Alzheimer's Often Attacks Area of Brain Responsible for Smell

Dorian Martin Health Guide
  • In 2004, we finally got Mom to agree to go through a battery of assessments to see if she had Alzheimer’s disease. It was terribly stressful for her because she had watched her own mother succumb to this condition and was terrified that she was going to succumb.  Our family gathered together for the doctor’s pronouncement at the end of the study. At that point, we had good news – Mom had mild cognitive impairment. (She would develop Alzheimer’s disease by the following year.) One of the doctor’s points was that Mom still had her sense of smell, which was a key indicator that she hadn’t developed Alzheimer’s disease.

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    I remember being fascinated at the time that the battery of assessments for Alzheimer’s disease included a test for this sense. In doing some research for this sharepost, I learned the sense of smell is controlled by the brain’s olfactory regions. Three regions in this part of the brain are stimulated when you use your sense of smell -- the orbitofrontal cortex located just above and behind the eyes, the insula located beneath the ears, and the piriform cortex located between the two previous brain areas. These olfactory regions also are active when we experience emotions and when we memorize events. Interestingly, unlike our other senses – which are controlled by the thalamus and can be “turned off” when we focus one sense intently on a specific task, such as reading – the sense of smell cannot be turned off while you are awake. Therefore, you will always detect scents if your sense of smell is working.

    And that brings us to smell and dementia. Many researchers have studied whether there is any linkage between the sense of smell and this cognitive condition. A meta-analysis conducted by researchers from the University of Michigan and the Ann Arbor VA Medical Center looked at approximately 1,200 studies on the sense of smell and Alzheimer’s. Their review determined that there is an association between the loss of smell and Alzheimer’s disease; however, the researchers did not find enough evidence to determine that the loss of smell alone can predict if the disease is present. They pointed out that multiple reasons can be behind the loss of smell, including aging, exposure to toxic agents, or a decreased level of hydration.

    However, a more recently published study out of the University of Florida tried to identify a way to assess the sense of smell in order to confirm a diagnosis of Alzheimer’s disease.  This study involved 94 participants. Of those, 24 had mild cognitive impairment, 18 had early stage Alzheimer’s disease, 26 had other types of dementia and 26 didn’t have any cognitive impairment.

    Participants were asked to close their eyes and mouths and breathe through only one nostril at a time. The researchers then held an opened container of peanut butter at the end of a 30-centimeter ruler. They then moved the container up 1 centimeter whenever the participant exhaled until the participant detected the peanut butter’s smell. At this point, the researchers measured the distance between the participant’s nostril and the container of peanut butter. After a 90-second break, the test was repeated using the other nostril. Throughout this experimentation, the researchers did not know who had been diagnosed with Alzheimer’s disease.

  • This evaluation found that people with early stage Alzheimer’s disease did not detect the odor of peanut butter when using their left nostril until the container was 5.1 centimeters away. In comparison, these participants could smell the peanut butter when it was 17.4 centimeters away from their right nostril.  The researchers pointed out that this finding might make sense since the degeneration of the brain when Alzheimer’s is present occurs more often in the left hemisphere as opposed to the right hemisphere.

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    So what if your loved one is losing the sense of smell? I’d encourage you to consult a doctor about this and not assume that the loved one is developing Alzheimer’s or dementia. The peanut butter test should be considered as only one assessment in a battery of tests that may be used to make a diagnosis.

    Primary Sources for This Sharepost:

    Cleveland Clinic. (2013). Peanut butter test may detect Alzheimer’s.

    Frasnelli, J. (2011). With which part of the brain do we smell?

    Stamps, J.J., et al. (2013). A brief olfactory test for Alzheimer’s disease. Journal of the Neurological Sciences.

    U.S. Department of Veterans Affairs. (ND). Does failing sense of smell predict Alzheimer’s?

Published On: May 06, 2014