Inferring elastic properties of an fcc crystal from displacement correlations: subspace projection and statistical artifacts

We compute the effective dispersion and vibrational density of states (DOS) of two-dimensional subregions of three-dimensional face-centered-cubic crystals using both a direct projection-inversion technique and a Monte Carlo simulation based on a common underlying Hamiltonian. We study both a (111) and (100) plane. We show that for any given direction of wave vector, both (111) and (100) show an anomalous ω(2)∼q regime at low q where ω(2) is the energy associated with the given mode and q is its wave number. The ω(2)∼q scaling should be expected to give rise to an anomalous DOS, D(ω), at low ω: D(ω)∼ω(3) rather than the conventional Debye result: D(ω)∼ω(2). The DOS for (100) looks to be consistent with D(ω)∼ω(3), while (111) shows something closer to the conventional Debye result at the smallest frequencies. In addition to the direct projection-inversion calculation, we perform Monte Carlo simulations to study the effects of finite sampling statistics. We show that finite sampling artifacts act as an effective disorder and bias D(ω), giving a behavior closer to D(ω)∼ω(2) than D(ω)∼ω(3). These results should have an important impact on the interpretation of recent studies of colloidal solids where the two-point displacement correlations can be obtained directly in real-space via microscopy.

Obsessive-compulsive symptoms in at-risk mental states for psychosis: associations with clinical impairment and cognitive function

OBJECTIVE

Obsessive-compulsive symptoms (OCS) constitute a major comorbidity in schizophrenia. Prevalence estimations of OCS for patients with at-risk mental states (ARMS) for psychosis vary largely. It is unclear how ARMS patients with or without comorbid OCS differ regarding general psychosocial functioning, psychotic and affective symptoms and neurocognitive abilities.

METHOD

At-risk mental states patients (n = 233) from the interventional trial PREVENT (Secondary Prevention of Schizophrenia) were stratified according to the presence or absence of comorbid OCS and compared on several clinical variables.

RESULTS

Patients, who fulfilled the criteria for obsessive-compulsive disorder (OCD) or presented with subclinical OCS (ARMSposOCS sample), did not significantly differ from patients without OCS (ARMSnegOCS) with regard to gender, age, premorbid verbal intelligence and levels of education. Furthermore, similar severity of depressive syndromes, basic cognitive, attenuated psychotic and brief limited intermittent psychotic symptoms were found. However, ARMSposOCS patients showed more impairment of psychosocial functioning and higher general psychopathology. In contrast, they scored higher in cognitive tasks measuring working memory and immediate verbal memory.

CONCLUSION

Findings extend upon previous results due to the multidimensional assessment. Subsequent longitudinal studies might elucidate how comorbid OCS influence differential treatment response, especially to cognitive behavioural interventions and the transition rates to psychosis.

[The glutamate hypothesis of schizophrenia]

For many years, the dopamine hypothesis of schizophrenia has been the leading theory explaining the aetiology of schizophrenia. However, since the first observation showed that NMDA-receptor antagonists (e. g., PCP) can induce all kinds of schizophrenia symptoms in humans, the glutamate hypothesis of schizophrenia has been established as an additional explanation model. Apart from the PCP-induced psychoses, many other findings from all areas of modern neuroscience have confirmed and extended the glutamate hypothesis. This review discusses the available evidence for the glutamate hypothesis and puts the different findings into relation. Consecutively, the possibilities for a pharmacological modulation of the glutamate system and recent clinical trials are discussed. To sum up, one could note that the glutamate hypothesis of schizophrenia is now well-established. The development of glutamatergic antipsychotics is still in the early stages, but there is hope for a new generation of antipsychotics based on the glutamate hypothesis of schizophrenia. However, recent findings from registration trials could not provide positive findings for the recently developed glutamatergic drugs.

Single donor-derived strongyloidiasis in three solid organ transplant recipients: case series and review of the literature

Donor-derived Strongyloides stercoralis infections in transplant recipients are a rare but recognized complication. In this case series, we report donor-derived allograft transmission of Strongyloides in three solid organ transplant recipients. Following detection of infection in heart and kidney-pancreas recipients at two different transplant centers, a third recipient from the same donor was identified and diagnosed. S. stercoralis larvae were detected in duodenal aspirates, bronchial washings, cerebrospinal fluid, urine and stool specimens. Treatment with ivermectin and albendazole was successful in two of the three patients identified. The Centers for Disease Control and Prevention was contacted and performed an epidemiologic investigation. Donor serology was strongly positive for S. stercoralis antibodies on retrospective testing while all pretransplant recipient serum was negative. There should be a high index of suspicion for parasitic infection in transplant recipients and donors from endemic regions of the world. This case series underscores the need for expanded transplant screening protocols for Strongyloides. Positive serologic or stool tests should prompt early treatment or prophylaxis in donors and recipients as well as timely notification of organ procurement organizations and transplant centers.

Transcranial brain stimulation in schizophrenia: targeting cortical excitability, connectivity and plasticity

Transcranial magnetic stimulation (TMS) is a very popular tool used within neuroscience. This and other associated techniques allow the in vivo investigation of cortical excitability, cortical connectivity and cortical plasticity. Schizophrenia is a brain disorder and various theories other than the dopamine hypothesis have been developed to describe its underlying neurobiology. Supported by animal and post mortem studies, findings from TMS studies indicate that schizophrenia is a disease of reduced cortical inhibition and impaired intra- and intercortical connectivity. Further studies using repetitive TMS and other plasticity-inducing techniques have shown that cortical plasticity is altered in schizophrenia patients, supporting the recently discussed plasticity deficiency theory of schizophrenia. This review gives an introduction to the most frequently applied techniques, describes findings in schizophrenia patients and discusses these findings with regard to the neurotransmitters and associated receptors involved. In summary, there is emerging evidence of an important pathophysiological interplay between reduced inhibition, impaired connectivity and reduced plasticity in schizophrenia patients. Gamma-aminobutyric-acid-receptors and glutamtergic N-Methyl-D-aspartic-acid-receptors are most likely to be involved in this complex interplay, which may reflect a disturbed signal-to-noise ratio in schizophrenia patients. This review will discuss this issue with regard to the available treatment options and will give implications for future research and therapeutic strategies regarding disinhibition and neuroplasticity in schizophrenia.

Comorbid substance abuse in first-episode schizophrenia: effects on cognition and psychopathology in the EUFEST study

Studies and meta-analyses investigating the influence of substance use disorder (SUD) (substance abuse or dependence) on psychopathology and neurocognitive function in schizophrenia patients have revealed controversial results. Most studies did only have small samples and did not focus exclusively on first-episode schizophrenia patients.

METHOD

In a post-hoc analysis of the European First Episode Schizophrenia Trial (EUFEST) psychopathology and cognitive performances of patients with (FE-SUD, N=119, consisting of N=88 patients with persisting SUD at baseline and N=31 patients with previous SUD) and without SUD (FE-non-SUD, N=204) were compared at baseline and 6 months follow-up. Neurocognitive assessment included the Rey Auditory Verbal Learning Test (RAVLT); Trail Making Tests A and B (TMT), Purdue Pegboard and Digit-Symbol Coding.

RESULTS

In total 31.1% of patients reported SUD, and 22.2% of patients used cannabis. There were no significant differences between patients with and without SUD concerning PANSS scores, extrapyramidal motor symptoms or neurocognitive measures except better performance in psychomotor speed (TMT-A, p=0.033, Cohen's d=0.26) in patients with SUD at 6 months follow-up. Interestingly, SUD patients with ongoing substance use at follow-up showed elevated positive symptoms (PANSS positive score, p=0.008, Cohen's d=0.84) compared to those who abstained. PANSS scores at baseline were increased in patients with an onset of SUD before the age of 16 years. In addition we found a correlation between longer duration of cannabis use and higher cognitive performance as well as reduced symptom improvement and more extrapyramidal motor symptoms in patients with higher frequency of cannabis consumption.

CONCLUSIONS

FE-SUD and FE-non-SUD show similar psychopathology and neuropsychological performances at baseline and during the first 6 months of antipsychotic treatment.