Asymmetric Interhemispheric Transfer in the Auditory Network: Evidence from TMS, Resting-State fMRI, and Diffusion Imaging

Abstract

Hemispheric asymmetries in human auditory cortical function and structure are still highly debated. Brain stimulation approaches can complement correlational techniques by uncovering causal influences. Previous studies have shown asymmetrical effects of transcranial magnetic stimulation (TMS) on task performance, but it is unclear whether these effects are task-specific or reflect intrinsic network properties. To test how modulation of auditory cortex (AC) influences functional networks and whether this influence is asymmetrical, the present study measured resting-state fMRI connectivity networks in 17 healthy volunteers before and immediately after TMS (continuous theta burst stimulation) to the left or right AC, and the vertex as a control. We also examined the relationship between TMSinduced interhemispheric signal propagation and anatomical properties of callosal auditory fibers as measured with diffusion-weighted MRI. We found that TMS to the right AC, but not the left, resulted in widespread connectivity decreases in auditory-and motor-related networks in the resting state. Individual differences in the degree of change in functional connectivity between auditory cortices after TMS applied over the right AC were negatively related to the volume of callosal auditory fibers. The findings show that TMS-induced network modulation occurs, even in the absence of an explicit task, and that the magnitude of the effect differs across individuals as a function of callosal structure, supporting a role for the corpus callosum in mediating functional asymmetry. The findings support theoretical models emphasizing hemispheric differences in network organization and are of practical significance in showing that brain stimulation studies need to take network-level effects into account.

Development of large-scale functional networks from birth to adulthood: A guide to the neuroimaging literature

“…As an example, simulation experiments using structure-function models have predicted that even purely focal and transient perturbations in activity should result in diffuse network reorganization that affects distant brain systems (Alstott et al, 2009; Honey and Sporns, 2008; Misic et al, 2015). In our recent paper, we presented experimental validation of these ideas through focal pharmacogenetic inactivation (Grayson et al, 2016), and similar findings were presented by (Andoh et al, 2015) using cortical transcranial magnetic stimulation. Both works demonstrate a causal effect on distributed resting-state connectivity and other neurophysiological signatures, driven by cascading neuronal interactions.…”

“…As a proof-of-principle, recent studies have found that even purely local, experimentally induced perturbations (e.g. exogenous stimulation or inactivation) result in widespread, complex neurophysiological changes, which are at least partly explainable as local interactions with global network structure (Andoh et al, 2015; Grayson et al, 2016; Gu et al, 2015a; Misic et al, 2015). By extension, one could reason that developmental modifications in brain FC, whether normative or pathological, are also best understood via an emerging network science that merges structural and functional connectivity data.…”

Magnetic stimulation of visual cortex impairs perceptual learning

“…It can be noted that TMS on a specific area may induce not only local but also distant effects on the activity of large-scale brain networks (Eldaief et al, 2011) (Cocchi et al, 2015 (Andoh et al, 2015)and subsequent behavioral impairment (Ruff et al, 2006). Accordingly, since IPS is hierarchically higher than the targeted visual areas and exhibits a large number of connections, its stimulation may affect both regions functionally and anatomically connected within the DAN as well as the lowlevel visual areas top-down controlled by IPS during visuo-spatial attention tasks (Bressler et al, 2008).…”

Non-Invasive Brain Stimulation in Dementia: A Complex Network Story

“…Inhibitory cTBS over the somatosensory cortex (S1) reduced FC between the stimulated region and functionally connected motor network regions [42]. Similarly, cTBS over the bilateral auditory cortex reduced FC within the auditory network [41]. These studies suggest that cTBS may be more effective than ctDCS in inhibiting FC.…”