The Bipolar Spectrum: can brain scans resolve diagnostic uncertainty?
The concept of manic-depression was extended some years back to cover less extreme manifestations characterised by hypomania (Bipolar II), as well as the classical form, defined by mania (Bipolar I). But other forms (perhaps less dramatic, though still a cause of much suffering) also exist.
These ‘softer’ forms of bipolar illness appear to blur into unipolar depression and perhaps also with the category which has been termed, borderline personality disorder. Although there has been a trend to view psychiatric disorders as points on a spectrum, rather than as discrete, encapsulated diagnoses, many psychiatrists would hesitate to equate borderline personality disorder and bipolar illness. Ultimately the matter will be resolved when we fully grasp the underlying neurobiology of affective disorders.
A new paper from researchers based in Sydney provides an authoritative and balanced account of the current state of our knowledge. The authors elegantly summarise the functional MRI literature across the hypothesised spectrum. One feature appears to be common across the various disorders – limbic hyperactivity. Perhaps this is not so surprising as the limbic system is the ‘seat’ of emotion, and all the various disorders/forms are characterised by emotional upset.
But there also appear to be differences. For example, the orbitofrontal cortex (a higher centre, which ‘dampens’ and regulates emotion) appears to be underactive in bipolar I, but not in unipolar depression nor in borderline personality disorder.
Further work will be needed before clear-cut conclusions can be drawn. The authors conclude…”Eventually, as the respective signatures of personality-based emotional dysregulation and bipolar mood dysregulation become increasingly crisp, we may be able to use functional neural profile to assist in clarifying diagnosis or treatment options in clinically muddy presentations, although a great deal of work will need to be done before imaging will be sufficiently robust to be used in this manner.”
The full paper can be read here:
http://www.expert-reviews.com/doi/pdfplus/10.1586/ern.12.126
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