Reduced prefrontal oxygenation during object and spatial visual working memory in unpolar and bipolar depression

Altered prefrontal brain activity (e.g. hypofrontality) during cognitive tasks such as working memory is a core neuroimaging marker in unipolar (UNI) and bipolar (BI) depression. The present study investigated for the first time UNI (n = 16) and BI patients (n = 14) in a working memory task including different processes (storage and matching) and components (object and spatial visual) with functional near-infrared spectroscopy (fNIRS) over the prefrontal cortex. In healthy controls (n = 15) comparable to both patient groups, changes of oxygenated and deoxygenated haemoglobin indicated increased ventro-lateral, dorso-lateral prefrontal and superior frontal cortex activity for object and spatial visual working memory storage as compared to the control condition. In contrast, both patient groups showed diminished brain activity in all working memory conditions. Results revealed unspecific deficits that did not allow the differentiation between unipolar and bipolar depression in dependence of working memory processes or components. However, fNIRS can be considered as a valid, easy manageable, low cost and rapid tool for measuring (diminished) prefrontal cortex functions.