) are presented as a method to create a tomographic EEG. Three-dimensional information about the x,y,z location of the sources of event-related potentials is corroborated through the use of experimental design and coregistration with MRI and PET. Once the three-dimensional location of event-related potential dipole sources is identified and corroborated, pseudoinverse procedures are used to derive a new EEG voltage sequence from each of the dipoles. Each derived EEG dipole time series is analogous to recording EEG from a deeply implanted electrode and constitutes a four-dimensional tomographic EEG (i.e., three-dimensional space plus time). EEG coherence and phase analyses are then performed on the dipole-derived time series to study the temporal and spatial dynamics of neural network switching during voluntary finger movements. The purpose of this article is to demonstrate a new method to exploit the time domain dynamics of neural network switching in behaving human subjects.

Brain↗
PubMed1992

Cyclic cortical reorganization during early childhood.

EEG coherence was computed from 8 left and 8 right intrahemispheric electrode pairs from 253 children ranging in mean age from 6 months to 7 years. The first derivative of mean coherence was computed in order to study growth spurts or rapid changes in mean coherence over the early childhood period. Growth spurts in EEG coherence were approximately 6 months to 1 year in duration and involved a cyclical process composed of a sequential lengthening of intracortical connections in the left hemisphere and a sequential contraction of intracortical connections in the right hemisphere. Each growth spurt cycle had a period of approximately 2 to 4 years and involved both a rostral-caudal expansion and contraction as well as a lateral-to-medial rotation. Data support the view that the functions of the left and right hemisphere are established early in human development through complementary developmental sequences and that these sequences appear to recapitulate differences in adult hemispheric function.

Age Factors↗
PubMed1991

Comprehensive predictions of outcome in closed head-injured patients. The development of prognostic equations.

A comprehensive diagnostic evaluation was administered to 162 closed head-injured patients within 1 to 21 days (mean, 7.5 days) after injury. Each evaluation consisted of (1) power spectral analyses of electroencephalogram (EEG) recorded from 19 scalp locations referenced to age-matched norms, (2) brainstem auditory evoked potentials, (3) computed tomography (CT)-scan, and (4) Glasgow Coma Score (GCS) at time of admission (GCS-A) and at time of EEG test (GCS-T). Functional outcome at one year following injury was assessed using the Rappaport Disability Rating Scale (DRS), which measures the level of disability in the six diagnostic categories of (1) eye opening, (2) best verbal response, (3) best motor response, (4) self-care ability for feeding, grooming, and toileting, (5) level of cognitive functioning, and (6) employability. The ability of the different diagnostic measures to predict outcome at one year following injury was assessed using stepwise discriminant analyses to identify patients in the extreme outcome categories of complete recovery versus death and multivariate regression analyses to predict patients with intermediate outcome scores. The best combination of predictor variables was EEG and GCS-T, which accounted for 74.6% of the variance in the multivariate regression analysis of intermediate outcome scores and 95.8% discriminant accuracy between good outcome and death. The best single predictors of outcome in both the discriminant analyses and the regression analyses were EEG coherence and phase. A gradient of prognostic strength of diagnostic measures was EEG phase greater than EEG coherence greater than GCS-T greater than CT-scan greater than EEG relative power. The value of EEG coherence and phase in the assessment of diffuse axonal injury was discussed.

Activities of Daily Living↗
PubMed1990

Cortical reorganization in deaf children.

Topographic mapping of the cerebral cortex of 79 deaf children and a group of matched hearing children was performed, using measures of electroencephalographic coherence, phase, and power. Deaf children manifested higher coherence and lower phase in certain left hemispheric areas, suggesting less neural differentiation; but lower coherence and higher phase in certain right hemispheric areas, suggesting greater differentiation. Deaf children had higher total power in bilateral frontal cortex than did hearing children. The data also suggested compensatory functioning in the visual cortex of the deaf subjects. The pattern of results varied somewhat in relation to cause of deafness. These findings support the hypothesis that prelingual deafness results in a partial reorganization of cerebral cortex.

Adolescent↗
PubMed1990

Ingestion of carbohydrates varying in complexity produce differential brain responses.

Variations in the complexity of carbohydrate substances were studied with respect to their differential effects on brain function. Glucose, sucrose, fructose and corn starch were each administered as part of an oral carbohydrate tolerance test during 17 test trials. Brain EEG changes and blood glucose levels were monitored concurrently throughout a 5 hour period. The glucose solution produced more substantial EEG effects than the other three carbohydrate solutions. Absolute blood glucose level was the primary determinant of electrocortical changes found predominantly in the left parietal-occipital and left temporal cortical regions. Implications for the study and evaluation of cognitive function were discussed.

Brain↗
PubMed1989

EEG discriminant analyses of mild head trauma.

Measures of EEG power spectral analyses were obtained from a total of 608 mild head trauma patients and 108 age-matched normal subjects. A training-set discriminant function was first developed from 264 mild head-injured patients and 83 age-matched controls yielding an overall discriminant classification accuracy of 94.8%. The first independent cross-validation of the discriminant function using 130 mild head trauma patients and 21 age-matched normals yielded a discriminant classification accuracy of 96.2% for the trauma patients and 90.5% for the normals. A second independent cross-validation of the discriminant function using 51 patients and measures of test-retest reliability from 93 patients yielded classification accuracies ranging between 77.8% and 92.3%. A third independent cross-validation of 70 mild head-injured patients tested at a different location with a different EEG computer system yielded a discriminant accuracy of 92.8%. The discriminating EEG power spectral analyses indicated 3 classes of neurophysiological variables which are attributable to mechanical head injury: (1) increased coherence and decreased phase in frontal and frontal-temporal regions; (2) decreased power differences between anterior and posterior cortical regions; and (3) reduced alpha power in posterior cortical regions.

Adolescent↗
PubMed1987

Human cerebral hemispheres develop at different rates and ages.

The development of the cerebral hemispheres was assessed by using measures of electroencephalographic coherence and phase in 577 children ranging in age from 2 months to early adulthood. Two categories of age-dependent change in electroencephalographic coherence and phase were noted: continuous growth processes that were described best by an exponential growth function, and discrete growth spurts that appeared in specific anatomical locations at specific postnatal periods. The left and right hemispheres developed at different rates and with different postnatal onset times with the timing of growth spurts overlapping the timing of the major developmental stages described by Piaget.

Adolescent↗
PubMed1986

Computerized EEG analyses of autistic children.

Electroencephalographic measures of the neurophysiological dysfunction underlying autism have been nonspecific and incomplete. Studies using electroencephalographic methods have been fraught with subject sampling bias, a lack of standardized techniques and measures, and a lack of appropriate control groups. Low-functioning autistic children with age-matched normals, age-matched mentally handicapped, and mentally age-matched normal toddlers were tested using a computerized electroencephalographic technique. The autistic children showed significantly more slow wave activity and less alpha, as well as less inter- and intrahemispheric asymmetry than either normal or mentally handicapped children. In general, electroencephalographic features of autistic children closely resembled those of the toddlers, supporting a model of maturational lag as the key descriptor for autistic CNS functioning. A model of diminished cortical differentiation is proposed to account for the low level of intellectual functioning.

Adolescent↗
PubMed1986

Cortico-cortical associations and EEG coherence: a two-compartmental model.

EEG coherence was computed from 19 scalp locations from 189 children ranging in age from 5 to 16 years. Tests of spatial homogeneity of EEG coherence were conducted by comparing EEG coherence as a function of different interelectrode distances in the anterior-to-posterior versus posterior-to-anterior directions. Highly significant inhomogeneities were observed since greater coherence was present in the anterior-to-posterior direction than in the posterior-to-anterior directions. Greater coherence was also present in frontal derivations than in posterior derivations and from the right hemisphere in comparison to the left hemisphere. These data indicate that at least two separate sources of EEG coherence were present (1) coherence produced through the action of short length axonal connections, and (2) coherence produced through the action of long distance connections. Measures of phase delays as a function of interelectrode distance supported the development of a 'two-compartmental' model of EEG coherence in which different features of coherence are produced by different length fiber systems. Based on this model a number of hypotheses were developed to explain differences in connectivity between left and right hemispheres and frontal versus occipital cortex.

Adolescent↗
PubMed1978

Treatment of acute gonococcal conjunctivitis.

Because of the remarkable increasing incidence of gonorrhea, there is danger that gonococcal conjunctivitis also will increase. The ability of the gonococcus to rapidly cause corneal destruction and become increasingly resistant to penicillin make it imperative for ophthalmologists to keep up to date on effective treatment methods. A treatment schedule for acute gonococcal conjunctivitis is presented.

Adolescent↗