caspi et al

  • Hemispheric Specialization:

    • The right Anterior Cingulate Cortex (ACC) actively modulates visual processing areas during visuospatial decision-making, increasing its influence on the right intraparietal sulcus (IPS) in a context-dependent manner.

    • This modulation is specific to visuospatial decisions and is frontal control (right ACC) influencing parietal (IPS) networks.

    • Hemispheric specialization is best understood as dynamic functional interactions within and between hemispheres, rather than fixed unilateral activations, with demands driving specialization.

  • Influence of Life Stress on Depression (Caspi et al., 2003):

    • A functional polymorphism in the serotonin transporter gene (5-HTTLPR) moderates the impact of stressful life events on depression.

    • Individuals carrying one or two copies of the short 's' allele of 5-HTTLPR exhibit a significantly stronger depressive response to stressful life events compared to those homozygous for the long 'l' allele.

    • This study provides key empirical evidence for a gene-by-environment (G × E) interaction within the diathesis-stress model of depression.

  1. The Research Question (RQ) was likely: How does a functional polymorphism in the serotonin transporter gene (5-HTTLPR) moderate the impact of stressful life events on depression?

  2. The Independent Variables (IVs) were:

    • Stressful life events.

    • Functional polymorphism in the serotonin transporter gene (5-HTTLPR), specifically the presence of one or two copies of the short 's' allele versus being homozygous for the long 'l' allele.

  3. The Dependent Variable (DV) was the depressive response or depression.

  4. They tested it by observing and comparing individuals with different 5-HTTLPR genotypes (those with one or two copies of the short 's' allele versus those homozygous for the long 'l' allele) and measuring their depressive responses to stressful life events.

  5. They took steps to control by comparing different genetic groups (those with 's' alleles versus those homozygous for 'l' alleles) to understand the interaction effect, rather than just isolated genetic or environmental effects. The comparison itself serves as a control for genetic variation.

  6. They found:

    • Individuals carrying one or two copies of the short 's' allele of 5-HTTLPR exhibited a significantly stronger depressive response to stressful life events.

    • Individuals homozygous for the long 'l' allele showed a weaker depressive response to stressful life events.

    • This provided key empirical evidence for a gene-by-environment (G $\times$ E) interaction within the diathesis-stress model of depression.