Biomedical subjects

S Guich

Publications and source records attributed to S Guich.

9 recordsLinked to original sources

PubMed2001

Eeg alpha rhythm and glucose metabolic rate in the thalamus in schizophrenia.

Positron emission tomography with uptake of [(18)F]fluorodeoxyglucose (FDG) and quantitative EEG were simultaneously performed in 18 medication-free patients with schizophrenia and in 13 normal volunteers. Subjects performed the Continuous Performance Task (CPT) during FDG uptake. Correlations were calculated between alpha power during the CPT and glucose metabolic rate (GMR) in thalamic regions and between alpha power during the CPT and GMR in occipital cortices. Regression analyses were used to describe the prediction of GMR in the occipital cortices and in the thalamic regions of occipital alpha power. In normal controls, we found (1) significant negative correlations between absolute alpha power and GMR in the left occipital cortex, (2) significant positive correlations between normalized alpha power and GMR in the right and left lateral thalamus and (3) combined effects of GMR in the thalamic regions and the occipital cortices on alpha power, which accounted for 98% of the variance of alpha power. In patients with schizophrenia, we found no significant correlations between alpha power and GMR in the occipital cortices or between alpha power and GMR in the thalamic regions. Correlation coefficients between absolute alpha power and GMR in the left occipital cortex and between normalized alpha power and GMR in the left lateral thalamus were significantly different in normal subjects compared to schizophrenic patients. The present findings provide evidence for involvement of the thalamus in the generation of alpha rhythm in humans. Furthermore, the present results suggest differences in thalamocortical circuits between normal controls and schizophrenic subjects.

Adult↗

PubMed2000

Ketosis with enhanced GABAergic tone promotes physiological changes in transcendental meditation.

Transcendental meditation (TM) is a stylized form of physical and mental relaxation which is associated with changes in the secretion and release of several pituitary hormones. The hormonal changes induced by TM mimic the effects of the inhibitory neurotransmitter gamma aminobutyric acid (GABA). It is hypothesized that TM produces changes in pituitary hormone secretion by enhancing hypothalamic GABAergic tone as a result of TM associated ketosis. Ketosis enhances the entry of glutamate, the amino acid substrate of GABA into synaptosomes, making more glutamate available for conversion to GABA through the glutamate decarboxylase pathway.

Brain↗

PubMed1998

A method of basal forebrain anatomical standardization for functional image analysis.

Functional as well as structural assessment of the basal forebrain has mostly focused on the dorsal caudate and putamen in axial slices where they are easily outlined or their centers located with stereotaxic methods. The more ventral extent of the basal forebrain, where the irregular form and indistinct boundaries of the nucleus accumbens and substantia innominata are difficult to trace and where the brain's ventral surface may contribute partial volume artifacts to measurement, has been less studied. We present a method based on coronal sections, landmarks placed on clearly visible anchor points, and the computational technique of thin-plate spline warping which allows the alignment of groups of individuals to common coordinates for pixel-by-pixel statistical mapping. The reliability of the landmarks across independent raters yields a median absolute difference of 1.3-1.6 mm. The validity of the method is confirmed by variance maps which reveal significant decreases in variance over spindle and bounding box alignment.

Adult↗

PubMed1995

EEG delta, positron emission tomography, and memory deficit in Alzheimer's disease.

Quantitative scalp EEG from 32 channels and the cerebral glucose metabolic rate from the 32 underlying cortical positions as assessed by positron emission tomography (PET) with 18F-2-deoxyglucose (FDG) were obtained on 36 patients with mild to moderate senile dementia of the Alzheimer type and 17 age- and sex-matched normal control subjects. Subjects performed a verbal memory task during uptake of FDG. There were significant correlations between both delta amplitude and metabolic rate and memory performance during FDG uptake. Patients with Alzheimer's disease had significantly greater left temporal delta amplitude and lower glucose metabolic rates. Both EEG delta in microvolts and metabolic rate had similar diagnostic sensitivity, but PET had fewer false positives among normals. The left amygdala had the highest sensitivity and percent correct diagnosis of any brain area. Temporal lobe EEG delta activity showed higher correlations with hippocampal metabolic rate than metabolic rate directly under the electrode.

Aged↗

PubMed1994

Investigation of computer lung model-predicted DLCO during single-breath maneuvers.

A computer model based on the theoretical gas absorption equations of Martonen and Wilson (J. Math. Biol. 14: 203-220, 1982) was developed to predict changes in single-breath diffusing capacity of the lung for carbon monoxide (DLCO) with alterations in anatomic dead space, alveolar volume, and inspiratory time. The computer model predictions were compared with results obtained from normal subjects performing DLCO maneuvers under correspondingly altered conditions to assess the validity of the Martonen-Wilson equations. In normal subjects, a theoretical "ideal" single-breath DLCO was derived from measured DLCO and adjusted to instantaneous inspiratory and expiratory times with this three-phase computer model. Clinical single-breath DLCO measurements with increased external dead space and inspiratory and expiratory times in normal subjects correlated well with our mathematical model predictions (all r > 0.80, P < 0.001) but did not correlate closely with the predicted effects of alveolar volume on DLCO. This study demonstrates that uniform gas absorption equations of Martonen and Wilson closely predict changes in observed DLCO with systematic variation of inspiratory and expiratory time in normal subjects at full lung volume and appear to be a reasonable estimation of normal physiological events during single-breath carbon monoxide absorption.

Adult↗

PubMed1990

Glucose metabolic rate in normals and schizophrenics during the Continuous Performance Test assessed by positron emission tomography.

Local cerebral uptake of glucose labelled with fluorine-18 was measured by positron emission tomography in 13 patients with schizophrenia and 37 right-handed volunteers. Patients received no medication for a minimum of 31 days and a mean of 30 weeks. The subjects were administered the labelled deoxyglucose just after the beginning of a 32-minute sequence of blurred numbers as visual stimuli for the Continuous Performance Test. In normal controls, task performance was associated with increases in glucose metabolic rate in the right frontal and right temporoparietal regions; occipital rates were unchanged. Patients with schizophrenia showed both absolutely and relatively reduced metabolic rates in the frontal cortex and in the temporoparietal regions compared with normal controls.

Adult↗

PubMed1987

Plasma thyroid hormones, thyroid stimulating hormone, and insulin during acute hypometabolic states in man.

Acute behavioral rest states in man are associated with marked hormonal and metabolic changes. In order to complete a hormonal profile of these states and to identify possible metabolic regulators, we measured thyroid hormones (T3 and T4), thyroid stimulating hormone (TSH), and insulin during the stylized mental practice of "transcendental mediation" (TM) and during ordinary unstylized eyes closed rest. Except for TSH, which declined acutely, hormone levels were normal and stable throughout the experiment. The stability of T3 and T4, and insulin make it unlikely that these hormones regulate the acute metabolic changes associated with these behavioral states. Decreased TSH, along with stable thyroid hormone levels, may suggest change of the set point for feedback control of TSH secretion during TM and is consistent with primarily neural modulation of TSH secretion by this behavior.

Adult↗

PubMed1987

Marked reduction of forearm carbon dioxide production during states of decreased metabolism.

We studied oxygen consumption, carbon dioxide production and acid/base changes in 62 subjects during two hypometabolic states (35 during transcendental mediation and 27 during unstylized rest). The results indicate that, during these hypometabolic states, arterial-venous CO2 content difference declines, and that during transcendental meditation, arterial-venous CO2 content difference briefly disappears. This change is due to both an increase of arterial CO2 content and a decrease of venous CO2 content. Similar, but opposite and smaller, changes occurred in arterial and venous O2 content. Respiratory quotient was low at all times and decreased during the hypometabolic states. These results are consistent with the hypothesis that, during hypometabolic states significant ketogenesis is induced, and provision of energy from the normally predominant process of beta-oxidation of fat becomes sufficient to provide energy for greatly reduced activity without entry of two carbon fragments into the tricarboxylic acid cycle; under these conditions, biochemical feedback mechanisms inhibit the tricarboxylic acid cycle. The net result of these metabolic changes could explain the major observations: absent carbon dioxide production while oxygen consumption declines but continues and the venous effluent contains more acid.

Adult↗

PubMed1985

Modulation of red cell metabolism by states of decreased activation: comparison between states.

Marked decline of red cell metabolism has been described during the acute state of decreased activation associated with the stylized mental technique of transcendental meditation (TM) in long-term meditators (5-10 years regular elicitation, TM instructors). It is not known whether unstylized rest is accompanied by a similar effect and it is not known what effector(s) may contribute to red cell metabolic changes in these states. In the present study ordinary, unstylized rest was found to be accompanied by small increase of red cell glycolytic rate. Apparently, either repeated elicitation of TM behavior or some special feature of this practice become associated with new mechanisms of metabolic control than those previously in operation. Although the data of this study do not permit isolation of the precise psychological determinants of this effect, the range of possible physiological effectors can be delimited. Blood pH, PCO2, PO2, and phosphate can be eliminated as significant for red cell metabolic control during both TM and rest, and based upon related studies, several known hormones such as insulin, T3, T4, arginine vasopressin, oxytocin, prolactin and growth hormone can also be eliminated as responsible effector(s).

Acid-Base Equilibrium↗