Abstract
Background: Cognitive function is heterogeneous in psychosis. The cognitive abilities of the patients may remain intact (preserved), are affected by the illness (deteriorated), or are deficient early before illness onset (compromised). As we had earlier found an association between medial temporal lobe structures and overall cognitive function in psychosis, we sought to examine whether the medial temporal lobe structures differ among the distinct cognitive subtypes.
Methods: One hundred and eighty patients with psychotic spectrum disorders (including schizophrenia, schizoaffective, brief psychotic disorder, schizophreniform, and bipolar disorder with psychosis) were classified according to the cognitive subtypes: preserved (n = 74), deteriorated (n = 79), and compromised (n = 24). Cognitive profiling was based on the discrepancy between their current global cognitive scores and premorbid cognitive estimates, which was modeled on data from 122 healthy subjects. Using structural MRI data acquired from the subjects, we compared the volumes of the medial temporal lobe structures of the amygdala and hippocampus across the groups. We also tracked the medial temporal lobe structures in a subset of 58 patients who have follow-up MRI, cognitive, and global functioning data 2–7 years later.
Results: The proportion of cognitive subtypes do not differ among diagnostic categories (chronic, brief, or affective psychosis). There was no difference between the volumes of the both the amygdala and hippocampus between the cognitively preserved patients and healthy controls. Conversely, the hippocampus was found to be reduced in the cognitively deteriorated and compromised group compared with the preserved group. The amygdala was smaller in the compromised group compared with the preserved and deteriorated group. Over time, the hippocampus continued to exhibit volume decline in the deteriorated compared with the preserved group, which correlated with selective deterioration in the cognitive domain of verbal memory, as well as global functioning.
Conclusion: Differential patterns of amygdalar and hippocampal volumes were found in individuals of distinct cognitive subtypes across the psychotic spectrum. Volume decline of the hippocampus in the cognitively deteriorated group paralleled the further downward slide in selective cognitive processes and global functioning. Our findings suggest that variations in the trajectories of medial temporal lobe structures may underlie the differences in cognitive trajectories in psychosis.