Neuroanatomical and Functional Correlates in Bipolar Disorder (BD): A Narrative Review

The incidence of mood disorders in the general population is quite high. Among the most common is bipolar disorder (BD), often associated with severe mood disorders, psychotic changes (e.g., delusions, hallucinations), impulsivity, and self-harm. However, its correct diagnosis is challenging, primarily due to the heterogeneity of clinical and symptomatic features, as well as individual differences among patients, such as comorbidity with other disorders (e.g., borderline personality disorder). Therefore, to improve understanding of its etiology and pathogenesis, refining the diagnosis must be a priority. Given the breadth and complexity of the evidence in the literature, we believe it is useful to provide a clear and comprehensive summary of the neuroanatomical and dysfunctional alterations observed, with particular attention to the prefrontal cortex, anterior cingulate cortex, cerebral ventricles, amygdala, hippocampus, cerebellum, and white matter. Through functional neuroimaging investigations it is possible to distinguish two main forms of bipolarism: the first (BD-I) is the most severe form, both in terms of manifested symptoms and in the structural and functional alterations detected; the second (BD-II) is the less severe form, which presents attenuated symptoms and mild or medium-severe alterations compared to the normotype criteria. Literature highlights the need to identify a precise study model, whether neuro-evolutionary or neuro-progressive or mixed, capable of offering clinical therapists greater scientific basis on which to anchor their diagnostic interpretations, and certainly the use of functional neuroimaging technology can be a good option even if it still presents costs that are not easily and freely sustainable by patients.