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Mapping Brain Activity of Patients with Smell Dysfunction

We then proceeded to perform another series of studies in patients with smell loss.

Purpose: Our next goal was, to use functional MRI (fMRI) to develop an objective, noninvasive technique by which patients with smell loss could be identified, their abnormalities quantitated, their results compared to findings in normal subjects and visual representation of their central nervous system (CNS) pathology obtained.

Methods: fMRI brain scans were obtained in eight patients with hyposmia in response to three olfactory stimuli (pyridine, menthone, amyl acetate) in three coronal brain sections selected from anterior to posterior temporal brain regions using multislice FLASH MRI and results were compared to similar studies performed in 17 normal subjects. Activation images were derived using correlation analysis and ratios of area of brain activated to total brain area were obtained.

Results: Brain activation to each stimulus was lower in each section in patients compared to normal subjects and reached statistical significance for mean activation for each odor and in six of the nine individual sections studied. Activation in patients was found in regions previously associated with CNS processing of olfactory stimuli in normal subjects but activation in patients was much less, particularly in inferior frontal and cingulate gyral regions of frontal cortex and in regions of medial and posterior temporal cortex.

Conclusion: These results demonstrate quantitative CNS changes in smell function in response to olfactory stimuli in patients with hyposmia, demonstrate a novel, objective method by which these patients can be identified and provide maps of the CNS changes associated with their smell loss.

In the accompanying photograph we compared the response to pyridine in a representative normal subject (top, 22y woman) with that in a representative patient with allergic rhinitis (bottom, 37y man). This vapor induced the greatest degree of activation in both normal subjects and patients with hyposmia, Three brain sections, anterior, middle and posterior are shown from left to right. In the normal subject, activation is observed in each section. Anterior section: activation observed in frontal cortex, bilaterally, in the posterior medial orbitofrontal cortex and in the left temporal tip; Middle section: activation observed in the frontal cortex, bilaterally, in the right cingulate cortex and in the temporal cortex, bilaterally; Posterior section: activation observed in frontal cortex, bilaterally, in the left cingulate cortex and near the left hippocampus. In the patient, activation is observed in each section but markedly less than that observed in the normal subject. Anterior section: activation observed in frontal cortex, bilaterally, but there is no inferior frontal cortex activity; Middle section: activation observed only in left frontal cortex; Posterior section: activation observed in posterior frontal cortex, bilaterally and at the posterior portion of the right insular cortex. The yellow-red color of activated areas reflect a continuum of activation over a range of correlation coefficients from 0.7 (yellow) to red (to 1.0)
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22-year-old woman


37-year-old man

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