Although fMRI is great for a lot of things, it also presents challenges, especially for auditory neuroscience. Echoplanar imaging is loud, and this acoustic noise can obscure stimuli or change the cognitive demand of a task (Peelle, 2014). In addition, patients with implanted medical devices can't be scanned.
My lab has been working with Joe Culver's optical radiology lab to develop a solution to these problems using high-density diffuse optical tomography (HD-DOT). Similar to fNIRS, HD-DOT uses light spectroscopy to image oxygenated and deoxygenated blood signals, related to the BOLD response in fMRI. HD-DOT also incorporates realistic light models to facilitate source reconstruction—this of huge importance for studies of cognitive function and facilitates combining results across subjects. A detailed description of our current large field-of-view HD-DOT system can be found in Eggebrecht et al. (2014).
Because HD-DOT is relatively new, an important first step in using it for speech studies was to verify that it is indeed able to capture responses to spoken sentences, both in terms of effect size and spatial location. Mahlega Hassanpour is a PhD student who enthusiastically took on this challenge. In our paper now out in NeuroImage (Hassanpour et al., 2015), Mahlega used a well-studied comparison of syntactic complexity looking at sentences containing subject-relative or object-relative center embedded clauses (taken from our previous fMRI study; Peelle et al 2010).
Consistent with previous fMRI work, we found a sensible increase from a low level acoustic control condition (1 channel vocoded speech) to subject-relative sentences to object-relative sentences. The results were seen at both the single subject level (with some expected noise) and the group level.
We are really glad to see nice responses to spoken sentences with HD-DOT and are already pursuing several other projects. More to come!
Eggebrecht AT, Ferradal SL, Robichaux-Viehoever A, Hassanpour MS, Dehghani H, Snyder AZ, Hershey T, Culver JP (2014) Mapping distributed brain function and networks with diffuse optical tomography. Nature Photonics 8:448-454. doi:10.1038/nphoton.2014.107
Hassanpour MS, Eggebrecht AT, Culver JP, Peelle JE (2015) Mapping cortical responses to speech using high-density diffuse optical tomography. NeuroImage 117:319–326. doi:10.1016/j.neuroimage.2015.05.058 (PDF)
Peelle JE, Troiani V, Wingfield A, Grossman M (2010) Neural processing during older adults' comprehension of spoken sentences: Age differences in resource allocation and connectivity. Cerebral Cortex 20:773-782. doi:10.1093/cercor/bhp142 (PDF)