SEARCH · PubMed Health

Results for “cortical structure”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources

PubMed1996

Fos expression in rat visual cortex induced by ocular input of ultraviolet light.

We used immunostaining for the cellular transcription factor Fos to assess patterns of neuronal activation in rat visual cortex during exposure to ultraviolet light. Exposure to monochromatic ultraviolet light (lambda max 360 nm: half-bandwidth 8.8 nm, 10 microW/cm2 at eye level) induced strong expression of Fos immunoreactivity in the primary visual cortex and associated cortical visual areas of dark-adapted rats. The stimulatory effect of ultraviolet light on Fos expression was related to exposure duration, was independent of stimulus novelty or phase of the circadian cycle in which exposure occurred, and it was mediated by a mechanism located in the eye. These results demonstrate that ocular input of ultraviolet light is capable of altering neuronal activity in cortical structures involved in visual processing and are consistent with the hypothesis that rodents may use ultraviolet light for vision.

Animals↗

PubMed1982

Effects of ethanol on visual evoked responses in monkeys performing a memory task.

The effects of ethanol on behavior and visual evoked potentials were investigated in monkeys performing a visual short-term memory task. Ethanol induced a dose-dependent deficit in performance and a prolongation of visuo-motor reaction time. The normal patterns of ocular motility were concomitantly altered. The potentials elicited in the lateral geniculate nucleus, the striate cortex, the inferotemporal cortex, the amygdala, and the mesencephalic reticular formation by a colored stimulus used by the animal in the task were attenuated by the alcohol in dose-related manner. In contrast, potentials elicited in the striate cortex and reticular formation by a brief and diffuse flash were augmented under the influence of the substance. It is inferred that ethanol can increase the reactivity of reticular and cortical structures to undifferentiated stimuli, while at the same time interfering with the basic mechanisms of visual attention and perception.

Animals↗

PubMed1992

Ontogenesis of nocturnal organization of sleep spindles: a longitudinal study during the first 6 months of life.

Ontogenesis of sleep spindles was studied on overnight longitudinal recordings in 12 full-term infants at 1.5-3-4.5 and 6 months of life. Six parameters (density, duration, frequency, amplitude, asymmetry and asynchrony) were analyzed during both slow wave sleep (SII and delta) and during 5 periods of the night. Results show a significant increase of most parameters between 1.5 and 3 months of age. All spindle patterns developed quite rapidly during the first 3 months of infancy, possibly reflecting developmental changes in thalamo-cortical structures and maturation of the physiological system that produces spindles. The density of 12-14 Hz spindle frequency was higher in stage II when compared to stage delta, as in adults. Our data confirm previous reports on spindle ontogenesis and give a more complete aspect of this ontogenesis in relation to sleep development. Three months of age appeared to be a turning point in maturational processes and might reflect changes in central nervous system activity and behavior which take place during that period. Sleep spindle evolution seems to be an accurate reflection of the slow wave sleep (SWS) development, and our results are discussed in terms of the developmental aspect of SWS production and characterization of sleep stages in young infants. Concordance between quantitative aspects and nocturnal organization leads us to consider that the individualization of slow wave sleep (SWS) in infants occurs from 4.5 months of life.

Aging↗

PubMed1987

Kindling of audiogenic seizures in Wistar rats: an EEG study.

The EEG of 20 Wistar rats inbred for audiogenic seizures was recorded during 40 daily auditory stimuli 90 s long. The first stimuli provoked wild running, with no cortical EEG abnormality, and then a tonic phase with a characteristic EEG of a brief flat trace 2 to 3 s long followed by low-amplitude regular activity, 10 to 12 c/s, lasting 40 to 60 s. The lack of paroxysmal EEG patterns suggests that the cortex plays only a minor role in audiogenic seizure development. After 5 to 15 daily stimuli, the EEG during the running period exhibited brief spike and spike-wave discharges preceding the EEG pattern of the tonic phase. After a few more daily stimuli these paroxysmal discharges progressively increased in amplitude and duration, overlapping with the regular activity of the tonic phase. After 20 to 30 stimuli, only high-amplitude spikes and spike-waves, 1 to 10 c/s, were seen for 40 to 120 s. The modified EEG persisted 2 to 4 months after daily stimulation was discontinued. Thus, with stimulus repetition, a paroxysmal discharge progressively involved cortical structures. These data suggest that repetition of audiogenic seizures induced a phenomenon related to kindling in Wistar rats susceptible to sound-induced epilepsy.

Acoustic Stimulation↗

PubMed1987

Recovery of integrative central nervous function after one hour global cerebro-circulatory arrest in normothermic cat.

Functional and metabolic recovery of a female cat is described which survived for 1 year following 1 hour global cerebro-circulatory arrest at normothermia. Ischemia was produced by intrathoracal occlusion of the innominate, the left subclavian and both mammary arteries. Following ischemia the animal was kept under intensive care for 46 h. EEG and evoked potentials began to recover after 3 h following ischemia, and spontaneous respiration returned promptly on the 2nd day when the animal was weaned from the respirator. The neurological deficit score declined from a maximum of 395 immediately after ischemia to 158 during the first week and to 40 within 4 weeks. At this time the animal was slightly ataxic but she was able to walk and to feed and clean herself. One year after ischemia EEG and evoked potentials were normal. Morphological studies and the autoradiographic evaluation of protein biosynthesis revealed an almost normal pattern in cortical structures but there was almost complete atrophy of dorsal hippocampus and striatum leading to enlargement of the ventricular system. These observations demonstrate that despite these lesions the central nervous system is able to recover integrative neurological function after cerebro-circulatory arrest in normothermia of as long as 1 h.

Animals↗

PubMed1995

Effect of thyroxine on the development of somatosensory and visual evoked potentials in the rat.

The thyroid hormone thyroxine (T4), administered post-natally to neonatal rats, has been shown to accelerate development of auditory function, as expressed by auditory nerve-brainstem evoked responses. This study investigated whether this earlier development was also reflected in other sensory modalities. Rat pups were injected with T4 from the day of birth for 10 consecutive days. Somatosensory evoked potentials, both from the cortex and from sub-cortical structures, and flash-elicited visual evoked potentials (VEP), were recorded at various ages up to 3 months. The recordings were compared with those from control rats from the same litters. Only a minimal difference was found between the experimental and control groups, the most significant being in the VEP at age 12 days, by which time the eyes of most of the experimental rats had opened, which was not the case for the majority of control rats. This difference disappeared with eye-opening in the control rats. Although T4 is known to affect myelinization and synaptic transmission in developing rat brain, this apparently only minimally affects the functioning of the brain as expressed by evoked potentials, both in the short and long term. The main effect of neonatal hyperthyroidism in these rats appeared to be accelerated development of the end organ (the eye and the ear).

Age Factors↗

PubMed1988

Reversal of a trimethyltin-induced learning deficit by desglycinamide-8-arginine vasopressin.

Trimethyltin (TMT) is an organometal neurotoxin which produces lesions primarily in the limbic system. Selectivity seems to depend upon the dose, but the hippocampus and related entorhinal cortical structures, of importance for learning and memory, are most often described as target sites. We have previously demonstrated that subjects treated with a moderate dose of TMT prior to acquisition sessions, are unable to learn a forward autoshaping task with a 6 sec delay of reinforcement, but are capable of acquiring the same task when no delay of reinforcement is used. These data suggested that the performance deficit is one of learning (i.e. consolidation) rather than of memory (i.e. storage), retrieval, or sensorimotor impairment. To more rigorously test this hypothesis, we determined if performance of a task already learned would be impaired by the neurotoxin. Adult male Long Evans rats were given 10 acquisition sessions of 24 trials, following which TMT (6.0 mg/kg, p.o.) was administered. One month later, these rats performed the lever-touching behavior as well as controls, despite the fact that the same dose of TMT interfered with learning if given one month prior to acquisition sessions, thus confirming our hypothesis. In a second experiment we determined if the peptide analog of vasopressin, desglycinamide-8-arginine vasopressin (DGAVP), could reverse a learning deficit in a population of non-learners. Rats were treated with TMT or water vehicle one month prior to autoshaping. TMT significantly retarded acquisition. After 10 sessions of 12 trials each, non-learners (i.e. rats treated with TMT that failed to associate the lever with delivery of a reinforcer) were administered saline or DGAVP (7.5 micrograms/kg, s.c.) 1 hr before sessions 11-13; treatment was discontinued prior to sessions 14 and 15. Peptide treated subjects showed evidence of acquisition and exhibited higher levels of lever-directed behavior than saline treated nonlearners. Performance was maintained after DGAVP treatment was discontinued, indicating that the learning-enhancing action of DGAVP was not transient or state-dependent.

Animals↗

PubMed1989

Regional cerebral glucose metabolic rate in human sleep assessed by positron emission tomography.

The cerebral metabolic rate of glucose was measured during nighttime sleep in 36 normal volunteers using positron emission tomography and fluorine-18-labeled 2-deoxyglucose (FDG). In comparison to waking controls, subjects given FDG during non-rapid eye movement (NREM) sleep (primarily stages 2 and 3) showed about a 23% reduction in metabolic rate across the entire brain. This decrease was greater for the frontal than temporal or occipital lobes, and greater for basal ganglia and thalamus than cortex. Subjects in rapid eye movement (REM) sleep tended to have higher cortical metabolic rates than waking subjects. The cingulate gyrus was the only cortical structure to show a significant increase in glucose metabolic rate in REM sleep in comparison to waking. The basal ganglia were relatively more active on the right in REM sleep and symmetrical in NREM sleep.

Brain↗

PubMed1988

Regional concentrations of GABA, serotonin and noradrenaline in brain at onset of seizures induced by lindane (gamma-hexachlorocyclohexane).

The main objective of this study was to determine the modifications induced by the pesticide lindane (gamma-hexachlorocyclohexane) in the regional concentration of neurotransmitters in brain, taking the tonic-clonic seizure as the main sign of its neurotoxic action. The animals were given lindane (150 mg/kg p.o. in olive oil) and killed at the onset of the first seizure (mean latency time: 18.3 +/- 5.5 min, n = 16). The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and the biogenic amines noradrenaline (NA) and serotonin (5-HT), as well as its corresponding acidic metabolite, were determined by high performance liquid chromatography with fluorimetric or electrochemical detection in different areas of the brain: hippocampus, mesencephalon, colliculi, frontal cortex, parietal cortex, striatum and thalamus. The concentration of GABA in whole tissue was only significantly decreased in the colliculi. The concentration of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were decreased in the colliculi, striatum and frontal cortex, suggesting a decreased synthesis and release of 5-HT, but increased in the parietal cortex. The concentration of NA was significantly decreased in the parietal cortex. Thus, the results indicate that lindane induces some modifications of the concentration of neurotransmitters in cortical structures, basal nuclei, midbrain and colliculi. These changes may be consequent upon the proposed interaction of lindane with the GABAergic system, although a direct action of lindane on other neurotransmitter systems cannot be excluded.

Animals↗

PubMed1995

Ocular space exploration in the dark and its relation to subjective and objective body orientation in neglect patients with parietal lesions.

Eye movements of neglect patients with right parietal lesions were recorded during ocular searching for a (non-existent) target in complete darkness. With respect to the objective orientation of the sagittal midplane, ocular exploration was biased toward the ipsilesional side. However, in relation to the patients' subjective localization of the sagittal midplane in space, exploratory eye movements were symmetrically distributed to the subjective "left" and "right" as observed in non-brain-damaged controls. The present results further support the hypothesis that the essential aspect leading to spatial neglect is a disturbance of those cortical structures that are crucial for computing egocentric, body-centred coordinates that allow use to determine our body position in space and that are necessary for visuomotor coordination and exploration of space. In neglect patients the central coordinate transformation seems to work with a systematic error resulting in a deviation of the spatial reference frame to the ipsilesional side. Consequences of this deviation are a displacement of subjective localization of body orientation and--to the same degree--of the spatial area in which motor behavior (here exploratory eye movements) is executed.

Aged↗

PubMed1994

Verbal recall and recognition as a function of depth of encoding in patients with unilateral temporal lobectomy.

The hypothesis that impairment in cognitive organization is a significant causal factor in the verbal memory impairment known to follow left anterior temporal (LT) lobectomy was tested by assessing verbal recall and recognition as a function of depth of encoding in 20 patients with LT lobectomy (19 in the recognition condition), 20 patients with right temporal lobectomy and 20 normal control subjects. Subjects first made decisions regarding either the physical, phonemic or semantic aspects of 48 words. After the encoding phase, a free recall test was given, followed by a recognition test. As expected, the verbal memory of the LT group was impaired in both the recall and recognition conditions. However, the LT group followed the pattern of the other two groups in recalling and recognizing more words which had been subjected to semantic analysis. These findings do not support the hypothesis that a disruption in the normal relationship between cognitive organization and memory contributes to the memory impairment following LT lobectomy. In contrast the verbal recall of the LT group failed to follow the pattern of the other two groups in that it did not benefit from phonemic encoding. Taken together, these findings support the notion that left anterior temporal-lobe cortical structures are more specialized for the evocation of the sound of a word than for those processes that underlie the recall of semantically encoded verbal material.

Adult↗

PubMed1989

The effect of thalamic stimulation in processing of verbal stimuli in dichotic listening tasks: a case study.

In dichotic listening tasks, the (dominant) right ear's superiority in processing verbal stimuli has been attributed to its direct anatomic connection with the left dominant hemisphere. The role played by extralinguistic factors, such as attention and functional tuning of the associated cortical structures, has not been carefully examined. This investigation was undertaken to evaluate the effects of the left thalamic electric stimulation on the processing (recognition and recall) of dichotically presented CVC verbal stimuli in a patient being treated for chronic pain. We report the positive effects of electric stimulation (confirmed by increased subcortical metabolic activity using SPECT, a brain imaging technique) on the processing of dichotically presented verbal stimuli.

Attention↗

PubMedDate not supplied

Two methods for flat-mounting cortical tissue.

Two procedures are described which allow cortical grey matter to be unfolded and flattened. Tangential sections of the flat-mounted tissue can reveal clear histological views of horizontal variations in cortical structure and function; these anatomical variations would be hard to see in sections cut by conventional techniques. Examples are presented from non-human primate tissue, but the technique has also been used successfully in a number of other mammalian species, including man. Advantages and disadvantages of the various methods for extracting topographical patterns from the cortex are discussed.

Animals↗

PubMed1994

Defensive reactions evoked by activation of NMDA receptors in distinct sites of the inferior colliculus.

The inferior colliculus (IC) is primarily involved in conveying auditory information to higher cortical structures. Recently we have shown that this structure may also be part of a brain system commanding defensive behaviour. There is evidence that the neural substrates responsible for defensive behaviour in the inferior colliculus are regulated by GABAergic, serotonergic and opioid mechanisms and that these substrates may also be depressed by benzodiazepines as part of their anxiolytic action. Here we present evidence for the involvement of excitatory amino acids in the IC in the expression of defensive reactions. Microinjections of NMDA (5-40 nmol)--an excitatory amino acid--into the ventrolateral division of the central nucleus of the IC of rats placed inside a circular arena induced aversive reactions, characterized by running, rearing, and jumping. This hyperactivity was interspersed by immobility states which often progressed to convulsive seizures. These reactions were inhibited by the NMDA specific antagonist AP7 previously microinjected into the IC. It is suggested that NMDA receptor mediated mechanisms are called into play during the display of the defensive behaviour.

Animals↗

PubMed1995

Sensations and brain processes.

A hypothesis on the physiological conditions of consciousness is presented. It is assumed that the occurrence of states of consciousness causally depends on the formation of complex representational structures. Cortical neural networks that exhibit a high representational activity develop higher-order, self-referential representations as a result of self-organizing processes. The occurrence of such states is identical with the appearance of states of consciousness. The underlying physiological processes can be identified. It is assumed that neural assemblies instantiate mental representations; hence consciousness depends on the rate at which large active assemblies are generated. The formation of assemblies involves the activation of the N-methyl-D-aspartate receptor channel complex which controls different forms of synaptic plasticity including rapid changes of the connection strengths. The various causes of unconsciousness (e.g., anaesthetics or brain stem lesions) have a common denominator: they directly or indirectly inhibit the formation of assemblies.

Animals↗

PubMed1995

Visual perception and phenomenal consciousness.

In the (re-)animated debate on consciousness we focus on three questions: Who has consciousness? What is its neuronal basis? What is its function? Regarding the first, we suggest that consciousness is exclusive to living organisms able to distinguish self from non-self. It may be restricted further to organisms who possess a repertoire of overt and covert behaviour which can be voluntarily modified and suppressed. This requires an intermediary neuronal net mediating between sensory input and behavioural output. What are the properties of this net which distinguish unalloyed information processing per se from conscious representation? To tackle this second question, we use the visual system and the functional losses that result from lesions at its different levels, and differentiate a reflexive, a phenomenal, and a consciously accessible stage of visual processing. We suggest that the latter two represent two distinct aspects of consciousness. Blindsight, a neurological example of visual processing in the absence of phenomenal vision, could help to elucidate the neuronal basis of phenomenality, and the special role of striate cortex. Like the patients, our monkeys with unilateral striate cortical removal show evidence not just of residual visual processing, but of the same absence of phenomenal vision, opening routes to further exploring the details of its neuronal implementation. The second aspect, conscious access to presently or previously processed information, is likely to require higher cortical structures, and may depend on the stage of phenomenal representations. In patients with blindsight, both aspects are lost, and it is conceivable that a loss of phenomenality generally causes a loss of conscious accessibility. One important function of phenomenal representations, our third question, would then be to allow conscious retrieval and manipulation of currently processed or formerly stored information, enabling organisms to consciously think and plan.

Animals↗

PubMed1988

Reorganization of cerebellar cell suspension transplanted into the weaver mutant cerebellum and immunohistochemical detection of synaptic formation.

Dissociated cells prepared from the cerebellar primordia of normal 15-day mouse embryos were grafted into the cerebellum of 1-month-old weaver mutant mice which are characterized by degeneration of cerebellar granule cells during the early postnatal period. The growth of the grafted cells was investigated at 1 month after the operation. Implanted cells were highly developed to form a large mass of tissue in the host cerebellar folia. Histological examination revealed that a trilaminar cortical structure was partially developed in certain areas of the grafted tissue. The implanted granule-like cells were labeled with [3H]thymidine which was injected into the host, suggesting that the granule-like cells actively proliferate in the host cerebellum after the transplantation. In this area, strong immunoreactivity with synapsin I was detected indicating that the dissociated granule cells of the cerebellar primordia are able to develop a synaptic organization in the weaver mouse cerebellum.

Animals↗

PubMed1992

Effects of tobacco smoking on the topographic EEG II.

1. Tobacco smokers are well aware of the long term hazards of tobacco smoking, yet they continue to smoke. Presumably people smoke because of short term gains due to nicotine. 2. The mechanism by which nicotine is a drug reinforcer still needs a great deal of study. The specific aim of the present study was to determine the effects of tobacco smoking on the topographic EEG of 12 hr deprived heavy tobacco smokers. 3. Seven normal adult tobacco smokers of mixed sex were recruited into the study and compared with six normal nonsmokers of similar age and sex. 4. A Grass Model 8-24D EEG and 16 different scalp monopolar electrodes were used to record the EEG using both ears as reference before and after smoking. EKG lead II was recorded on channel 17. Blood pressure was measured by auscultation. Exhaled CO was measured using a CO detector. Computer analysis of the EEG data was run of line on a Zenith 386/25 microcomputer using RHYTHM 7.1. The same system was used to store the EEG in digitized form. The maximum number of 4 sec artifact free epochs in a 3 min recording period with eyes open and then closed was used before and after low and high nicotine tobacco or sham smoking. 5. The hypothesis of this research was confirmed, i.e., that tobacco smoking of high nicotine cigarettes (about 2.0 mg/cigarette) would cause a shift in EEG alpha rhythm to higher frequencies in more diffuse midline cortical structures. In other studies an increase in alpha rhythm has been correlated with an awake relaxed behavioral state. 6. A heart rate increase was a more sensitive index of tobacco smoking than an increase in arterial blood pressure. Exhaled smoking CO levels correlated with the nicotine and tar content of the cigarette.

Adult↗