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Table 1 Summary of pathological and imaging evidence of parasympathetic nervous system and olfactory system involvement in PD

From: The underlying mechanism of prodromal PD: insights from the parasympathetic nervous system and the olfactory system

Structure α-syn pathology Structural imaging Functional imaging Molecular imaging
Vagus nerve Positive NA NA NA
Gastrointestinal tract Controversy NA NA Decreased 11C-donepezil standard uptake values in the small intestine and pancreas following a rostral-caudal gradient [43]
Olfactory bulb Positive Bilateral reduction of olfactory bulb volume [64, 65, 68] NA NA
Olfactory tract Positive Bilateral increase of mean diffusivity [66, 67] NA NA
Olfactory cortex Positive Decrease of olfactory sulcus depth; decrease of piriform cortex volume [68, 71] Reduced activation in amygdala and hippocampal formation after olfactory stimulation [7274]; decreased regional homogeneity and functional connectivity within olfactory cortex and decreased connectivity within limbic/paralimbic networks [75] Reduced glucose metabolism in bilateral medial prefrontal cortex and parieto-occipito-temporal cortex [76]; positive correlations between UPSIT scores and acetylcholinesterase activities in hippocampal formation, amygdala and neocortex [70]; positive correlations between UPSIT scores and vesicular monoamine transporter type 2 binding potential in striatum [70]; positive correlations between UPSIT scores and dopamine transporter binding potential in hippocampus, amygdala and striatum [78]