Increased amplitude of hippocampal low frequency fluctuations in early psychosis: A two-year follow-up study

Neuroimaging studies have revealed hippocampal hyperactivity in schizophrenia. In the early stage of the illness, hyperactivity is present in the anterior hippocampus and is thought to spread to other regions as the illness progresses. However, there is limited evidence for changes in basal hippocampal function following the onset of psychosis. Resting state functional MRI signal amplitude may be a proxy measure for increased metabolism and disrupted oscillatory activity, both consequences of an excitation/inhibition imbalance underlying hippocampal hyperactivity. Here, we used fractional amplitude of low frequency fluctuations (fALFF) to test the hypothesis of progressive hippocampal hyperactivity in a two-year longitudinal case-control study. We found higher fALFF in the anterior and posterior hippocampus of individuals in the early stage of non-affective psychosis at study entry. Contrary to our hypothesis of progressive hippocampal dysfunction, we found evidence for normalization of fALFF over time in psychosis. Our findings support a model in which hippocampal fALFF is a marker of psychosis vulnerability or acute illness state rather than an enduring feature of the illness.

Automated summary

Neuroimaging studies have shown that there is hippocampal hyperactivity in patients with schizophrenia, with the hyperactivity spreading to other regions as the illness progresses. However, there is limited evidence for changes in basal hippocampal function following the onset of psychosis. This study used fractional amplitude of low frequency fluctuations (fALFF) to investigate the hypothesis of progressive hippocampal hyperactivity in patients with non-affective psychosis. The findings indicate that there is higher fALFF in the anterior and posterior hippocampus in the early stage of psychosis, but there is evidence for the normalization of fALFF over time. This suggests that hippocampal fALFF may be a marker of vulnerability to psychosis or an acute illness state, rather than a persistent feature of the illness.