Biomedical subjects

J Doyon

Publications and source records attributed to J Doyon.

3 recordsLinked to original sources

PubMed1992

A congenital anomaly of vitamin B12 metabolism: a study of three cases.

The clinical and morphologic findings of three patients with metabolic acidosis, methylmalonic aciduria, and homocystinuria are presented. The clinical evolution of the patients was similar and was characterized in the first weeks of life by failure to thrive, hypotonia, and lethargy associated with pancytopenia and hepatic dysfunction, eventually progressing to severe respiratory insufficiency and renal failure consistent with a hemolytic-uremic syndrome. The patients died at 40, 45, and 75 days of age. Biochemical analyses and complementation studies revealed a congenital anomaly of vitamin B12 metabolism (cobalamin C disease). Postmortem morphologic findings in all three cases were dominated by a thrombotic microangiopathy of the kidneys and lungs, diffuse hepatic steatosis, and megaloblastic changes in the bone marrow. A severe gastritis with striking cystic dysplastic mucosal changes and total absence of parietal and chief cells was a consistent finding in all three cases, the rest of the gastrointestinal tract appearing essentially normal. Cobalamin C disease is an intracellular defect of cobalamin metabolism with possible recessive inheritance that can result in multiorgan failure early in life, with a thrombotic microangiopathy and unusual changes in the gastric mucosa.

Humans↗

PubMed1991

Right temporal-lobe contribution to global visual processing.

The performance of 92 patients with unilateral temporal- or frontal-lobe excisions and 35 normal control subjects was tested under two experimental conditions (global, local) of a Stroop-type reaction-time task, employing either hierarchically structured letters or abstract designs as stimuli. In the local condition, subjects were asked to focus their attention on the small forms and to ignore the large form, whereas they were instructed to do the reverse in the global condition. The results showed that, in the local condition, the patients with right temporal-lobe lesions were less affected than the other groups by interference from the global aspect of the stimulus. This reduced sensitivity to the overall configuration of the stimulus was unrelated to the extent of hippocampal removal or to the presence of visual-field defects. These findings support the hypothesis that the human right temporal neocortex contributes to the global processing of visual information.

Adolescent↗

PubMed1991

Role of the right temporal lobe in visual-cue learning during repeated pattern discriminations.

The ability to acquire visual cues for discriminating between two targets against a background of visually similar items was examined in 64 patients with unilateral temporal- or frontal-lobe excisions and 20 normal control subjects. The subjects were tested on two versions (letters and abstract designs) of a visual cue-learning task that was an adaptation and extension of RABBITT's (Am. J. Psychol. 80, 1-13, 1967) visual-search paradigm. For both versions, the material consisted of two packs of cards, each containing a different set of background letters or designs. Subjects were required to sort the cards into two piles according to which of two targets was present on the card. On the letter task, all groups took longer to sort when the background letters were changed after three learning trials. With abstract designs, patients with right temporal-lobe lesions failed to show this interference effect after three learning trials, but they, like other groups, did so after six. This slowness in learning was related neither to the extent of hippocampal removal nor to visual-field defects. It is argued that the right temporal neocortex plays a role in incremental learning of visual cues during repeated pattern discriminations.

Adolescent↗