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Biomedical subjects

D M Baxter

Publications and source records attributed to D M Baxter.

10 recordsLinked to original sources
PubMed1989

The origins of utilization behaviour.

Utilization behaviour has previously been described clinically by Lhermitte (1983). An experimental investigation is reported of utilization behaviour in a patient with a localized inferior medial bifrontal lesion. The patient picked up and used irrelevant objects not only when place directly in front of him--the procedure developed by Lhermitte--but also when he had been instructed to carry out other tasks and his attention had not been directed to the objects. The behaviour occurred most frequently in the brief intervals between tasks, and more often when auditory-verbal rather than visuomotor tasks were being performed. The results are interpreted within an information-processing model of frontal lobe function. A differentiation is made between two forms of utilization behaviour--an 'incidental' form, as exhibited by the patient, and an 'induced' form where it occurs only when Lhermitte's procedure is adopted.

Behavior↗
PubMed1987

Transcoding sound to spelling: single or multiple sound unit correspondence?

We report a detailed analysis of the written spelling of an aphasic patient, KT, in whom no viable comprehension could be demonstrated despite accurate repetition and fluent speech (transcortical sensory aphasia). His spelling conformed in all respects with the definition of an orthographic/lexical dysgraphic such that his writing of regular, orthographically unambiguous words and nonsense syllables was entirely satisfactory. Lexical variables such as word class or word frequency had no effect on his performance. Irregular or ambiguously spelled words were selectively impaired. An independent measure of orthographical ambiguity was defined in relation to the frequency with which a phoneme was represented by a particular grapheme and the number of alternative graphemes for the same sound. For the majority of sounds studied, KT was able to demonstrate the use of all the most frequent alternative transcoding units for each sound but he did not use them in the same frequency with which they occurred in written English. Thus his performance bore little or no relationship to predictions based on single phoneme/grapheme counts and there was unequivocal evidence for his ability to use multiple sound-unit correspondences.

Aphasia, Wernicke↗
PubMed1986

Ideational agraphia: a single case study.

A case study investigates the writing, spelling and praxic skills of one patient who was found to have a selective impairment in his ability to write letters and words in the absence of difficulty in copying these same letters and words. He appeared to have difficulty accessing the correct motor programmes or sequences for writing which we term "ideational agraphia" analagous to the syndrome of ideational apraxia. These findings are related to Margolin's information-processing model of writing.

Aged↗
PubMed1985

Category specific phonological dysgraphia.

The present case study describes a phonological dysgraphic with intact comprehension who had difficulties spelling certain classes of words. Nouns were easier than adjectives which in turn were easier than verbs and function words. A difference between verbs and nouns remained even when level of concreteness was controlled. The findings are discussed in relation to current models of the organization of spelling in relation to other cognitive skills.

Aged↗
PubMed1984

Physical properties and lipid composition of brain membranes from ethanol tolerant-dependent mice.

DBA/2 mice were made tolerant to and dependent on ethanol by administration of an ethanol-containing liquid diet for 7 days. Fluorescent probe molecules were used to estimate the fluidity and ethanol sensitivity of brain synaptic membranes from these mice. The fluorescence polarization of cis- parinarate , trans- parinarate , and 1,6-diphenyl-1,3,5-hexatriene (probes of the membrane core) and 1-(4- trimethylammoniumphenyl )-6-phenyl-1,3,5-hexatriene (a probe of the membrane surface) was higher in membranes from ethanol tolerant-dependent mice than in membranes from control mice. The decrease in fluorescence polarization produced by in vitro exposure to ethanol was attenuated in membranes from ethanol tolerant-dependent mice when 1,6-diphenyl-1,3,5-hexatriene was used as the probe, but not when 1-(4- trimethylammoniumphenyl )-6-phenyl-1,3,5-hexatriene was used. These results indicate that chronic ingestion of ethanol decreased the fluidity and the ethanol sensitivity of the synaptic membranes. In contrast to the alterations observed with intact membranes, liposomes of lipids extracted from synaptic membranes of control and ethanol tolerant-dependent mice did not differ in their physical properties. Analysis of membrane lipids demonstrated that chronic ethanol treatment selectively decreased the unsaturated acyl groups of phosphatidylserine without altering the acyl composition of other phospholipids or sphingolipids. The amount of each phospholipid was not changed, but membrane cholesterol was decreased by chronic ethanol ingestion. Use of 2-dimensional thin-layer chromatography allowed the quantitation of 10 different gangliosides. The concentrations of these lipids were unchanged in synaptic membranes from ethanol tolerant-dependent mice. Thus, the changes in membrane physical properties produced by chronic ingestion of ethanol may be due, at least in part, to altered acyl composition of phosphatidylserine. The differences observed between intact membranes and extracted lipids suggest, however, that chronic ethanol treatment also produced changes in the lipid arrangement or lipid-protein interactions of the intact membranes.

Alcoholic Intoxication↗
PubMed1984

Gangliosides enhance the membrane actions of ethanol and pentobarbital.

The physical properties of vesicles containing phosphatidylcholine (PC) and gangliosides were evaluated by the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene, trans- parinarate (probes of the lower acyl regions), and 1-(4- trimethylammoniumphenyl )-6-phenyl-1,3,5-hexatriene (a probe of the glycerol backbone and upper acyl regions). Exposure of PC vesicles to ethanol produced a decrease in polarization of fluorescence of these probes, but large concentrations (200-600 mM) were required. Incorporation of 10 mole% rat brain synaptic gangliosides into the PC vesicles enhanced the effect of ethanol by several-fold. Synaptic gangliosides also enhanced the effect of ethanol on vesicles containing cholesterol in addition to PC. Comparison of mono-, di-, tri-, and asialogangliosides , sphingosine, and sphingomyelin indicated the importance of the oligosaccharide moiety, but not the sialic acid residues, in the enhancement of ethanol action by gangliosides. Variation of assay temperature and the acyl composition of the PC demonstrated that gangliosides increased the effects of ethanol only if the lipids were near the phase transition temperature. Gangliosides also produced a marked enhancement of the effect of pentobarbital on fluorescence polarization of probes in PC vesicles. The membrane partioning of pentobarbital was increased by gangliosides, but it was not clear that this increase in drug concentration in the membrane was sufficient to account for the large change in fluorescence polarization. These results suggest that ganglioside content may be an important determinant of the effects of alcohols and barbiturates on biomembranes. In particular, the high drug sensitivity of neuronal membranes may be related to the enrichment of gangliosides in these membranes.

Animals↗
PubMed1983

Neglect dysgraphia.

A phonological dysgraphic syndrome is documented in a left handed man with a right-hemisphere lesion. His spelling was significantly affected by word length but neither word frequency nor the orthographical irregularity or word class proved to be relevant variables. Words were spelled equally efficiently forwards as backwards. A clear gradient of letter errors was shown to exist with letters on the left being mis-spelled more often than letters on the right of a word, irrespective of word length. These findings are discussed in terms of current models of spelling and their relevance to theories of unilateral neglect.

Attention↗