Biomedical subjects

O Vitouch

Publications and source records attributed to O Vitouch.

8 recordsLinked to original sources

PubMed2001

Restriction of task processing time affects cortical activity during processing of a cognitive task: an event-related slow cortical potential study.

As is known from psychometrics, restriction of task processing time by the instruction to respond as quickly and accurately as possible leads to task-unspecific cognitive processing. Since this task processing mode is used in most functional neuroimaging studies of human cognition, this may evoke cortical activity that is functionally not essential for the particular task under investigation. Using topographic recordings of event-related slow cortical potentials, two experiments have been performed to investigate whether cortical activity during processing of a visuo-spatial imagery task is substantially influenced by the time provided to process the task. Furthermore, it was investigated whether this effect is additionally modulated by a subject's task-specific ability. The instruction to respond as quickly and accurately as possible led to increased negative slow cortical potential amplitudes over parietal and frontal regions and significantly interacted with task-specific ability. While cortical activity recorded over parietal and frontal regions was different between subjects with low and high spatial ability when processing time was unrestricted, no such differences were found between ability groups when subjects were instructed to answer both quickly and accurately. These results suggest that restricting processing time has considerable effects on the amount and the pattern of brain activity during cognitive processing and should be taken into account more explicitly in the experimental design and interpretation of neuroimaging studies of cognition.

Adolescent↗

PubMed2000

[123I]-beta-CIT SPECT imaging shows reduced brain serotonin transporter availability in drug-free depressed patients with seasonal affective disorder.

BACKGROUND: Numerous findings indicate alterations in brain serotonin systems in seasonal affective disorder (SAD). [(123)I]-2-beta-carbomethoxy-3-beta-(4-iodophenyl)-tropane ([(123)I]-beta-CIT) labels serotonin transporters (5-HTTs) in the midbrain. We performed a [(123)I]-beta-CIT single photon emission computer tomography (SPECT) study under the hypothesis of lower [(123)I]-beta-CIT binding reflecting reduced central 5-HTT availability in depressed SAD patients. METHODS: Depressed SAD patients and healthy control subjects were investigated using [(123)I]-beta-CIT SPECT 4 hours and again 24 hours after tracer injection. Subjects had either never used psychotropic medication or had been drug-free for at least 6 months prior to the investigation. Specific-to-nondisplaceable partition coefficient (V(3)") was calculated for the thalamus-hypothalamus and the midbrain-pons; the cerebellum served as a reference region. RESULTS: Patients showed a reduction in V(3)" in thalamus-hypothalamus (2.41+/-0.3 vs. 2.84+/-0.4; p = .026) 24 hours post tracer injection (p.i.). No difference between patients and control subjects was found in midbrain-pons (1.31+/-0.2 vs. 1.42+/-0.2; p = .39). No differences were detected in the SPECT acquisitions 4 hours p.i. CONCLUSIONS: Depressed SAD patients showed lower specific-to-nondisplaceable [(123)I]-beta-CIT binding in the region of interest (ROI) thalamus-hypothalamus. The small size of the midbrain-pons ROI may have contributed to the failure to show a difference in this ROI as well. Similar to reduced midbrain 5-HTT availability in nonseasonal depression, depression in SAD seems to be associated with reduced 5-HTT availability to the thalamus-hypothalamus.

Adult↗

PubMed1999

Differences in the ability to process a visuo-spatial task are reflected in event-related slow cortical potentials of human subjects.

Recent positron emission tomography (PET) and electroencephalographic (EEG) studies suggest that higher ability in a cognitive task is associated with a more efficient neuronal processing of this task. However, the validity and generalizability of these studies is limited for several reasons. We investigated 20 male and 18 female human subjects with good vs. poor spatial ability performing a visuo-spatial task (cube test). Processing-related slow event-related potentials were recorded via 22 electrodes, evenly distributed over the scalp. Significant differences between good and poor performers were found in both sexes: poor subjects showed higher activity in the parietal region, and their topography was more extended into fronto-central regions. Since the amount and topography of brain activity may vary considerably depending on subjects' ability, we conclude that careful (experimental) control of task-specific ability of subjects is mandatory for cognitive neuroscience studies.

Adult↗

PubMed1998

Effects of tryptophan depletion in drug-free depressed patients who responded to total sleep deprivation.

BACKGROUND: There is some evidence that sleep deprivation (SD) might exert its antidepressant properties by involving serotonergic mechanisms. We investigated the effects of short-term tryptophan depletion (TD) on depressed patients who responded to a single night of total SD. METHODS: Drug-free depressed inpatients (n = 30) were randomly assigned to either TD or sham depletion. Tryptophan depletion was induced by a 24-hour low-tryptophan diet (day 1) followed the next morning by ingestion of a tryptophan-free amino acid mixture (day 2). During sham depletion, the diet and the amino acid beverage were supplemented with tryptophan. Sleep deprivation was performed from day 1 until day 2. Only SD responders received the amino acid beverage the morning after SD. Behavioral ratings and total and free plasma tryptophan levels were obtained before and after the test sessions. RESULTS: Twenty-two of 30 patients showed a favorable outcome after SD. As predicted, TD significantly lowered total and free plasma tryptophan levels, whereas both levels increased during sham depletion. No acute effects on mood were observed during the day after SD in either treatment group. Unexpectedly, TD, but not control testing, prevented the depressive relapse after the recovery night in most of the patients. CONCLUSIONS: Tryptophan depletion did not reverse the antidepressant effects of SD, but it prevented the relapse beyond a night of recovery sleep. These findings suggest that SD does not act via a single monoamine-related mechanism, but they allow the assumption that TD may induce neurochemical alterations that transiently improve depression.

Adult↗

PubMed1998

Effects of tryptophan depletion in fully remitted patients with seasonal affective disorder during summer.

BACKGROUND: Deficiencies in brain serotonin function are believed to play an important role in the pathophysiology of seasonal affective disorder/winter type (SAD). However, no direct evidence has been reported so far that lowered brain serotonin activity causes the symptoms of SAD. METHODS: We studied 11 SAD patients who had suffered recurrent winter depressive episodes of SAD and were fully recovered and off treatment during the summer. In a randomized, balanced, double-blind crossover design patients received two amino acid beverages, one containing tryptophan and the other containing no tryptophan but otherwise identical. Behavioural ratings and plasma total and free tryptophan concentrations were assessed at baseline before administration of the amino acid beverages and at several time points afterwards. RESULTS: The tryptophan-free amino acid beverage induced significant decreases of plasma total and free tryptophan levels and both levels increased during sham depletion (condition x time interaction: P < 0.001). Tryptophan depletion, but not sham depletion caused a transient return of depressive symptoms (condition x time interaction: P < 0.001). CONCLUSIONS: The present study demonstrates that SAD patients in remission during the summer are vulnerable to a return of depression when depleted of tryptophan. This finding supports the importance of serotonergic mechanisms in the pathophysiology of SAD.

Adult↗

PubMed1997

Cortical activity of good and poor spatial test performers during spatial and verbal processing studied with Slow Potential Topography.

Whether essential processing of spatial information is lateralized asymmetrically in the human cortex is still a matter of debate. In this study, items of an Item Response Theory calibrated test for spatial ability were used to ensure stimulus homogeneity and validity. Subjects were preselected as extreme groups of good and poor spatializers. Mapping of true DC-recorded slow potential shifts (SPSs) resulted in distinctly discriminable topographies with spatial and verbal-analytic material as well as with spatial performance groups within the spatial block. Left fronto-central negativity maxima in the verbal condition clearly contrasted with occipito-parietal peak activity in the spatial condition. Poor spatializers showed higher amplitudes as well as a tendency to asymmetric activity in right parietal (parieto-temporal) areas, whereas in good spatializers the activity was localized symmetrically in occipital and occipito-parietal regions. The findings emphasize the importance of the right posterior cortex for spatial processing (negativity maxima at occipital and right parietal sites) and suggest a task-specific lower cortical efficiency or, seen from a processing perspective, a higher Investment of Cortical Effort (ICE) on the part of poor spatializers.

Adult↗

PubMed1997

Rapid tryptophan depletion in drug-free depressed patients with seasonal affective disorder.

OBJECTIVE: Brain serotonin systems might be involved in the pathophysiology of seasonal affective disorder. The authors tested whether tryptophan depletion alters the mood of depressed patients with seasonal affective disorder. METHOD: Eleven drug-free depressed patients with seasonal affective disorder underwent tryptophan depletion in a placebo-controlled, double-blind crossover study. Tryptophan depletion was induced by a 24-hour low-tryptophan diet and by ingestion of a tryptophan-free amino acid beverage. During control testing the diet and the beverage were supplemented with tryptophan. Behavioral ratings and plasma total and free tryptophan levels were obtained before the diet started and several times after administration of the beverages. RESULTS: The diet and the tryptophan-free amino acid drink reduced plasma total and free tryptophan levels by 79.0% and 87.5%, respectively. Both levels increased during control testing. No significant behavioral changes were induced by tryptophan depletion or control testing. CONCLUSIONS: The failure of tryptophan depletion to exacerbate the depressive syndrome suggests that dysfunctional serotonergic activity does not play a primary, direct role in the pathogenesis of winter depression.

Acute Disease↗

PubMed1994

Empirical contribution to the question of sex-dependent inheritance of spatial ability.

The X-linked recessive gene hypothesis, a theory to predict the mode of genetic inheritance of spatial ability, was tested using a new Rasch-calibrated space test, the Three-dimensional Cube Test (Gittler, 1990). This allowed solving the homogeneity problem (insufficient unidimensionality of test material) by which earlier research in this field was affected. The empirical correlations from our sample of 134 families were compared with the theoretically predicted values. Present data do no corroborate the model; however, the problems of its general falsification are discussed. The fact that differences in performance in favour of males exist in the parental generation but not in the filial generation accentuates the importance of environmental factors.

Adolescent↗