Frontal haemodynamic responses in depression and the effect of electroconvulsive therapy

Background: Reduced frontal cortex metabolism and blood flow in depression may be associated with low mood and cognitive impairment. Further reduction has been reported during a course of electroconvulsive therapy (ECT) but it is not known if this relates to mood and cognitive changes caused by ECT.
Aims: To investigate frontal function while undertaking cognitive tasks in depressed patients compared with healthy controls, and following ECT in patients.
Methods: We measured frontal haemodynamic responses to a category verbal fluency task and a working memory N-back task using portable functional near infra-red spectroscopy (fNIRS) in 51 healthy controls and 18 severely depressed patients, 12 of whom were retested after the fourth treatment of a course of ECT. Mood was assessed using the Montgomery Åsberg Depression Rating Scale and cognitive function using category Verbal Fluency from the Controlled Oral Word Association Test and Digit Span backwards.
Results: Compared to healthy controls, depressed patients had bilaterally lower frontal oxyhaemoglobin (HbO) responses to the cognitive tasks, although this was only significant for the N-Back task where performance correlated inversely with depression severity in patients. After four ECT HbO responses were further reduced during the Verbal Fluency task but the changes did not correlate with mood or cognitive changes.
Discussion: Our results confirmed a now extensive literature showing impaired frontal fNIRS HbO responses to cognitive tasks in depression, and showed for the first time that these are further reduced during a course of ECT. Further research is needed to investigate the biology and clinical utility of fNIRS in psychiatric patients.