The putative impact of metabolic health on default mode network activity and functional connectivity in neuropsychiatric disorders.

The default mode network (DMN) describes a distributed network of brain regions that are predominantly activated and engaged during periods of spontaneous, stimulus independent thought (i.e., at rest) and remain quiescent during attention-demanding, goal-directed tasks. Replicated evidence in functional neuroimaging studies suggests that midline cortical and subcortical brain regions responsible for memory, self-relevant emotional and mental processes, as well as information integration comprise the DMN. The DMN is posited to represent self-referential mental activity via a dynamic interplay of cognitive and emotional processes by integrating information from the external environment with introspective thoughts to generate an autobiographical concept of the self. It has been amply documented that irregularities in the DMN and its functional connectivity are associated with various neuropsychiatric disorders. Moreover, accumulating evidence also suggests that individuals with select medical disorders (i.e., metabolic disorders) demonstrate alterations in DMN activity and functional connectivity. However, there is a paucity of data evaluating whether individuals with metabolically-based medical conditions, exhibiting altered DMN activity and functional connectivity, are at increased risk for developing neuropsychiatric disorders. Likewise, potential mechanisms (e.g., altered brain metabolism, insulin resistance) mediating these changes and their implications for novel treatment approaches have yet to be elucidated. Taken together, the overarching aim of this review is to provide a synthetic overview that suggests that this neural circuit may represent a common (or convergent) substrate affected in individuals with select neuropsychiatric and metabolic disorders.