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Biomedical subjects

M E Raichle

Publications and source records attributed to M E Raichle.

At least 217 records · Page 12Linked to original sources
PubMedDate not supplied

A focal brain abnormality in panic disorder, a severe form of anxiety.

Panic disorder is characterized by recurrent anxiety attacks in the absence of a frightening stimulus. It is a common disorder, affecting 2-5% of the general population and 10-14% of patients seen in cardiology practice. Infusion of sodium (DL)lactate precipitates an anxiety attack in most persons with this disorder but rarely does so in normal controls, suggesting a neurobiological basis for the problem. Despite this observation, the pathophysiology of panic disorder remains unknown. We have now used positron emission tomography to measure cerebral blood flow (CBF) in patients with panic disorder in the absence of a panic attack. Analysis of CBF in regions thought to mediate symptoms of panic, anxiety and vigilance reveals a significant (P less than 0.005) abnormal asymmetry of CBF (left less than right) located in a region of the parahippocampal gyrus. This asymmetry was present in seven patients with panic disorder and a positive response to lactate infusion but was absent in six normal controls and in three patients with panic disorder associated with a negative response to lactate. We believe this to be the first study to identify a discrete brain abnormality in patients with this severe form of anxiety.

Anxiety Disorders↗
PubMedDate not supplied

Mapping human visual cortex with positron emission tomography.

Positron-emission tomography (PET) can localize functions of the human brain by imaging regional cerebral blood flow (CBF) during voluntary behaviour. Functional brain mapping with PET, however, has been hindered by PET's poor spatial resolution (typically greater than 1 cm). We have developed an image-analysis strategy that can map functional zones not resolved by conventional PET images. Brain areas selectively activated by a behavioural task can be isolated by subtracting a paired control-state image from the task-state image, thereby removing areas not recruited by the task. When imaged in isolation the centre of an activated area can be located very precisely. This allows subtle shifts in response locale due to changes in task to be detected readily despite poor spatial resolution. As an initial application of this strategy we mapped the retinal projection topography of human primary visual cortex. Functional zones separated by less than 3 mm (centre-to-centre) were differentiated using PET CBF images with a spatial resolution of 18 mm. This technique is not limited to a particular brain area or type of behaviour but does require that the increase in CBF produced by the task be both intense and focal.

Cerebrovascular Circulation↗
PubMedDate not supplied

Direct comparison of episodic encoding and retrieval of words: an event-related fMRI study.

Functional magnetic resonance imaging (fMRI) was used to compare directly episodic encoding and retrieval. During encoding, subjects studied visually presented words and reported via keypress whether each word represented a pleasant or unpleasant concept (intentional, deep encoding). During the retrieval phase, subjects indicated (via keypress) whether visually presented words had previously been studied. No reliable differences were found during the recognition phase for words that had been previously studied and those that had not been studied. Areas preferentially active during encoding (relative to retrieval) included left superior frontal cortex, medial frontal cortex, left superior temporal cortex, posterior cingulate, left parahippocampal gyrus, and left inferior frontal gyrus. Regions more active in retrieval than encoding included bilateral inferior parietal cortex, bilateral precuneus, right frontal polar cortex, right dorsolateral prefrontal cortex, and right inferior frontal/insular cortex.

Adult↗
PubMedDate not supplied

Practice-related changes in human brain functional anatomy during nonmotor learning.

Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can be used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.

Adult↗
PubMedDate not supplied

PET activation of posterior temporal regions during auditory word presentation and verb generation.

Previous studies using positron emission tomography (PET) report blood flow changes in superior and middle temple gyri associated with auditory and language tasks (Petersen et al., 1988, 1989; Wise et al., 1991; Demonet et al., 1992; Howard et al., 1992; Sergent et al., 1992; Zatorre et al., 1992; Petrides et al., 1993; Raichle et al., 1994; Fiez et al., 1995). An important issue is whether these changes reflect the activation of a single functional region or multiple regions with distinct functional contributions. In the present study, we examined this issue by focusing upon two tasks for which we have previously reported posterior temporal blood flow changes: listening to auditorily presented words (Petersen et al., 1988, 1989), and generation of a verb in response to a visually presented noun (Raichle et al., 1994); see also Wise et al. (1991). We began by further characterizing a left temporoparietal region of change previously associated with auditory word presentation. This previously reported response was replicated, and the results were extended by demonstrating presentation of pseudowords also produced activation. We next asked whether the activation associated with auditory word presentation could be distinguished from that associated with the generation of verbs in response to visually presented nouns. It was found that the activations associated with these two tasks could be both functionally and spatially dissociated. Thus, two posterior temporal areas associated with auditory word presentation and verb generation appear to represent distinct areas concerned with word processing. More generally, the results demonstrate an approach for assessing the independence of two activated areas.

Acoustic Stimulation↗
PubMedDate not supplied

Multiple foci in parietal and frontal cortex activated by rubbing embossed grating patterns across fingerpads: a positron emission tomography study in humans.

Somatosensory representations occupy parietal postcentral gyral (S1) and lateral sulcal-opercular cortex (S2). To address the issue of possible multiple activation foci in these regions and possible differences due to stimulating skin directly or through an imposed tool, we studied changes in cerebral blood flow with positron emission tomography during passive tactile stimulation of one or two fingertips. Restrained fingers were rubbed with embossed gratings using a rotating drum stimulator in 11 subjects. For different scans, gratings touched the skin directly for optimal stimulation of cutaneous receptors (called skin mode stimulation) or indirectly through an imposed guitar plectrum snugly fitted to the same fingers (called tool mode stimulation). The latter was expected to stimulate deep receptors better. Subjects estimated roughness after each scan. Direct skin contact activated statistically validated foci in both hemispheres. On the contralateral side these foci occurred in the anterior and posterior limbs of the postcentral gyrus and on the ipsilateral side only in the posterior limb. Tool mode stimulation activated one contralateral focus that was in the posterior limb of the postcentral gyrus. These results suggest at least two maps for distal fingertips in S1 with the anterior and posterior foci corresponding, respectively, to activations in area 3b and the junction between areas 1 and 2. In contralateral S2, skin mode stimulation activated a peak that was anterior and medial to a focus associated with tool mode stimulation. The magnitude of PET counts contralateral to stimulation was greater in the anterior S1 and the S2 regions during initial scans but reversed to more activation in the posterior S1 during later scans. These short-term practice effects suggest changes in neural activity with stimulus novelty.

Adult↗
PubMedDate not supplied

Top-down modulation of early sensory cortex.

Data from nine previous studies of human visual information processing using positron emission tomography were reanalyzed to contrast blood flow responses during passive viewing and active discriminations of the same stimulus array. The analysis examined whether active visual processing (i) increases blood flow in medial visual regions early in the visual hierarchy and (ii) decreases blood flow in auditory and somatosensory cortex. Significant modulation of medial visual regions was observed in six of nine studies, indicating that top-down processes can affect early visual cortex. Modulations showed several task dependencies, suggesting that in some cases the underlying mechanism was selective (e.g. analysis-or feature-specific) rather than non-selective. Replicable decreases at or near auditory Brodmann area (BA) left 41/42 were observed in two of five studies, but in different locations. Analyses that combined data across studies yielded modest but significant decreases. Replicable decreases were not found in primary somatosensory cortex but were observed in an insular region that may be a somatosensory association area. Decreases were also noted in the parietal operculum (perhaps SII) and BA 40. These results are inconsistent with a model in which the precortical input to task-irrelevant sensory cortical areas is broadly suppressed.

Auditory Cortex↗
PubMedDate not supplied

Tactile attention tasks enhance activation in somatosensory regions of parietal cortex: a positron emission tomography study.

We used positron emission tomography to study cortical regions mediating tactile attention. Cues selectively directed subjects to attend to the roughness or duration of contact with embossed gratings that rubbed against a single fingertip with controlled speed and force. The task required discriminating between paired gratings that differed in tactile features of roughness and/or length. For different blocks of trials, cues directed attention to one tactile feature or indicated a divided attention strategy to a change in either feature. All attention conditions unambiguously activated several somatosensory foci in the parietal cortex, including somatotopically appropriate portions of the primary somatosensory cortex in the postcentral gyrus (S1) and the secondary somatosensory region (S2) within parietal opercular regions. There was no evidence for separate processing foci for selective and divided attention strategies, or for selectively attending to roughness versus stimulus duration. We observed a greater magnitude blood flow change in S2 versus S1 during attention tasks, which suggests that S2 might actually influence S1 activity. Despite these differences, modulation of S1 and S2 supports concepts of early selection in tactile attention. There were also examples of non-sensory foci in frontal cortex, anterior cingulate gyrus and bilateral superior parietal regions at the fundus of the postcentral sulcus. Posterior parietal regions observed in this study did not overlap foci seen in studies of visual attention. Thus, the posterior parietal region may be subdivided into modality-specific subregions, each of which processes information needed to attend to a specific modality. These non-sensory areas may constitute a network that provides a source of modulating influences on the earlier stage, sensory areas.

Adolescent↗
PubMedDate not supplied

A stereotactic method of anatomical localization for positron emission tomography.

Extant methods for anatomical localization within a physiological image are inadequate for precise regional correlations between anatomy and physiology. We have developed a method for determining the location of any region of interest within a positron emission tomographic (PET) image by transformation of the tomographic location coordinates into coordinates within a stereotactic atlas of the human brain. The specific anatomical assumptions of this approach were identified and validated within groups of normal subjects by means of measurements made from lateral skull radiographs and nuclear magnetic resonance proton images. A high degree of accuracy and reproducibility was demonstrated when this technique was applied to groups of normal subjects by determining the anatomical location of two physiologically defined PET areas: the cavernous sinus and visually responsive cortex. This method is simple to implement and highly objective. Generalization of the localization procedure for use with structural tomography is readily accomplished.

Brain↗