Neural correlates of 'functional' symptoms in neurology.

Functional symptoms are neurological deficits that are not explained by organic lesions in the nervous system, but usually associated with emotional "psychogenic" disturbances. These symptoms are common and can affect any aspect of elementary neurological function, presenting clinicians with difficulties in definition, diagnosis, and treatment. Although current concepts explain functional symptoms in the context of "psychogenic" stress, the exact nature of these symptoms remains largely unknown. Recent functional neuroimaging studies have shifted understanding of these deficits from a psychological and psychodynamic model to a neurobiological model. This review highlights the advances made using functional neuroimaging techniques in patients suffering from two conditions: unilateral loss of motor function and psychogenic parkinsonism. The evidence suggests that areas including the prefrontal and parietal cortices, anterior cingulate cortex, thalamus, and basal ganglia may be implicated. Future studies, assessing patients at different phases of their illness and using newer techniques such as functional MRI, are needed to extend current findings on functional symptoms.