Another Angle on Alzheimer’s Disease and Smell?
Is reduced size of olfactory brain areas cause or effect?
The link between Alzheimer’s disease and smell loss is one of the most thoroughly documented instances of a neuropathological process impacting odor perception. In fact, further studies of the clinical correlation don’t add much value at this point.
More interesting is whether the AD-smell link tells us anything interesting about the neural and cognitive organization of odor perception. We’ve known since 1987 that neuritic plaques and neurofibrillary tangles characteristic of AD are found in the olfactory bulb. In other words, the disease may interfere with the earliest neural processing stages of odor.
Now an MRI study by Al-Otaibi et al. suggests that parts of the olfactory cortex show reduced volume in AD. Could this reflect another aspect of the disease process? Perhaps. But we also know that acquired anosmia leads to reduced olfactory bulb volume, almost like a disuse atrophy. So it is also possible that Al-Otaibi et al.’s finding is just a secondary consequence—in other words, the AD neuropathology disrupts smell processing which in turn shrinks the olfactory cortex.
Al-Otaibi, M., Lessard-Beaudoin, M., Castellano, C. A., Gris, D., Cunnane, S. C., & Graham, R. K. (2020). Volumetric MRI demonstrates atrophy of the olfactory cortex in AD. Current Alzheimer Research, 17(10), 904–915.