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Mirror Neurons: Introduction
In January of this year, a group of teenagers, nearly all girls, in the small town of Le Roy in western New York suddenly came down with severe Tourette-like symptoms. The case attracted extensive media attention and has been the subject of articles in the Huffington Post and New York Times, stories on local news stations, as well as YouTube and Facebook posts. Two of the girls also appeared on the Today Show, accompanied by their distraught mothers. Environmental toxins from the town's old Jell-O® factories, a 1970 toxic train accident, PANDAS (pediatric autoimmune neuropsychiatric disorders associated with Streptococcus infection), and other unlikely etiologies have been put forward as possible explanations for this unusual phenomenon, but neurologists have confidently diagnosed conversion disorder. It is a classic case of mass hysteria.
Conversion Disorder and Mass Hysteria
Conversion disorder, or hysteria, dates back at least to the days when Egyptians were writing on papyrus rather than tweeting on Twitter. The term indicates "a disturbance of body function that is characterized by neurological, sensory, or motor symptoms for which the available medical explanations either do not explain, or fail to account for the severity of, the patient's impairment." Conversion disorder affecting groups of people (mass hysteria) often occurs in schools or other closed communities. Odors or gas leaks (perceived or real) are common contemporary triggers.
Neurobiology of Conversion Disorder
To understand conversion disorder from a neurobiological standpoint, one must accept that the mind is the product of the brain. Multiple models have been proposed to explain conversion reactions. Freud proposed the concept of "conversion" of intolerable memories into somatic symptoms. The concept of "neodissociation" has been suggested, in which a patient with loss of function, such as hysterical visual loss, still processes visual stimuli that influences his or her behavior, yet he or she is not consciously aware of the visual input. Conversion symptoms have also been attributed to "rogue representations" of sensory data that are mistakenly integrated into consciousness.
Another theory suggests that conversion states are a protective strategy that invoke a prelearned behavioral state. One complex hypothesis implicates "false body mapping," requiring dysfunction in a circuit that contains the cingulate cortex, insula, thalamus, brainstem nuclei, amygdala, ventromedial prefrontal centers, supplemental motor area, and other key areas. Another postulate is dysfunction of the striatothalamocortical pathways, which control sensorimotor function and voluntary motor behavior. Advances in neuroimaging, such as functional MRI (fMRI), magnetoencephalography (MEG), SPECT, and transcranial magnetic stimulation (TMS), are supplying the tools to scientifically investigate the neurologic circuitry involved.
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