Dynamic gating in the nucleus accumbens: Behavioral state-dependent synchrony with the prefrontal cortex and hippocampus

Contextual and sensory information, goals, and the motor plan to achieve them are integrated in the nucleus accumbens (NA). Although this integration needs flexibility to operate in a variety of environments, models of NA function rarely consider changing behavioral states. Here, intracellular recordings in anesthetized rats revealed rapid changes in the synchronization between NA up states and prefrontal cortical (PFC) local field potentials (LFPs). The synchronization of the NA with the PFC and ventral hippocampus also varied over time in awake rats, depending on the behavioral state of the animal: NA LFPs followed hippocampal theta rhythms during spatial exploration, but not during an operant task when they were instead synchronized with slower PFC rhythms. These data indicate that the ability of the NA to follow cortical inputs can rapidly change, allowing for a mechanism that could select an optimal response for a given behavioral condition

A systematic experimental neuropsychological investigation of the functional integrity of working memory circuits in major depression

Verbal and visuospatial working memory (WM) impairment is a well-documented finding in psychiatric patients suffering from major psychoses such as schizophrenia or bipolar affective disorder. However, in major depression (MDD) the literature on the presence and the extent of WM deficits is inconsistent. The use of a multitude of different WM tasks most of which lack process-specificity may have contributed to these inconsistencies. Eighteen MDD patients and 18 healthy controls matched with regard to age, gender and education were tested using process- and circuit-specific WM tasks for which clear brain-behaviour relationships had been established in prior functional neuroimaging studies. Patients suffering from acute MDD showed a selective impairment in articulatory rehearsal of verbal information in working memory. By contrast, visuospatial WM was unimpaired in this sample. There were no significant correlations between symptom severity and WM performance. These data indicate a dysfunction of a specific verbal WM system in acutely ill patients with MDD. As the observed functional deficit did not correlate with different symptom scores, further, longitudinal studies are required to clarify whether and how this deficit is related to illness acuity and clinical state of MDD patients

Patients with schizophrenia show deficits of working memory maintenance components in circuit-specific tasks

Working memory (WM) deficits are a neuropsychological core finding in patients with schizophrenia and also supposed to be a potential endophenotype of schizophrenia. Yet, there is a large heterogeneity between different WM tasks which is partly due to the lack of process specificity of the tasks applied. Therefore, we investigated WM functioning in patients with schizophrenia using process- and circuit-specific tasks. Thirty-one patients with schizophrenia and 47 controls were tested with respect to different aspects of verbal and visuospatial working memory using modified Sternberg paradigms in a computer-based behavioural experiment. Total group analysis revealed significant impairment of patients with schizophrenia in each of the tested WM components. Furthermore, we were able to identify subgroups of patients showing different patterns of selective deficits. Patients with schizophrenia exhibit specific and, in part, selective WM deficits with indirect but conclusive evidence of dysfunctions of the underlying neural networks. These deficits are present in tasks requiring only maintenance of verbal or visuospatial information. In contrast to a seemingly global working memory deficit, individual analysis revealed differential patterns of working memory impairments in patients with schizophrenia

Econometric analysis of the cattle cycle in the United States

This study has been made to further explain the cattle cycle in the United States and in three selected regions. Structural models of the cattle cycle are specified and estimated, and hypotheses about their parameters are tested. For this study, the cattle cycle is divided into three cycles that include the inventory cycle, the price and income cycle and the slaughter and import cycle. Further analysis is then made to determine the important explanatory variables within each cycle. Several simultaneous equation models are constructed of the form: y\u27 (t)C + x\u27 (t)B + u\u27 (t) = o\u27 where y\u27 (t), x\u27 (t) and u\u27 (t) are the row vectors, respectively, of the jointly dependent variables, the predetermined variables and the unobserved disturbances in the equations and where C and B are the matrices of the coefficients of the jointly dependent variables and of the predetermined variables, respectively

The functional neuroanatomy of human working memory revisited. Evidence from 3-T fMRI studies using classical domain-specific interference tasks

In the present event-related functional magnetic resonance imaging study, the neural implementation of human working memory was reinvestigated using a factorial design with verbal and visuospatial item-recognition tasks each performed under single-task conditions, under articulatory suppression, and under visuospatial suppression. This approach allowed to differentiate between brain systems subserving domain-specific working memory processes and possible neural correlates of more "central" executive or storage functions. The results of this study indicate (1) a domain-specific functional-neuroanatomical organization of verbal and visuospatial working memory, (2) a dual architecture of verbal working memory in contrast to a unitary macroscopic architecture of visuospatial working memory, (3) possible neural correlates for a domain-unspecific "episodic buffer" in contrast to a failure to find brain areas attributable to a "central executive," and (4) competition for neuronal processing resources as the causal principle for the occurrence of domain-specific interference in working memory

On the Second Law of thermodynamics and the piston problem

The piston problem is investigated in the case where the length of the cylinder is infinite (on both sides) and the ratio $m/M$ is a very small parameter, where $m$ is the mass of one particle of the gaz and $M$ is the mass of the piston. Introducing initial conditions such that the stochastic motion of the piston remains in the average at the origin (no drift), it is shown that the time evolution of the fluids, analytically derived from Liouville equation, agrees with the Second Law of thermodynamics. We thus have a non equilibrium microscopical model whose evolution can be explicitly shown to obey the two laws of thermodynamics.Comment: 29 pages, 9 figures submitted to Journal of Statistical Physics (2003

Diagnosis-specific effect of familial loading on verbal working memory in schizophrenia

Working memory disturbances are a frequently replicated finding in schizophrenia and less consistent also in schizoaffective disorder. Working memory dysfunctions have been shown to be heritable and have been proposed to represent a promising endophenotype of schizophrenic psychoses. In the present study, we investigated the effects of familial loading on performance rates in circuit-specific verbal and visuospatial working memory tasks in matched samples of schizophrenic patients (from multiply affected or uniaffected families), schizoaffective patients (from multiply affected or uniaffected families), and healthy subjects. We found a significant interaction effect between familial loading and diagnosis in terms of a diagnosis-specific detrimental effect of familial loading on the performance of schizophrenic (but not schizoaffective) patients in the articulatory rehearsal task. This finding of a circuit-specific verbal working memory deficit in schizophrenic patients with additional familial loading is consistent with prior studies, which provided evidence for the existence of specific subgroups of schizophrenic patients with selective working memory impairments and for diagnosis-specific dysfunctions of the articulatory rehearsal mechanism in schizophrenic, but not in schizoaffective patients. Together, these findings suggest that the genetic risk for (a subtype of) schizophrenia may be associated with dysfunctions of the brain system, which underlies the articulatory rehearsal mechanism, the probably phylogenetically youngest part of human working memory