Speech training alters consonant and vowel responses in multiple auditory cortex fields

Abstract

Speech sounds evoke unique neural activity patterns in primary auditory cortex (A1). Extensive speech sound discrimination training alters A1 responses. While the neighboring auditory cortical fields each contain information about speech sound identity, each field processes speech sounds differently. We hypothesized that while all fields would exhibit training-induced plasticity following speech training, there would be unique differences in how each field changes. In this study, rats were trained to discriminate speech sounds by consonant or vowel in quiet and in varying levels of background speech-shaped noise. Local field potential and multiunit responses were recorded from four auditory cortex fields in rats that had received 10 weeks of speech discrimination training. Our results reveal that training alters speech evoked responses in each of the auditory fields tested. The neural response to consonants was significantly stronger in anterior auditory field (AAF) and A1 following speech training. The neural response to vowels following speech training was significantly weaker in ventral auditory field (VAF) and posterior auditory field (PAF). This differential plasticity of consonant and vowel sound responses may result from the greater paired pulse depression, expanded low frequency tuning, reduced frequency selectivity, and lower tone thresholds, which occurred across the four auditory fields. These findings suggest that alterations in the distributed processing of behaviorally relevant sounds may contribute to robust speech discrimination.

Central Gain Restores Auditory Processing following Near-Complete Cochlear Denervation

“…Moreover, the increased gain needed to restore activity levels to a homeostatic set point can push cortical networks towards unstable states of heightened excitability that may underlie tinnitus and hyperacusis (Auerbach et al, 2014). Further recovery in temporal processing fidelity (Engineer et al, 2015; Zhou and Merzenich, 2008) and complex sound discrimination (Whitton et al, 2014) may be possible in the sensory impaired if these default compensatory processes are augmented by sensory rehabilitation paradigms that engage untapped Hebbian plasticity mechanisms.…”

Degraded neural and behavioral processing of speech sounds in a rat model of Rett syndrome

“…All speech discrimination training tasks and procedures were identical to the speech discrimination training in our previous studies (C T Engineer et al, 2014b, 2014c; Engineer et al, 2015, 2008; Perez et al, 2013; Shetake et al, 2011). Rats were first trained to press a lever in response to the target speech sound ‘dad’.…”

“…For this speech in noise task, rats were trained to press the lever in response to the target sound ‘dad’, and refrain from pressing the lever in response to any of the previously trained non-target sounds (‘bad’, ‘gad’, ‘sad’, ‘tad’, ‘deed’, ‘dood’, and ‘dud’). The speech-shaped background noise was presented in blocks at 0, 48, 54, 60, and 72 dB, as in our previous studies (Centanni et al, 2014; Engineer et al, 2015; Shetake et al, 2011). Each rat trained on the speech in noise task for 15 days.…”

“…All recording procedures were identical to the recording procedures in our previous studies (C T Engineer et al, 2014a, 2014c; Engineer et al, 2015). In each rat, local field potential and multi-unit responses were recorded from 4 auditory fields: anterior auditory field (AAF), primary auditory cortex (A1), ventral auditory field (VAF), and posterior auditory field (PAF).…”

Shank3‐deficient rats exhibit degraded cortical responses to sound

“…Sounds were presented from a free-field speaker (TDT, FF1) located 10 cm from the left ear. All recording procedures were identical to our previous studies Engineer, Centanni, Im, & Kilgard, 2014b;Engineer et al, 2014c;Engineer, Rahebi, Buell, Fink, & Kilgard, 2015b].…”