fMRI 2008: Review and Update
Functional Magnetic Resonance Imaging (fMRI) is less than 20 years old, yet has provided unique insight into auditory, language, and cognitive processing. fMRI is non-invasive and measures hemodynamic (blood flow and circulation) changes associated with enhanced neural activity (Logothetis, 2008).In essence, the fMRI compares brain activity with and without specific stimulation. Stimulation can be intrinsic or extrinsic, such as cognitive thought, memory, recognition tasks, music, speech, noise, light, pain, smells, heat, cold etc.When a sound is perceived and neurons in the central auditory nervous system are stimulated, local blood flow increases and these changes are captured and revealed using fMRI. Specifically, as active nerves consume oxygen, more oxygen is carried by hemoglobin via the red blood cells. As oxygen is used by nerves, blood flow to that region increases, and again, the changes in blood flow are reflected in the fMRI through a technique called Blood Oxygen Level Dependent (BOLD) fMRI.
Specifically, BOLD fMRI has been used to demonstrate that auditory processing in patients with Chronic Fatigue Syndrome (CFS) is different than in controls (Lange, 2005). Lange et. al. theorized that CFS patients used more of their frontal and parietal lobes than controls to process challenging auditory information. Their work showed CFS patients can process challenging auditory information as accurately as controls but they involve more extensive regions of their brain to accomplish the task.
Previous psycho-physical and neuro-physiologic tests have demonstrated how sensory loss in one area can lead to increased functional sensitivity in another area. Dieterich (2007) and colleagues demonstrated the first evidence of visual substitution for chronic bilateral vestibular failure through use of fMRI.
Yetkin (2004) and colleagues used fMRI to trace the cortical and sub-cortical auditory pathways of a pure tone, as it traversed the medial geniculate body, inferior colliculus, lateral lemniscus, superior olivary complex and the cochlear nucleus.
The potential for fMRI to help define pathways and processes in auditory neuropathy/dys-synchrony, all manner of vestibular studies, auditory processing, and other auditory-stimuli-based phenomena is vast and essentially unlimited. fMRI is arguably the best tool for gaining insight brain functions (Logothetis, 2008).
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology.
For More Information, References and Recommendations:
Dieterich, M., Bauermann, T., Best, C, Stoeter, P and Schlindwein, P. (2007): Evidence for Cortical Visual Substitution of Chronic Bilateral Vestibular Failure: An fMRI Study. Brain, 2007, August; 130 (pt 8):2108-16, Epub 2007, Jun 15.
Lange, G., Steffener, J., Cook, D.B., Bly, B.M., Christodoulou, C., Liu, W.C., DeLuca, J and Natelson, B.H. (2005): Objective Evidence of Cognitive Complaints in Chronic fatigue Syndrome: A BOLD fMRI Study of Verbal Working Memory.
Logothetis, N.K. (2008): What we can and what we cannot do with fMRI. Nature, Vol 453, Jun 12, 2008.doi:10.1038/nature06976.
Yetkin, F.Z., Roland, P.S., Mendelsohn, D.B and Purdy, P.D. (2004) Functional magenetic Imaging of Activation in Subcortical Pathway. Laryngoscope. 114 (1) : 96-101January.