The sense of smell (olfactory sense) works to match up odorant molecules in the air and memories stored in the brain. Those memories are not housed in a single place, but instead extend across many regions. Consequently, proper functioning of smell is quite sensitive to damage in the brain. In particular, during onset of Alzheimer’s, smell is also the first sense to be affected: the hallmark protein tangles of Alzheimer’s appear early in the olfactory bulb. But besides Alzheimer’s, traumatic brain injury (TBI) and Parkinson’s also affect the olfactory sense.
The three studies listed below all made use of the University of Pennsylvania Smell Identification Test (UPSIT), in which 40 common odourants are embedded in microcapsules in the pages of a booklet. A person being tested scratches the relevant strip and sniffs the odor (“scratch and sniff”), then chooses from one of four options in order to identify what they think they are smelling. The test is well-validated. Consequently, the use of the UPSIT is a promising inexpensive preliminary screening tool for Alzheimer’s as well as TBI.
Links to four articles together with three research publications have been posted in Alzheimers > Diagnosis & Tests:
Odor identification and Alzheimer disease biomarkers in clinically normal elderly