The tetrad of Parkinson's disease (PD) including tremor, rigidity, akinesia and postural instability are attributed to the loss of dopaminergic neurons in the substantia nigra. Both environmental factors and genetic predisposition are supposed to be implicated in the initiation and progression of the disease. Particularly, much attention has been focused on α-synuclein (αSYN) since αSYN is not only found in Lewy bodies characteristic of PD, but also mutations in the gene for αSYN can cause inherited forms of PD. Recent studies have shown that αSYN can be secreted into the extracellular milieu, thereby propagate Lewy pathology to neighboring cells in a prion-like manner. This concept sounds attractive as an acceptable explanation for the stereotypic distribution of Lewy pathology in PD. In addition to the classic motor symptoms, a variety of non-motor manifestations may affect on the patient's quality of life. Of all, hyposmia is prevalent in PD and may precede the onset of motor symptoms. We found that odor identification test scores correlated positively with the impairment of short-term memory and visuospatial functions. Furthermore, our data from fear-conditioning experiment indicated that the key player in the processing of emotional memories appears to be the amygdala, which has tight connections to primary olfactory areas.
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