Olfactory-evoked regional cerebral blood flow in Alzheimer's disease

Olfaction is impaired in Alzheimer's disease (AD). It was hypothesized that AD would reduce olfactory-evoked perfusion in mesial temporal olfactory (p iriform) cortex, where neuropathology begins. Seven AD patients and 8 elder ly controls (ECs) underwent olfactory threshold and identification tests an d olfactory stimulation during positron emission tomography. Odor identific ation was impaired in AD. but threshold was not. Olfactory stimulation in E Cs activated right and left piriform areas and right anterior ventral tempo ral cortex. AD patients had less activation in right piriform and anterior ventral temporal cortex but not in the left piriform area. Although orbital cortex did not activate in ECs. there was a significant between-groups dif ference in this area. Right piriform activation correlated with odor identi fication. impaired odor identification likely reflects sensory cortex dysfu nction rather than cognitive impairment. Given olfactory bulb projections t o the mesial temporal lobe. olfactory stimulation during functional imaging might detect early dysfunction in this region.