Investigating thought disorder in schizophrenia: evidence for pathological activation.

BACKGROUND: Previous research has yielded evidence for enhanced semantic priming in formal thought-disordered schizophrenia patients, a result that fits well with the hypothesis of disinhibited processes of spreading activation in this population. OBJECTIVE: The current study examined whether hyper priming among schizophrenia patients is an outcome of further spreading of activation of a node or a result of farther activation of nodes in the semantic network. We also try to shed light on the fate of this activation. METHODS: The present study tested this hypothesis by using semantic and identical priming in two different experiments. SOA (stimulus onset asynchrony) was manipulated (240 ms vs. 740 ms) within block. It is assumed that among healthy individuals, performance relies on a balance between activation and inhibition processes, contrary to in schizophrenic individuals. In order to examine this hypothesis, we compared formal thought-disordered schizophrenia patients, non thought-disordered schizophrenia patients, and healthy controls. RESULTS: For thought-disordered schizophrenia patients, we found a large positive semantic effect and identical priming effect (129 ms and 154 ms, respectively) only with short SOA. SOA and type of priming did not modulate priming effects in the control groups. CONCLUSIONS: This result supports the claim that there is a lack of inhibitory processes among thought-disordered patients. Hyper priming in the thought-disorder group may be an outcome of hyper activation followed by rapid decay below baseline threshold.

The rate of consanguineous marriages among parents of schizophrenic patients in the Arab Bedouin population in Southern Israel.

Consanguinity may contribute to the incidence of schizophrenia in offspring despite the usually accepted polygenic model of schizophrenia inheritance. Bedouin Arab families in southern Israel have a high rate of cousin marriages as do families throughout most Arab societies. We studied consanguinity in the parents of schizophrenic patients admitted in a defined catchment area of southern Israel, compared to a control group of parents of all infants born to Bedouin mothers in this catchment area. There was a small but significant increase in the rate of cousin marriages among the parents of schizophrenia patients compared to parents of infant controls. These results are consistent with claims that inbreeding can contribute to the incidence of schizophrenia even as a polygenic illness. However, the absence of a better matched control group limits confidence in the results.

Neuroleptics reverse attentional effects in schizophrenia patients.

Patients with schizophrenia show attention deficit characterized by a larger validity effect (fast responses to cued than uncued stimuli) in the right visual field than in the left visual field. In addition, schizophrenia patients do not show inhibition of return (IOR--a mechanism that enables efficient visual search), unless attention is summoned back to the center after the peripheral cue. The present study examined the short-term effect of neuroleptic medications on these two components of visual spatial attention in schizophrenia patients. In order to do this we tested schizophrenia patients that were treated with long-acting neuroleptic medication. These patients were treated once a month, which allowed us to test them with either low or high levels of medication. Here we show that neuroleptic medications reverse the attentional hemispheric asymmetry. In the group with a high level of medication fast RTs to cued trials were found in the right visual field, while in the group with a low level of medication the opposite pattern was found - fast RTs to cued trials were found in the left visual field. In addition, level of medication did not influence IOR - regardless of the level of medication, IOR was observed only when attention was summoned back to the center, unlike control group. These finding suggest an imbalance in dopaminergic activity, possibly in subcortical structures such as the basal ganglia. This study also shows a dissociation between the two components of visual orienting of attention and suggests that facilitation and inhibition are independent processes.

No evidence for association between NOTCH4 and schizophrenia in a large family-based and case-control association analysis.

OBJECTIVES: An analysis of 80 British parent-offspring trios by Wei and Hemmings in 2000 revealed thre1e out of five markers within the NOTCH4 locus to be strongly associated with schizophrenia. In our present study, we have examined NOTCH4 markers in large samples of German and Palestinian-Arab origin. METHODS: Our study population comprised a German case-control sample (n=512 schizophrenia patients and n=232 controls) and two independent parent-offspring trio samples of German (n=159 trios) and Palestinian-Arab (n=208 trios) descent. We examined a total of ten single nucleotide polymorphisms within the NOTCH4 locus and the adjacent loci, spanning a region of approximately 100 kb. RESULTS: Neither single marker nor haplotype analyses showed association with schizophrenia. In addition, analyses of the German case-control and trio samples revealed no significant association between NOTCH4 polymorphisms and early-onset schizophrenia. CONCLUSIONS: Our results suggest that NOTCH4 is unlikely to play a major role in the genetic predisposition to schizophrenia in the German or the Palestinian-Arab population.