Does paired stimulation of the cochlea and the vagus nerve induce cortical map plasticity?

In hearing rats, acoustic stimulation of the cochlea paired with electric stimulation of the vagus nerve (VNS) has been successfully used to restore normal cortical frequency tuning following noise-induced pathological expansion of receptive fields (Engineer et al., Nature 470, 2011). Here we explored whether pairing electric stimulation of the cochlea with VNS (CI/VNS) is effective in reversing deafness-induced degradations in CI-channel selectivity. Gerbils were bilaterally deafened and implanted with a CI and an electrode around the ipsilateral (left) vagus nerve. Analogous to prior pairings of pure tones with VNS (Engineer et al., 2011), single channel CI stimulation was paired with brief pulses of VNS for several weeks. Acutely deafened gerbils and deafened gerbils with CI-only stimulation served as controls. Microelectrode mapping techniques were used to construct spectral cortical maps for multichannel CI stimulation.

In deaf gerbils, paired CI/VNS had no effect on spectral selectivity in the auditory cortex. To exclude species-specific (rat vs. gerbil) and stimulus-specific (acoustic vs. electric) differences between the two studies as potential causes underlying the lack of VNS-induced plasticity, we paired VNS with tones in hearing gerbils. No changes were observed in the cortical representation of the VNS-paired acoustic signal.

In summary, pairing electric or acoustic stimulation of the auditory nerve with VNS failed to induce cortical map plasticity. These findings contrast with prior results obtained in hearing rats. Our results suggest that the potential for paired VNS to direct AC receptive field plasticity may be species specific. Additional factors that might have prevented replication of the results by Engineer and colleagues (2011) will be discussed.

Publication History

Publication Date:
18 April 2018 (online)