Neuroimaging of Functional Neurological Symptoms

Abstract

Functional neurological symptoms, or conversion disorders, have been described since the beginning of written medicine. Although originally attributed to a uterine disorder and first described as in a gynaecological text by the Middle Ages they were recognised as disorder of brain then of psyche. In the nineteenth century Charcot described them as being caused by a functional neurological lesion; one that evaded the availbel techniques of the day. A century on the technique shave become available that allow a search for these putative mechansims. In this chapter we review diagnosis and clinical presentation of functional symptoms which allows to speculate on potential mechanisms and hypothesise about potential target areas and paradigms for imaging. We then review all the imaging studies up until the end of 2012. To date the imaging conducted, both structural and functional, allow to be reasonably secure in concluding that functional neurological symptms are a genuine entity and not simply feigned. We cannot however make any claims that the underpinning mechansims of FNS have been resolved. We speculate that there are overly sensitive amygdala fear responses (i.e. abnormal response to stimuli (even objectively neutral stimuli), possibly conditioned by previous learning experiences) that drive changes in networks mediating ­perceptual experiences and/or movement plans. These changes, in the presence of abnormal self-directed attention (cf. prefrontal activations in functional imaging studies), are capable of producing movements or perceptual experiences which are not associated with a normal sense of self-agency and are therefore interpreted by patients as involuntary symptoms of an underlying disease.