Neurobiology of Cocaine-Induced Organic Brain Impairment: Contributions from Functional Neuroimaging

The present review is directed at imparting the current knowledge regarding functional neuroimaging as a tool for enhancing the understanding of cerebrophysiologic and neurobehavioral consequences of stimulant abuse. Stimulants like cocaine are capable of inducing clinically significant neurocognitive impairment through direct action on the brain, and indirectly through other organs that influence cerebral physiology. Neurochemical dysregulation including profound effects on the serotonergic and dopaminergic systems have substantial physiological and neurobehavioral consequences. Brain hemorrhages, transient ischemic attacks, strokes, and seizures frequently follow cocaine use. The residual cerebropathologic consequences of cocaine are seen only in significant or pronounced brain events when structural neuroimaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) are employed. However, recent research with newer functional neuroimaging techniques such as single photon emission, positron emission tomography, and quantitative electroencephalography have revealed high rates of significant alteration in brain function among cocaine users, with negative structural imaging studies. These findings are often associated with impairment on neuropsychological evaluation, also in the absence of positive findings on CT and MRI. Both cerebral metabolic and hypoperfusion anomalies are seen, especially in anterior and temporal brain regions. Observed changes can persist for months, and for some patients, may represent a permanent change in brain functioning.     

Health care need: three interpretations

The argument that scarce health care resources should be distributed so that patients in 'need' are given priority for treatment is rarely contested. In this paper, we argue that if need is to play a significant role in distributive decisions it is crucial that what is meant by need can be precisely articulated. Following a discussion of the general features of health care need, we propose three principal interpretations of need, each of which focuses on separate intuitions. Although this account may not be a completely exhaustive reflection of what people mean when they refer to need, the three interpretations provide a starting-point for further debate of what the concept means in its specific application. We discuss combined interpretations, the meaning of grading needs, and compare needs-based priority setting to social welfare maximisation.     

Unconscious color priming occurs at stimulus- not percept-dependent levels of processing

Although past studies have shown that visual information can be processed without awareness, the types and levels of this processing have yet to be determined. We used metacontrast masking to explore unconscious priming effects of white, blue, and green stimuli generated on a color video display. We found that a white prime tends to act more like a green than a blue one. Color confusions among unmasked and masked primes and calibrations of the display phosphors show that physical rather than perceptual properties of the stimuli best explain the white prime's effects. We conclude that unconscious color priming in normal observers occurs at early wavelength-dependent levels of processing prior to later color-percept-dependent levels.     

A semi-persistent adult ocular dominance plasticity in visual cortex is stabilized by activated CREB

The adult cerebral cortex can adapt to environmental change. Using monocular deprivation as a paradigm, we find that rapid experience-dependent plasticity exists even in the mature primary visual cortex. However, adult cortical plasticity differs from developmental plasticity in two important ways. First, the effect of adult, but not juvenile monocular deprivation is strongly suppressed by administration of barbiturate just prior to recording visual evoked potentials, suggesting that the effect of adult experience can be inactivated acutely. Second, the effect of deprivation is less persistent over time in adults than in juveniles. This correlates with the known decline in CREB function during maturation of the visual cortex. To compensate for this decline in CREB function, we expressed persistently active VP16-CREB and find that it causes adult plasticity to become persistent. These results suggest that in development and adulthood, the regulation of a trans-synaptic signaling pathway controls the adaptive potential of cortical circuits.     

Child sexual abuse: offenders,disclosure, and school-based initiatives

Children are being sexually abused at an alarming rate. Prevalence estimates suggest that one out of four girls and one out of ten boys experience sexual abuse. This paper examines the devastating impact of child sexual abuse and explores the contributions of school-based interventions to remedy the problem.     

Attitudes toward illegal immigration: a cross-national methodological comparison

This research is an examination of the generalizability of a Likert-type scale originally devised to measure attitudes toward illegal immigrants (IA) in the United States. The current authors administered this scale across 4 national samples using several methodological procedures. Undergraduate students (631) responded to the IA scale (R. Ommundsen & K. S. Larsen, 1997) at the University of Oslo, Oregon State University, the University of Copenhagen, and Vrije University of Amsterdam. The authors' main purpose was to evaluate the adequacy of the 20-item IA scale by examining possible problems with method and translation. A translation study carried out with the Danish, Norwegian, and Dutch samples (N = 299) showed that the various national versions were fairly accurate and contained largely the same meanings. The use of procrustes analysis of the IA scale yielded 3 factors in all 4 national samples. The coefficient of congruence of these 3 orthogonally rotated factor matrices, with the U.S. factor matrix as target, varied from .80 to .95, supporting the cross-national robustness of the scale. In the search for a more economical cumulative scale, a Mokken analysis yielded a 5-item scale that represented the aforementioned 3 factors and was stable across national samples.     

Connectionist simulation of attitude learning: asymmetries in the acquisition of positive and negative evaluations

Connectionist computer simulation was employed to explore the notion that, if attitudes guide approach and avoidance behaviors, false negative beliefs are likely to remain uncorrected for longer than false positive beliefs. In Study 1, the authors trained a three-layer neural network to discriminate "good" and "bad" inputs distributed across a two-dimensional space. "Full feedback" training, whereby connection weights were modified to reduce error after every trial, resulted in perfect discrimination. "Contingent feedback," whereby connection weights were only updated following outputs representing approach behavior, led to several false negative errors (good inputs misclassified as bad). In Study 2, the network was redesigned to distinguish a system for learning evaluations from a mechanism for selecting actions. Biasing action selection toward approach eliminated the asymmetry between learning of good and bad inputs under contingent feedback. Implications for various attitudinal phenomena and biases in social cognition are discussed.