Showing papers on "Resting state fMRI published in 1991"

Positron emission tomography in Alzheimer's disease in relation to disease pathogenesis: a critical review.

Abstract: PET studies of brain metabolism and blood flow in Alzheimer's disease (AD) patients lead to the following conclusions: (a) Reductions in "resting state" regional brain metabolism are roughly proportional to dementia severity. (b) These reductions are greater in association than in primary sensory and motor neocortical regions, and correlate with the distribution of neuropathology and cell loss postmortem. (c) Demented but not nondemented Down syndrome adults also have worse metabolic reductions in the association than primary neocortices, suggesting an equivalent pathological process in demented Down syndrome and AD patients. (d) Brain metabolic patterns in AD patients are heterogeneous, belonging to at least four distinct metabolic groups that correspond to different patterns of cognitive and behavioral abnormalities; the metabolic patterns have not been shown to be related to disease etiology. (e) Abnormal right-left metabolic asymmetries in mildly demented AD patients can retain their initial directions for as long as 48 months; these asymmetries precede and predict the cognitive "discrepancies" that later appear, such that moderately demented patients with disproportionate visuospatial compared with language deficits, or disproportionate visual recall compared with verbal recall, have a greater metabolic reduction in the right than left hemisphere, and vice versa. (f) Parietal association/frontal association metabolic ratios also retain their direction over time; in moderately demented patients, relative hypometabolism in the prefrontal association cortex is related to deficits in verbal fluency and attention to simple sets, whereas relative hypometabolism in the parietal association cortex correlates with failure in arithmetic, verbal comprehension, drawing, and immediate memory for visuospatial location. (g) Although metabolically spared compared with the association cortices, the primary sensory cortices, basal ganglia, thalamus, and cerebellar hemispheres show metabolic declines in AD using high-resolution PET scanners, possibly due to their connections with more pathologically affected regions. (h) Early metabolic deficits in AD are hypothesized to arise from synaptic failure in association cortical areas; such failure in the occipitotemporal visual cortex can be reversed in mildly to moderately demented AD patients who are capable of performing a face-matching task.

Cerebrocerebellar relationship during behavioral activation: a PET study.

Abstract: The effect of behavioral activation on cerebral and cerebellar glucose metabolism was studied in normal subjects when performing either a verbal memory task or a tactile somatosensory task. Each subject was also studied in a resting state control condition, either 1 h earlier or later than the activation task. Compared to the resting state, both tasks produced asymmetrical metabolic activation, which was opposite in direction within the cerebral and cerebellar hemispheres. In both tasks, the difference of activation of CMRglc in the right and left hemispheres in the cerebellum was negatively correlated with that in the sensory-motor region. This apparently coupled metabolic activation of one cerebellum and areas within the opposite cerebral hemisphere represents the inverse of the crossed cerebellar diaschisis phenomenon commonly observed when a vascular lesion affects one cerebral hemisphere and hypometabolism occurs in the opposite cerebellum. Because these correlations were selective and concordant with known anatomical connections, and were found in two different tasks, they suggest strong functional connections between these specific brain regions.

Stability of resting deoxyglucose metabolic values in PET studies of schizophrenia

Abstract: Positron emission tomography (PET) and the deoxyglucose method were used to determine the test-retest stability of regional cerebral glucose metabolism in 8 male schizophrenic patients and 11 normal control subjects, scanned twice under baseline (resting) conditions. Normal and schizophrenic subjects showed comparable stability of regional metabolism. When the regional values were scaled to compensate for the effects of changes in whole brain metabolism, the resulting mean regional changes were reduced to about 1-2% in both groups. This study demonstrates that the baseline resting state is an appropriate reference state for schizophrenic subjects in deoxyglucose PET experiments.

Complex sensory cross integration deficits in a case of corpus callosum agenesis with bilateral language representation: positron-emission-tomography and neuropsychological findings.

Abstract: A 45-year-old right-handed patient with total callosal agenesis and absence of the anterior commissure was examined neuropsychologically and with magnetic resonance and positron emission tomography (PET with 18FDG) of the brain PET results showed, in the resting state, a bilateral metabolic reduction in the hippocampal formation and a left hemispheric reduction in the amygdala, thalamus and in the occipital and temporoparietal junction areas of the cerebral cortex Under speech activation hypermetabolic glucose activity was observed bilaterally in the region of the Wernicke area and within the left Broca area Neuropsychologically, on the whole the patient behaved normally, the exceptions being an inability to associate olfactory stimuli with words, a clear left ear advantage in dichotic listening, and a similar high performance in recognizing verbal stimuli presented tachistoscopically to either hemisphere From comparing the patient's behavior with that of other acallosals it appears that highly individual variants of cerebral organization and/or reorganization result from the lack of the brain's main commissural system and that the processing of sensory information deviates considerably especially in cases in whom the two main telencephalic commissures--corpus callosum and anterior commissure--are absent

The metabolic requirements of functional activity in the human brain: a positron emission tomography study.

Abstract: In the resting state it is well established that the energy demands of the mammalian brain are met by the oxidation of glucose (Siesjo, 1978). Changes in the functional activity of the brain (e.g., motor activity, speech, vision, audition, somesthesis) are accompanied by increases in local blood flow and glucose utilization (for a review of this extensive literature see Raichle, 1987). It had been generally assumed that the energy demands accompanying these phasic changes in neural activity were also supported by glucose oxidation supporting the large energy expenditures required to maintain membrane ionic gradients. The increase in local blood flow had been considered a response to oxygen depletion and metabolite excess in the form of carbon dioxide.

Asymmetries of brain glucose metabolism and memory in the healthy elderly

Abstract: The relation of discrepancies between visual and verbal memory to right‐left asymmetries of resting state brain glucose metabolism was studied in 11 healthy elderly subjects. Short‐ and long‐term memory were measured with experimental continuous recognition tests. Regional cerebral metabolic rates for glucose were determined with positron emission tomography (PET) using 18F‐fluoro‐2‐deoxy‐D‐glucose. Long‐term memory discrepancy was related to parietal and hemispheric metabolic asymmetries, such that subjects with better visual than verbal memory had higher right than left brain glucose metabolic rates, whereas others showed the opposite pattern. These results show that specific visual and verbal memory abilities in the healthy elderly are related to regional differences in cerebral cortical metabolism.

Functional brain studies with H2(15)O-PET: strategies and problems for approaching higher brain functions with H2(15)O-PET.

Abstract: Activation study using H2(15)O and PET is promising as a noninvasive approach to higher brain functions in humans. However before reaching a more complex paradigm, many fundamental problems need to be solved. In this study, we investigated the following issues: (1) reproducibility of regional cerebral blood flow in the resting state as measured by this method, (2) effect of physiological stimulation on cerebral blood flow, and (3) identification of activated areas on anatomical structures. Our data suggest that relative CBF images and their paired subtraction are more suitable for tapping functional localization. Changes in rCBF in the association cortex for more complicated tasks are, in general, smaller than those in the primary cortex. Combined display of PET images with three-dimensional reconstructed brain surface MR images was the most reliable technique for anatomical identification of the activated site.

EEG Mapping while Listening to a Text: Differences Between Controls and Schizophrenics

Abstract: An EEG mapping study was conducted in controls and schizophrenic males while they were listening to a text. In controls, changes in EEG parameters were observed mainly in brain areas related to language comprehension. These changes were not present in schizophrenics who differed also with a reduction in local and interhemispheric coherences when in a resting state with eyes closed.