ACHE and Mental deterioration: The connection between olfactory impairment and cognitive decline was further revealed by PET studies: positive correlations between UPSIT scores and acetylcholinesterase (AChE) activities were found in the hippocampal formation, amygdala and neocortex (R = 0.56, P < 0.0001; R = 0.50, P < 0.0001; R = 0.46, P = 0.0003; respectively); while limbic AChE activity also correlated positively with executive cognitive ability (r = 0.36, P = 0.006) and verbal memory (r = 0.29, P = 0.03) [70].