Biological Bases of Psychological Disorders (7A) Practice Test

In a double-blind, placebo-controlled study of major depressive disorder (MDD), researchers measured cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA; a serotonin metabolite) at baseline and after 6 weeks of treatment. Participants were randomized to an SSRI or placebo. Depressive symptoms were assessed with the Hamilton Depression Rating Scale (HDRS; higher = worse).

Data (mean ± SD):

• SSRI group (n = 28): baseline CSF 5-HIAA $= 19.8 \pm 4.1$ ng/mL; week-6 CSF 5-HIAA $= 27.6 \pm 5.0$ ng/mL; HDRS change $= -11.2 \pm 6.0$
• Placebo group (n = 27): baseline CSF 5-HIAA $= 20.3 \pm 4.3$ ng/mL; week-6 CSF 5-HIAA $= 21.1 \pm 4.6$ ng/mL; HDRS change $= -3.1 \pm 5.4$ Within the SSRI group, increase in 5-HIAA correlated with symptom improvement ($r = -0.52$).

Based on these findings, which conclusion regarding serotonergic signaling is most consistent with the data?

A study tested whether reduced prefrontal control is associated with obsessive-compulsive disorder (OCD). Adults with OCD (n = 24) and controls (n = 24) completed a response-inhibition task during fMRI. Mean dorsolateral prefrontal cortex (DLPFC) activation (task − baseline, a.u.) and mean error rate (%) were:

• OCD: DLPFC $= 0.31 \pm 0.12$; errors $= 14.5 \pm 4.2$
• Controls: DLPFC $= 0.44 \pm 0.15$; errors $= 10.2 \pm 3.8$ Across all participants, DLPFC activation correlated with fewer errors ($r = -0.46$).

Which conclusion is most consistent with these data regarding brain structure/function in OCD?