Intracortical depth analyses of frequency-sensitive regions of human auditory cortex using 7T fMRI

Abstract

Despite recent advances in auditory neuroscience, the exact functional organization of human auditory cortex (AC) has been difficult to investigate. Here, using reversals of tonotopic gradients as the test case, we examined whether human ACs can be more precisely mapped by avoiding signals caused by large draining vessels near the pial surface, which bias blood-oxygen level dependent (BOLD) signals away from the actual sites of neuronal activity. Using ultra-high field (7T) fMRI and cortical depth analysis techniques previously applied in visual cortices, we sampled 1 mm isotropic voxels from different depths of AC during narrow-band sound stimulation with biologically relevant temporal patterns. At the group level, analyses that considered voxels from all cortical depths, but excluded those intersecting the pial surface, showed (a) the greatest statistical sensitivity in contrasts between activations to high vs. low frequency sounds and (b) the highest inter-subject consistency of phase-encoded continuous tonotopy mapping. Analyses based solely on voxels intersecting the pial surface produced the least consistent group results, even when compared to analyses based solely on voxels intersecting the white-matter surface where both signal strength and within-subject statistical power are weakest. However, no evidence was found for reduced within-subject reliability in analyses considering the pial voxels only. Our group results could, thus, reflect improved inter-subject correspondence of high and low frequency gradients after the signals from voxels near the pial surface are excluded. Using tonotopy analyses as the test case, our results demonstrate that when the major physiological and anatomical biases imparted by the vasculature are controlled, functional mapping of human ACs becomes more consistent from subject to subject than previously thought.

Feature-dependent intrinsic functional connectivity across cortical depths in the human auditory cortex

“…The intra-subject variabilities at the intermediate and superficial depths were significantly smaller than that at the deep depth (one-tailed t -test: nd–nd = 0.1–0.3, p  = 0.006; nd–nd = 0.1–0.5, p  < 0.0001; nd–nd = 0.1–0.7, p  < 0.0001; nd–nd = 0.1–0.9, p  = 0.003). These results corroborated with the previous finding 21 that the superficial depth of the auditory cortex has a reletively large inter-subject variability due to more physiological and anatomical bias imparted by the venous vasculature towards the pial surface. However, the lowest inter- and intra-subject variability were found in the intermediate cortical depth.…”

Functional connectivity corresponding to the tonotopic differentiation of the human auditory cortex

“…In this study, in addition to determining that the RS‐FC between the HAC and other brain regions is frequency‐selective, we also have other findings. For instance, the task‐activation findings replicated previous findings showing that the tonotopic organization of the HAC has a high‐to‐low‐to‐high pattern across HG (Ahveninen et al, ; Da Costa et al, ; Humphries et al, ; Moerel, 2017). The additional prominent HFRs extending from the posterior STG to the anterior STG is also consistent with previous studies (Humphries et al, ).…”

Extensive tonotopic mapping across auditory cortex is recapitulated by spectrally-directed attention, and systematically related to cortical myeloarchitecture

“…Stimulus-and attentionally-driven tonotopic organization outside of auditory core. In line with results from previous fMRI studies Woods et al, 2009;Humphries et al, 2010;Barton et al, 2012;Dick et al, 2012;Moerel et al, 2012;Saenz and Langers, 2014;Thomas et al, 2015;De Martino et al, 2015b;Ahveninen et al, 2016;Leaver and Rauschecker, 2016;Riecke et al, 2016), there is stimulus-driven tonotopic mapping extending well beyond auditory core, spanning the temporal plane and continuing into the superior temporal sulcus (STS). As shown in Fig.…”

“…1f). We time-reversed runs stepping down in frequency and averaged them with runs stepping up in frequency (Sereno et al, 1995;Dick et al, 2012;Ahveninen et al, 2016). Cross-subject averaging of phase-encoded mapping data was performed using a method described previously (Hagler et al, 2007) in which the real and imaginary components of the signal with respect to the stepped cycle were sampled to the cortical surface and then averaged across subjects, preserving any phase information that was coherent over subjects.…”