BOLD responses in human auditory cortex are more closely related to transient MEG responses than to sustained ones.
Blood oxygen level dependent-functional magnetic resonance imaging (BOLD-fMRI) and magnetoencephalographic (MEG) signals are both coupled to postsynaptic potentials, although their relationship is incompletely understood. Here, the wide range of BOLD-fMRI and MEG responses produced by auditory cortex was exploited to better understand the BOLD-fMRI/MEG relationship. Measurements of BOLD and MEG responses were made in the same subjects using the same stimuli for both modalities. The stimuli, 24-s sequences of click trains, had duty cycles of 2.5, 25, 72, and 100%. For the 2.5% sequence, the BOLD response was elevated throughout the sequence, whereas for 100%, it peaked after sequence onset and offset and showed a diminished elevation in between. On the finer timescale of MEG, responses at 2.5% consisted of a complex of transients, including N(1)m, to each click train of the sequence, whereas for 100% the only transients occurred at sequence onset and offset between which there was a sustained elevation in the MEG signal (a sustained field). A model that separately estimated the contributions of transient and sustained MEG signals to the BOLD response best fit BOLD measurements when the transient contribution was weighted 8- to 10-fold more than the sustained one. The findings suggest that BOLD responses in the auditory cortex are tightly coupled to the neural activity underlying transient, not sustained, MEG signals.
Gutschalk
Alexander
A
Department of Neurology, Ruprecht-Karls-Universität Heidelberg, 69120 Heidelberg, Germany. Alexander.Gutschalk@med.uni.heidelberg.de
Hämäläinen
Matti S
MS
Melcher
Jennifer R
JR
D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008954:Models, Biological; D010100:Oxygen / Q000097:blood*; D011930:Reaction Time; D055366:Synaptic Potentials / Q000502:physiology*; D013997:Time Factors
D010100:Oxygen