Benefit and limitation of combining MEG and fMRI to study correlates of perception in the auditory cortex.

J Acoust Soc Am. 2012 Apr;131(4):3387

Authors: Gutschalk A, Steinmann I, Wiegand K, Dykstra A

Abstract
MEG is a strong tool for cognitive hearing research, because it allows for studying the brain's function in silence and with high temporal precision. However, MEG's ability to clearly separate neighboring sources, e.g. primary and secondary auditory cortex, is limited. While fMRI is more precise with respect to the latter requirement, it lacks the previous two advantages. Here we will demonstrate two examples of combined MEG and fMRI: The first example is perceptual awareness under informational masking. MEG revealed a distinct negative response that is evoked when listeners indicated to be aware of targets in presence of an informational masker, but not when targets were successfully masked. Earlier activity from primary auditory cortex was evoked by all targets and was independent of perceptual awareness. Nevertheless, fMRI shows that activity related to awareness is, at least in part, also generated in the primary auditory cortex. The second example is periodicity pitch; while MEG has consistently revealed responses related to periodicity and supposedly pitch in lateral Heschl's gyrus, fMRI results have been inconsistent. In a direct comparison, we could show that fMRI activity is not predominantly related to the evoked pitch response in MEG, demonstrating limitations for the combination of the techniques.

PMID: 22501923 [PubMed - in process]