Dissociating hippocampal versus basal ganglia contributions to learning and transfer

Based on prior animal and computational models, we propose a double dissociation between the associative learning deficits observed in patients with medial temporal (hippocampal) damage versus patients with Parkinson's disease (basal ganglia dysfunction). Specifically, we expect that basal ganglia dysfunction may result in slowed learning, while individuals with hippocampal damage may learn at normal speed. However, when challenged with a transfer task where previously learned information is presented in novel recombinations, we expect that hippocampal damage will impair generalization but basal ganglia dysfunction will not. We tested this prediction in a group of healthy elderly with mild-to-moderate hippocampal atrophy, a group of patients with mild Parkinson's disease, and healthy controls, using an "acquired equivalence" associative learning task. As predicted, Parkinson's patients were slower on the initial learning but then transferred well, while the hippocampal atrophy group showed the opposite pattern: good initial learning with impaired transfer. To our knowledge, this is the first time that a single task has been used to demonstrate a double dissociation between the associative learning impairments caused by hippocampal versus basal ganglia damage/dysfunction. This finding has implications for understanding the distinct contributions of the medial temporal lobe and basal ganglia to learning and memory.     

Meconium and neurotoxicants: searching for a prenatal exposure timing.

BACKGROUND: Exposure to organochlorine compounds (OCs) has been a subject of interest in recent years, given their potential neurotoxicity. Meconium is easily available and accumulates neurotoxicants and/or metabolites from the 12th week of gestation. AIMS: To determine whether neurotoxicants, specifically OCs, could be detected in serially collected meconium, and to compare the results with those obtained in cord blood samples. METHODS: A sample of cord blood and three serial stool samples were analysed in 10 newborns. Pentachlorobenzene (PeCB), hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane (p,p'-DDT) and its metabolite dichlorodiphenyl dichloroethylene (p,p'-DDE), and hexachlorocyclohexane isomers (alpha-, beta-, gamma-, and delta-HCH) were analysed by gas chromatography. RESULTS: From serial stool collection and analysis in newborns, there was an increase in the concentrations of HCB, p,p'-DDE, PCBs, and beta-HCH between the first and last stools of the newborn. Levels of DDT diminished as pregnancy progressed. Concentrations in cord blood were positively associated with concentrations in meconium for p,p'-DDE and beta-HCH. CONCLUSIONS: Meconium is a very useful instrument for the investigation of fetal exposure to neurotoxicants; serial collection and analysis of meconium should estimate the timing and degree of in utero exposure of the fetus to neurotoxicants. Analysis and interpretation of neurotoxicants in meconium results is a complex process. Measurement in meconium of a wide range of neurotoxic substances should facilitate early identification of harmful exposures, and enable rehabilitation and instigation of preventive measures.     

Children's use of motor vehicle restraints: maternal psychological distress, maternal motor vehicle restraint practices, and sociodemographics.

OBJECTIVE: To determine the relative contribution of maternal psychological distress, maternal restraint use, and sociodemographic characteristics to the likelihood that a child would not be restrained in a motor vehicle. METHODS: We examined data on 6251 children aged 0-17 years from the 1998 National Health Interview Survey. The level of children's motor vehicle restraint use (low vs high) was examined by maternal psychological distress and motor vehicle restraint use. Multivariate regression analyses were used to model the odds of children's low use of motor vehicle restraints, controlling for potential confounders. RESULTS: According to maternal reports, more than 10% of children and nearly 13% of mothers reported low use of motor vehicle restraints. Multivariate analyses revealed that maternal use of restraints and psychological distress were both independently related to children's use of restraints, with maternal low use as the stronger correlate. Older children were more likely than younger children to be low users of motor vehicle restraints if the mother reported that she was a low user of restraints. Families with male children, black and Hispanic mothers, and 4 or more members reported lower use of restraints for their children. CONCLUSIONS: Children's low use of motor vehicle restraints was associated with low levels of maternal motor vehicle restraint use and maternal psychological distress. Moreover, maternal motor vehicle restraint practices become increasingly important as children age. Health care providers should consider maternal motor vehicle restraint use, maternal psychological distress, and child age in addition to sociodemographics when assessing children's motor vehicle safety.     

Atypical neural messengers

Notions of what constitutes a neurotransmitter have changed markedly with the advent in the past decade of synaptic molecules, which satisfy key neurotransmitter criteria but differ radically from classical transmitters. Thus, NO and carbon monoxide are neither stored in synaptic vesicles nor released by exocytosis. These gases do not act via traditional receptors on postsynaptic membranes. In addition, zinc, stored together with glutamate in synaptic vesicles, appears to act as an 'antagonist' co-transmitter at the NMDA receptor, and although localized exclusively to glia, D-serine fulfills most neurotransmitter criteria as an endogenous ligand for the 'glycine' site of NMDA receptors.     

Relationships between felt accountability as a stressor and strain reactions: the neutralizing role of autonomy across two studies

Felt accountability, conceptualized as a workplace stressor, has been gaining increased attention in terms of its importance for explaining variance in work attitudes and behaviors. Building on these investigations, the present research tests in 2 studies a conceptualization that positions job autonomy as a moderator of the relationships between felt accountability and strain reactions. In Study 1, the interactions of Felt Accountability x Job Autonomy on job tension and job satisfaction were investigated. As hypothesized, the results demonstrated that autonomy neutralized the dysfunctional effects of accountability for each outcome. Study 2 extended the findings from Study 1 by replicating the form of the interactive effects, with job satisfaction and emotional exhaustion serving as strain reactions. Implications, strengths and limitations, and suggestions for future research are discussed.     

Diagnostic utility of positron emission tomography-computed tomography for predicting malignancy in cystic neck masses in adults

OBJECTIVES: Combined positron emission tomography and computed tomography (PET-CT) is used for the diagnostic evaluation and staging of squamous cell carcinoma of the head and neck (SCCHN). By superimposing anatomic localization of CT with the physiologic data of PET, occult primary and metastatic neoplasms might be identified. Because the diagnostic algorithm for cystic neck masses in adults often overlaps with the work-up of cancer of unknown primary site, we evaluated the utility of PET-CT scans to identify the presence of malignancy and the location of primary tumor. STUDY DESIGN: Single-institution retrospective case review series. METHODS: We reviewed the PET-CT imaging of cystic neck masses occurring in five patients over 40 years of age with significant risk factors for SCCHN and correlated this information with histopathology. RESULTS: In each patient in our series, the PET portion of a combined PET-CT was misleading, whereas the CT examination was more suggestive of the correct pathology. Ultimately, clinical judgment and endoscopic evaluation, guided by CT findings, were most valuable for distinguishing malignant versus benign processes and identifying the primary tumor sites. CONCLUSIONS: PET-CT may not be a reliable modality for identifying malignancy in adults with suspicious cystic neck masses. A thorough clinical evaluation by an experienced head and neck surgeon, in conjunction with contrast-enhanced CT, may be sufficient to facilitate the optimal management of such patients.