The exact mechanism affecting the inherited vulnerability has not been established, and the precise etiology of Tourette syndrome is not known. Tics are believed to result from dysfunction in the central nervous system,[8] in the cortical and subcortical regions, the thalamus, basal ganglia, and frontal cortex of the brain.[3] Neuroanatomic models implicate failures in circuits connecting the brain's cortex and subcortex,[5] and imaging techniques implicate the basal ganglia and frontal cortex.[14][15][16] Research presents considerable evidence that abnormal activity of the brain chemical, or neurotransmitter, dopamine, is involved.[17] Dopamine excess or supersensitivity of the postsynaptic dopamine receptors may be an underlying mechanism of Tourette syndrome.[18][19][20][21] Other neurotransmitters may also be involved.[12]