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

Abstract

Summary: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 H 2 O) in a test tube held immediately beneath the nostrils was compared to the response to sterile H 2 O 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 ( 2 test, P ‫ס‬ 0.03). Response amplitudes to vanilla in the patient group were within the range of those to sham stimuli.

Altered Frontal and Temporal Brain Function during Olfactory Stimulation in Adult Attention-Deficit/Hyperactivity Disorder

“…As the primary olfactory cortex is located in the medial orbitofrontal cortex, our measurements probably pertain to secondarylevel processes of odour perception, resulting in higher variability due to interindividual differences in cognitive processing. Activation in the reported brain areas is in accordance with the fNIRS [26][27][28][29][30] and fMRI literature [47] , giving support to the assumption that our results are no chance findings. Nevertheless future studies require improved technical (olfactometer) and methodical (higher number of stimulus presentations) approaches.…”

“…Increases in O 2 Hb and decreases in HHb concentrations are highly correlated with the blood oxygenation level-dependent signal changes measured with functional magnetic resonance imaging [20] and are reliable indicators of brain activation for sensory [21][22][23][24] and higher cognitive brain functions [24,25] in respective brain areas. Olfactory stimulation in healthy subjects has been shown to induce changes in O 2 Hb and HHb in the frontopolar, orbitofrontal, and temporal cortex [26][27][28][29][30] .…”

How to detect and reduce movement artifacts in near-infrared imaging using moving standard deviation and spline interpolation

“…The concentration changes of O 2 Hb, HHb and tHb are calculated using (i) the modified Lambert-Beer law (Delpy et al 1988, Sassaroli & Fantini 2004 or (ii) the diffusion approximation of the Boltzmann transport equation for the semi-infinite boundary condition (Arridge et al 1992). NIRI enables the measurement of evoked hemodynamic responses during stimulation of areas of the brain like the visual cortex (Karen et al 2008), motor cortex (Haensse et al 2005), auditory cortex (Zaramella et al 2001) and olfactory cortex (Fladby et al 2004). In this context, the terms "functional near-infrared spectroscopy" (fNIRS) or "functional near-infrared imaging" (fNIRI) are used.…”

Cerebrovascular hemodynamic correlates of aging in the Lou/c rat: A model of healthy aging

“…Memory performance was also recently correlated to hippocampal CBF 0 in healthy older adults (61-86 years) (Heo et al, 2010). Agerelated differences in the hemodynamic response to functional activation observed in neuroimaging studies are either a consequence of modified vascular reactivity or changes in neural and metabolic response to stimuli or both (Aizenstein et al, 2004;Ances et al, 2009;D'Esposito et al, 2003;Eppinger et al, 2007;Fladby et al, 2004;Herrmann et al, 2006;Langenecker et al, 2004;Mehagnoul-Schipper et al, 2002;Restom et al, 2007;Zysset et al, 2006). Aged brains show less lateralized and less specific regions of activation Lu et al, 2008), with greater response variability and noise (D'Esposito et al, 2003), and different effect sizes, which may be attributed to brain atrophy, or increased spatial variability.…”