Vigilance behavior, or watch keeping, involves the focusing of attention on the detection of subtle changes in the environment that occur over a long period of time. We investigated the time course of changes in brain activity during the continuous performance of a 60-min auditory vigilance task. The task required the detection of an intensity drop that occurred in 5% of the auditory stimuli. Six 1-min samples of cerebral blood flow (CBF) and electroencephalographic (EEG) activity were obtained at l0-min intervals during the vigilance performance. Changes in CBF were measured by means of positron emission tomography (PET). Performance data (hits, false alarms, reaction time) were analyzed across six 10-min blocks. Eight healthy male volunteers participated in the study. During the 60-min test, the number of correct detections (hits) did not change, but both the reaction time and EEG activity in the theta (4 to 7 Hz) range progressively increased across testing. CBF in several subcortical structures (thalamus, substantia innominata, and putamen) and cortical areas (ventrolateral, dorsolateral, and orbital frontal cortex; parietal cortex; and temporal cortex) decreased as a function of time-on-task; changes in the cortical regions were limited to the right hemisphere. Blood flow also decreased in the temporalis muscles. At the same time, CBF increased in several visual cortical areas including the left and right fusiform gyri. Furthermore, the thalamic blood-flow response co-varied with that in the substantia innominata, the ponto-mesencephalic tegmentum, and the anterior cingulate cortex. The right ventrolateral-frontal blood-flow response covaried with that in the right parietal, orbitofrontal, and dorsolateral frontal cortex. 'Iko main conclusions are drawn from the obtained data. First, we suggest that the observed time-related changes in reaction time, EEG activity, and blood flow in the temporalis muscles are related to changes in the level of arousal (alertness) and that CBF changes in the thalamus-related neural circuitry represent a brain correlate of such changes. Second, we speculate that time-related CBF decreases in cortical regions of the right hemisphere underlie a shift from controlled to automatic attentional processing of the auditory stimuli.
Despite neuropathological and electrophysiological evidence for the involvement of parahippocampal structures in temporal lobe epilepsy (TLE), little attention has been paid to morphometric measurements of these structures in patients with TLE. Using high resolution MRI, we previously showed that the volume of the entorhinal cortex was decreased in patients with TLE. The purpose of this study was: (i) to determine whether changes in the volume of the perirhinal cortex and posterior parahippocampal cortex were detectable by MRI; and (ii) to study the distribution and degree of atrophy in mesial temporal structures including the hippocampal head, body and tail, amygdala, entorhinal cortex, perirhinal cortex and posterior parahippocampal cortex. MRI volumetric analysis was performed using a T(1)-weighted three-dimensional gradient echo sequence in 20 healthy subjects and 25 TLE patients with intractable TLE. In patients with either left or right TLE, the hippocampal head, body and tail and the entorhinal and perirhinal cortices ipsilateral to the seizure focus were significantly smaller than in normal controls. The mean volume of the posterior parahippocampal cortex was not different from that of normal controls. Within the hippocampus, the hippocampal head was more atrophic than the hippocampal body and hippocampal tail. Within the parahippocampal region, the entorhinal cortex was more severely affected than the perirhinal cortex. Our MRI results confirm pathological findings of damage in the mesial temporal lobe, involving not only the hippocampus and the amygdala, but also the entorhinal and perirhinal cortices. The pattern of atrophy may be explained by cell loss secondary to a disruption of entorhinal-hippocampal connections as a result of privileged electrical dialogue between these two structures.
Although conventional proton magnetic resonance imaging has increased our ability to detect brain tumors, it has not enhanced to nearly the same degree our ability to diagnose tumor type. Proton magnetic resonance spectroscopy is a safe, noninvasive means of performing biochemical analysis in vivo. Using this technique, we characterized and classified tissue from normal brains, as well as tissue from the five most common types of adult supratentorial brain tumors. These six tissue types differed in their pattern across the six metabolites measured. 'Leaving-one-out' linear discriminant analyses based on these resonance profiles correctly classified 104 of 105 spectra, and, whereas conventional preoperative clinical diagnosis misclassified 20 of 91 tumors, the linear discriminant analysis approach missed only 1. Thus, we have found that a pattern-recognition analysis of the biochemical information obtained from proton magnetic resonance spectroscopy can enable accurate, noninvasive diagnosis of the most prevalent types of supratentorial brain tumors.
We reviewed 107 blood flow activation studies carried out with positron emission tomography and published between January 1993 and November 1996. These studies had reported their findings as peaks of significant difference in cerebral blood-flow (CBF) between two scans/tasks and had located the peaks in standardized stereotaxic space. We coded each task along several dimensions, including the type and rate of input and output, the types of cognitive processes, and the relative difficulty of tasks within a study. Based on this coding, a difference score (A-B) was calculated for each subtraction. Subsequently, the frequency distributions of the difference scores for subtractions yielding a peak in the anterior cingulate region (cingulate peak) were compared with those distributions obtained from subtractions without a cingulate peak (no cingulate-peak). The cingulate peak subtractions (n = 158) differed from the no cingulate peak subtractions (n = 229) in terms of difficulty level (p = 0.001) and the presence of a remote memory component (p = 0.01). Regional differences in the frequency distribution of certain task parameters, such as difficulty level, recent memory and the use of the hand for responding, were also observed when peaks found in the anterior cingulate cortex (ACC) were further classified as located in the rostral vs caudal ACC, supracallosal vs subcallosal ACC, and limbic vs paralimbic parts of the supracallosal ACC. We conclude that task difficulty plays a major role in modulating blood-flow response in the ACC, possibly interacting with other parameters such as the nature of the response and memory demands.
Surgery is a safe and effective treatment for drug-resistant temporal lobe epilepsy (TLE). However, bilateral electroencephalographic (EEG) abnormalities are frequently present, making presurgical lateralization difficult. New magnetic resonance (MR) techniques can help; proton magnetic resonance spectroscopic imaging (MRSI) can detect and quantify focal neuronal damage or dysfunction based on reduced signals from the neuronal marker N-acetylaspartate, and magnetic resonance imaging (MRI)-based measurements of amygdala-hippocampal volumes (MRIVol) can improve the detection of atrophy of these structures. We performed proton MRSI and MRIVol in 100 consecutive patients with medically intractable TLE to determine how well these techniques agreed with the lateralization by extensive EEG investigation. We found that the EEG, MRSI, and MRIVol findings were highly concordant. The MRSI was abnormal in 99 of 100 patients (bilateral in 54%). The MRIVol was abnormal in 86 of 98 patients (bilateral in 28%). We obtained lateralization in 83% of patients using MRIVol alone, in 86% using MRSI alone, and in 90% by combining MRSI and MRIVol (vs 93% lateralization by EEG). MRSI was abnormal in 12 patients with normal MRIVol. The combination of proton MRSI and MRIVol can lateralize TLE accurately and noninvasively in the great majority of patients. By reducing reliance on EEG, these imaging techniques could reduce prolonged presurgical evaluation and make seizure surgery available to more patients.
Multiple sclerosis (MS), the most frequent demyelinating disease, is characterized by a variable disease course. The majority of patients starts with relapsing remitting (RR) disease; approximately 50-60% of these patients progress to secondary progressive (SP) disease. Only about 15% of the patients develop a progressive disease course from onset, termed primary progressive multiple sclerosis (PPMS); the underlying pathogenic mechanisms responsible for onset of the disease with either PPMS or relapsing remitting multiple sclerosis (RRMS) are unknown. Patients with PPMS do not show a female predominance and usually have a later onset of disease compared to patients with RRMS. Monozygous twins can be concordant or discordant for disease courses indicating that the disease course is not only genetically determined. Primary progressive multiple sclerosis and secondary progressive multiple sclerosis (SPMS) share many similarities in imaging and pathological findings. Differences observed among the different disease courses are more of a quantitative than qualitative nature suggesting that the different phenotypes are part of a disease spectrum modulated by individual genetic predisposition and environmental influences. In this review, we summarize the knowledge regarding the clinical, epidemiological, imaging, and pathological characteristics of PPMS and compare those characteristics with RRMS and SPMS.
The pars opercularis occupies the posterior part of the inferior frontal gyrus. Electrical stimulation or damage of this region interferes with language production. The present study investigated the morphology and morphometry of the pars opercularis in 108 normal adult human cerebral hemispheres by means of magnetic resonance imaging. The brain images were transformed into a standardized proportional steoreotaxic space (i.e. that of Talairach and Tournoux) in order to minimize interindividual brain size variability. There was considerable variability in the shape and location of the pars opercularis across brains and between cerebral hemispheres. There was no significant difference or correlation between left and right hemisphere grey matter volumes. There was also no significant difference between sex and side of asymmetry of the pars opercularis. A probability map of the pars opercularis was constructed by averaging its location and extent in each individual normalized brain into Talairach space to aid in localization of activity changes in functional neuroimaging studies.
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