A functional connectivity based approach to visualize the event related changes in depression through cognitive information processing during working memory tasks

Depression is an affective mood disorder characterized by impaired cognitive functioning. This study was designed to elicit and visualize event-related changes during information encoding, maintenance and retrieval processes of working memory in depression. Electroencephalographic signals recorded during performance of 2 memory tasks were used for analysis. The alpha, beta, theta and gamma powers were computed using Welch power density estimation method. The magnitude of event related changes derived from these band powers were used to visualize the difference in functional connectivity between the groups. The results revealed a complete absence of alpha desynchronization (p<0.01), theta synchronization (p<0.01) and gamma synchronisation (p<0.05) in the depressed group for the difficult task. Since alpha desynchronisation is related to information capacity, theta synchronisation to information encoding and retrieval and gamma synchronisation to information transmission, it was concluded that there was a definite impairment of memory and cognitive processing in depression which was reflected in task performance and as compensatory and weak connectivities between the different lobes. The significance of this result was highlighted by SASI values (p<0.001) which were positive in the prefrontal cortex and parietal lobe for the depressed group indicating a negative approach/withdrawal response to the requirements of the difficult task.