Auditory Cortex Research Articles

Binaural Interaction Component and Behavioral Auditory Processing in the Elderly with Hearing Loss: Preliminary Study

Purpose: The binaural interaction component (BIC) is presumed to reflect binaural hearing abilities, including spatial hearing. This study aims to record BIC amplitudes and examine their relationship with behavioral auditory tests.Methods: Nine elderly adults with hearing loss (eight males and one female) participated in this study. The BIC was derived from the wave V amplitude of the auditory brainstem response (ABR) and the N1-P2 amplitude of the auditory late latency response (ALR). Behavioral auditory processing tests, including sentence recognition scores, localization scores, and masking level difference, were obtained and analyzed with respect to electrophysiological BICs.Results: BICs were more reliably identified in ALR compared to ABR. The ALR BIC elicited by a 2,000 Hz tone burst showed a significant correlation with sentence recognition scores in both quiet and noise, as well as localization scores at 2,000 Hz. Other variables also demonstrated significant interrelationships.Conclusion: This study suggests that the ALR BIC elicited by a 2,000 Hz tone burst may be a key physiological component representing spatial hearing abilities in individuals with hearing loss. More robust conclusions can be drawn from future studies with larger sample sizes and more sophisticated designs.

The Neural Correlates of Central Auditory Dysfunction in Chronic Tinnitus: A Multimodal Approach.

It was aimed at assessing the connection between tinnitus and central auditory dysfunction using both central auditory tests (CATs) and diffusion tensor imaging (DTI) for brain regions that are crucial for central auditory processing. This prospective case-control study included 15 patients with persistent tinnitus and 20 healthy volunteers as controls. They underwent CATs for memory, attention, and DTI. The Tinnitus Handicap Inventory (THI) Questionnaire was applied as well. From several brain regions, the values of mean diffusivity (MD) and fractional anisotropy (FA) were determined. Comparing both groups, the tinnitus group showed statistically worse values as regards the CATs (memory for content, sequence memory, speech perception in noise (SPIN) at different signal-to-noise ratios, "SNRs") compared with the control group. As regards DTI, the tinnitus group showed decreased FA in several brain areas, including the cingulum, prefrontal-cortex (PFC), insula, and hippocampus. Furthermore, the tinnitus group showed significantly higher MD in the cingulum, BA-46, and amygdala compared with the control group. FA values of BA-46 were positively correlated with the SPIN-SNR-10 scores. Also, FA values of the middle cingulum were positively correlated with SPIN-SNRzero scores. MD values at BA-46 were negatively correlated with SPIN-SNR-10. THI scores were negatively correlated with FA at BA-46; however, they were positively correlated with MD at the amygdala. Central auditory dysfunction may be linked to the underlying neurophysiological changes in chronic tinnitus. Level 2 Laryngoscope, 2024.

Toward an endophenotype for ADHD: Exploring the duration mismatch negativity in drug-free children with ADHD

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent disorders in children that is considered to affect early stages of information processes. Inefficient processing of temporal information, which is a vital auditory processing skill suggests itself as a potential candidate for investigating ADHD deficits. The Research Domain Criteria (RDoC), a neuroscience-based research framework, has been introduced to study mental illness without relying on pre-established diagnostic categories. In this regard, Mismatch Negativity (MMN) has been considered an ideal electrophysiological marker for investigating ADHD deficits. This study investigates alterations in the amplitude and latency of the MMN component in response to changes in the duration and Inter-Stimulus Interval (ISI) of basic sound stimuli within an oddball task. The MMN paradigm was employed to examine duration deviations in ADHD (n = 25, 84% male, mean age: 7.3 years, SD = 2.01) compared to Control group of typically developing (TD) children (n = 25, 72% male, mean age: 7.2 years, SD = 1.92). Participants with ADHD were introduced from an accredited psychiatrist. TD children were recruited from social media and online forms. Both groups were matched in terms of gender, age and IQ. The psychological tests conducted in this study included Conners’ Parent Rating Scale (CPRS), Gilliam Autism Rating Scale|Third Edition (Gars3), Sensory profile questionnaire and Edinburgh Handedness inventory. Our findings revealed reduced MMN amplitudes in response to two blocks of duration and ISI-based deviations in ADHD children. To elaborate in greater detail, at Fz, in Duration and ISI block, respectively, the ADHD group showed an amplitude of −1.2097 ± 0.2938 and −0.8553 ± 0.4423, while the normal group showed an amplitude of −1.8325 ± 0.3689 and −2.0855 ± 0.3802. Additionally, at Cz, the ADHD group exhibited a shorter amplitude (-1.2515 ± 0.3261 and −0.9367 ± 0.3432) compared to the normal group (−2.1319 ± 0.4445 and −2.7561 ± 0.4883), in the duration and ISI blocks, respectively. Furthermore, children with ADHD display longer MMN latencies in both experimental blocks, suggesting atypical responses. To provide more detail, at Fz, the ADHD group displayed MMN latencies of 239.68 ± 5.059 and 226.88 ± 4.885 in the Duration and ISI blocks, respectively, whereas the normal group showed MMN latencies of 228.56 ± 6.584 and 213.56 ± 4.153. Similarly, at Cz, the ADHD group exhibited longer MMN latencies (234.40 ± 5.741 and 231.44 ± 5.464) compared to the normal group (227.52 ± 6.710 and 218.00 ± 5.261) in the Duration and ISI blocks, respectively. Our findings were interpreted in the context of the internal clock model, which involves the pace of an internal pacemaker regulated by dopamine (DA) levels. The convergence of MMN and auditory timing abnormalities within the RDoC framework suggests their potential as endophenotypes for ADHD, highlighting the significance of sensory processing in understanding the disorder.

Assessing Binaural Auditory Processing in Native Tamil Speaking Children.

The objective of this study is to develop and validate the Binaural Fusion Test (BFT) in the Tamil language for children with learning disability. As many children with learning disability exhibit an auditory processing deficit there is a need for language specific assessment tool for these children. The BFT in Tamil comprises 100 words organized into four lists, with each list containing 25 words. A total of 84 children with normal auditory processing and 45 children diagnosed with learning difficulties were administrated the BFT in Tamil. Test-retest reliability was evaluated in a sample of 30 children who exhibited normal auditory processing. The results of BFT in children with normal auditory processing demonstrated satisfactory reliability by the Cronbach Alpha test. A statistically significant difference was seen in the mean scores of BFT in Tamil when comparing the groups. The present study offers novel normative data for the binaural fusion test in Tamil, which has not been previously documented in the existing literature. For children, the BFT in Tamil, which is a part of the CAPD test battery, can be used to find binaural interaction deficiencies.

Optimizing spatial accuracy in electroencephalography reconstruction through diffuse optical tomography priors in the auditory cortex.

Diffuse optical tomography (DOT) enhances the localization accuracy of neural activity measured with electroencephalography (EEG) while preserving EEG's high temporal resolution. However, the spatial resolution of reconstructed activity diminishes for deeper neural sources. In this study, we analyzed DOT-enhanced EEG localization of neural sources modeled at depths ranging from 11-25 mm in simulations. Our findings reveal systematic biases in reconstructed depth related to DOT channel length. To address this, we developed a data-informed method for selecting DOT channels to improve the spatial accuracy of DOT-enhanced EEG reconstruction. Using our method, the average absolute reconstruction depth errors of DOT reconstruction across all depths are 0.9 ± 0.6 mm, 1.2 ± 0.9 mm, and 1.2 ± 1.1 mm under noiseless, low-level noise, and high-level noise conditions, respectively. In comparison, using fixed channel lengths resulted in errors of 2.6 ± 1.5 mm, 5.0 ± 2.6 mm, and 7.3 ± 4.5 mm under the same conditions. Consequently, our method improved the depth accuracy of DOT reconstructions and facilitated the use of more accurate spatial priors for EEG reconstructions, enhancing the overall precision of the technique.

Neurophysiological, structural, and molecular alterations in the prefrontal and auditory cortices following noise-induced hearing loss

It is well established that hearing loss can lead to widespread plasticity within the central auditory pathway, which is thought to contribute to the pathophysiology of audiological conditions such as tinnitus and hyperacusis. Emerging evidence suggests that hearing loss can also result in plasticity within brain regions involved in higher-level cognitive functioning like the prefrontal cortex; findings which may underlie the association between hearing loss and cognitive impairment documented in epidemiological studies. Using the 40-Hz auditory steady state response to assess sound-evoked gamma oscillations, we previously showed that noise-induced hearing loss results in impaired gamma phase coherence within the prefrontal but not the auditory cortex. To determine whether region-specific structural or molecular changes accompany this differential plasticity following hearing loss, in the present study we utilized Golgi-Cox staining to assess dendritic organization and synaptic density, as well as Western blotting to measure changes in synaptic signaling proteins in these cortical regions. We show that following noise exposure, impaired gamma phase coherence within the prefrontal cortex is accompanied by alterations in pyramidal cell dendritic morphology and decreased expression of proteins involved in GABAergic (GAD65) and glutamatergic (NR2B) neurotransmission; findings that were not observed in the auditory cortex, where gamma phase coherence remained unchanged post-noise exposure. In contrast to the noise-induced effects we observed in the prefrontal cortex, plasticity in the auditory cortex was characterized by an increase in NR2B suggesting increased excitability, as well as increases in the synaptic proteins PSD95 and synaptophysin within the auditory cortex. Overall, our results highlight the disparate effect of noise-induced hearing loss on auditory and higher-level brain regions as well as potential structural and molecular mechanisms by which hearing loss may contribute to impaired cognitive and sensory functions mediated by the prefrontal and auditory cortices.

The impact of tinnitus on speech perception in noise: a systematic review and meta-analysis.

Tinnitus is a condition that causes people to hear sounds without an external source. One significant issue arising from this condition is the difficulty in communicating, especially in the presence of noisy backgrounds. The process of understanding speech in challenging situations requires both cognitive and auditory abilities. Since tinnitus presents unique challenges, it is important to investigate how it affects speech perception in noise. In this review, 32 articles were investigated to determine the effect of tinnitus on the effect of speech in noise perception performance. Based on the meta-analysis performed using a random-effects model, meta-regression was used to explore the moderating effects of age and hearing acuity. A total of 32 studies were reviewed, and the results of the meta-analysis revealed that tinnitus significantly impacts speech in terms of noise perception performance. Additionally, the regression analysis revealed that age and hearing acuity are not significant predictors of speech in noise perception. Our findings suggest that tinnitus affects speech perception in noisy environments due to cognitive impairments and central auditory processing deficits. Hearing loss and aging also contribute to reduced speech in noise performance. Interventions and further research are necessary to address individual challenges associated with continuous subjective tinnitus.

Music reward sensitivity is associated with greater information transfer capacity within dorsal and motor white matter networks in musicians.

There are pronounced differences in the degree to which individuals experience music-induced pleasure which are linked to variations in structural connectivity between auditory and reward areas. However, previous studies exploring the link between white matter structure and music reward sensitivity (MRS) have relied on standard diffusion tensor imaging methods, which present challenges in terms of anatomical accuracy and interpretability. Further, the link between MRS and connectivity in regions outside of auditory-reward networks, as well as the role of musical training, have yet to be investigated. Therefore, we investigated the relation between MRS and structural connectivity in a large number of directly segmented and anatomically verified white matter tracts in musicians (n = 24) and non-musicians (n = 23) using state-of-the-art tract reconstruction and fixel-based analysis. Using a manual tract-of-interest approach, we additionally tested MRS-white matter associations in auditory-reward networks seen in previous studies. Within the musician group, there was a significant positive relation between MRS and fiber density and cross section in the right middle longitudinal fascicle connecting auditory and inferior parietal cortices. There were also positive relations between MRS and fiber-bundle cross-section in tracts connecting the left thalamus to the ventral precentral gyrus and connecting the right thalamus to the right supplementary motor area, however, these did not survive FDR correction. These results suggest that, within musicians, dorsal auditory and motor networks are crucial to MRS, possibly via their roles in top-down predictive processing and auditory-motor transformations.

The efficacy of transcranial random noise stimulation in treating tinnitus: a systematic review.

This review aims to examine the effects of transcranial random noise stimulation (tRNS) on tinnitus and to determine the optimal treatment parameters, if possible. A comprehensive search, including MEDLINE, PubMed, EMBASE, CINAHL, SCOPUS, and PEDro, was conducted to determine experiments studying the effects of tRNS on tinnitus from inception to March 1, 2024. The Physiotherapy Evidence Database (PEDro) scale was used to evaluate the quality of the included studies. Seven studies met the eligibility criteria. A total of 616 patients with non-pulsatile tinnitus (mean age 50.93 years; 66% males) were included in this review. The included studies ranged from 3 to 8 out of 10 (median = 7) on the PEDro scale. The results showed that tRNS is an effective intervention in reducing tinnitus symptoms. The evidence for the effects of tRNS on people with chronic non-pulsatile tinnitus is promising. Administering tRNS with an intensity of 1-2mA, high-frequency (101-650Hz), using a 35cm² electrode size over the auditory cortex and DLPFC, for 20min with eight sessions may demonstrate the desired tRNS effects. The tRNS stimulation should be contralateral for unilateral tinnitus and bilaterally for bilateral tinnitus. Combining tRNS with other concurrent interventions may show superior effects in reducing tinnitus compared to tRNS alone. Further high-quality studies with larger sample sizes are strongly needed.

Neural correlates of phonetic categorization under auditory (phoneme) and visual (grapheme) modalities.

We tested whether the neural mechanisms of phonetic categorization are specific to speech sounds or generalize to graphemes (i.e., visual letters) of the same phonetic label. Given that linguistic experience shapes categorical processing, and letter-speech sound matching plays a crucial role during early reading acquisition, we hypothesized sound phoneme and visual grapheme tokens representing the same linguistic identity might recruit common neural substrates, despite originating from different sensory modalities. Behavioral and neuroelectric brain responses (ERPs) were acquired as participants categorized stimuli from sound (phoneme) and homologous letter (grapheme) continua each spanning a /da/ - /ga/ gradient. Behaviorally, listeners were faster and showed stronger categorization of phoneme compared to graphemes. At the neural level, multidimensional scaling of the EEG revealed responses self-organized in a categorial fashion such that tokens clustered within their respective modality beginning ∼150-250 ms after stimulus onset. Source-resolved ERPs further revealed modality-specific and overlapping brain regions supporting phonetic categorization. Left inferior frontal gyrus and auditory cortex showed stronger responses for sound category members compared to phonetically ambiguous tokens, whereas early visual cortices paralleled this categorical organization for graphemes. Auditory and visual categorization also recruited common visual association areas in extrastriate cortex but in opposite hemispheres (auditory = left; visual=right). Our findings reveal both auditory and visual sensory cortex supports categorical organization for phonetic labels within their respective modalities. However, a partial overlap in phoneme and grapheme processing among occipital brain areas implies the presence of an isomorphic, domain-general mapping for phonetic categories in dorsal visual system.

Touch Helps Hearing: Evidence From Continuous Audio-Tactile Stimulation.

Identifying target sounds in challenging environments is crucial for daily experiences. It is important to note that it can be enhanced by nonauditory stimuli, for example, through lip-reading in an ongoing conversation. However, how tactile stimuli affect auditory processing is still relatively unclear. Recent studies have shown that brief tactile stimuli can reliably facilitate auditory perception, while studies using longer-lasting audio-tactile stimulation yielded conflicting results. This study aimed to investigate the impact of ongoing pulsating tactile stimulation on basic auditory processing. In experiment 1, the electroencephalogram (EEG) was recorded while 24 participants performed a loudness-discrimination task on a 4-Hz modulated tone-in-noise and received either in-phase, anti-phase, or no 4-Hz electrotactile stimulation above the median nerve. In experiment 2, another 24 participants were presented with the same tactile stimulation as before, but performed a tone-in-noise detection task while their selective auditory attention was manipulated. We found that in-phase tactile stimulation enhanced EEG responses to the tone, whereas anti-phase tactile stimulation suppressed these responses. No corresponding tactile effects on loudness-discrimination performance were observed in experiment 1. Using a yes/no paradigm in experiment 2, we found that in-phase tactile stimulation, but not anti-phase tactile stimulation, improved detection thresholds. Selective attention also improved thresholds but did not modulate the observed benefit from in-phase tactile stimulation. Our study highlights that ongoing in-phase tactile input can enhance basic auditory processing as reflected in scalp EEG and detection thresholds. This might have implications for the development of hearing enhancement technologies and interventions.

Evaluating Changes in Adult Cochlear Implant Users' Brain and Behavior Following Auditory Training.

To describe the effects of two types of auditory training on both behavioral and physiological measures of auditory function in cochlear implant (CI) users, and to examine whether a relationship exists between the behavioral and objective outcome measures. This study involved two experiments, both of which used a within-subject design. Outcome measures included behavioral and cortical electrophysiological measures of auditory processing. In Experiment I, 8 CI users participated in a music-based auditory training. The training program included both short training sessions completed in the laboratory as well as a set of 12 training sessions that participants completed at home over the course of a month. As part of the training program, study participants listened to a range of different musical stimuli and were asked to discriminate stimuli that differed in pitch or timbre and to identify melodic changes. Performance was assessed before training and at three intervals during and after training was completed. In Experiment II, 20 CI users participated in a more focused auditory training task: the detection of spectral ripple modulation depth. Training consisted of a single 40-minute session that took place in the laboratory under the supervision of the investigators. Behavioral and physiologic measures of spectral ripple modulation depth detection were obtained immediately pre- and post-training. Data from both experiments were analyzed using mixed linear regressions, paired t tests, correlations, and descriptive statistics. In Experiment I, there was a significant improvement in behavioral measures of pitch discrimination after the study participants completed the laboratory and home-based training sessions. There was no significant effect of training on electrophysiologic measures of the auditory N1-P2 onset response and acoustic change complex (ACC). There were no significant relationships between electrophysiologic measures and behavioral outcomes after the month-long training. In Experiment II, there was no significant effect of training on the ACC, although there was a small but significant improvement in behavioral spectral ripple modulation depth thresholds after the short-term training. This study demonstrates that auditory training improves spectral cue perception in CI users, with significant perceptual gains observed despite cortical electrophysiological responses like the ACC not reliably predicting training benefits across short- and long-term interventions. Future research should further explore individual factors that may lead to greater benefit from auditory training, in addition to optimization of training protocols and outcome measures, as well as demonstrate the generalizability of these findings.

A Characterization of Central Auditory Processing in Parkinson's Disease.

Research indicates that people with Parkinson's disease (PwPs) may experience challenges in both peripheral and central auditory processing, although findings are inconsistent across studies. Due to the diversity of auditory measures used, there is a need for standardized, replicable hearing assessments to clarify which aspects of audition are impacted in PWPs and whether they are linked to motor and non-motor symptoms. To characterize auditory processes and their possible alteration in PwPs. To address this, we collected a comprehensive set of standardized measures of audition using PART, a digital testing platform designed to facilitate replication. Additionally, we examined the relationship between auditory, cognitive, and clinical variables in PwPs. We included 44 PwPs and 54 age and education matched healthy controls. Assessments included detection of diotic and dichotic frequency modulation, temporal gaps, spectro-temporal broad-band modulation, and speech-on-speech masking. We found no statistically significant differences in auditory processing measures between PwPs and the comparison group (ps > 0.07). In PwPs, an auditory processing composite score showed significant medium size correlations with cognitive measures (0.39 < r<0.41, ps < 0.02) and clinical variables of motor symptom severity, quality of life, depression, and caretaker burden (0.33 < r<0.52, ps < 0.03). While larger datasets are needed to clarify whether PwPs experience more auditory difficulties than healthy controls, our results underscore the importance of considering auditory processing on the symptomatic spectrum of Parkinson's disease using standardized replicable methodologies.

Dynamic gating of perceptual flexibility by non-classically responsive cortical neurons.

The ability to flexibly respond to sensory cues in dynamic environments is essential to adaptive auditory-guided behaviors. Cortical spiking responses during behavior are highly diverse, ranging from reliable trial-averaged responses to seemingly random firing patterns. While the reliable responses of 'classically responsive' cells have been extensively studied for decades, the contribution of irregular spiking 'non-classically responsive' cells to behavior has remained underexplored despite their prevalence. Here, we show that flexible auditory behavior results from interactions between local auditory cortical circuits comprised of heterogeneous responses and inputs from secondary motor cortex. Strikingly, non-classically responsive neurons in auditory cortex were preferentially recruited during learning, specifically during rapid learning phases when the greatest gains in behavioral performance occur. Population-level decoding revealed that during rapid learning mixed ensembles comprised of both classically and non-classically responsive cells encode significantly more task information than homogenous ensembles of either type and emerge as a functional unit critical for learning. Optogenetically silencing inputs from secondary motor cortex selectively modulated non-classically responsive cells in the auditory cortex and impaired reversal learning by preventing the remapping of a previously learned stimulus-reward association. Top-down inputs orchestrated highly correlated non-classically responsive ensembles in sensory cortex providing a unique task-relevant manifold for learning. Thus, non-classically responsive cells in sensory cortex are preferentially recruited by top-down inputs to enable neural and behavioral flexibility.

Altered neural synchronization in response to 2 Hz amplitude-modulated tones in the auditory cortex of children with Autism Spectrum Disorder: An MEG study

ObjectiveSome studies have hypothesized that atypical neural synchronization at the delta frequency band in the auditory cortex is associated with phonological and language skills in children with Autism Spectrum Disorder (ASD), but it is still poorly understood. This study investigated this neural activity and addressed the relationships between auditory response and behavioral measures of children with ASD. MethodsWe used magnetoencephalography and individual brain models to investigate 2 Hz Auditory Steady-State Response (ASSR) in 20 primary-school-aged children with ASD and 20 age-matched typically developing (TD) controls. ResultsFirst, we found a between-group difference in the localization of the auditory response, so as the topology of 2 Hz ASSR was more superior and posterior in TD children when comparing to children with ASD. Second, the power of 2 Hz ASSR was reduced in the ASD group. Finally, we observed a significant association between the amplitude of neural response and language skills in children with ASD. ConclusionsThe study provided the evidence of reduced neural response in children with ASD and its relation to language skills. SignificanceThese findings may inform future interventions targeting auditory and language impairments in ASD population.

Neuroplasticity of Speech-in-Noise Processing in Older Adults Assessed by Functional Near-Infrared Spectroscopy (fNIRS)

Functional near-infrared spectroscopy (fNIRS), a non-invasive optical neuroimaging technique that is portable and acoustically silent, has become a promising tool for evaluating auditory brain functions in hearing-vulnerable individuals. This study, for the first time, used fNIRS to evaluate neuroplasticity of speech-in-noise processing in older adults. Ten older adults, most of whom had moderate-to-mild hearing loss, participated in a 4-week speech-in-noise training. Their speech-in-noise performances and fNIRS brain responses to speech (auditory sentences in noise), non-speech (spectrally-rotated speech in noise) and visual (flashing chequerboards) stimuli were evaluated pre- (T0) and post-training (immediately after training, T1; and after a 4-week retention, T2). Behaviourally, speech-in-noise performances were improved after retention (T2 vs. T0) but not immediately after training (T1 vs. T0). Neurally, we intriguingly found brain responses to speech vs. non-speech decreased significantly in the left auditory cortex after retention (T2 vs. T0 and T2 vs. T1) for which we interpret as suppressed processing of background noise during speech listening alongside the significant behavioural improvements. Meanwhile, functional connectivity within and between multiple regions of temporal, parietal and frontal lobes was significantly enhanced in the speech condition after retention (T2 vs. T0). We also found neural changes before the emergence of significant behavioural improvements. Compared to pre-training, responses to speech vs. non-speech in the left frontal/prefrontal cortex were decreased significantly both immediately after training (T1 vs. T0) and retention (T2 vs. T0), reflecting possible alleviation of listening efforts. Finally, connectivity was significantly decreased between auditory and higher-level non-auditory (parietal and frontal) cortices in response to visual stimuli immediately after training (T1 vs. T0), indicating decreased cross-modal takeover of speech-related regions during visual processing. The results thus showed that neuroplasticity can be observed not only at the same time with, but also before, behavioural changes in speech-in-noise perception. To our knowledge, this is the first fNIRS study to evaluate speech-based auditory neuroplasticity in older adults. It thus provides important implications for current research by illustrating the promises of detecting neuroplasticity using fNIRS in hearing-vulnerable individuals.

Anatomical and behavioral correlates of auditory perception in developmental dyslexia.

Developmental dyslexia is typically associated with difficulties in basic auditory processing and in manipulating speech sounds. However, the neuroanatomical correlates of auditory difficulties in developmental dyslexia (DD) and their contribution to individual clinical phenotypes are still unknown. Recent intracranial electrocorticography findings associated processing of sound amplitude rises and speech sounds with posterior and middle superior temporal gyrus (STG), respectively. We hypothesize that regional STG anatomy will relate to specific auditory abilities in DD, and that auditory processing abilities will relate to behavioral difficulties with speech and reading. One hundred and ten children (78 DD, 32 typically developing, age 7-15 years) completed amplitude rise time and speech in noise discrimination tasks. They also underwent a battery of cognitive tests. Anatomical MRI scans were used to identify regions in which local cortical gyrification complexity correlated with auditory behavior. Behaviorally, amplitude rise time but not speech in noise performance was impaired in DD. Neurally, amplitude rise time and speech in noise performance correlated with gyrification in posterior and middle STG, respectively. Furthermore, amplitude rise time significantly contributed to reading impairments in DD, while speech in noise only explained variance in phonological awareness. Finally, amplitude rise time and speech in noise performance were not correlated, and each task was correlated with distinct neuropsychological measures, emphasizing their unique contributions to DD. Overall, we provide a direct link between the neurodevelopment of the left STG and individual variability in auditory processing abilities in neurotypical and dyslexic populations.

Network resonance and the auditory steady state response

The auditory steady state response (ASSR) arises when periodic sounds evoke stable responses in auditory networks that reflect the acoustic characteristics of the stimuli, such as the amplitude of the sound envelope. Larger for some stimulus rates than others, the ASSR in the human electroencephalogram (EEG) is notably maximal for sounds modulated in amplitude at 40 Hz. To investigate the local circuit underpinnings of the large ASSR to 40 Hz amplitude-modulated (AM) sounds, we acquired skull EEG and local field potential (LFP) recordings from primary auditory cortex (A1) in the rat during the presentation of 20, 30, 40, 50, and 80 Hz AM tones. 40 Hz AM tones elicited the largest ASSR from the EEG acquired above auditory cortex and the LFP acquired from each cortical layer in A1. The large ASSR in the EEG to 40 Hz AM tones was not due to larger instantaneous amplitude of the signals or to greater phase alignment of the LFP across the cortical layers. Instead, it resulted from decreased latency variability (or enhanced temporal consistency) of the 40 Hz response. Statistical models indicate the EEG signal was best predicted by LFPs in either the most superficial or deep cortical layers, suggesting deep layer coordinators of the ASSR. Overall, our results indicate that the recruitment of non-uniform but more temporally consistent responses across A1 layers underlie the larger ASSR to amplitude-modulated tones at 40 Hz.

Preserved functional organization of auditory cortex in two individuals missing one temporal lobe from infancy

Human cortical responses to natural sounds, measured with fMRI, can be approximated as the weighted sum of a small number of canonical response patterns (components), each having interpretable functional and anatomical properties. Here, we asked whether this organization is preserved in cases where only one temporal lobe is available due to early brain damage by investigating a unique family: one sibling missing their left temporal lobe from infancy, another missing the right temporal lobe from infancy, and a third anatomically neurotypical. None of the siblings manifested behavioral deficits. We analyzed fMRI responses to diverse natural sounds within the intact hemispheres of these individuals and compared them to 12 neurotypical participants. All siblings manifested typical-like auditory responses in their intact hemispheres. These results suggest that the development of the auditory cortex in each hemisphere does not depend on the existence of the other hemisphere, highlighting the redundancy and equipotentiality of the bilateral auditory system.

Decoding contextual influences on auditory perception from primary auditory cortex.

Perception can be highly dependent on stimulus context, but whether and how sensory areas encode the context remains uncertain. We used an ambiguous auditory stimulus - a tritone pair - to investigate the neural activity associated with a preceding contextual stimulus that strongly influenced the tritone pair's perception: either as an ascending or a descending step in pitch. We recorded single-unit responses from a population of auditory cortical cells in awake ferrets listening to the tritone pairs preceded by the contextual stimulus. We find that the responses adapt locally to the contextual stimulus, consistent with human MEG recordings from the auditory cortex under the same conditions. Decoding the population responses demonstrates that cells responding to pitch-class-changes are able to predict well the context-sensitive percept of the tritone pairs. Conversely, decoding the individual pitch-class representations and taking their distance in the circular Shepard tone space predicts the opposite of the percept. The various percepts can be readily captured and explained by a neural model of cortical activity based on populations of adapting, pitch-class and pitch-class-direction cells, aligned with the neurophysiological responses. Together, these decoding and model results suggest that contextual influences on perception may well be already encoded at the level of the primary sensory cortices, reflecting basic neural response properties commonly found in these areas.