Showing papers by "Gereon R. Fink published in 1996"

Cerebral Representation of One’s Own Past: Neural Networks Involved in Autobiographical Memory

Abstract: We studied the functional anatomy of affect-laden autobiographical memory in normal volunteers. Using H2 15O positron emission tomography (PET), we measured changes in relative regional cerebral blood flow (rCBF). Four rCBF measurements were obtained during three conditions: REST, i.e.,, subjects lay at rest (for control); IMPERSONAL, i.e., subjects listened to sentences containing episodic information taken from an autobiography of a person they did not know, but which had been presented to them before PET scanning (nonautobiographical episodic memory ecphory); and PERSONAL, i.e., subjects listened to sentences containing information taken from their own past (autobiographical episodic memory ecphory). Comparing IMPERSONAL with REST (nonautobiographical episodic memory ecphory) resulted in relative rCBF increases symmetrically in both temporal lobes including the temporal poles and medial and superior temporal gyri. The same loci, however, with a stronger lateralization to the right hemisphere were activated in the comparison PERSONAL to REST (autobiographical episodic memory ecphory). In addition, the right temporomesial, right dorsal prefrontal, right posterior cingulate areas, and the left cerebellum were activated. A comparison of PERSONAL and IMPERSONAL (autobiographical vs nonautobiographical episodic memory ecphory) demonstrated a preponderantly right hemispheric activation including primarily right temporomesial and temporolateral cortex, right posterior cingulate areas, right insula, and right prefrontal areas. The right temporomesial activation included hippocampus, parahippocampus, and amygdala. These results suggest that a right hemispheric network of temporal, together with posterior, cingulate, and prefrontal, areas is engaged in the ecphory of affect-laden autobiographical information.

Where in the brain does visual attention select the forest and the trees

Abstract: THE perceptual world is organized hierarchically: the forest consists of trees, which in turn have leaves. Visual attention can emphasize the overall picture (global form) or the focal details of a scene (local components)1. Neuropsychological studies have indicated that the left hemisphere is biased towards local and the right towards global processing. The underlying attentional and perceptual mechanisms are maximally impaired by unilateral lesions to the temporal and parietal cortex2,3. We measured brain activity of normal subjects during two experiments using 'hierarchically' organized figures. In a directed attention task, early visual processing (prestriate) areas were activated: attention to the global aspect of the figures activated the right lingual gyrus whereas locally directed attention activated the left inferior occipital cortex. In a subsequent divided attention task, the number of target switches from local to global (and vice versa) covaried with temporal–parietal activation. The findings provide direct evidence for hemispheric specialization in global and local perception; furthermore, they indicate that temporal–parietal areas exert attentional control over the neural transformations occurring in prestriate cortex.

Regional cerebral glucose metabolism and postmortem pathology in Alzheimer’s disease

Abstract: In four patients with an antemortem diagnosis of probable Alzheimer’s disease (AD) regional cerebral glucose metabolism (rCMRGl) was studied prospectively by positron emission tomography (PET) and compared with postmortem semiquantitative neuropathology. The interval between the last PET study and autopsy was 1.3±0.8 years. In comparison with age-matched controls, the AD patients showed predominant temporoparietal hypometabolism spreading to other cortical and subcortical regions during serial PET scans. All patients had neuropathological findings typical for AD. There was a significant relationship between rCMRGl and density of senile plaques (SP) in one patient (τ = -0.86, P < 0.05). SP were distributed quite homogeneously in all regions examined. Neurofibrillary tangles (NFT) were concentrated focally in the hippocampus-amygdala-entorhinal complex. In the context of widespread developing cortical hypometabolism, the predilection of NFT for involvement in limbic areas suggests a disruption of projection neurons as the pathogenetic process of cortical dysfunction.

Cerebral activation during the exertion of sustained static force in man

Abstract: The aim of our study was to determine alterations of cerebral activity during prolonged static force exertion Regional cerebral blood flow (rCBF) was measured using H2(15)O positron emission tomography (PET) while six male normal subjects pressed a morse-key with their right index finger with a constant force of 20% of their maximal voluntary contraction (MVC) for different periods of time (15-45 min) Exertion of static force led to activation which was at least as extensive as that during exertion of repetitive dynamic force pulses Despite a considerable sense of fatigue and increased effort at the end of a 45 min key press, no compensatory changes of activity were detected in motor or sensory related structures The right dorsolateral prefrontal cortex demonstrated a significant correlation between rCBF and duration of key-press, possibly reflecting processes over-riding fatigue Prominent basal ganglia activation was demonstrated in this static force task, but not in a previous force task involving repetitive dynamic force pulses This suggests that sustained exertion of a static force is an active process modulated, at least in part, by the basal ganglia

Human cerebral activity with increasing inspiratory force: a study using positron emission tomography

Abstract: Human cerebral activity with increasing inspiratory force: a study using positron emission tomography. J. Appl. Physiol. 81(3): 1295-1305, 1996.--The major aim of this study was to use positron emission tomography (PET) to assess dose-dependent effects of inspiratory loads on relative regional cerebral blood flow as an indication of neuronal activation and recruitment. Six normal men underwent H2 15O-PET scanning during unloaded breathing and with external inspiratory loads (generating mouth pressures of -5, -10, and -15 cmH2O); positive-pressure ventilation against relaxed respiratory muscles acted as control. During unloaded breathing, the supplementary motor area was significantly activated. With the addition of the smallest load, activations also occurred in the right premotor area and bilaterally in the superolateral motor cortex (MI) in areas previously shown to be activated with deeper breathing. There was little further change in these areas with greater loads. Additional force-related activations occurred in the inferolateral sensorimotor cortex, parietal cortex, and midbrain/hypothalamus. The results suggest that volitionally induced increases in inspiratory muscle force are achieved via a complex integration of neuronal activations in cortical and subcortical regions associated with motor control.

Heterogeneity of cerebral hemodynamics and metabolism in carotid artery disease

Abstract: Methods : Eight patients with severe unilateral carotid stenosis (>70%) were evaluated using PET to assess parametric changes in cerebral blood flow, blood volume, metabolic rate for oxygen, metabolic rate for glucose, oxygen extraction fraction and glucose extraction fraction. We performed these examinations because clinical history and physical exam results suggested possible cerebral vascular disease. Four patients were neurologically asymptomatic with other signs of peripheral vascular disease (e.g., episodic vertigo, TIA and claudication). All patients had normal neurologic examinations and normal CT or MRI studies. PET images were analyzed by two methods. First, regions of interest were used for the entire hemisphere, vascular territories and borderzones. Regions ipsilateral to the carotid stenosis were compared to respective regions in the contralateral hemisphere using Student's t-test. Second, visual inspection of each image was performed. Results : Statistical analysis demonstrated no significant differences between hemodynamic and metabolic parameters for regions ipsilateral to the carotid stenosis and contralateral homotopic reference regions. Upon visual examination, however, all patients had focal changes in either cerebral blood flow, blood volume, glucose extraction fraction and/or oxygen extraction fraction. Conclusion : Visual inspection is important in the evaluation of pathophysiological changes caused by unilateral carotid stenosis. Clinical decisions in patients with carotid artery disease should be based on careful visual examinations and statistical analyses of appropriately selected regions.

CHAPTER 79 – Individual Hemodynamic vs. Metabolic Functional Anatomy of Repeating Words: A Study Using MRI-Guided Positron Emission Tomography

Abstract: This chapter investigates the hemodynamic anatomy of repeating words using the same activation paradigm as Herholz and co-workers, the same equipment, and the same data analysis, but measuring relative regional cerebral blood flow. This is done to compare the magnitude and location of metabolic and hemodynamic changes associated with a simple word repetition task. Eight H 2 15 O-PET (positron emission tomography) relative regional cerebral blood flow measurements are performed on a high-resolution scanner following the intravenous injection of 370 MBq radioactive labeled water. PET scans are performed in a random order during four runs each of the word repetition task and a resting state. Data are acquired in 3D mode for 90-second starting with a iv injection of the radioactive tracer. Data are scattered and attenuation corrected. For morphological localization of PET measured changes in relative regional cerebral blood flow (rCBF), magnetic resonance imaging (MRI) is performed in a superconducting 1 T instrument. The results show consistent increases in relative rCBF with repeating words seen in each individual bilaterally in the superior temporal gyrus, the lower knee of the pre- and post central gyrus corresponding to the vocalization area of the sensorimotor cortex, and the supplementary motor area (SMA).