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Biomedical subjects

L Marshall

Publications and source records attributed to L Marshall.

116 records · Page 7Linked to original sources
PubMedDate not supplied

Adrenocorticotropin widens the focus of attention in humans. A nonliner electroencephalographic analysis.

OBJECTIVE: This study examined the effects of ACTH 4-10, a fragment of adrenocorticotropin (ACTH) with known central nervous system (CNS) activity, on the dimensional complexity of the ongoing electroencephalographic (EEG) activity. Stressful stimuli cause ACTH to be released from the pituitary, and as a neuropeptide ACTH may concurrently exert adaptive influences on the brain's processing of these stimuli. Previous studies have indicated an impairing influence of ACTH on selective attention. METHODS: Dimensional complexity of the EEG, which indexes the brain's way of stimulus processing, was evaluated while subjects performed tasks with different attention demands. Sixteen healthy men (23 to 33 years) were tested once after placebo and another time after administration of ACTH 4-10 (1.25 mg intravenously (i.v.), 30 minutes before testing). The EEG was recorded while subjects were presented with a dichotic listening task (consisting of the concurrent presentation of tone pips to the left and right ear). Subjects either a) listened to pips in both ears (divided attention), or b) listened selectively to pips in one ear (selective attention), or c) ignored all pips. RESULTS: Dimensional complexity of the EEG was higher during divided than selective attention. ACTH significantly increased the EEG complexity during selective attention, in particular over the midfrontal cortex (Fz, Cz). CONCLUSIONS: The effects support the view of a de-focusing action of ACTH during selective attention that could serve to improve the organism's adaptation to stress stimuli.

Adrenocorticotropic Hormone↗
PubMedDate not supplied

The relationship between loudness and reaction time in normal hearing listeners.

Equal-loudness contours were constructed from magnitude estimation judgements in 10 normal-hearing listeners. Equal-latency contours were constructed from auditory reaction time measurements in these same listeners. the stimuli were pure tones ranging from 250-4000 Hz in octave intervals. Equal-loudness contours were in good agreement with those obtained by previous researchers, and the equal-latency curves were in good agreement with the equal-loudness contours.

Adult↗
PubMedDate not supplied

Changes in number and type of errors on repetition of acoustically distorted sentences as a function of age in normal children.

The intelligibility of recorded sentences, distorted by binaural switching, interruption, and low-pass filtering, was investigated in 53 children ranging in age from five to eleven and in adults. All had normal hearing. The sentence vocabulary was pretested for comprehension, articulation errors were evaluated in a way so as not to influence test results, and length and structure of the sentences were controlled. The results indicated that although the performance of children increased with age, the 11-year-old group had not attained adult performance. Error analyses showed that most errors for all age groups were acoustically unrelated to the distorted message, although adults made more acoustically related errors than did children. When children made errors in sentences, other errors (e.g., substitutions) were made to preserve the syntax or semantic integrity of the message.

Adult↗
PubMedDate not supplied

Intravenous infusion pharmacokinetics of desferrioxamine in thalassaemic patients.

Pharmacokinetic investigation of desferrioxamine (DFO) was conducted in 11 thalassaemic patients following continuous intravenous infusion of 50 mg/kg/24 hr over 48 hr. Serial venous blood samples were obtained at regular time intervals during and on stopping DFO infusion. Plasma samples were processed with the addition of radioactive iron (59Fe) to stabilize free ligand forms of DFO and its metabolites. This resulted in the formation of both radioactive and nonradioactive forms of ferrioxamine and its metabolites. Following solid-phase extraction, plasma samples were analyzed by a reversed-phase HPLC and monitored by simultaneous UV-visible radioactive detection. DFO was found to be eliminated from the blood in a biexponential manner with a systemic clearance of 0.50 +/- 0.24 liters/hr/kg. The terminal half-life was 3.05 +/- 1.30 hr, and the volume of distribution was 1.88 +/- 1.0 liters/kg at the terminal phase and 1.35 +/- 0.65 liters/kg at steady state. The AUC of DFO was 354 +/- 131 mumol/liter.hr. The major metabolite of DFO, DFO-metabolite B, has an initial half-life of 1.33 +/- 0.61 hr and is usually present at lower concentrations relative to the parent compound with an AUC of 191 +/- 106 mumol/liter.hr.

Chromatography, High Pressure Liquid↗