A scoping review of near infrared spectroscopy studies employing a verbal fluency task in bipolar disorder.

ABSTRACT Background : Deficits in cognitive functioning, including attention, memory, and executive functions, along with impairments in language production, are present in patients with bipolar disorder (BD) patients during mood phases, but also during euthymia. The Verbal fluency tasks (VFT), being able to evaluate integrity of a wide range of cognitive domains and represent, can be used to screen for these disturbances. Neuroimaging studies, including Near-InfraRed Spectroscopy (NIRS), have repeatedly showed widespread alterations in the prefrontal and temporal cortex during the performance of VFT in BD patients. This review aims to summarize the results of NIRS studies that evaluated hemodynamic responses to the VFT in prefrontal and temporal regions in BD patients. Methods : We performed a scoping review of studies evaluating VFT-induced activation in prefrontal and temporal regions in BD patients, and the relationship between NIRS data and various clinical variables. Results : 15 studies met the inclusion criteria. In BD patients, compared to healthy controls, NIRS studies showed hypoactivation of the dorsolateral prefrontal Cortex, ventrolateral prefrontal cortex and anterior temporal regions. Moreover, clinical variables, such as depressive symptoms and social adaptation, were negatively correlated with hemodynamic responses in prefrontal and temporal regions, while a positive correlation were reported for manic symptoms and impulsivity measures. Limitations : The heterogeneity of the studies in term of methodology, study design and clinical characteristics of the samples limited the comparability of the findings. Conclusions : Thanks to its non-invasiveness, good time-resolution and less constrained setting, NIRS technique could represent a useful tool for the evaluation of prefrontal and temporal haemodynamic correlates of cognitive performances in BD patients.