Electroacupuncture Promotes Neuroplasticity of Central Auditory Pathway: An Auditory Evoked Potentials Study.

Our previous studies found that electroacupuncture at the right Zhongzhu acupoint (TE3) can enhance auditory recovery in rats with noise-induced hearing loss. Here, we investigated the changes in auditory brainstem response (ABR) and long late latency (LLR) evoked potential to explain the mechanisms of electroacupuncture at TE3. The auditory evoked potentials were recorded, including ABR and LLR, at baseline and on day 3 (D3), D5, and D8 after baseline. The 2-Hz electroacupuncture at the right TE3 was applied on D3, D4, and D5 in the electroacupuncture group but not in the control group. In ABR, compared with the control group, the latency shift of waves I (0.298 ± 0.033 vs -0.045 ± 0.057 ms), III (0.718 ± 0.038 vs -0.163 ± 0.130 ms), and V (1.160 ± 0.082 vs -0.207 ± 0.138 ms) on D3 (all p < 0.01) and of wave V (0.616 ± 0.433 vs -0.352 ± 0.209 ms, p < 0.05) on D5 was greater in the electroacupuncture group than that in the control group. Moreover, the interpeak latency shift of I-III (0.420 ± 0.041 vs -0.118 ± 0.177 ms) and I-V (0.863 ± 0.088 vs -0.162 ± 0.156 ms) on D3 (both p < 0.05) and of III-V (0.342 ± 0.193 vs -0.190 ± 0.110 ms) and I-V (0.540 ± 0.352 vs -0.343 ± 0.184 ms) on D5 (both p < 0.05) was greater in the electroacupuncture group than that in the control group. In LLR, the latency shift of P0 was greater in the electroacupuncture group than in the control group on D3 (3.956 ± 2.975 vs -1.178 ± 1.358 ms, p < 0.01) and D5 (2.200 ± 1.889 vs -0.311 ± 1.078 ms, p < 0.05). These findings indicate that electroacupuncture at the right TE3 can modulate the neuroplasticity of the central auditory pathway, including the brain stem and the primary and secondary auditory cortex.

Effect of Electroacupuncture on Noise-Induced Hearing Loss in Rats.

Acupuncture has long been used to relieve some inner ear diseases such as deafness and tinnitus. The present study examined the effect of electroacupuncture (EA) on noise-induced hearing loss (NIHL) in animals. A NIHL rat model was established. Electroacupuncture pretreatment at 2 Hz or posttreatment at the right Zhongzhu (TE3) acupoint was applied for 1 hour. Auditory thresholds were measured using auditory brainstem responses (ABRs), and histopathology of the cochlea was examined. The results indicated that the baseline auditory threshold of ABR was not significantly different between the control (no noise), EA-only (only EA without noise), noise (noise exposure only), pre-EA (pretreating EA then noise), and post-EA (noise exposure then posttreating with EA) groups. Significant auditory threshold shifts were found in the noise, pre-EA, and post-EA groups in the immediate period after noise exposure, whereas auditory recovery was better in the pre-EA and post-EA groups than that in the noise group at the three days, one week (W1), two weeks (W2), three weeks (W3), and four weeks(W4) after noise stimulation. Histopathological examination revealed greater loss of the density of spiral ganglion neurons in the noise group than in the control group at W1 and W2. Although significant loss of spiral ganglion loss happened in pre-EA and post-EA groups, such loss was less than the loss of the noise group, especially W1. These results indicate that either pretreatment or posttreatment with EA may facilitate auditory recovery after NIHL. The detailed mechanism through which EA alleviates NIHL requires further study.

Subcortical neural representation to Mandarin pitch contours in American and Chinese newborns.

Voice pitch carries important information for speech understanding. This study examines the neural representation of voice pitch at the subcortical level, as reflected by the scalp-recorded frequency-following responses from ten American and ten Chinese newborns. By utilizing a set of four distinctive Mandarin pitch contours that mimic the English vowel /yi/, the results indicate that the rising and dipping pitch contours produce significantly better tracking accuracy and larger response amplitudes than the falling pitch contour. This finding suggests a hierarchy of potential stimuli when testing neonates who are born in a tonal or non-tonal linguistic environment.

Pitch perception and frequency-following responses elicited by lexical-tone chimeras.

OBJECTIVE: Previous research has shown the usefulness of utilizing auditory chimeras in assessing a listener's perception of the envelope and fine structure for an acoustic stimulus. However, research comparing and contrasting behavioral and electrophysiological responses to this stimulus type is scarce. DESIGN: Two sets of chimeric stimuli were constructed by interchanging the envelopes and fine-structures of the rising/yi(2)/and falling/yi(4)/Mandarin pitch contours that were filtered through 1, 2, 4, 8, 16, 32, and 64 frequency banks. Behavioral pitch-perception tasks were administered through a two-alternative, forced-choice paradigm. Electrophysiological responses were measured through scalp-recorded frequency-following responses (FFRs) to the lexical-tone chimeras. STUDY SAMPLE: Twenty American and twenty Chinese adults were recruited. RESULTS: A two-way analysis of variance showed significance (p < 0.05) within and across the filter bank and language background factors for the behavioral measurements, while the frequency-following response demonstrated a significance only across the filter banks. CONCLUSIONS: Perceptual importance of envelope cues increases starting from 16 filter banks, while the FFR accuracy and magnitude decreases with increasing number of filter banks. These results can be useful in assessing experience-dependent neuroplasticity and in designing speech processing strategies for cochlear-implant users who speak tonal or non-tonal languages around the globe.

Hyperbaric oxygen upregulates cochlear constitutive nitric oxide synthase.

BACKGROUND: Hyperbaric oxygen therapy (HBOT) is a known adjuvant for treating ischemia-related inner ear diseases. Controversies still exist in the role of HBOT in cochlear diseases. Few studies to date have investigated the cellular changes that occur in inner ears after HBOT. Nitric oxide, which is synthesized by nitric oxide synthase (NOS), is an important signaling molecule in cochlear physiology and pathology. Here we investigated the effects of hyperbaric oxygen on eardrum morphology, cochlear function and expression of NOS isoforms in cochlear substructures after repetitive HBOT in guinea pigs. RESULTS: Minor changes in the eardrum were observed after repetitive HBOT, which did not result in a significant hearing threshold shift by tone burst auditory brainstem responses. A differential effect of HBOT on the expression of NOS isoforms was identified. Upregulation of constitutive NOS (nNOS and eNOS) was found in the substructures of the cochlea after HBOT, but inducible NOS was not found in normal or HBOT animals, as shown by immunohistochemistry. There was no obvious DNA fragmentation present in this HBOT animal model. CONCLUSIONS: The present evidence indicates that the customary HBOT protocol may increase constitutive NOS expression but such upregulation did not cause cell death in the treated cochlea. The cochlear morphology and auditory function are consequently not changed through the protocol.

Evaluation of two algorithms for detecting human frequency-following responses to voice pitch.

OBJECTIVE: Voice pitch carries important cues for speech perception in humans. Recent studies have shown the feasibility of recording the frequency-following response (FFR) to voice pitch in normal-hearing listeners. The presence of such a response, however, has been dependent on subjective interpretation of experimenters. The purpose of this study was to develop and test an automated procedure including a control-experimental protocol and response-threshold criteria suitable for extracting FFRs to voice pitch, and compare the results to human judgments. DESIGN: A set of four Mandarin tones (Tone 1 flat; Tone 2 rising; Tone 3 dipping; and Tone 4 falling) were prepared to reflect the four contrastive pitch contours. Two distinctive algorithms, short-term autocorrelation in the time domain and narrow-band spectrogram in the frequency domain, were used to estimate the Frequency Error, Slope Error, Tracking Accuracy, Pitch Strength and Pitch-Noise Ratio of the recordings from individual listeners as well as the power and false-positive rates of each algorithm. STUDY SAMPLE: Eleven native speakers (five males; age: mean ± SD = 31.4 ± 4.7 years) of Mandarin Chinese were recruited. RESULTS: The results demonstrated that both algorithms were suitable for extracting FFRs and the objective measures showed comparable results to human judgments. CONCLUSIONS: The automated procedure used in this study, including the use of the control-experimental protocol and response thresholds used for each of the five objective indices, can be used for difficult-to-test patients and may prove to be useful as an assessment and diagnostic method in both clinical and basic research efforts.