Tinnitus and Transcranial Magnetic Stimulation
from Seminars in Hearing
Tinnitus is a frequent disorder that is very difficult to treat. Both functional imaging studies in patients and electrophysiological studies in animals suggest that hyperactivity in the central auditory system due to increased synchronicity may cause tinnitus. Targeted modulation of tinnitus-related cortical activity has been proposed as a promising new treatment. Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive method that can focally modulate cortical activity. This technique has been used to diagnose and treat tinnitus. Single sessions of high-frequency rTMS over the temporal cortex have been used to suppress tinnitus transiently and could become a useful predictor for treatment outcome of epidural stimulation. Another approach uses rTMS as a treatment for tinnitus by applying repeated sessions of low-frequency rTMS to induce a lasting reduction of excitability in the auditory cortex. Beneficial effects of treatment have been consistently demonstrated in several controlled studies. However results are characterized by high interindividual variability and only moderate effect sizes. Convincing evidence indicates that rTMS represents a promising tool for diagnosis and treatment of tinnitus. Further development of this technique will depend on a more detailed understanding of the neurobiological effects that mediate the clinical effects of TMS.
Frequency-specific coupling in the cortico-cerebellar auditory system
from the Journal of Neurosphysiology
Induced oscillatory activity in the auditory cortex peaks at around 40Hz in humans. Using regional cerebral blood flow (rCBF) and positron emission tomography (PET) we previously confirmed frequency-selective cortical responses to 40Hz tones in auditory primary cortices and concomitant bilateral activation of the cerebellar hemispheres. In this study, using functional magnetic resonance imaging (fMRI) we estimated the influence of 40Hz auditory stimulation on the coupling between auditory cortex and Superior Temporal Sulcus (STS) and Crus II, using a dynamic causal model (DCM) of the interactions between medial geniculate nuclei, auditory STG/STS and the cerebellar Crus II auditory region. Specifically, we tested the hypothesis that 40Hz-selective responses in the cerebellar Crus II auditory region could be explained by frequency-specific enabling of interactions in the auditory cortico-cerebellar-thalamic loop. Our model comparison results suggest that input from auditory STG/STS to cerebellum is enhanced selectively at gamma band frequencies around 40 Hz.
Cortical Mechanisms of Speech Perception in Noise
from the Journal of Speech, Language, and Hearing Research
Purpose: The present study examines the brain basis of listening to spoken words in noise, which is a ubiquitous characteristic of communication, with the focus on the dorsal auditory pathway.
Method: English-speaking young adults identified single words in 3 listening conditions while their hemodynamic response was measured using fMRI: speech in quiet, speech in moderately loud noise (signal-to-noise ratio [SNR] 20 dB), and in loud noise (SNR –5 dB).
Results: Behaviorally, participants’ performance (both accuracy and reaction time) did not differ between the quiet and SNR 20 dB condition, whereas they were less accurate and responded slower in the SNR –5 dB condition compared with the other 2 conditions. In the superior temporal gyrus (STG), both left and right auditory cortex showed increased activation in the noise conditions relative to quiet, including the middle portion of STG (mSTG). Although the right posterior STG (pSTG) showed similar activation for the 2 noise conditions, the left pSTG showed increased activation in the SNR –5 dB condition relative to the SNR 20 dB condition.
Conclusion: We found cortical task-independent and noise-dependent effects concerning speech perception in noise involving bilateral mSTG and left pSTG. These results likely reflect demands in acoustic analysis, auditory–motor integration, and phonological memory, as well as auditory attention.
Magnetoencephalography for research of auditory cortex
Conclusion. The results could indicate that, during phylogeny and human ontogeny, the central nervous system has enhanced the speech activity from any other activity even though other frequencies could be relevant for survival. Objective. People of all ages can experience alterations of auditory perception that progressively increase with aging. The whole approach to these alterations needs not only peripheral (cochlear) or brainstem studies but also an analysis of the auditory cortex. In fact, auditory evoked fields (AEF) may contribute to the understanding of the neural correlate of sound awareness. Subjects and methods. The M100 response after pure tone stimulation (five frequencies ranging from 500 to 8000 Hz) was analyzed in a group of nine adult subjects with normal hearing, older than 25 years of age and under 40 years old. Average M100 field intensity was calculated for all magnetoencephalography (MEG) channels in a 60 ms window around the M100 waveform. Results. The results indicate a more intense cortical response to main speech frequencies (0.5 to 2 kHz) as compared with other frequencies not involved in human conversation.
Histologic Characterization of Human Scarred Vocal Folds
from the Journal of Voice
Vocal fold scarring remains a significant problem. Although several animal models have been developed to improve our understanding of the histopathology, the histologic features of scarred human vocal folds have rarely been reported. The present case studies aimed to define the histologic changes of scarred human vocal folds caused by cordectomy or cordotomy. Ten patients with the scarred vocal folds were involved in this study. Nine patients with early glottic cancer underwent endoscopic cordectomy, and one patient underwent superficial cordotomy for idiopathic scar. The postcordectomy or cordotomy scar was biopsied or resected 3-13 months after the original procedure. After confirming absence of any tumor in cancer patients, the remaining specimens were used in the present study. Histologic examination investigated deposition of extracellular matrix (ECM) including collagen, elastin, hyaluronic acid (HA), fibronectin, and decorin in the lamina propria of the scarred vocal folds. There was a wide range of variation in the deposition of ECM in scarred vocal folds. Excessive and disorganized collagen deposition was observed in most cases that had undergone deep resection of the lamina propria, whereas deposition of collagen was mild and well organized after superficial resection. Decorin was retained in all cases after superficial cordectomy or cordotomy, but varied after deep resection. Deposition of elastin, HA, and fibronectin varied regardless of depth of injury. Histology of scarred vocal folds may vary with degree of injury and individual healing mechanism.
Right-Hemisphere Auditory Cortex Is Dominant for Coding Syllable Patterns in Speech
from the Journal of Neuroscience
Cortical analysis of speech has long been considered the domain of left-hemisphere auditory areas. A recent hypothesis poses that cortical processing of acoustic signals, including speech, is mediated bilaterally based on the component rates inherent to the speech signal. In support of this hypothesis, previous studies have shown that slow temporal features (3–5 Hz) in nonspeech acoustic signals lateralize to right-hemisphere auditory areas, whereas rapid temporal features (20–50 Hz) lateralize to the left hemisphere. These results were obtained using nonspeech stimuli, and it is not known whether right-hemisphere auditory cortex is dominant for coding the slow temporal features in speech known as the speech envelope. Here we show strong right-hemisphere dominance for coding the speech envelope, which represents syllable patterns and is critical for normal speech perception. Right-hemisphere auditory cortex was 100% more accurate in following contours of the speech envelope and had a 33% larger response magnitude while following the envelope compared with the left hemisphere. Asymmetries were evident regardless of the ear of stimulation despite dominance of contralateral connections in ascending auditory pathways. Results provide evidence that the right hemisphere plays a specific and important role in speech processing and support the hypothesis that acoustic processing of speech involves the decomposition of the signal into constituent temporal features by rate-specialized neurons in right- and left-hemisphere auditory cortex.
Effective and Structural Connectivity in the Human Auditory Cortex
from the Journal of Neuroscience
Language processing involves multiple neuronal structures in the human auditory cortex. Although a variety of neuroimaging and mapping techniques have been implemented to better understand language processing at the level of the auditory cortex, much is unknown regarding how and by what pathways these structures interact during essential tasks such as sentence comprehension. In this study, the effective and structural connectivity at the level of the auditory cortex were investigated. First, blood oxygenation level-dependent (BOLD) responses were measured with time-resolved functional magnetic resonance imaging (fMRI) during audition of short sentences. Once BOLD activation maps were obtained, the effective connectivity between primary auditory cortex and the surrounding auditory regions on the supratemporal plane and superior temporal gyrus (STG) were investigated using Granger causality mapping (GCM). Effective connectivity was observed between the primary auditory cortex and (1) the lateral planum polare and anterior STG, and (2) the lateral planum temporale and posterior STG. By using diffusion tensor probabilistic mapping (DTPM), rostral and caudal fiber pathways were detected between regions depicting effective connectivity. The effective and structural connectivity results of the present study provide further insight as to how auditory stimuli (i.e., human language) is processed at the level of the auditory cortex. Furthermore, combining BOLD fMRI-based GCM and DTPM analysis could provide a novel means to study effective and structural connectivity not only in the auditory cortex, but also in other cortical regions.
Functional imaging of unilateral tinnitus using fMRI
Conclusions. This article shows that the inferior colliculus plays a key role in unilateral subjective tinnitus. Objectives. The major aim of this study was to determine tinnitus-related neural activity in the central auditory system of unilateral tinnitus subjects and compare this to control subjects without tinnitus. Subjects and methods. Functional MRI (fMRI) was performed in 10 patients (5 males) with unilateral tinnitus (5 left-sided, 5 right-sided) and 12 healthy subjects (6 males); both groups had normal hearing or mild hearing loss. fMRI experiments were performed using a 3T Philips Intera Scanner. Auditory stimuli were presented left or right and consisted of dynamically rippled broadband noise with a sound pressure level of 40 or 70 dB SPL. The responses of the inferior colliculus and the auditory cortex to the stimuli were measured. Results. The response to sound in the inferior colliculus was elevated in tinnitus patients compared with controls without tinnitus.
Volume of Left Heschl’s Gyrus and Linguistic Pitch Learning
from Cerebral Cortex
Research on the contributions of the human nervous system to language processing and learning has generally been focused on the association regions of the brain without considering the possible contribution of primary and adjacent sensory areas. We report a study examining the relationship between the anatomy of Heschl’s Gyrus (HG), which includes predominately primary auditory areas and is often found to be associated with nonlinguistic pitch processing and language learning. Unlike English, most languages of the world use pitch patterns to signal word meaning. In the present study, native English-speaking adult subjects learned to incorporate foreign pitch patterns in word identification. Subjects who were less successful in learning showed a smaller HG volume on the left (especially gray matter volume), but not on the right, relative to learners who were successful. These results suggest that HG, typically shown to be associated with the processing of acoustic cues in nonspeech processing, is also involved in speech learning. These results also suggest that primary auditory regions may be important for encoding basic acoustic cues during the course of spoken language learning.
Human Cortical Responses to the Speech Envelope
from Ear and Hearing
Objective: To evaluate the response of the human auditory cortex to the temporal amplitude-envelope of speech. Responses to the speech envelope could be useful for validating the neural encoding of intelligible speech, particularly during hearing aid fittings-because hearing aid gain and compression characteristics for ongoing speech should more closely resemble real world performance than for isolated brief syllables.
Design: The speech envelope comprises energy changes corresponding to phonemic and syllabic transitions. Envelope frequencies between 2 and 20 Hz are important for speech intelligibility. Human event-related potentials were recorded to six different sentences and the sources of these potentials in the auditory cortex were determined. To improve the signal to noise ratio over ongoing electroencephalographic recordings, we averaged the responses over multiple presentations, and derived source waveforms from multichannel scalp recordings. Source analysis led to bilateral, symmetrical, vertical, and horizontal dipoles in the posterior auditory cortices. The source waveforms were then cross-correlated with the low frequency log-envelopes of the sentences. The significance and latency of the maximum correlation for each sentence demonstrated the presence and latency of the brain’s response. The source waveforms were also cross-correlated with a simple model based on a series of overlapping transient responses to stimulus change (the derivative of the log-envelope).
Results: Correlations between the log-envelope and vertical dipole source waveforms were significant for all sentences and for all but one of the participants (mean r = 0.35), at an average delay of 175 (left) to 180 (right) msec. Correlations between the transient response model (P1 at 68 msec, N1 at 124 msec, and P2 at 208 msec) and the vertical dipole source waveforms were detected for all sentences and all participants (mean r = 0.30), at an average delay of 6 (right) to 10 (left) msec.
Conclusions: These results show that the human auditory cortex either directly follows the speech envelope or consistently reacts to changes in this envelope. The delay between the envelope and the response is approximately 180 msec.
Direct Electrical Stimulation of Heschl’s Gyrus for Tinnitus Treatment
from Laryngoscope
Objectives/Hypothesis: The purpose of the study was to determine the effect of electrical stimulation of the auditory cortex in patients with tinnitus.
Study Design: Nonrandomized clinical trial.
Methods: Two patients with debilitating tinnitus refractory to conventional therapies were treated. Patients were evaluated with validated questionnaires and psychoacoustic measures to determine the frequency and pitch of their tinnitus. Tones at these frequencies were then presented to the first patient (RP) under magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) to determine the tonotopic map for these frequencies in Heschl’s gyrus. These tonotopic sites were targeted for implant with a quadripolar electrode. In the second patient (MV), only the fMRI tonotopic map was performed. These fMRI results detected an area of increased activity, which was selected as the site for the implanted bipolar electrode.
Results: Patient RP (bilateral tinnitus for 2 years) has experienced a sustained reduction to near elimination of tinnitus with intracerebral implanted electrodes, whereas patient MV (unilateral tinnitus for 7 years) had an unsustained reduction in her tinnitus.
Conclusion: These findings suggest that the perception and annoyance of tinnitus may be modulated or reduced through electrical stimulation of the auditory cortex. These unsustained effects for patient MV may have been influenced by the longstanding nature of her tinnitus or by another reason as yet undetermined.
Nonlinearities and Contextual Influences in Auditory Cortical Responses Modeled with Multilinear Spectrotemporal Methods
from the Journal of Neuroscience
The relationship between a sound and its neural representation in the auditory cortex remains elusive. Simple measures such as the frequency response area or frequency tuning curve provide little insight into the function of the auditory cortex in complex sound environments. Spectrotemporal receptive field (STRF) models, despite their descriptive potential, perform poorly when used to predict auditory cortical responses, showing that nonlinear features of cortical response functions, which are not captured by STRFs, are functionally important. We introduce a new approach to the description of auditory cortical responses, using multilinear modeling methods. These descriptions simultaneously account for several nonlinearities in the stimulus–response functions of auditory cortical neurons, including adaptation, spectral interactions, and nonlinear sensitivity to sound level. The models reveal multiple inseparabilities in cortical processing of time lag, frequency, and sound level, and suggest functional mechanisms by which auditory cortical neurons are sensitive to stimulus context. By explicitly modeling these contextual influences, the models are able to predict auditory cortical responses more accurately than are STRF models. In addition, they can explain some forms of stimulus dependence in STRFs that were previously poorly understood.
Sparse Representation Of Sounds In The Unanesthetized Auditory Cortex
How do neuronal populations in the auditory cortex represent sounds? Although sound-evoked neural responses in the anesthetized auditory cortex are mainly transient, recent experiments in the unanesthetized preparation have emphasized subpopulations with other response properties.
Published this week in the open-access journal PLoS Biology, Tomas Hromadka, Anthony Zador, and colleagues show how they quantified the relative contributions of these different subpopulations in the auditory cortex of awake head-fixed rats.
Level dependence of contextual modulation in auditory cortex
from the Journal of Neurosphysiology
Responses of cortical neurons to sensory stimuli within their receptive fields can be profoundly altered by the stimulus context. In visual and somatosensory cortex, contextual interactions have been shown to change sign from facilitation to suppression depending on stimulus strength. Contextual modulation of high contrast stimuli tends to be suppressive, but for low contrast stimuli tends to be facilitative. This trade-off may optimize contextual integration by cortical cells, and has been suggested to be a general feature of cortical processing, but it remains unknown whether a similar phenomenon occurs in auditory cortex. Here we used whole cell and single unit recordings to investigate how contextual interactions in auditory cortical neurons depend on the relative intensity of masker and probe stimuli in a two-tone stimulus paradigm. We tested the hypothesis that relatively low level probes should show facilitation, whereas relatively high level probes should show suppression. We found that contextual interactions were primarily suppressive across all probe levels, and that relatively low level probes were subject to stronger suppression than high level probes. These results were virtually identical for spiking and subthreshold responses. This suggests that, unlike visual cortical neurons, auditory cortical neurons show maximal suppression rather than facilitation for relatively weak stimuli.
Lend me your ears — and the world will sound very different
from EurekAlert.org
Recognising people, objects or animals by the sound they make is an important survival skill and something most of us take for granted. But very similar objects can physically make very dissimilar sounds and we are able to pick up subtle clues about the identity and source of the sound. Scientists funded by the Biotechnology and Biological Sciences Research Council (BBSRC) are working out how the human ear and the brain come together to help us understand our acoustic environment. They have found that the part of the brain that deals with sound, the auditory cortex, is adapted in each individual and tuned to the world around us. We learn throughout our lives how to localise and identify different sounds. It means that if you could hear the world through someone else’s ears it would sound very different to what you are used to.
Representation of auditory filter phase characteristics in the cortex of human listeners
from the Journal of Neurosphysiology
Harmonic tone complexes with component phases, adjusted using a variant of a method proposed by Schroeder (IEEE Trans Inf Theory 16: 85-89, 1970), can produce pure-tone masked thresholds differing by more than 20 dB. This phenomenon has been qualitatively explained by the phase characteristics of the auditory filters on the basilar membrane which differently affect the flat envelopes of the Schroeder-phase maskers. We examined the influence of auditory-filter phase characteristics on the neural representation in the auditory cortex by investigating cortical auditory evoked fields (AEF). We found that the P1m component exhibited larger amplitudes when a long-duration tone was presented in a repeating linearly downward sweeping (Schroeder positive, or m+) masker than in a repeating linearly upward sweeping (Schroeder negative, or m-) masker. We also examined the neural representation of short-duration tone pulses presented at different temporal positions within a single period of three maskers differing in their component phases (m+, m-, and sine phase m0). The P1m amplitude varied with the position of the tone pulse in the masker and depended strongly on the masker waveform. The neuromagnetic results in all cases were consistent with the perceptual data obtained with the same stimuli and with results from simulations of neural activity at the output of cochlear preprocessing. These findings demonstrate that phase effects in peripheral auditory processing are accurately reflected up to the level of the auditory cortex.
Hearing Illusory Sounds in Noise: Sensory-Perceptual Transformations in Primary Auditory Cortex
from the Journal of Neuroscience
A sound that is interrupted by silence is perceived as discontinuous. However, when the silence is replaced by noise, the target sound may be heard as uninterrupted. Understanding the neural basis of this continuity illusion may elucidate the ability to track sounds of interest in noisy auditory scenes, but yet little is known. In the present functional magnetic resonance imaging study in humans we report that activity in primary auditory cortex reflects perceived continuity of illusory tones in noise. Exploiting a parametric manipulation of the illusory stimuli, we show that stimulus-evoked activity does not correlate with the basic acoustic properties of tones or noises, but rather with the abstract dependencies among them. Importantly, changes of neural responses to acoustically identical stimuli parallel changes of listeners’ report of perceived continuity of these same stimuli, thus confirming the perceptual nature of these responses. Our findings show that, beyond the sensory representation of an auditory scene, primary auditory areas play a constructive role in the grouping of scene segments into unified auditory percepts.
Selective Attention Modulates Activity In The Human Auditory Cortex
The results of a study conducted by researchers of the Helsinki University of Technology TKK Laboratory of Computational Engineering (Jaakko Kauramaki, Iiro Jaaskelainen and Mikko Sams) indicate that selective attention has significant effects on the activity of the human auditory cortex. The neural basis of selective attention has been one of the greatest unresolved questions in science.
Pharmacological modulation of learning-induced plasticity in human auditory cortex
from Restorative Neurology and Neuroscience
Purpose: Converging evidence from animals and humans indicate that the primary auditory cortex is continuously reshaped in an experience-dependent way. Reorganisation in primary auditory cortex can be observed at the level of receptive fields, topographic maps and brain activations measured with neuroimaging methods. Several neuromodulatory systems were shown to contribute to such an experience-dependent reorganization.
Methods: This paper reviews evidence addressing the cholinergic, noradrenergic, dopaminergic and serotonergic modulation of learning-, experience-, and injury-induced plasticity in the auditory cortex.
Results: Regarding learning-induced plasticity in the auditory cortex most studies have investigated the role of the cholinergic system and shown that ACh is essential for this form of rapid plasticity. Nevertheless there is also evidence that the catecholamines dopamine and noradrenaline might contribute to learning- and experience-induced changes in the auditory cortex.
Conclusions: I suggest, that the available experimental data on cholinergic and noradrenergic modulation of plasticity offers a promising basis for potential pharmacological interventions to aid recovery of aural functions.
Neuroplasticity of sign language: Implications from structural and functional brain imaging
from Restorative Neurology and Neuroscience
Purpose: The present study was designed to investigate the neural correlates of German Sign Language (Deutsche Gebärdensprache; DGS) processing. In particular, was expected the impact of the visuo-spatial mode in sign language on underlying neural networks compared to the impact of the interpretation of linguistic information.
Methods: For this purpose, two groups of participants took part in a functional MRI study at 3 Tesla. One group consisted of prelingually deafened users of DGS, the other group of hearing non-signers naïve to sign language. The two groups were presented with identical video sequences comprising DGS sentences in form of dialoges. To account for substantial interindividual anatomical variability observed in the group of deaf participants, the brain responses in the two groups of subjects were analyzed with two different procedures.
Results: Results from a multi-subject averaging approach were contrasted with an analysis, which can account for the considerable inter-individual variability of gross anatomical landmarks. The anatomy-based approach indicated that individuals’ responses to proper DGS processing was tied up with a leftward asymmetry in the dorsolateral prefrontal cortex, anterior and middle temporal gyrus, and visual association cortices. In contrast, standard multi-subject averaging of deaf individuals during DGS perception revealed a less lateralized peri- and extrasylvian network. Furthermore, voxel-based analyses of the brains’ morphometry evidenced a white-matter deficit in the left posterior longitudinal and inferior uncinate fasciculi and a steeper slope of the posterior part of the left Sylvian Fissure (SF) in the deaf individuals.
Conclusion: These findings may imply that the cerebral anatomy of deaf individuals has undergone structural changes as a function of monomodal visual sign language perception during childhood and adolescence.
Induction of LTP-like changes in human auditory cortex by rapid auditory stimulation: An FMRI study
from Restorative Neurology and Neuroscience
Purpose: Previously we have shown that rapid sensory stimulation, in this case, auditory tone pips, can induce long-lasting plastic changes akin to Long Term Potentiation (LTP) within adult human sensory cortex. In a previous study, auditory LTP was reflected as an increase in the amplitude of the N1 component of the auditory event-related potential as measured by EEG. The goal of the present study was to investigate potential effects of LTP-like changes on the hemodynamic response of the human auditory cortex.
Methods: Silent sparse-sampled fMRI recordings were obtained while subjects passively listened to tone-pips both before and after a short block of rapidly presented auditory tone-pips (auditory tetanus) was delivered.
Results: The BOLD response within the primary auditory cortex was significantly enhanced after the auditory tetanus.
Conclusion: This is the first study demonstrating LTP-like changes of the hemodynamic response in the auditory system, and thus supports the growing literature demonstrating LTP can be induced in adult human cortex. These results have implications in the fields of perceptual learning and rehabilitation.
Variability in cortical representations of speech sound perception
from Clinical Linguistics and Phonetics
Recent brain mapping studies have provided new insights into the cortical systems that mediate human speech perception. Electrocortical stimulation mapping (ESM) is a brain mapping method that is used clinically to localize cortical functions in neurosurgical patients. Recent ESM studies have yielded new insights into the cortical systems that mediate speech perception and how these systems vary as a function of individual differences. ESM methods are described and findings from recent ESM studies of speech perception are reviewed. The clinical implications of these findings are discussed as they relate to current understanding of how individual differences in listening abilities are reflected in the underlying cortical representations.
Audiovisual Temporal Correspondence Modulates Human Multisensory Superior Temporal Sulcus Plus Primary Sensory Cortices
from the Journal of Neuroscience
The brain should integrate related but not unrelated information from different senses. Temporal patterning of inputs to different modalities may provide critical information about whether those inputs are related or not. We studied effects of temporal correspondence between auditory and visual streams on human brain activity with functional magnetic resonance imaging (fMRI). Streams of visual flashes with irregularly jittered, arrhythmic timing could appear on right or left, with or without a stream of auditory tones that coincided perfectly when present (highly unlikely by chance), were noncoincident with vision (different erratic, arrhythmic pattern with same temporal statistics), or an auditory stream appeared alone. fMRI revealed blood oxygenation level-dependent (BOLD) increases in multisensory superior temporal sulcus (mSTS), contralateral to a visual stream when coincident with an auditory stream, and BOLD decreases for noncoincidence relative to unisensory baselines. Contralateral primary visual cortex and auditory cortex were also affected by audiovisual temporal correspondence or noncorrespondence, as confirmed in individuals. Connectivity analyses indicated enhanced influence from mSTS on primary sensory areas, rather than vice versa, during audiovisual correspondence. Temporal correspondence between auditory and visual streams affects a network of both multisensory (mSTS) and sensory-specific areas in humans, including even primary visual and auditory cortex, with stronger responses for corresponding and thus related audiovisual inputs.
The mismatch negativity (MMN) in basic research of central auditory processing: A review
In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.
Preparatory Activity in Occipital Cortex in Early Blind Humans Predicts Auditory Perceptual Performance
from the Journal of Neuroscience
Early onset blindness leads to a dramatic alteration in the way the world is perceived, a change that is detectable in the organization of the brain. Several studies have confirmed that blindness leads to functional alterations in occipital cortices that normally serve visual functions. These reorganized brain regions respond to a variety of tasks and stimuli, but their specific functions are unclear. In sighted individuals, several studies have reported preparatory activity in retinotopic areas, which enhances perceptual sensitivity. “Baseline shifts,” changes in activity associated with a cue predicting an upcoming event, provides a marker for attentional modulation. Here we demonstrate that, in early blind subjects, medial occipital areas produced significant blood oxygenation level-dependent (BOLD) responses to a cue signaling an auditory discrimination trial but not to a cue indicating a no-trial period. Furthermore, the amplitude of the BOLD response in the anterior calcarine sulcus of early blind subjects correlated with their discrimination performance on the auditory backward masking task. Preparatory BOLD responses also were present in auditory cortices, although they were more robust in blind than sighted control subjects. The pattern of response in visual areas is similar to preparatory effects observed during visual selective attention in sighted subjects and consistent with the hypothesis that the mechanisms implicated in visual attention continue to modulate occipital cortex in the early blind. A possible source of this top-down modulation may be the frontoparietal circuits that retain their connectivity with the reorganized occipital cortex and as a result influence processing of nonvisual stimuli in the blind.
Concurrent Encoding of Frequency and Amplitude Modulation in Human Auditory Cortex: an Encoding Transition
from the Journal of Neurosphysiology
Complex natural sounds (e.g., animal vocalizations or speech) can be characterized by specific spectrotemporal patterns whose components change in both frequency (frequency modulation, FM) and amplitude (amplitude modulation, AM). The neural coding of AM and FM has been widely studied in humans and animals, but typically with either pure AM or pure FM stimuli. The neural mechanisms employed to perceptually unify AM and FM acoustic features remain unclear. Using stimuli with simultaneous sinusoidal AM (at rate fAM=37Hz) and FM (with varying rates fFM), magnetoencephalography (MEG) is used to investigate the elicited auditory steady state response (aSSR) at relevant frequencies (fAM, fFM, fAM ±fFM ). Previous work demonstrated that for sounds with slower FM dynamics (fFM <5Hz), the phase of the aSSR at fAM tracked the FM; in other words, AM and FM features were co-tracked and co-represented by ‘phase modulation’ encoding. This study explores the neural coding mechanism for stimuli with faster FM dynamics (up to 30 Hz), demonstrating that at faster rates (fFM>5Hz), there is a transition from pure phase modulation encoding to a single-upper-sideband (SSB) response (at frequency fAM+fFM ) pattern. We propose that this unexpected SSB response can be explained by the additional involvement of subsidiary amplitude modulation encoding responses, simultaneously to, and in quadrature with, the ongoing phase modulation. These results, using MEG to reveal a possible neural encoding of specific acoustic properties, demonstrate more generally that physiological tests of encoding hypotheses can be performed non-invasively, and on human subjects, complementing invasive, single-unit recordings in animals.
Temporal Dynamics of Adaptation to Natural Sounds in the Human Auditory Cortex
from Cerebral Cortex
We aimed at testing the cortical representation of complex natural sounds within auditory cortex by conducting 2 human magnetoencephalography experiments. To this end, we employed an adaptation paradigm and presented subjects with pairs of complex stimuli, namely, animal vocalizations and spectrally matched noise. In Experiment 1, we presented stimulus pairs of same or different animal vocalizations and same or different noise. Our results suggest a 2-step process of adaptation effects: first, we observed a general item-unspecific reduction of the N1m peak amplitude at 100 ms, followed by an item-specific amplitude reduction of the P2m component at 200 ms after stimulus onset for both animal vocalizations and noise. Multiple dipole source modeling revealed the right lateral Heschl’s gyrus and the bilateral superior temporal gyrus as sites of adaptation. In Experiment 2, we tested for cross-adaptation between animal vocalizations and spectrally matched noise sounds, by presenting pairs of an animal vocalization and its corresponding or a different noise sound. We observed cross-adaptation effects for the P2m component within bilateral superior temporal gyrus. Thus, our results suggest selectivity of the evoked magnetic field at 200 ms after stimulus onset in nonprimary auditory cortex for the spectral fine structure of complex sounds rather than their temporal dynamics.
Unimodal and cross-modal plasticity in the ‘deaf’ auditory cortex
from the International Journal of Audiology
Congenital auditory deprivation leads to deficits in the auditory cortex. The present review focuses on central aspects of auditory deprivation: development, plasticity, corticocortical interactions, and cross-modal reorganization. We compile imaging data from human subjects, electroencephalographic data from cochlear implanted children, and animal research on congenital deafness. Behavioral, electroencephalographic, and imaging data in humans correspond well to data behavioral and neurophysiological data obtained from congenitally deaf cats. The available data indicate that auditory deprivation leads to ‘decoupling’ of the primary auditory cortex from cognitive modulation of higher-order auditory areas. Higher-order auditory areas undergo a strong cross-modal reorganization and take-over new functions. Due to these and other deficits of intrinsic microcircuitry, the cortical column can not integrate bottom-up and top-down influences in deaf auditory cortex. In the ultimate consequence perceptual learning is compromised, resulting in sensitive periods.
Impact of mild hearing loss on neurological processes
from News-Medical.net
Mild to moderate forms of hearing loss can have a lasting impact on the auditory cortex, according to findings by researchers at New York University’s Center for Neural Science.
Multiple Stages of Auditory Speech Perception Reflected in Event-Related fMRI
from Cerebral Cortex
Speech processing in auditory cortex and beyond is a remarkable yet poorly understood faculty of the listening brain. Here we show that stop consonants, as the most transient constituents of speech, are sufficient to involve speech perception circuits in the human superior temporal cortex. Left anterolateral superior temporal cortex showed a stronger response in blood oxygenation level–dependent functional magnetic resonance imaging (fMRI) to intelligible consonantal bursts compared with incomprehensible control sounds matched for spectrotemporal complexity. Simultaneously, the left posterior superior temporal plane (including planum temporale [PT]) exhibited a noncategorical responsivity to complex stimulus acoustics across all trials, showing no preference for intelligible speech sounds. Multistage hierarchical processing of speech sounds is thus revealed with fMRI, providing evidence for a role of the PT in the fundamental stages of the acoustic analysis of complex sounds, including speech.
About the Callier Library
Callier Library is a satellite facility of The University of Texas at Dallas, McDermott Library. It is located at the Dallas, Texas campus of the Callier Center for Communication Disorders. The library supports the graduate-level programs and faculty in communications sciences which are located at the center. It also supports the work of clinicians in hearing and speech disorders who work at both campuses of the Callier Center. One of the missions of Callier Library is to be a useful source of information to the international community of researchers and clinicians in communication disorders. To that end, this web log of citations and news in the field has been built and maintained by Allen Clayton, the Callier Center Librarian.
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