In the BMC Neurology study, the patient group with olfactory impairment also had 14% less hippocampal volume than the non-impaired patient group. Odor identification ability is a complex function that relies on processing in a network of several brain regions, including the hippocampus, which is also involved in memory.
“When an odor enters the nose and activates the nerves in the olfactory bulb, information is sent directly to the entorhinal cortex next to the hippocampus, and from there to the hippocampus,” study co-author Asta Kristine Håberg, MD, PhD, a professor of neuroscience at Norwegian University of Science and Technology who is currently a Fulbright Scholar at the McKnight Brain Institute at the University of Arizona, Tucson, told Psychiatry Advisor.
“The earliest changes in Alzheimer’s dementia take place in the the entorhinal cortex and the hippocampus,” she added. “This is one reason why odor identification ability is considered a possible marker of dementia.”
Changes in these structures, such as loss of brain tissue, can lead to reductions in the ability to identify odors, and “a more rapid loss of brain tissue in the hippocampus is known to predispose for conversion of mild memory problems to Alzheimer’s dementia,” says Håberg.