Abstract
Physiological studies documented highly specific corticofugal modulations making subcortical centers focus processing on sounds that the auditory cortex (AC) has experienced to be important. Here, we show the effects of focal conditioning (FC) of the primary auditory cortex (FCAI) on auditory brainstem response (ABR) amplitudes and latencies in house mice. FCAI significantly increased ABR peak amplitudes (peaks I–V), decreased thresholds, and shortened peak latencies in responses to the frequency tuned by conditioned cortical neurons. The amounts of peak amplitude increases and latency decreases were specific for each processing level up to the auditory midbrain. The data provide new insights into possible corticofugal modulation of inner hair cell synapses and new corticofugal effects as neuronal enhancement of processing in the superior olivary complex (SOC) and lateral lemniscus (LL). Thus, our comprehensive ABR approach confirms the role of the AC as instructor of lower auditory levels and extends this role specifically to the cochlea, SOC, and LL. The whole pathway from the cochlea to the inferior colliculus appears, in a common mode, instructed in a very similar way.
Highlights
Species-specific adaptations and individual-specific adjustments are integrated in the responsiveness of the auditory cortex (AC) to a given sound (Ehret, 1997; Scheich and Ohl, 2011; Weinberger, 2011; Geissler et al, 2016)
Since our data analysis was restricted to the auditory brainstem response (ABR) to AC-conditioned frequencies, the discussion of our data will be focused on the effects of FCAI with this frequency match
This positive effect of FCAI on the contralateral cochlear sensitivity may not be mediated by the medial olivocochlear (MOC) system because its activation reduces contralateral cochlear compound action potential (CAP) amplitudes (Desmedt and Monaco, 1961; Mulders and Robertson, 2000; Groff and Liberman, 2003; Guinan, 2005; Elgueda et al, 2011) and leads to a reduction of the PI amplitude of the ABR (Burkard et al, 1993; Parham et al, 2001)
Summary
Species-specific (evolutionary) adaptations and individual-specific adjustments (experience and learning) are integrated in the responsiveness of the auditory cortex (AC) to a given sound (Ehret, 1997; Scheich and Ohl, 2011; Weinberger, 2011; Geissler et al, 2016). Corticofugal Augmentation of ABR centers (Zhang et al, 1997; Xiao and Suga, 2002; Yan and Ehret, 2002; Suga and Ma, 2003; Yan et al, 2005; Perrot et al, 2006; Zhou and Jen, 2007; Luo et al, 2008; Xiong et al, 2009; Liu et al, 2010, 2019; Suga, 2012; Bajo and King, 2013; Kong et al, 2014; Aedo et al, 2016) These subcortical changes reflect substantial corticofugal impact. It remains to be shown whether corticofugal effects just add up from the cochlea onwards to arrive as a predictable sum of effects at the cortical level or are newly and created at each processing level
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