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Biomedical subjects

D O Walter

Publications and source records attributed to D O Walter.

At least 19 recordsLinked to original sources
PubMed1992

Changes in brain functional connectivity in Alzheimer-type and multi-infarct dementia.

Clinical and neuropathological evaluation of elderly subjects with dementia has traditionally concentrated upon the focal distribution of brain disease, ignoring changes in the complex connections that link brain areas and that are crucial for cognition. We examined subjects with the two most common forms of dementia in the elderly (dementia of the Alzheimer type or DAT, and multi-infarct dementia or MID); and used electroencephalographic (EEG) coherence to examine the effects of these illnesses on the functional connections between brain areas. We studied coherence between brain areas known to be linked by two different types of connections: (i) dense narrow bands of long corticocortical fibres; (ii) broad complex networks of corticocortical and corticosubcortical fibres. Areas that were linked by dense narrow bands of long corticocortical fibres showed greatly diminished coherence in subjects with DAT; among MID subjects, this coherence was not significantly affected. Areas that were linked by broad connective networks showed the largest decreases in coherence among MID subjects. These findings are consistent with neuropathological evidence that Alzheimer's disease is a neocortical 'disconnection syndrome' in which there is a loss of structural and functional integrity of long corticocortical tracts. The findings further suggest that the vascular disease of MID most prominently affects broad fibre networks that may be more vulnerable to diffuse subcortical vascular damage. A ratio of coherence from complex corticocortical-corticosubcortical networks divided by coherence from long corticocortical tracts correctly classified 76% of subjects into DAT and MID categories. Overall, these results indicate that EEG coherence detects basic pathophysiological differences between subjects with DAT and MID, and that these differences may be clinically useful.

Aged↗
PubMed1991

Non-linear dynamics of electrocardiographic waveforms following cocaine administration.

We examined dynamics of ECG waveforms preceding and following 10 mg/kg intravenous administration of cocaine in freely moving cats. Cocaine induced substantial variation in ECG waveforms, as demonstrated by non-linear procedures of phase-plane plots and Poincaré analyses. Phase-plane plots revealed that waveform variation following cocaine administration was not randomly or uniformly distributed, but instead followed patterns of clustered organization with unvisited regions. These patterns are characteristic of chaotic distributions, and support the hypothesis that ECG waveform variation following cocaine does not degenerate into random patterns; instead, the variation follows deterministic, though chaotic patterns.

Animals↗
PubMed1991

Stable bimodal response to cholinomimetic drugs in Alzheimer's disease. Brain mapping correlates.

We investigated quantitative EEG brain mapping as a physiologic marker of drug response while studying the stability of intersubject variability in patients with Alzheimer's disease (AD) who were receiving bethanechol through intracerebroventricular (ICV) shunts. Two of the patients had previously demonstrated cognitive and behavioral improvements on medication; the third had cognitive deterioration complicated by agitated depression. All three patients were reexamined in a dose-response paradigm. Serial brain mapping examinations were performed along with brief cognitive testing. All patients showed drug responses that were comparable with responses during their initial dose-response phase. There were strong linear correlations between global decreases in 2 to 6 Hz slow-wave activity and cognitive improvement. Brain mapping demonstrated that slowing decreased in magnitude and field with increasing dose until optimal dose was reached; with supra-optimal doses, the magnitude and field of the slowing increased dramatically. These results suggest that the quality of cholinomimetic drug responses are stable over time in individual patients, and that magnitude and pattern of slow-wave activity as measured by brain mapping may be useful in monitoring treatment with cholinomimetic agents.

Alzheimer Disease↗
PubMed1989

Diagnosis and assessment of dementia using functional brain imaging.

Functional brain imaging using computer-analyzed electroencephalography was performed in 40 subjects: 15 with mild-to-moderate dementia of the Alzheimer's type (DAT), 13 with mild-to-moderate multi-infarct dementia (MID), and 12 age-matched controls. We examined three different parameters of brain electrical activity in these subjects: absolute slow-wave power, proportional power in all frequency bands, and ratios of high-frequency/low-frequency electrical activity (so-called "spectral ratios"). Spectral ratios were significantly more powerful in discriminating among groups than the other measures. Functional images using spectral ratios revealed that subjects with DAT have a characteristic left temporo-parietal defect which clearly distinguished them from subjects with MID and from control subjects. The severity of dementia was best assessed by examining absolute slow-wave power, which had the strongest linear correlation with mental status testing. Serial images from one subject with DAT over 3 years demonstrate both quantitative and qualitative shifts in slow-wave activity in the course of DAT. The study suggests that functional imaging may be more useful than either simple EEG or computer-analyzed EEG in assessing and diagnosing patients with suspected dementia.

Aged↗
PubMed1988

Alexithymia and the split brain: VI. Electroencephalographic correlates of alexithymia.

Electroencephalographic recordings of eight corpus callosotomy patients and eight precision-matched control subjects were obtained as subjects watched a film symbolically depicting death. A content-analytic measure of alexithymia was regressed on eight auto-spectral alpha-band intensity averages and on subsets of alpha-band coherence averages. Results were interpreted on the basis of three possible mechanisms of alexithymia: (1) Alexithymic subjects had more right-temporal alpha-band intensity, suggesting inadequate understanding of the film. (2) A possible lack of inner speech in alexithymics was suggested by their relative alpha abundance of the left frontal and left temporal channels but left parietal alpha desynchronization, and by their lower left frontotemporal but higher left parietofrontal and left parietotemporal coherences. (3) Alexithymic subjects had higher right frontal-left parietal and left frontal-left parietal coherences, suggesting possible interhemispheric inhibition of expression. Expressive subjects had higher right frontal-left temporal (and homologous interhemispheric frontal, parietal, and frontal) coherences, suggesting interhemispheric facilitation of verbal expression.

Adult↗
PubMed1987

Electroencephalographic spectra and coherence in the diagnosis of Alzheimer's-type and multi-infarct dementia. A pilot study.

The accurate diagnosis of dementia is difficult because there are no specific physiologic tests. Computer-analyzed electroencephalography (EEG) has shown promise as a tool for the differential diagnosis of dementia, but topographic methods for data collection and analysis have seldom been used. We used these methods to investigate EEG differences among three groups of elderly subjects: those with mild to moderate dementia of the Alzheimer's type (DAT), those with mild to moderate multi-infarct dementia (MID), and age- and sex-matched normal controls. The two groups of demented subjects were distinguished from the control group by a new criterion, the ratio of high-frequency to low-frequency electrical activity in the left temporal region, which was greatly diminished in demented subjects. Using this single variable, all control subjects and 15 of 18 demented subjects were correctly classified (sensitivity 83%, specificity 100%). The three misclassified subjects were among the least impaired subjects with DAT. Examination of coherence, or synchronization of the EEG signal, enabled us to distinguish subjects with DAT from those with MID. Using discriminant analysis of both EEG frequency and coherence, 92% (22/24) of subjects were accurately classified. These results justify further evaluation of topographic, computer-based EEG analysis as a test for the differential diagnosis of dementia.

Alzheimer Disease↗
PubMed1987

Alexithymia and the split brain. V. EEG alpha-band interhemispheric coherence analysis.

Electroencephalographic (EEG) recordings were obtained while 6 completely commissurotomized patients, 2 partially commissurotomized patients, and 8 precision-matched normal control subjects watched 4 times a film symbolically depicting death. Our hypothesis was that alexithymia--a diminished capability to verbally express moods, symbols, and feelings--would be greater for patients because loss of cerebral commissures reduces interhemispheric communication, separating right-hemisphere-dependent affective understanding and left-hemisphere-dependent verbalization. Path and covariance structure analyses confirmed that callosotomy decreased alpha-band EEG coherences (after adjustment for mean intrahemispheric coherence) between pairs of scalp electrode channels placed homologously over frontal, parietal, and temporal lobes of the brain. This result occurred both for an index of interhemispheric coherence and for a latent variable indicated by the 3 adjusted coherences. Reduced levels of interhemispheric coherence in turn increased alexithymia, for an overall index and for a latent variable indicated by lexical-level content-analytic measures of verbal responses to the filmic stimulus.

Adult↗
PubMed1986

Alexithymia: an experimental study of cerebral commissurotomy patients and normal control subjects.

This study assessed alexithymia in six patients with complete cerebral commissurotomy, two patients with partial commissurotomy, and eight matched control subjects. Comparisons were based on content-analytic measures of the subjects' spoken and written responses to a film that symbolically represented death and loss. The commissurotomized patients were more alexithymic on all four lexical-level variables, all six sentential-level variables, and all six global-level variables. Discriminant function analysis found a linear combination of four variables that effectively discriminated groups of fully commissurotomized, partially commissurotomized, and normal control subjects and correctly classified 15 of the 16 subjects.

Adult↗
PubMed1985

Alexithymia and the split brain. I. Lexical-level content analysis.

8 cerebral commissurotomy patients and 8 precision-matched normal control subjects were shown a 3-minute videotaped film symbolically depicting the deaths of a baby and of a boy. After each of 4 showings, all subjects were questioned about the symbolic and emotional contents of the film. Content analyses of the subjects' spoken and written responses were carried out on the lexical level. The commissurotomized patients, in comparison to their normal controls, used a lower percentage of affect-laden words, had a higher percentage of incomplete sentences, used a higher percentage of auxiliary verbs, and used a lower percentage of adjectives. Commissurotomy patients were significantly closer to the alexithymic pole of a factor derived from these 4 variables.

Adult↗
PubMed1985

Alexithymia and the split brain. II. Sentential-level content analysis.

The Hoppe-Bogen finding of alexithymia in 12 commissurotomy patients is examined, using 6 sentential-level items corresponding to 6 of the 8 key alexithymia items in the Beth Israel 'Psychosomatic Questionnaire'. 8 of the same commissurotomy patients and 8 precision-matched normal control subjects were shown a 3-min videotaped film about death. Content analyses of the subjects' spoken and written responses to this film were carried out, with directional support found for all items; however, only 2 of these differences in group means were statistically significant. The items were factor analyzed, and a 1-factor solution obtained. Factor score comparisons replicated the earlier study, as commissurotomy patients were found to be more alexithymic than normal controls.

Affective Symptoms↗
PubMed1985

Alexithymia and the split brain. III. Global-level content analysis of fantasy and symbolization.

8 commissurotomy patients and 8 precision-matched normal control subjects were shown a 3-min videotaped film about death. Content analysis of the subjects' spoken and written responses to this film was carried out on the global, interpretive level, for 2 fantasy and 4 symbolization variables. Commissurotomy patients were found to be significantly more alexithymic than normal controls for 3 of the symbolization variables, for factor-analytic measures of fantasy and symbolization, and for an over-all measure of alexithymia derived from these 2 factors and lexical-level and sentential-level measures of alexithymia.

Affective Symptoms↗
PubMed1985

Alexithymia and the split brain. IV. Gottschalk-Gleser content analysis, an overview.

A structural explanation of psychosomatic personality structure is proposed, that of a functional or physical deconnection of the two cerebral hemispheres. If the affective and symbolic energies of the right hemisphere cannot be externalized through verbal expressions of the left hemisphere (alexithymia), then they are apt to be directed inward, thereby contributing to psychosomatic personality structure. In an experiment, 8 cerebral commissurotomy patients and 8 precision-matched normal control subjects were shown a 3-minute videotaped film symbolically depicting the deaths of a baby and a boy. Gottschalk-Gleser content analysis of the subjects' verbal responses to the film was carried out for anxiety and hostility scales. A complex of shame and total anxiety in combination with hostility directed both inward and outward, was interpreted as an indicator of 'psychosomatic personality structure'. Cerebral commissurotomy patients showed a significantly higher level of psychosomatic personality structure than did normal controls.

Affective Symptoms↗
PubMed1984

Biological processing.

The organization of brain processes leading to language and movement show important parallels with one another and also express important aspects of biological organization in general. Four major differences between biological processes and their commonly proposed analogues, machine processes, are as follows. 1) Reduction is not simplification in biological analysis; rather the subsystems that result from separation of parts of a biological system are themselves complex, often potentially viable, systems. 2) Machine processes are typically generalized, or, if specialized, they are specialized by connecting general-type subsystems in special ways. But biological systems are typically specialized at many levels, both in subsystems and their connections. 3) The history of a biological system is often an intimate and inseparable part of its structure. Furthermore biological systems never develop alone or de novo. Not only do they develop in clusters of contemporaries, they also develop in the presence of an older generation and a "culture." 4) Not only do formal logics have some constraints that biological minds may not have (e.g., internal consistency and universality), formal logics require descriptions of qualitative phenomena in a language that is inadequate and (as a deeper issue) may always require parsing a meaningful whole into approximate parts (e.g., as in writing this abstract). Instances of contrasts between biological systems and machine-type systems are seen in language and movement phenomena, such as embodying a distinction between purposes and causes and having flexibly reorganizable subassemblies, multiple goals, and motor equivalence.

Brain↗
PubMed1984

Computerized topo-EEG spectral maps: difficulties and perspectives.

An electric potential measurement tells us only about the difference between two electrode locations. When prior experiments or present measurements prove that an electrode's location is inactive (especially in 'mono-polar' or scalp-to-reference technique), then EEG records and EEG maps can be interpreted regionally near each electrode location. Topographical mapping requires spatial interpolation which is one factor involved in spatial resolution. The interpolation algorithm has been studied by changing the power exponent n of the interelectrode distance d. When n is close to zero, interpolated values are all equal to the average of the four electric potential measurement Vs bounding the quadrilateral in which the interpolated points of the EEG map are located. When n is very high (n = 20 or higher), the values are essentially equal to the V which is at the minimum distance d. For n = 1, the map seems unlikely to represent the true scalp field. The choice between n = 2 and n = 3 is difficult, but n = 3 EEG mapping looks better (more plausible) and is our regular choice. The choice of recording/reporting method has also been studied. If the quantitative EEG map is linearly calculated from observations, the interpretation of record activity resulting from charge separation near the non-reference electrode attached to a particular channel is only possible when inactivity can be assured. This is completely different when the quantity mapped is not linearly calculated from observations (like power values or rms amplitudes in microvolts).(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Mapping↗
PubMed1981

Periodicity of sleep states is altered in infants at risk for the sudden infant death syndrome.

The normal succession of sleep and waking states through a night is disturbed in infants at risk for the sudden infant death syndrome. Compared with normal infants, siblings of the sudden infant death syndrome victims have longer intervals between active sleep epochs at particular times during the night in the newborn period and a decreased tendency to enter short waking periods at 2 and 3 months of age. The latter finding is interpreted as an increased tendency to remain asleep, or a relative failure to arouse from sleep in infants at risk.

Age Factors↗
PubMed1979

The maturation of vestibular nystagmus in infancy and childhood.

The displacements, durations, and velocities of the slow and fast components of both the primary and secondary nystagmus induced by constant angular acceleration were measured in 46 normal children 1 month to 11 years old. There were significant changes in nystagmus parameters in respect to maturation. The young infant had larger amplitude, higher velocity beats than the older child during both the primary and the secondary nystagmus. Parameters describing both the primary and the secondary nystagmus reached their peak values and terminated earlier in the infant than in the older child. Although the slow component velocity during secondary nystagmus was much slower than during the primary nystagmus at all ages, the secondary nystagmus/primary nystagmus ratio was significantly greater in early infancy. Thus, in infancy, as compared with later childhood, the vigor of the secondary nystagmus was disproportionately greater than the primary nystagmus. These results were discussed in relation to the maturation both of vestibular responsiveness and of vestibular adaptation.

Age Factors↗