Olfaction and Cognitive Impairment

Comprehensive List of Relevant Pathways for the Olfactory System by XenusG (CCBY 3.0)

I came across this paper (via the Alzforum) in which the researchers compared people with mild cognitive impairment (amnestic and non-amnestic), Alzheimer’s Type Dementia (DAT) and subjective cognitive impairment. The researchers found that people with amnestic mild cognitive impairment and DAT were less able to detect smells than the other participants. These findings replicated those from other studies and suggest that the olfactory apparatus can be a marker of the pathology leading to DAT.

Just to unpick this a bit further the rationale would be as follows. The olfactory apparatus is directly connected to the limbic system which also includes the hippocampi which are the key memory structures implicated in DAT. Amnestic MCI can be a precursor (although not invariably) to DAT and so both Amnestic MCI and DAT may share common pathological mechanisms.

Thus if the limbic system is affected by this pathology then not only will it affect memory but also olfaction (smell). Of course this is an oversimplified explanation. For instance there is no reason to suppose that all components of the Limbic system will be similarly affected by the same pathology. Regardless of the aetiology these findings do however suggest that there is a correlation between the sense of smell and the cognitive difficulties seen in amnestic MCI and also in DAT.

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