Pathophysiologic differences evident between schizophrenia, bipolar
MedWire News: Review findings reveal differences in the pathophysiology of bipolar disorder (BD) and schizophrenia, relating specifically to the medial temporal lobe and associated limbic regions.
Although the number of studies included in the review was limited, the findings may help clarify which aspects of pathophysiology are specific to each condition, given that BD and schizophrenia share a number of clinical features and certain susceptibility genes.
Heather Whalley (University of Edinburgh, UK) and colleagues identified 21 functional magnetic resonance imaging (fMRI) studies directly comparing BD and schizophrenia activation patterns. Studies included in the review investigated either emotion, reward, or memory (n=4); executive function or language tasks (n=11); or resting state or default mode networks (n=6).
Analysis of the studies totaling 729 patients and 465 healthy controls revealed relative over-activation in the medial temporal lobe and associated structures in patients with BD versus schizophrenia for tasks involving emotion or memory. Evidence of differences between the disorders in prefrontal regions was less consistent.
Indeed, three of the four studies investigating emotion, reward, and memory tasks showed that in BD patients there was a general over-activation of the limbic and mesolimbic regions compared with schizophrenia patients.
When the researchers analyzed studies relating to executive function or language tasks, they found widespread yet inconsistent differences between diagnoses in prefrontal regions. Four studies reported differences in the direction of schizophrenia relative to BD for medial and ventrolateral prefrontal regions, while one reported differences in reverse direction in the dorsolateral prefrontal cortex.
"Further studies… would be desirable to definitively categorize the diagnostic specificity, region, and direction of these prefrontal differences," say the authors.
Studies focusing on default mode networks or analysis of the resting state showed differences in the direction of BD in default mode regions including the posterior temporal and parietal cortex but not for prefrontal regions. However, findings in the reverse direction predominantly occurred in prefrontal regions including the lateral prefrontal cortex, frontal pole, and superior frontal gyrus.
Lastly, few studies reported significant symptom associations, but when they did, they generally implicated limbic regions in association with manic symptoms.
"Future studies examining symptom dimensions, risk-associated genes, and the effects of medication will aid clarification of the mechanisms behind these differences," write the researchers in Bipolar Disorders.
By Ingrid Grasmo