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Schizophrenia is a highly heritable disorder with undetermined neurobiological causes. Understanding the impact on brain anatomy of carrying genetic risk for the disorder will contribute to uncovering its neurobiological underpinnings.
To examine the effect of rare copy number variants (CNVs) associated with schizophrenia on brain cortical anatomy in a sample of unaffected participants from the UK Biobank.
We used regression analyses to compare cortical thickness and surface area (total and across gyri) between 120 unaffected carriers of rare CNVs associated with schizophrenia and 16 670 participants without any pathogenic CNV. A measure of cortical thickness and surface area covariance across gyri was also compared between groups.
Carrier status was associated with reduced surface area (β = −0.020 mm2, P < 0.001) and less robustly with increased cortical thickness (β = 0.015 mm, P = 0.035), and with increased covariance in thickness (carriers z = 0.31 v. non-carriers z = 0.22, P < 0.0005). Associations were mainly present in frontal and parietal areas and driven by a limited number of rare risk alleles included in our analyses (mainly 15q11.2 deletion for surface area and 16p13.11 duplication for thickness covariance).
Results for surface area conformed with previous clinical findings, supporting surface area reductions as an indicator of genetic liability for schizophrenia. Results for cortical thickness, though, argued against its validity as a potential risk marker. Increased structural thickness covariance across gyri also appears related to risk for schizophrenia. The heterogeneity found across the effects of rare risk alleles suggests potential different neurobiological gateways into schizophrenia's phenotype.
Fractional anisotropy in the uncinate fasciculus and the cingulum may be biomarkers for bipolar disorder and may even be distinctly affected in different subtypes of bipolar disorder, an area in need of further research.
This study aims to establish if fractional anisotropy in the uncinate fasciculus and cingulum shows differences between healthy controls, patients with bipolar disorder type I (BD-I) and type II (BD-II), and their unaffected siblings.
Fractional anisotropy measures from the uncinate fasciculus, cingulum body and parahippocampal cingulum were compared with tractography methods in 40 healthy controls, 32 patients with BD-I, 34 patients with BD-II, 17 siblings of patients with BD-I and 14 siblings of patients with BD-II.
The main effects were found in both the right and left uncinate fasciculus, with patients with BD-I showing significantly lower fractional anisotropy than both patients with BD-II and healthy controls. Participants with BD-II did not differ from healthy controls. Siblings showed similar effects in the left uncinate fasciculus. In a subsequent complementary analysis, we investigated the association between fractional anisotropy in the uncinate fasciculus and polygenic risk for bipolar disorder and psychosis in a large cohort (n = 570) of healthy participants. However, we found no significant association.
Fractional anisotropy in the uncinate fasciculus differs significantly between patients with BD-I and patients with BD-II and healthy controls. This supports the hypothesis of differences in the physiological sub-tract between bipolar disorder subtypes. Similar results were found in unaffected siblings, suggesting the potential for this biomarker to represent an endophenotype for BD-I. However, fractional anisotropy in the uncinate fasciculus seems unrelated to polygenic risk for bipolar disorder or psychosis.
Rafael Torrubia, Professor, Department of Psychological Medicine University of Barcelona, Spain,
César Ávila, Professor, Department of Psychology University of Jaume, Spain,
Xavier Caseras, Professor, Department of Psychological medicine University of Brcelona, Spain
Gray's (1970, 1981, 1982) personality theory, currently referred to as the Reinforcement Sensitivity Theory (RST) (Pickering, Díaz and Gray 1995) has defined the existence of three conceptual nervous systems that underlie three orthogonal personality dimensions. These systems reflect brain structures that influence sensitivity to reinforcing events and control the experience of emotion. The best known is the Behavioural Inhibition System (BIS); this system normally functions as a comparator, taking control of behaviour in response to signals of punishment, frustrative non-reward and novel stimuli. In terms of individual differences in personality, the BIS is related to the trait-anxiety dimension. As regards its relationship with Eysenckian dimensions, the BIS runs from the neurotic introvert quadrant (maximum BIS activity) to the stable extravert quadrant (minimum BIS activity). The second system is called the Behavioural Approach System (BAS) and is considered independent of the BIS; this system is responsible for approach behaviour in response to incentives (signals of reward or non-punishment). Individual differences in the functioning of the BAS are related to the impulsivity dimension of personality. This dimension is orthogonal to anxiety, and runs from stable introvert (minimum BAS activity) to neurotic extravert (maximum BAS activity) quadrants. The third system, the Fight-Flight System (FFS) is the most recently proposed of the three (Gray 1987a) and is the least clearly defined. It is activated by the presence of unconditioned aversive stimuli promoting fight or escape behaviour.
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