Olfactory Response in the Temporal Cortex of the Elderly Measured with Near-Infrared Spectroscopy: A Preliminary Feasibility Study

Abstract

The pathway for the olfactory response may be affected at an early stage of Alzheimer's disease. Measurement of the olfactory response in the elderly is therefore of particular interest. In this feasibility study, near-infrared spectroscopy was used to measure the olfactory response in 21 patients aged 56 to 79 years. Eight subjects had no memory complaints whereas 13 had subjective memory complaints, mild cognitive impairment, or very mild Alzheimer's disease. The optodes were placed over the temporal lobe, with the emitting optode over the pole and the receiving optode over the superior gyrus. The response to vanilla (1% in sterile H₂O) in a test tube held immediately beneath the nostrils was compared to the response to sterile H₂O only. Four control subjects had a clearly definable response with increased oxyhemoglobin and decreased deoxyhemoglobin bilaterally. The response was measured as the sum of the deviation of oxygenated and deoxygenated hemoglobin from baseline mean. With a cut-off determined after examination of responses to vanilla and sham stimulus, group difference was significant for response to vanilla (χ² test, P = 0.03). Response amplitudes to vanilla in the patient group were within the range of those to sham stimuli.