Radioactive tracer exchange in functional brain mapping.
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The activities of several single units (6-10) were recorded simultaneously in the auditory cortex and in frontal cortical areas of cats and monkeys. The response properties of the single units and the interaction between them were studied. It is shown that single units in both areas may participate in prolonged processes and be involved in more than one process. Adjacent neurons need not function in unison; while some neurons are activated, others may stay inactive. The interactions among adjacent neurons are weak, and can be modulated by sensory stimulation, and by arousal and behavioral states. These properties lead us to hypothesize that information is represented in the cortex by coactivation of sets of neurons rather than by independent modulation of the single-unit firing rate. A single unit may be a member of several representing sets. Thus, each neuron may participate in more than one function and each small cortical area may contain members of several functional sets. A mechanism for computing and transmitting information, based on converging-diverging links, between neuronal sets is described and tested by simulations and analysis of experimental data.
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The level of consciousness between the alert and drowsy states was classified into four stages (Alert, Resting I, Resting II, Drowsy) by studying three factors of the EEG patterns on 23 normal subjects. The eye movements recorded by electro-oculograph were divided into two groups, i.e. rapid eye movements (R type, r type) and slow eye movements (S type, s type). The occurrence of each type of eye movements was confirmed to change in close correspondence to the stages of consciousness. The eye movement on 43 cases with a disturbance of consciousness by metabolic disease were recorded longitudinally according to clinical states. The S type movements were predominantly observed in a state of clouding of consciousness, while the R type and R-S type were observed in a delirious state.
A brain imaging study was conducted in the case of a catatonic type of schizophrenia (DSM-IIIR) by applying (i) positron emission tomography (PET) and (ii) single photon emission computed tomography (SPECT). A PET study using [18F]-2-fluoro-2-deoxy-D-glucose revealed a lower glucose utilization in the dorsal frontal and parietal lobes of both cerebral hemispheres. Correlative SPECT studies using [123I]-iodoamphetamine showed a diminished regional cerebral blood flow in similar regions of the cerebral hemisphere. A three-dimensional volume rendering method of the SPECT images (TITAN) identified the dorsal region of the fronto-parietal lobe as the most severely affected region. These patterns of deficits implicated the role of the dorsal frontal and parietal lobes in the pathogenesis of catatonic syndromes.
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The influence of systemic blood pressure on blood-brain barrier leakage and hemorrhage in brain ischemia was evaluated in Sprague-Dawley rats with blood pressures at the lower and upper limit normally found in these animals when anesthetized on 70% N2O:30% O2. 24 h after unilateral cerebral microembolization - when significant increases in water content and barrier permeability and decrease in blood flow is present - the extravasation of Evans Blue-albumin and inulin as well as hemorrhage in the infarcted brain area was considerably more prominent in animals with the higher blood pressure. The findings imply that attempts to elevate pressure, as well as subacute surgical circulatory reconstruction to increase perfusion of an ischemic area, may be potentially harmful.
Precise and unbiased quantitation of the key element of nervous tissue has solved some long-standing problems in neuroscience and the new stereological methods are now very efficient tools for experimental testing of new (and old!) ideas and concepts. Technically, the "zipless" combination of new stereological methods with certain essential principles for observation and recognition is only beginning to be made.
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