Wisconsin Card Sorting Test performance following head injury: dorsolateral fronto-striatal circuit activity predicts perseveration.

The Wisconsin Card Sorting Test (WCST) has been argued to be a sensitive indicator of frontal lobe function. However, several recent studies have failed to find a consistent relationship between structural damage to this cortical area and perseveration on the test. In the present study, positron emission tomography (PET) imaging with 18F-fluorodeoxyglucose was used to examine the relationship of regional brain metabolism to perseverative responding on the WCST in patients with a history of closed-head injury. An inverse relationship was found between perseverative responses and metabolism in the right, but not the left, dorsolateral prefrontal cortex and caudate nucleus. Perseverative responding was not related to metabolism in several other regions of the frontal lobes and basal ganglia, including the putamen and the frontal poles bilaterally. These data suggest that the functional integrity of the right dorsolateral frontal-subcortical circuit is critical for WCST performance.

Statistical methods in the Fourier domain to enhance and classify images.

A mathematical model, for which rigorous methods of statistical inference are available, is described and techniques for image enhancement and linear discriminant analysis of groups are developed. Since the gray values of neighboring pixels in tomographically produced medical images are spatially correlated, the calculations are carried out in the Fourier domain to insure statistical independence of the variables. Furthermore, to increase the power of statistical tests the known spatial covariance was used to specify constraints in the spectral domain. These methods were compared to statistical procedures carried out in the spatial domain. Positron emission tomography (PET) images of alcoholics with organic brain disorders were compared by these techniques to age-matched normal volunteers. Although these techniques are employed to analyze group characteristics of functional images, they provide a comprehensive set of mathematical and statistical procedures in the spectral domain that can also be applied to images of other modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI).

Monitoring the source of memory in detoxified alcoholics.

The ability to monitor the source of remembered information and related reflective cognitive processes was examined in normal volunteers and detoxified alcoholics. Normal volunteers were very accurate judges of whether remembered events were presented as stimuli or were self-generated, even when memory was tested 2 days later. In contrast, a subgroup of otherwise cognitively unimpaired alcoholics demonstrated impairments in the ability to track the source of remembered knowledge and were also less able to inhibit intrusion errors in recalling information from memory. These findings provide preliminary evidence of an impairment in cognitive control functions in certain alcoholics. This conclusion is supported by associated findings indicating that, among alcoholics, performance on explicit memory tasks that required reflective cognitive operations were positively correlated with glucose utilization rates in left prefrontal, temporal, and posterior orbital frontal cortical regions.

Decreased cingulate and precuneate glucose utilization in alcoholic Korsakoff's syndrome.

Localized cerebral glucose utilization was determined for nine abstinent alcoholic men with Korsakoff's syndrome and 10 age-matched normal men who underwent positron emission tomography with [18F]2-fluoro-2-deoxyglucose (FDG). Patients with Korsakoff's syndrome showed relatively decreased glucose utilization in cingulate and precuneate areas. These decreases persisted even after correction for group differences in ventricular and sulcal cerebrospinal fluid measured on computed tomography. Electroencephalographic recordings at the time of FDG uptake showed no group differences, a finding that demonstrates that the metabolic differences could not be explained by differences in physiological arousal at the time of scanning. It is concluded that the decreased glucose utilization in the patients reflects a disruption of memory circuitry, the Papez circuit, caused by diencephalic lesions induced by thiamine deficiency.

Fully automated segmentation of cerebrospinal fluid in computed tomography.

A method is presented for automated delineation and measurement of cerebrospinal fluid (CSF) regions in computed tomographic (CT) sections. Regions of skull and scalp are removed by using a linear discriminant analysis approach. Beam-hardening artifact is reduced by subtracting from each section the average radial intensity profile, characterized by a polynomial function. Remaining intensity gradients are suppressed by implementing CSF segmentation with a local thresholding technique based on maximum-entropy principles. CSF fractions from 12 regions of interest (ROIs) were measured in 10 patients with alcoholic Korsakoff syndrome and 9 normal volunteers. The same ROIs were also assessed by an interactive segmentation method, which enabled the operator to compensate for beam-hardening distortions by selecting suitable threshold values for each ROI. Both methods identified the same ROIs as displaying statistically significant differences between the two subject groups. However, interactive segmentation underestimated sulcal CSF by 20-70%, which was confirmed by applying both methods to CT scans of an anthropomorphic phantom. Hence, in contrast to interactive thresholding, unsupervised segmentation relies on firmly fixed criteria that reduce the influence of beam-hardening distortions and provide more objective results.

Positron emission tomography as a technique for studying the chronic effects of alcohol on the human brain.

Positron emission tomography is a neuroradiographic imaging technique that is beginning to be used to study cerebral pathophysiology in detoxified alcoholics. Localized cerebral glucose utilization in alcoholics at rest is not dramatically affected in comparison to the relatively large alterations in anatomic structure, cognition, and brain electrical activity. It is anticipated that future research studies will include cognitive challenges and utilization of PET ligands being developed to bind to specific receptors in the brain.