Selective modulation of interhemispheric connectivity by transcranial alternating current stimulation influences binaural integration

Abstract

Brain connectivity plays a major role in the encoding, transfer, and integration of sensory information. Interregional synchronization of neural oscillations in the γ-frequency band has been suggested as a key mechanism underlying perceptual integration. In a recent study, we found evidence for this hypothesis showing that the modulation of interhemispheric oscillatory synchrony by means of bihemispheric high-density transcranial alternating current stimulation (HD-TACS) affects binaural integration of dichotic acoustic features. Here, we aimed to establish a direct link between oscillatory synchrony, effective brain connectivity, and binaural integration. We experimentally manipulated oscillatory synchrony (using bihemispheric γ-TACS with different interhemispheric phase lags) and assessed the effect on effective brain connectivity and binaural integration (as measured with functional MRI and a dichotic listening task, respectively). We found that TACS reduced intrahemispheric connectivity within the auditory cortices and antiphase (interhemispheric phase lag 180°) TACS modulated connectivity between the two auditory cortices. Importantly, the changes in intra- and interhemispheric connectivity induced by TACS were correlated with changes in perceptual integration. Our results indicate that γ-band synchronization between the two auditory cortices plays a functional role in binaural integration, supporting the proposed role of interregional oscillatory synchrony in perceptual integration.

Experience-dependent weakening of callosal synaptic connections in the absence of postsynaptic FMRP

“…This result suggests that reduced functional coherence between bilateral barrel cortices in Fmr1 KO mice could be due to a disrupted communication between the cortices through the weakened monosynaptic transmission. Interhemispheric functional connectivity is thought to shape perceptual integration including those involved in speech comprehension and global form processing, domains that are impaired in ASD (Booth and Happé, 2018;Friederici et al, 2007;Happe and Frith, 2006;Peiker et al, 2015;Preisig et al, 2021;Simon and Wallace, 2016). Based on fMRI results in the Fmr1 KO (Haberl et al, 2015;Zerbi et al, 2018), it is likely that FMRP promotes other "long-range" synaptic connections between cortical areas, such as ipsilateral connectivity between S1 and M1/M2, as well as cortical-subcortical structures.…”

Experience-dependent weakening of callosal synaptic connections in the absence of postsynaptic FMRP

“…Interhemispheric coherence in beta-gamma band is abolished by callosal cutting (Kiper et al, 1999; Munk et al, 1995), suggesting that the changes in interhemispheric synchrony we observe are due to decreased callosal connectivity. Interhemispheric functional connectivity is thought to shape perceptual integration including those involved in speech comprehension and global form processing, domains that are impaired in ASD (Booth and Happé, 2018; Friederici et al, 2007; Happe and Frith, 2006; Peiker et al, 2015; Preisig et al, 2021; Simon and Wallace, 2016). Based on fMRI results in the Fmr1 KO (Haberl et al ., 2015; Zerbi et al ., 2018), it is likely that FMRP promotes development of long-range connectivity between ipsilateral cortical areas, such as S1 and M1/M2, as well as cortical-subcortical structures.…”

The functional characterization of callosal connections

“…At the border between areas V1/V2, the CPNs had simple or complex or hypercomplex receptive fields, while the majority of callosal recipient neurons had complex receptive fields near the VM ( Innocenti, 1980 ; McCourt et al, 1990 ), in some conflict with the results obtained by identifying callosal neurons with antidromic stimulation (see Section 5.2 ). Finally, modulation of callosal connectivity has been shown by using bi-hemispheric transcranial alternating current stimulation, which in human subjects yields an interhemispheric oscillatory synchronization related to acoustic feature binding ( Preisig et al, 2021 ).…”