Involvement Of Auditory Cortex Research Articles

Evidence of both brainstem and auditory cortex involvement in categorical perception for Chinese lexical tones.

The categorical perception of lexical tones is important to understand tonal languages. Recent studies have provided electrophysiological evidence for the categorical perception of lexical tones at the cortical level; however, whether neural correlates exist at subcortical levels remain unknown. In this study, by using across-category and within-category lexical tone contrasts with the equivalent physical interval, we recorded deviance detection activities at both the brainstem (reflected by frequency following response) and cortical levels (reflected by mismatch negativity) simultaneously. We found that significantly enhanced intertrial phase-locking of frequency following response s was observed only during the across-category deviance detection, which indicates that phonological differences could be detected at the level of brainstem. In addition, the across-category deviants induced stronger mismatch negativity than within-category deviants. For the first time, our results demonstrate that neural correlates of categorical perception of lexical tones exist even in the brainstem, and suggests that both cortical and subcortical processes are involved in the coding and categorization of tonal information.

Auditory perception modulated by word reading.

Theories of embodied cognition positing that sensorimotor areas are indispensable during language comprehension are supported by neuroimaging and behavioural studies. Among others, the auditory system has been suggested to be important for understanding sound-related words (visually presented) and the motor system for action-related words. In this behavioural study, using a sound detection task embedded in a lexical decision task, we show that in participants with high lexical decision performance sound verbs improve auditory perception. The amount of modulation was correlated with lexical decision performance. Our study provides convergent behavioural evidence of auditory cortex involvement in word processing, supporting the view of embodied language comprehension concerning the auditory domain.

Functional near-infrared spectroscopy to probe state- and trait-like conditions in chronic tinnitus: a proof-of-principle study.

Objective. Several neuroscience tools showed the involvement of auditory cortex in chronic tinnitus. In this proof-of-principle study we probed the capability of functional near-infrared spectroscopy (fNIRS) for the measurement of brain oxygenation in auditory cortex in dependence from chronic tinnitus and from intervention with transcranial magnetic stimulation. Methods. Twenty-three patients received continuous theta burst stimulation over the left primary auditory cortex in a randomized sham-controlled neuronavigated trial (verum = 12; placebo = 11). Before and after treatment, sound-evoked brain oxygenation in temporal areas was measured with fNIRS. Brain oxygenation was measured once in healthy controls (n = 12). Results. Sound-evoked activity in right temporal areas was increased in the patients in contrast to healthy controls. Left-sided temporal activity under the stimulated area changed over the course of the trial; high baseline oxygenation was reduced and vice versa. Conclusions. By demonstrating that rTMS interacts with auditory evoked brain activity, our results confirm earlier electrophysiological findings and indicate the sensitivity of fNIRS for detecting rTMS induced changes in brain activity. Moreover, our findings of trait- and state-related oxygenation changes indicate the potential of fNIRS for the investigation of tinnitus pathophysiology and treatment response.

Tactile Temporal Processing in the Auditory Cortex

Perception of the outside world results from integration of information simultaneously derived via multiple senses. Increasing evidence suggests that the neural underpinnings of multisensory integration extend into the early stages of sensory processing. In the present study, we investigated whether the superior temporal gyrus (STG), an auditory modality-specific area, is critical for processing tactile events. Transcranial magnetic stimulation (TMS) was applied over the left STG and the left primary somatosensory cortex (SI) at different time intervals (60, 120, and 180 msec) during a tactile temporal discrimination task (Experiment 1) and a tactile spatial discrimination task (Experiment 2). Tactile temporal processing was disrupted when TMS was applied to SI at 60 msec after tactile presentation, confirming the modality specificity of this region. Crucially, TMS over STG also affected tactile temporal processing but at 180 msec delay. In both cases, the impairment was limited to the contralateral touches and was due to reduced perceptual sensitivity. In contrary, tactile spatial processing was impaired only by TMS over SI at 60-120 msec. These findings demonstrate the causal involvement of auditory areas in processing the duration of somatosensory events, suggesting that STG might play a supramodal role in temporal perception. Furthermore, the involvement of auditory cortex in somatosensory processing supports the view that multisensory integration occurs at an early stage of cortical processing.

Involvement of Auditory Cortex in Speech Production

In addition to their role in speech perception, the auditory cortical areas of the superior temporal lobe are important for the formation and maintenance of motor commands for speech production. Using a combination of neural network modeling, neuroimaging, and auditory perturbation experiments, we have characterized the network of brain regions involved in auditory feedback control of segmental aspects of speech. This network involves auditory error cells in bilateral posterior superior temporal cortex which become active when the current auditory feedback mismatches the auditory target for the current speech sound. Projections from these auditory cortical areas to the right hemisphere ventral premotor areas, then on to primary motor cortex, transform perceived auditory errors into corrective movement commands for the speech articulators. The DIVA model of speech production produces a close quantitative fit to acoustic data collected during unexpected auditory perturbation of speech and during sensorimotor adaptation to sustained auditory perturbations. Neuroimaging results motivate a modification of the model to include right ventral premotor cortical areas in the auditory feedback circuit for speech production. [Work supported by NIDCD, NSF.]

Electrical brain imaging evidences left auditory cortex involvement in speech and non-speech discrimination based on temporal features

BackgroundSpeech perception is based on a variety of spectral and temporal acoustic features available in the acoustic signal. Voice-onset time (VOT) is considered an important cue that is cardinal for phonetic perception.MethodsIn the present study, we recorded and compared scalp auditory evoked potentials (AEP) in response to consonant-vowel-syllables (CV) with varying voice-onset-times (VOT) and non-speech analogues with varying noise-onset-time (NOT). In particular, we aimed to investigate the spatio-temporal pattern of acoustic feature processing underlying elemental speech perception and relate this temporal processing mechanism to specific activations of the auditory cortex.ResultsResults show that the characteristic AEP waveform in response to consonant-vowel-syllables is on a par with those of non-speech sounds with analogue temporal characteristics. The amplitude of the N1a and N1b component of the auditory evoked potentials significantly correlated with the duration of the VOT in CV and likewise, with the duration of the NOT in non-speech sounds.Furthermore, current density maps indicate overlapping supratemporal networks involved in the perception of both speech and non-speech sounds with a bilateral activation pattern during the N1a time window and leftward asymmetry during the N1b time window. Elaborate regional statistical analysis of the activation over the middle and posterior portion of the supratemporal plane (STP) revealed strong left lateralized responses over the middle STP for both the N1a and N1b component, and a functional leftward asymmetry over the posterior STP for the N1b component.ConclusionThe present data demonstrate overlapping spatio-temporal brain responses during the perception of temporal acoustic cues in both speech and non-speech sounds. Source estimation evidences a preponderant role of the left middle and posterior auditory cortex in speech and non-speech discrimination based on temporal features. Therefore, in congruency with recent fMRI studies, we suggest that similar mechanisms underlie the perception of linguistically different but acoustically equivalent auditory events on the level of basic auditory analysis.

Time Course of Auditory Cortex Activation during Speech Processing

The purpose of the studies summarized in this report was to determine the time course of auditory cortex involvement in speech and language processing in the context of auditory object formation. Forty-one subjects took part in the three studies summarized in this report. In all three studies, subjects performed a choice-reaction task that required their pressing an appropriate button in response to auditory stimuli (speech/non-speech, good/worse fused phonemes, first/second language words) presented through earphones. Event-related potentials (ERPs) were recorded during performance of the task from 21 scalp electrodes, in addition to peri-ocular electrodes for monitoring eye movements. Current densities within the gray matter of the brain were estimated using the LORETA (low resolution electromagnetic tomography) method. In general, except for some periods, processing phonetic and linguistic information was associated with elevated activity in the left auditory cortex. Peaks in auditory cortex activation corresponded in time to scalp recorded peaks in the latencies of P1 and up to as late as P3. The adjacent posterior temporal areas showed a similar temporal pattern of activation, but tended to be less lateralized to the left, or even biased toward right hemisphere predominance, depending on the stimulus, particularly in the later time frames. The results indicate that the auditory cortex is engaged in auditory processing from its early stages and as long as a few hundreds of msec, even after cessation of the stimulus, defining sounds as distinct auditory objects and differentiating speech from non-speech material, relying on acoustic cues. Hemispheric dominance fluctuates to include activity in the 'non-dominant' hemisphere depending on stimulus type and stage of processing.

A combined functional in vivo measure for primary and secondary auditory cortices

Auditory evoked magnetic fields are reliable physiological in vivo markers of activity generated in auditory cortices. In recent years, several components of auditory evoked fields have been demonstrated with specific topographies within the auditory cortex in man. Their differential elicitation and analyses has rendered the discrimination of neural activities in primary vs. secondary auditory cortical fields possible. This in vivo measure may be of interest in a number of (neuro)psychiatric and neuropsychological disorders with central auditory deficits, in which in vivo anatomical measures do not allow a clear distinction of primary vs. secondary auditory cortex involvement. To help better understand the pathophysiology of such disorders, we developed and introduce a combined measure of steady-state field (SSR) and the N1 component of the transient evoked field. The acoustic stimulus for this paradigm consists of a 500-ms tone burst with 39-Hz amplitude modulation of the carrier frequency. This combined stimulation allows assessment of both auditory cortex components in one brief examination to be well tolerated by patients. We examined the source locations of SSR and N1 component with separate classical stimulation and combined stimulation within-session in healthy volunteer subjects. We demonstrate here that the distinct sources of steady-state (primary auditory cortex) and N1 (secondary auditory cortex) responses can be reliably measured without significant spatial distortion with this combined stimulation paradigm.

Bilateral Ablation of Auditory Cortex in Mongolian Gerbil Affects Discrimination of Frequency Modulated Tones but not of Pure Tones

This study examines the role of auditory cortex in the Mongolian gerbil in differential conditioning to pure tones and to linearly frequency-modulated (FM) tones by analyzing the effects of bilateral auditory cortex ablation. Learning behavior and performance were studied in a GO/NO-GO task aiming at avoidance of a mild foot shock by crossing a hurdle in a two-way shuttle box. Hurdle crossing as the conditioned response to the reinforced stimulus (CR+), as false alarm in response to the unreinforced stimulus (CR-), intertrial activity, and reaction times were monitored. The analysis revealed no effects of lesion on pure tone discrimination but impairment of FM tone discrimination. In the latter case lesion effects were dependent on timing of lesion relative to FM tone discrimination training. Lesions before training in naive animals led to a reduced CR+ rate and had no effect on CR- rate. Lesions in pretrained animals led to an increased CR- rate without effects on the CR+ rate. The results suggest that auditory cortex plays a more critical role in discrimination of FM tones than in discrimination of pure tones. The different lesion effects on FM tone discrimination before and after training are compatible with both the hypothesis of a purely sensory deficit in FM tone processing and the hypothesis of a differential involvement of auditory cortex in acquisition and retention, respectively.

Human auditory cortex electrophysiological correlates of the precedence effect: Binaural echo lateralization suppression

Echoes lagging shortly after a sound and originating from a different location blend with the sound source perceptually. The location of the fused “source+echoes” is dominated by the source, suggesting suppression of echo localization. This effect is diminished monaurally, implying involvement of binaural processing. The neural substrates underlying the echo localization suppression are still unclear. The electrophysiological indications of primary auditory cortex involvement in binaural suppression of echo lateralization are presented. Position judgment and auditory-evoked potentials (AEPs) were recorded to single- and pairs of binaural and monaural clicks. The pairs simulated a source and its echo. The binaural source+echo position judgment was dominated by the source at small echo lags. With lag increase, it shifted toward the echo. The AEPs were studied for binaural processes specific to a “real” echo, as opposed to an identical single sound (a “virtual” echo). A reduction in binaural peak amplitude and area and an increase in binaural peak latency were detected specifically in the real echo-evoked middle-latency component Pa. The binaural echo Pa suppression depended upon echo lag, although less strongly than the psychoacoustic position judgment. Pa is associated with primary auditory cortex activity, thus suggesting primary cortical involvement in echo-lateralization suppression.

Evidence for primary auditory cortex involvement in the echo suppression precedence effect: a 3CLT study.

An echo lagging shortly after a source and arising from another direction perceptually blends with the source, and the location of the fused 'source-echo' is dominated by the source location (the Precedence Effect). The neural substrates underlying the echo localization suppression are ambiguous. We recently suggested an auditory evoked potentials correlate of binaural echo lateralization suppression. A significant and specific reduction in binaural peak amplitude and area of the echo-evoked middle-latency component Pa was observed. The binaural echo-Pa suppression depended on echo lag and correlated with the psychophysical echo lateralization suppression. In this study, the echo-Pa generators were analyzed with 3CLT spatio-temporal analysis, in order to suggest the neural substrates involved in echo lateralization suppression. 3CLT enables reliable identification of components, based on rigid geometrical properties. The results suggest that the Pa1 subcomponent of Pa, associated with primary auditory cortex activity, fully accounts for the echo-Pa suppression. This physiological indication for primary auditory cortex involvement in the precedence effect is the first in humans.

Functional involvement of auditory cortex in fine frequency discrimination of biosonar signals in the bat

The auditory cortex of the mustached bat, Pteronotus parnellii, has a highly specialized region, the DSCF (Doppler‐shift constant frequency) area, which overrepresents the frequencies of Doppler‐shifted echoes (about 61 kHz), and, hence, may play a role in the fine frequency discrimination necessary for detailed velocity measurements (Suga, 1984). This function of the DSCF area was behaviorally tested using reversible ablation with muscimol, a potent GABA agonist (Hilosaka et al., 1985). Bats were trained on a discriminated shock avoidance task requiring a leg flexion response. The stimuli were trains of artificial pulse‐echo pairs (tone bursts). For S +, the pulse and echo were the same frequency (e.g., 61.0 kHz), while, for S −, they were different frequencies (e.g., 61.0 and 61.1 kHz). Following baseline testing, 0.1–0.2 μl of muscimol (1 μg/μl saline) was bilaterally applied to the DSCF area. The bats failed on previously successful discriminations of small frequency differences (e.g., 50 Hz), but suc...

Evidence for a contribution of the auditory cortex to audiospinal facilitation in man.

Facilitation of the spinal monosynaptic reflex by auditory stimulation has been demonstrated previously in animals and man. Analysis of the time course of audiospinal facilitation (ASF) in normal subjects is reported. The role of the cerebral cortex in the control of audiospinal facilitation was investigated in 32 patients with anatomically well-circumscribed lesions, the precise topography of which was determined stereotaxically. Lesions of the caudal part (Heschl's gyrus and temporal plane) of the superior temporal gyrus selectively depressed ASF evoked by contralateral auditory stimulation. In contrast, lesions in temporal, parietal and occipital lobes had no effect. Results obtained with frontal lobe lesions were not homogeneous. The specific involvement of auditory cortex in the gating of behavioral audiomotor reactions is discussed.

Involvement of cortical and thalamic auditory regions in retention of differential bradycardiac conditioning to acoustic conditioned stimuli in rabbits

Our previous findings indicate that lesions in the medial division of the medial geniculate nucleus (mMGN) prevent the acquisition of differential conditioning of bradycardia to acoustic stimuli in rabbits. In the present experiment, the effect of lesions in mMGN on retention of differential bradycardiac conditioning was examined. In addition, the possible involvement of auditory cortex in differential conditioning was investigated. Electrodes were chronically implanted in mMGN, the ventral division of the medial geniculate nucleus (vMGN), or auditory cortex. After 7 days of recovery, animals received one differential Pavlovian conditioning session. At the end of the session, lesions were produced through the implanted electrodes. All animals demonstrated differential bradycardiac conditioning during the prelesion session. Animals with vMGN lesions also demonstrated differential conditioning during the postlesion session. However, mMGN and auditory cortex lesion animals failed to demonstrate differential conditioning during the postlesion session due to an increased response magnitude to the unpaired tone (CS−). These data support the hypothesis that mMGN plays a role in differential conditioning of bradycardia to tonal stimuli. In addition, these findings suggest that a possible corticothalamic pathway may be involved in the inhibition of the response to the CS−.

Scalp distribution of human auditory evoked potentials. II. Evidence for overlapping sources and involvement of auditory cortex

The scalp distributions of human auditory evoked potentials (AEPs) between 20 and 250 msec were investigated using non-cephalic reference recordings. AEPs to binaural click stimuli were recorded simulataneously from 20 scalp locations over the right hemisphere in 11 subjects. Computer-generated isovoltage topographic maps at high temporal resolution were used to assess the stability of AEP scalp distributions over time and relate them to major peaks in the AEP wave forms. For potentials between 20 and 60 msec, the results demonstrate a stable scalp distribution of dipolar form that is consistent with sources in primary auditory cortex on the superior temporal plane near the temporoparietal junction. For potentials between 60 and 250 msec, the results demonstrate changes in AEP morphology across electrode locations and changes in scalp distribution over time that lead to two major conclusions. First, AEPs in this latency period are generated by multiple sources which partially overlap in time. Second, one or more regions of auditory cortex contribute significantly to AEPs in this period. Additional data are needed to determine the relative contribution of auditory cortex sources on the superior temporal plane and the lateral temporal surface and to identify AEP sources outside the temporal lobe.