Assessment of Effects of Chronic Mobile Phone Usage on Auditory Functions: A Study at a Tertiary Care Teaching Hospital in Northern India

Genuine concerns are being increased regarding potential health risks associated with the radiation exposure while using mobile devices. To study the effects of mobile phone usage on auditory functions. The detailed history of the patient was obtained with special emphasis on total cumulative usage [in years], average daily use [in minutes]. According to the years of exposure, subjects were divided into Group A (< 5 years of exposure) and Group B (> 5 years of exposure) and according to the average daily usage of mobile phones, subjects were divided into Group 1 (< 60 min daily usage) and Group 2 (> 60 min of daily usage). After that systemic examination was done. Audiological testing included pure tone audiometry (PTA) with extended high frequencies (0.250-12 kHz), Otoacoustic emissions (OAE) and Auditory Brainstem response (ABR) testing and middle latency response (MLR) were performed. Out of 100 subjects, maximum subjects (38%) in the present study were in the age group of 21-30 years with male: female ratio of 1.6:1. The main associated complaints in the subjects at the time of enrolment in the study included ear warmth (34%) followed by aural fullness (20%) and tinnitus (17%). In Group A, mild SNHL was seen in 3 (11.54%) subjects in whom 2 had > 60 min average daily use and 1 had < 60 min daily use. In Group B 19 (25.68%) subjects had mild SNHL out of which 6 were in Group 2 and 13 were in Group 1. In group B 2 (2.7%) subjects had moderate SNHL. Increase in latencies of Na and Pa were noted with prolonged and frequent exposure to mobile phones in MLR. It is advised to limit the usage of mobile phones so as to reduce the damage caused by EMRs to the auditory system.

Evidence of central involvement in essential tremor: a detailed study of auditory pathway physiology

Essential tremor (ET) is a common tremor disorder that is likely neurodegenerative. The pathophysiology of ET involves the cerebellum and its connections in the brainstem and thalamus. Hearing dysfunction has been shown to be a non-motor finding in ET patients. A limited number of studies have suggested that cochlear pathology is the cause, but studies have not evaluated the integrity of the primary auditory pathway in ET. The main aim of this study is to investigate the integrity of the auditory pathway via auditory brainstem response (ABR) and auditory middle latency response (AMLR), thereby allowing us to evaluate the auditory pathway from the 8th cranial nerve to the cerebral cortex. Sixteen ET patients and sixteen age- and gender-matched controls (64 ears) were evaluated. In the ABR study, we detected prolongation of wave V peak latencies (ms) in ET (p = 0.02). In the AMLR study, P0 (p = 0.03), Pa (p = 0.008), Na (p = 0.03), and Nb (p = 0.01) waves differed between the two groups. Eleven ET patients and four control subjects had abnormal electrophysiological findings (ABR or AMLR or both) (68.8% vs. 25%, p = 0.01). Tremor duration was greater in ET patients with abnormal electrophysiological findings (p = 0.01). Finally, we observed prolongation of latencies after the ABR III wave, indicating that abnormalities exist within the superior olivary complex. For the first time, our research provides evidence that ET-related pathology is present at the subcortical and cortical levels of the auditory pathway.

Auditory Lateralization Training Effects on Binaural Interaction Component of Middle Latency Response in Children Suspected to Central Auditory Processing Disorder

Many children with central auditory processing disorder (C)APD suffer from spatial processing disorder and benefit from binaural processing training including auditory lateralization training. There are subjective tests for evaluating auditory training effects in children with (C)APD but they rely on patient's attention and cooperation so there is a need for appropriate objective tests. The aim of present study was investigating effects of auditory lateralization training on binaural interaction component (BIC) of middle latency response (MLR). This study was an analytical interventional study. Sixty children suspected to (C)APD (40 boys and 20 girls) were selected based on inclusion criteria and were divided into two groups: control and training group. Auditory lateralization training included 12 formal sessions under headphone by using interaural time difference and performed as a game. MLR (monaural right ear, monaural left ear and binaural) and monaural selective auditory attention test (mSAAT) tests were performed in all the cases. BIC was calculated by subtracting binaural response from summed monaural responses. Covariance test showed that BIC latency decreased and BIC amplitude increased significantly and mSAAT score increased significantly in training group after auditory lateralization training (p value ≤ 0.001). In present study BIC of MLR had potential to show underlying neurophysiologic changes after auditory lateralization training in children suspected to (C)APD objectively. It is in agreement with behavioral improvements after training (mSAAT improvements).

Assessing visual modulation along the human subcortical auditory pathway

Experience of the world is inherently multisensory. It has been suggested that audiovisual modulation occurs as early as subcortical auditory stages. However, this was based on the frequency-following response, a measure recently found to be significantly generated from cortical sources. It therefore remains unclear whether subcortical auditory processing can indeed be modulated by visual information. We aimed to trace visual modulation along the auditory pathway by comparing auditory brainstem response (ABR) and middle-latency response (MLR) between unimodal auditory and multimodal audiovisual conditions. EEG activity was recorded while participants attended auditory clicks and visual flashes, either synchronous or asynchronous. No differences between auditory and audiovisual responses were observed at ABR or MLR levels. It suggested that ascending auditory processing does not seem to be modulated by visual cues at subcortical levels, at least for rudimentary stimuli. Multimodal modulation in the auditory brainstem observed in previous studies might therefore originate from cortical sources and top-down processes. More studies are needed to further disentangle subcortical and cortical influences on audiovisual modulation along the auditory pathway.

The contribution of inferior colliculus activity to the auditory brainstem response (ABR) in mice

In mice, the auditory brainstem response (ABR) is frequently used to assess hearing status in transgenic hearing models. The diagnostic value of the ABR depends on knowledge about the anatomical sources of its characteristic waves. Here, we studied the contribution of the inferior colliculus (IC) to the click-evoked scalp ABR in mice. We demonstrate a non-invasive correlate of the IC response that can be measured in the scalp ABR as a slow positive wave P₀ with peak latency 7-8 ms when recorded with adequate band-pass filtering. Wave P₀ showed close correspondence in latency, magnitude and shape with the sustained part of evoked spiking activity and local field potentials (LFP) in the central nucleus of the IC. In addition, the onset peaks of the IC response were related temporally to ABR wave V and to some extent to wave IV. This relation was further supported by depth-dependent modulation of the shape of ABR wave IV and V within the IC suggesting generation within or in close vicinity to the IC. In conclusion, the slow ABR wave P₀ in the scalp ABR may represent a complementary non-invasive marker for IC activity in the mouse. Further, the latency of synchronized click-evoked activity in the IC supports the view that IC contributes to ABR wave V, and possibly also to ABR wave IV.

Subcortical correlates of auditory perceptual organization in humans

To make sense of complex auditory scenes, the auditory system sequentially organizes auditory components into perceptual objects or streams. In the conventional view of this process, the cortex plays a major role in perceptual organization, and subcortical mechanisms merely provide the cortex with acoustical features. Here, we show that the neural activities of the brainstem are linked to perceptual organization, which alternates spontaneously for human listeners without any stimulus change. The stimulus used in the experiment was an unchanging sequence of repeated triplet tones, which can be interpreted as either one or two streams. Listeners were instructed to report the perceptual states whenever they experienced perceptual switching between one and two streams throughout the stimulus presentation. Simultaneously, we recorded event related potentials with scalp electrodes. We measured the frequency-following response (FFR), which is considered to originate from the brainstem. We also assessed thalamo-cortical activity through the middle-latency response (MLR). The results demonstrate that the FFR and MLR varied with the state of auditory stream perception. In addition, we found that the MLR change precedes the FFR change with perceptual switching from a one-stream to a two-stream percept. This suggests that there are top-down influences on brainstem activity from the thalamo-cortical pathway. These findings are consistent with the idea of a distributed, hierarchical neural network for perceptual organization and suggest that the network extends to the brainstem level.

Spatial auditory regularity encoding and prediction: Human middle-latency and long-latency auditory evoked potentials

By encoding acoustic regularities present in the environment, the human brain can generate predictions of what is likely to occur next. Recent studies suggest that deviations from encoded regularities are detected within 10-50ms after stimulus onset, as indicated by electrophysiological effects in the middle latency response (MLR) range. This is upstream of previously known long-latency (LLR) signatures of deviance detection such as the mismatch negativity (MMN) component. In the present study, we created predictable and unpredictable contexts to investigate MLR and LLR signatures of the encoding of spatial auditory regularities and the generation of predictions from these regularities. Chirps were monaurally delivered in an either regular (predictable: left-right-left-right) or a random (unpredictable left/right alternation or repetition) manner. Occasional stimulus omissions occurred in both types of sequences. Results showed that the Na component (peaking at 34ms after stimulus onset) was attenuated for regular relative to random chirps, albeit no differences were observed for stimulus omission responses in the same latency range. In the LLR range, larger chirp-and omission-evoked responses were elicited for the regular than for the random condition, and predictability effects were more prominent over the right hemisphere. We discuss our findings in the framework of a hierarchical organization of spatial regularity encoding. This article is part of a Special Issue entitled SI: Prediction and Attention.

Temporal lobe epilepsy surgery modulates the activity of auditory pathway

The purpose of this paper is to evaluate the effects of the anterior temporal lobectomy on the functional state of the auditory pathway in a group of drug-resistant epileptic patients, linking the electrophysiological results to the resection magnitude. Twenty-seven patients with temporal lobe epilepsy and a matched control group were studied. Auditory brainstem and middle latency responses (ABR and MLR respectively) were carried out before and after 6, 12 and 24 months surgical treatment. The volume and longitude of temporo-mesial resected structures were estimated on magnetic resonance images taken 6 months after surgery. Before the intervention the patients showed a significant delay of latency in waves III, V, Pa and Nb, with an increase in duration of I-V interval in comparison with healthy subjects (Mann-Whitney U-test, p<0.05). After resection, additional significant differences in waves I and Na latency were observed. Na and Pa waveforms showed a tendency to increase in amplitude, which became statistically significant 12 months after surgery for right hemisphere lobectomized patients in the midline electrode, and in Pa waveform for all patients in the temporal electrodes ipsilateral to resection (Wilcoxon test, p<0.05). In general, latency variations of MLR correlated with resection longitude, while changes in amplitude correlated with the volume of the resection in the middle temporal pole and amygdala (Pearson' correlation test, p<0.05). As a result, we assume that anterior temporal lobectomy provokes functional modifications into the auditory pathway, probably related to an indirect modulation of its activity by the temporo-mesial removed structures.