Brain Regions In Response Research Articles

Gender differences in regional brain response to visceral pressure in IBS patients

In two experiments including a total of 30 irritable bowel syndrome patients, symptom-mimicking rectal pressure stimuli elicited changes in regional neural activation as measured by positron electron tomography (PET) cerebral blood flow images. Although most stimuli were not rated as painful, rectal pressure increased regional cerebral blood flow (rCBF) in areas commonly associated with somatic pain, including the anterior cingulate, insula, prefrontal cortex, thalamus, and cerebellum. Despite similar stimulus ratings in male and female patients, regional activations were much stronger for males. In both experiments, rectal pressure activated the insula bilaterally in males but not in females. Insula activation was associated most strongly with objective visceral pressure, whereas anterior cingulate activation was associated more with correlated ratings of subjective discomfort. The insula is discussed as a visceral sensory cortex. Several possible reasons for the insula gender effect are proposed.

Functional magnetic resonance imaging neuroactivation studies in normal subjects and subjects with the narcoleptic syndrome. Actions of modafinil

Functional magnetic resonance imaging (fMRI) can be used to detect regional brain responses to changes in sensory stimuli. We have used fMRI to determine the amount of visual and auditory cortical activation in 12 normal subjects and 12 subjects with the narcoleptic syndrome, using a multiplexed visual and auditory stimulation paradigm. In both normal and narcoleptic subjects, mean cortical activation levels during the presentation of periodic visual and auditory stimulation showed no appreciable differences with either age or sex. Normal subjects showed higher levels of visual activation at 10:00 hours than 15:00 hours, with a reverse pattern in narcoleptic subjects (P = 0.007). The group differences in spatial extent of cortical activation between control and narcoleptic subjects were small and statistically insignificant. The alerting action, and imaging response, to a single oral dose of the sleep-preventing drug modafinil 400 mg were then determined and compared with placebo in both the 12 normal (8 given modafinil, 4 placebo) and 12 narcoleptic subjects (8 modafinil, 4 placebo). Modafinil caused an increase in self-reported levels of alertness in 7 of 8 narcoleptic subjects, but there was no significant difference between mean pretreatment and post-treatment activation levels as determined by fMRI for either normal or narcoleptic syndrome subjects given modafinil. However, in the modafinil-treated group of 8 normal and 8 narcoleptic subjects, there was a clock time independent correlation between the initial level of activation as determined by the pretreatment scan and the post-treatment change in activation (visual, P = 0.002; and auditory, P = 0.001). No correlation was observed in placebo-treated subjects (P = 0.99 and 0.77, respectively). Although limited by the small number of subjects, and the lack of an objective measure of alertness, the findings of this study suggest that low cortical activation levels in both normal and narcoleptic subjects are increased following the administration of modafinil. Functional magnetic resonance imaging may be a valuable addition to established studies of attention.

Demonstration in vivo of reduced serotonin responsivity in the brain of untreated depressed patients.

For over 25 years, it has been hypothesized that major depression is due to a deficiency of available serotonin or subsensitivity of key serotonin receptors in relevant brain regions. Direct evidence supporting this hypothesis has been lacking because of the difficulty in studying regional brain serotonergic function. The authors have developed a method for visualizing in vivo regional brain responses to serotonin release by comparing regional brain glucose metabolism after administration of the serotonin-releasing drug dl-fenfluramine, relative to placebo. Results with healthy subjects (N = 6) were compared to those obtained with drug-free inpatients with moderately severe major depression (N = 6). Healthy subjects had several areas of statistically significant increases in metabolism, mostly in the left prefrontal and temporoparietal cortex, and areas of decreased metabolism, such as in the right prefrontal cortex. In contrast, the depressed patients had no areas of increase or decrease in metabolism, differing significantly from healthy subjects. Results with patients resembled those with healthy subjects (N = 10) who were scanned twice without active drug on either occasion. This study provides the first direct visualization of blunted regional brain responses to serotonin release in the brain of patients with major depression, a finding that supports the hypothesis of impaired serotonergic transmission in depression.

Brain Tumors Do Not Affect Thiopental Dosing Requirements

We used the biphasic electroencephalographic (EEG) response to increasing concentrations of thiopental to measure regional brain responses to thiopental. Eight patients with cortical parietal brain tumors, 3.3 (SD 1.3) cm in diameter, and eight control patients with lung cancer and normal brain computed tomography scans received thiopental by infusion (50-75 mg/min) until burst suppression (50% isoelectric activity) on the EEG occurred. Infusion lasted 10.7 (SD 2.4) min, and the average dose of thiopental administered was 810 (SD 170) mg [11.2 (SD 1.9) mg/kg]. During infusion the EEG was continuously recorded from the F3, F4, P3, and P4 electrodes. On-line power spectral analysis was performed, and data were saved for later analysis. Four EEG parameters [log beta (15-30 Hz) power, percent beta power, spectral edge 95% and spectral edge 70%] were plotted against calculated brain concentration of thiopental [using an assumed plasma-effect site rate constant (ke0) of 0.58] for each individual. Three points were measured on each curve (50% upslope, peak, and zero intercept) to quantitate the EEG response. Statistical comparisons were performed between the following sets of data: EEG response at electrode closest to brain tumor versus electrode farthest from tumor (in the same patient); and electrodes closest to brain tumors (parietal P3 and P4) versus same electrode pair in control patients (patients with thoracic tumors) using analysis. No differences were found in any comparison. Thus, the presence of a brain tumor does not affect the response of the brain in this region to thiopental as measured using EEG.

Review : Mapping Brain Pathophysiology and Higher Cortical Function with Magnetic Resonance Imaging

Advances in magnetic resonance imaging (MRI) have moved the technology beyond its application solely as a diagnostic test to become a tool for addressing questions of in vivo pathophysiology and higher cortical function in humans. Diffusion-weighted MRI measures the apparent rate of translational movement of water molecules through brain parenchyma. This measurement can be used to determine axonal orientation within white matter, to define regions of tissue edema, and to permit early identification of ischemic neuronal injury related to impairment of Na+-K +-ATPase activity in experimental and human stroke. Changes in various aspects of cerebral perfusion—blood volume, blood flow, and hemoglobin oxygen saturation—can be mea sured with MRI, and altered cerebrovascular circulation and regional brain activation can thereby be inves tigated. Echo planar imaging is a method of ultrafast data acquisition with MRI—individual images are ac quired on the order of 100 msec. Echo planar imaging makes diffusion and perfusion measurements more practicable for diverse applications and allows for the study of temporal characteristics of regional brain responses to stimuli. Diffusion and perfusion MRI, generally termed functional MRI, are tools for studying in vivo brain physiology with MRI and are being applied to a broad range of questions in neuroscience. The Neuroscientist 1:221-235, 1995

PET measurement of regional cerebral blood flow changes during noise stimulation

Positron emission tomographic (PET) studies of regional cerebral blood flow (rCBF) using the steady‐state 0–15 carbon dioxide (CO2) method allows within‐subject stimulation and control studies to be performed in the same session. Using this technique, we previously reported data suggesting that broadband white noise increased rCBF significantly. In the present study, we examined the temporal course of these changes. Six normal volunteers were studied with eyes covered while CO2 was inhaled through nasal prongs. Fourteen serial 1‐min images were acquired in the following sequence: 2‐min quiet, 6‐min auditory stimulation, 6‐min quiet. Arterial blood was automatically sampled every 18 s. The stimulation protocols replicated conditions used previously to study the physiological effects of noise [J. Meyer‐Delius, Automobile Tech. J. 59, 293 (1957)], with broadband white noise presented binaurally through earphones at 90 dBA with an on/off cycle of 30 s. Region of interest (ROI) data were obtained for at least 30 regions across 9 planes for each of the 14 time frames using a thresholding technique. Transient rCBF increases occurred in most ROI's within the first 1–3 min. Increased rCBF was also observed after the stimulation period ended, most consistently in cerebellum and paracentral regions where 10%–30% increases were seen in all subjects. These results suggest that rCBF changes with auditory stimulation have a significant temporal component that is not uniform across brain regions. This component must be defined when regional brain response to auditory stimulation is studied.