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At least 1,297 records · Page 72Linked to original sources
PubMed2004

Mapping brain function in freely moving subjects.

Expression of many fundamental mammalian behaviors such as, for example, aggression, mating, foraging or social behaviors, depend on locomotor activity. A central dilemma in the functional neuroimaging of these behaviors has been the fact that conventional neuroimaging techniques generally rely on immobilization of the subject, which extinguishes all but the simplest activity. Ideally, imaging could occur in freely moving subjects, while presenting minimal interference with the subject's natural behavior. Here we provide an overview of several approaches that have been undertaken in the past to achieve this aim in both tethered and freely moving animals, as well as in nonrestrained human subjects. Applications of specific radiotracers to single photon emission computed tomography and positron emission tomography are discussed in which brain activation is imaged after completion of the behavioral task and capture of the tracer. Potential applications to clinical neuropsychiatry are discussed, as well as challenges inherent to constraint-free functional neuroimaging. Future applications of these methods promise to increase our understanding of the neural circuits underlying mammalian behavior in health and disease.

Animals↗
PubMed1979

Influences of adrenocortical hormones on pituitary and brain function.

Adrenocortical secretions influence neuroendocrine function and behavior, and it is possible to recognize separate physiologic actions of gluco- and mineralocorticoids. The search for neuroanatomical sites and cellular modes of adrenocorticoid action has revealed a system of putative glucocorticoid receptors in neurons of the hippocampus, septum, amygdala, and entorhinal cortex, and in the pituitary. No part of the brain is totally devoid of receptor activity, however, and glial cells may also contain glucocorticoid receptors. Mineralocorticoid receptors are less well characterized neuroanatomically or biochemically. One reason for this is the considerable degree to which both gluco- and mineralocorticoids bind to both classes of receptors in vitro. Another reason may be the overwhelming quantitative predominance of glucocorticoid over mineralocorticoid receptors in neural tissue. Glucocorticoid receptors of the pituitary, which have a high avidity for dexamethasone, appear to participate in the delayed negative feedback effects of glucocoticoids. Functional correlates of neural glucocorticoid receptors remain to be clearly established. Among the possibilities are several reported effects on hippocampal neural activity that have an onset latency of 20--30 min and a duration of several hours. The relative rapidity of such effects does not preclude genomic mediation, as genomic effects of glucocorticoids on thymus lymphocytes have been detected within as little as 15 min of steroid application [117]. What are not so far explained by the intracellular receptor mechanism are the extremely rapid effects of glucocorticoids such as the rate-sensitive negative feedback on CRF and ACTH secretion. These may involve a direct action of the steroid on cell membranes in the pituitary and hypothalamus.

Adrenal Cortex↗
PubMed1992

The relative effects of hypoxic hypoxia and carbon monoxide on brain function in rabbits.

New Zealand white rabbits were exposed to control conditions (n = 11), or to either a progressive hypoxic hypoxia produced by dilution of oxygen (O2) with nitrogen (n = 10) or a 1% carbon monoxide (CO) admixture for 15 min (n = 11). Both exposures caused a significant increase in cerebral blood flow (CBF) of up to 300% such that O2 delivery to the brain was unchanged. In the hypoxia group, a cortical somatosensory evoked response (CSER) was unaffected until the arterial O2 tension was below 20 mmHg. At this time, the rabbits became hypotensive, O2 delivery to the brain decreased dramatically and the CSER could not be elicited. In contrast, despite the maintenance of O2 delivery to the brain during and after the CO exposure, the CSER voltages were halved during the exposure and only recovered to about 80% of baseline subsequently. We conclude that the primary toxicity of CO to the brain in rabbits is not due to a reduction in O2 delivery.

Animals↗
PubMedDate not supplied

A brief episode of severe arterial hypertension induces delayed deterioration of brain function and worsens blood flow after transient multifocal cerebral ischemia.

Transient arterial hypertension occurs sporadically following cerebral air embolism and may occur during the acute phase of stroke. This study used an animal model of multifocal cerebral ischemia induced by air embolism and reversed by recompression to assess the effect of induced hypertension on the evoked response recovery, local cerebral blood flow, intracranial pressure, and brain water in 19 anesthetized dogs (Canis familiaris). Six received 0.4 ml of air via the internal carotid artery, 8 received intracarotid air and 10 micrograms/kg norepinephrine to produce transient hypertension, and 5 received intracarotid saline and norepinephrine. The average evoked response recovery in the air-only group was 58.3 +/- 7.7% (mean +/- SEM) of control after 4 hours of recompression; the air plus hypertension group recovery was 15.4 +/- 2.7% (p less than 0.01). The final evoked response in the dogs receiving hypertension alone did not differ from control values. Seven of 8 dogs in the air plus hypertension group had very low blood flows; only 1 of 4 in the air-only group had very low flows. The amount of brain water and the intracranial pressure were not detectably different at the end of treatment among all 3 groups. These results support a role for endothelial damage produced by air and hypertension in potentiating the process of postischemic hypoperfusion.

Animals↗
PubMed2005

Differential adaptation of neurocognitive brain functions to recurrent hypoglycemia in healthy men.

Antecedent hypoglycemia is known to attenuate hormonal and symptomatic responses to subsequent hypoglycemia. Whether this pertains also to hypoglycemia-induced cognitive dysfunction is controversially discussed. Neurocognitive adaptation might essentially depend on the type of function. Here, we compared the influence of recurrent hypoglycemia in 15 healthy men on counterregulatory hormones, subjective symptoms of hypoglycemia, short-term memory performance (word recall), and performance on an auditory attention task (oddball). The attention task was also used to record event-related brain potential (ERP) indicators of stimulus processing. In each subject, three consecutive hypoglycemic clamps were performed, two on day 1 and the third on day 2. Neurocognitive testing was performed during baseline and at two different hypoglycemic plateaus (2.8 and 2.5 mmol/l) during the first and last clamp. As expected, hormonal responses were significantly reduced to the last as compared to the first hypoglycemia indicating adaptation. Subjective symptoms also decreased in response to recurrent hypoglycemia. Short-term memory performance deteriorated distinctly on the first hypoglycemic clamp, but maintained the normal level on the last clamp (P=0.006). Likewise, the impairment in reaction time (P=0.022) and response accuracy (P=0.005) was distinctly smaller on the last than first hypoglycemia. In parallel, the hypoglycemia-induced decrease in P3 amplitude (P=0.019) and the increase in P3 latency (P=0.049) were diminished with recurrent hypoglycemia, indicating that late stages of controlled stimulus processing likewise adapted. In contrast, the distinct decrease in amplitudes of the N1 and P2 components of the ERP (preceding the P3) was closely comparable in response to the first and last hypoglycemia (P>0.3). Together results indicate an adaptation to recurrent hypoglycemia for signs of controlled stimulus processing presumably involving hippocampo-prefrontocortical circuitry, while earlier automatic stages of processing appear to be spared.

Adaptation, Psychological↗
PubMed2001

Distribution of sex steroid hormone receptors in the avian brain: functional implications for neural sex differences and sexual behaviors.

Developmental and seasonal changes in the production of androgens, estrogens, and progestins seem to control sex-specific differentiation and seasonal changes in appetitive and consummatory sexual behaviors of birds. This results in profound sex differences in the quality (sex-specific) or quantity (sex-typical) of behaviors such as courtship, territoriality, or copulation. Steroids affect the brain by binding to intracellularly located receptors. The same brain areas express androgen, estrogen, and progesterone receptors in male and female brains. Sex differences in these genetically determined patterns occur in the size of neuron populations that intrinsically express sex steroid receptors. Further permanent sex differences are subsequent to degenerative fates of receptor expressing neuron populations during ontogeny. Transient sex differences in receptor expression appear to be due to area-specific up- and down-regulation of receptor levels, reflecting transient changes in the level of circulating steroids, changes in environmental conditions, or in the physiological status of the individuals. In particular, intrinsic sex differences in the expression pattern of sex steroid receptors and steroid-independent regulation of the expression level of these receptors in the brain are limiting mechanisms for gonad-dependent sexual development and activities.

Animals↗
PubMed1993

[Brain function in infants up to 2 years old with mild craniocerebral trauma].

Clinical and electroencephalographic examinations of 644 infants with a history of a mild craniocerebral injury (CCI) have shown that CCI runs a graver course if experienced after perinatal encephalopathy. The EEG readings permit an objective evaluation of the results of the clinical and neurological examinations of the children and determination of the involvement of the subcortical and stem brain structures into the pathological process. By the end of the second year of life, especially after perinatal encephalopathy, mild CCI produces mild or moderate irritation of the stem structures of the brain in half the children which should be taken into account in the pathogenetic therapy.

Brain↗
PubMed1993

Neuromagnetic mapping of brain function.

Magnetic source imaging, a technique that combines magnetoencephalography (MEG) and magnetic resonance (MR) imaging, was used to localize the somatosensory and auditory cortex in seven healthy subjects. Functional neuromagnetic data were obtained with a 37-channel biomagnetometer. Structural MR imaging data were obtained with a 1.5-T superconducting imager. Coordinates used in defining MEG and MR imaging space were reconciled to produce magnetic source images that displayed the putative locations of somatosensory and auditory activity in relation to brain anatomy. Sources of somatosensory activity were typically localized to the postcentral gyrus; sources of auditory activity were localized to the superior temporal plane. Extension of these results to patients with tumors (or other disorders) that distort normal brain anatomy has the potential to make noninvasive magnetic source imaging examinations clinically useful in guiding neurosurgical interventional procedures.

Adult↗
PubMed2001

Imaging brain function in humans at 7 Tesla.

This article describes experimental studies performed to demonstrate the feasibility of BOLD fMRI using echo-planar imaging (EPI) at 7 T and to characterize the BOLD response in humans at this ultrahigh magnetic field. Visual stimulation studies were performed in normal subjects using high-resolution multishot EPI sequences. Changes in R(*)(2) arising from visual stimulation were experimentally determined using fMRI measurements obtained at multiple echo times. The results obtained at 7 T were compared to those at 4 T. Experimental data indicate that fMRI can be reliably performed at 7 T and that at this field strength both the sensitivity and spatial specificity of the BOLD response are increased. This study suggests that ultrahigh field MR systems are advantageous for functional mapping in humans. Magn Reson Med 45:588-594, 2001.

Brain↗
PubMedDate not supplied

[Study of higher brain function in first grade students and its relationship with reading and writing acquisition].

INTRODUCTION: The study of higher cortical functions gives valuable information and new insights in the understanding of the complex functioning of the central nervous system. Developmental neurological examination is an important semiologic tool in the evaluation of cortical functions. OBJECTIVE: The main of this study was to evaluate, using the neurological developmental exam, cortical functions and their association with learning. PATIENTS AND METHODS: This was an observational, analytic and transversal study with a random and proportional sample (484 children) of first grade students of Porto Alegre, Brazil. Chi-square and ANOVA tests were used, with a significant p value < 0.05. RESULTS AND CONCLUSION: Results show that altered neurologic performance disturbs reading and writing acquisition. This study, showed an association between altered neurological developmental examination and WISC subtests (numbers, figure completion and code), with learning disorders.

Brain↗
PubMed1975

Brain function and behavior. I. Emotion and sensory phenomena in psychotic patients and in experimental animals.

For the past 25 years, the research program of the Tulane University Department of Psychiatry and Neurology has been directed primarily to the development of treatment for patients with certain psychiatric and neurological disorders that have been resistant to commonly used therapy. In the course of investigations, using a variety of approaches, new techniques have evolved which have permitted simultaneous exploration of brain activity and behavior. The data reported substantiate an anatomical localization in the brain for the syndrome of psychotic behavior. Further, observations in patients, coupled with animal investigations, have led to the demonstration of brain pathways and previously undisclosed anatomical connections which provide a physical substrate for the clinically observed relation between perception and emotionality. These findings provide a basis for the development of specific biological methods for the treatment of behavioral disorders.

Animals↗
PubMed2006

CS-US preexposure effects on trace eyeblink conditioning in young rats: potential implications for functional brain development.

Recent studies of delay eyeblink conditioning (EBC) in young rats have demonstrated different effects of various conditioned and unconditioned stimulus (CS-US) preexposure conditions on learning at different ages. The present study extends this research to trace EBC. Subjects experienced 1 of 3 preexposure conditions (paired CS-US, unpaired CS-US, or no stimuli) at either 20 or 24 days of age. Four days later, they were conditioned using either trace (Experiment 1) or delay (Experiment 2) EBC parameters. Results were similar at both ages tested. Paired preexposure facilitated acquisition of delay but not trace relative to context preexposure. Unpaired preexposure impaired acquisition of both delay and trace. These behavioral findings provide a foundation for hypotheses about the functional maturation of cerebellar, hippocampal, and entorhinal learning circuits.

Age Factors↗
PubMed2003

Electrical impedance tomography of human brain function using reconstruction algorithms based on the finite element method.

Electrical impedance tomography (EIT) is a recently developed technique which enables the internal conductivity of an object to be imaged using rings of external electrodes. In a recent study, EIT during cortical evoked responses showed encouraging changes in the raw impedance measurements, but reconstructed images were noisy. A simplified reconstruction algorithm was used which modelled the head as a homogeneous sphere. In the current study, the development and validation of an improved reconstruction algorithm are described in which realistic geometry and conductivity distributions have been incorporated using the finite element method. Data from computer simulations and spherical or head-shaped saline-filled tank phantoms, in which the skull was represented by a concentric shell of plaster of Paris or a real human skull, have been reconstructed into images. There were significant improvements in image quality as a result of the incorporation of accurate geometry and extracerebral layers in the reconstruction algorithm. Image quality, assessed by blinded subjective expert observers, also improved significantly when data from the previous evoked response study were reanalysed with the new algorithm. In preliminary images collected during epileptic seizures, the new algorithm generated EIT conductivity changes which were consistent with the electrographic ictal activity. Incorporation of realistic geometry and conductivity into the reconstruction algorithm significantly improves the quality of EIT images and lends encouragement to the belief that EIT may provide a low-cost, portable functional neuroimaging system in the foreseeable future.

Adult↗
PubMed1999

MRI-SPECT fusion for the synthesis of high resolution 3D functional brain images: a preliminary study.

Medical imaging being a fast-expanding field, multimodal data fusion appears more and more as a key element for the optimal use of images. By fusion, we mean the combination of several information sources (in particular images), with the aim of providing either more condensed or more pertinent information. The long term scope of this work would be to improve the interpretation of 3D brain images, providing extra elements for the diagnosis and patient follow up. This preliminary study is part of a wider context: the medical follow up of patients suffering from probable Alzheimer disease observed in single photon emission tomography by fusion after registration with magnetic resonance images. Several information combination techniques based on the possibility theory are presented. A new operator, more specifically adapted to the fusion of anatomical and functional images, as well as a high resolution functional image synthesis technique are proposed. A first comparative study of fusion techniques is then proposed. Although no thorough test protocol has been defined, these preliminary results are encouraging, giving access to a wide field of potential clinical applications.

Aged↗
PubMed2002

Brain function and effects of shift work: implications for clinical neuropharmacology.

Night or shift work is to a relevant extent unavoidable, suits a growing preference for flexibility and is predicted to spread. However, a significant percentage of shift workers report discomfort or health problems and they often (15-20% of cases) move to different occupations. Apart from social implications, the issue has medical and scientific relevance, with evidence suggesting that the circadian rhythm phases are neither equivalent nor interchangeable with respect to function and performance. Shift work may affect the gastrointestinal and cardiovascular functions, alter the hormonal and sleepiness cycles, favor sleep disturbances of medical relevance, interfere with behavior and social life and increase the risk of accidents (e.g. road accidents). The implications for clinical (neuro)pharmacology are relevant and, in several instances, critical. Shift work can interfere with mechanisms regulating drug kinetics in peripheral compartments and action at selective brain sites, either directly or through effects on the gastrointestinal/hormonal cycles. In this paper, the relevant literature is reviewed and original data on the effects of shift work are reported. Basic and clinical research should take into account the possible effects on drug action of an active life and working schedule in inappropriate phases of the circadian cycles and the risk of inadequate drug dosing or unexpected abnormal action in subjects under long-term or chronic treatment. A scientific approach, action by the scientific community involved in pharmacological research and monitoring by the regulating agencies are advisable. Regulation may help reduce the medical and social impact and improve quality of life.

Accident Proneness↗
PubMed1989

Abnormal brain-stem function (brain-stem auditory evoked response) correlates with acoustic cry features in term infants with hyperbilirubinemia.

We hypothesized that changes in brain-stem auditory evoked responses related to bilirubin would be associated with changes in cry because of the anatomic proximity in the brain stem of cranial nerves 8 (auditory) and 9 to 12 (vagal complex, which controls cry). Brain-stem auditory evoked responses and computerized cry analysis were used to study the concurrent effects of moderate hyperbilirubinemia on auditory function and cry. Fifty term infants were divided equally into two groups on the basis of serum bilirubin concentrations: low (less than 8 mg/dl; 136) mumol/L and moderate (10 to 20 mg/dl, 170 to 342 mumol/L). Forty-three infants had successful tracings of brain-stem auditory evoked responses recorded with a Cadwell model 5200A evoked response unit during two successive trials, and a cry recording of each infant was analyzed by computer. The moderate serum bilirubin group had an increase in percent cry phonation (p less than 0.02) and an increase in the variability of the first formant (p less than 0.04) in comparison with the low serum bilirubin group. Serum bilirubin values correlated positively with brain-stem conduction time (r = 0.36, p less than 0.01), percent phonation (r = 0.42, p less than 0.004), and variability of the first formant (r = 0.39, p less than 0.02). Percent phonation, the voiced component produced by increased neural control, correlated with the interpeak of waves latencies I to III (r = 0.32, p less than 0.03) and brain-stem conduction time (wave I to V) (r = 0.35, p less than 0.01). We conclude that hyperbilirubinemia affects adjoining areas of the brain stem that control hearing and cry production.

Brain Stem↗
PubMed2001

Sustained human chemosignal unconsciously alters brain function.

The human chemosignal, Delta 4,16-androstadien-3-one modulates psychological state without being consciously discernible as an odor. This study demonstrates that Delta 4,16-androstadien-3-one (androstadienone) alters cerebral glucose utilization both in subcortical regions and in areas of the neocortex not exclusively associated with olfaction. These widely distributed changes are consistent with modulation of an integrated neural network for regulation of emotional and attentional states. This is the first study to demonstrate the effects of a sustained chemosignal on brain metabolism and to show that they are similar to those of long acting chemical substances that affect psychological states. Moreover, this provides the first evidence that a human chemosignal has distributed effects on cortical processes and brain metabolism even when it is not detected consciously.

Adult↗