This fMRI study is about modelling the effective connectivity between Heschl's gyrus (HG) and the superior temporal gyrus (STG) in human primary auditory cortices. MATERIALS #ENTITYSTARTX00026;
In this study, the asymmetry of the main effects of action, background and tonal frequency during a pitch memory processing
were investigated by means of brain activation. Eighteen participants (mean age 27.6 years) were presented with low and
high frequency tones in quiet and in noise. They listen, discriminate and recognize the target tone against the final tone
in a series of four distracting tones. The main effects were studied using the analysis of variance (ANOVA) with action (to
wring (rubber bulb) vs. not to wring), background (in quiet vs. in noise) and frequency (low vs. high) as the factors (and
levels respectively). The main effect of action is in the right pre-central gyrus (PCG), in conformation with its contralateral
behavior. The main effect of background indicated the bilateral primary auditory cortices (PAC) and is right lateralized,
attributable to white noise. The main effect of frequency is also observed in PAC but bilaterally equal and attributable to
low frequency tones. Despite the argument that the temporo-spectral lateralization dichotomy is not especially rigid as
revealed by the main effect of frequency, right lateralization of PAC for the respective main effect of background clearly
demonstrates its functional asymmetry suggesting different perceptual functionality of the right and left PAC.
The effects of background noise on speech-evoked cortical auditory evoked potentials (CAEPs) can provide insight into the physiology of the auditory system. The purpose of this study was to determine background noise effects on neural coding of different phonemes within a syllable. CAEPs were recorded from 15 young normal-hearing adults in response to speech signals /s/, /ɑ/, and /sɑ/. Signals were presented at varying signal-to-noise ratios (SNRs). The effects of SNR and context (in isolation or within syllable) were analyzed for both phonemes. For all three stimuli, latencies generally decreased and amplitudes generally increased as SNR improved, and context effects were not present; however, the amplitude of the /ɑ/ response was the exception, showing no SNR effect and a significant context effect. Differential coding of /s/ and /ɑ/ likely result from level and timing differences. Neural refractoriness may result in the lack of a robust SNR effect on amplitude in the syllable context. The stable amplitude across SNRs in response to the vowel in /sɑ/ suggests the combined effects of (1) acoustic characteristics of the syllable and noise at poor SNRs and (2) refractory effects resulting from phoneme timing at good SNRs. Results provide insights into the coding of multiple-onset speech syllables in varying levels of background noise and, together with behavioral measures, may help to improve our understanding of speech-perception-in-noise difficulties.
The present study discussed functional reorganization and alteration in respond to the slow-growing tumour,
hemangiopericytoma in the occipital cortex. Visual evoked field (VEF) and auditory evoked field (AEF) using
magnetoencephalography (MEG) was used to evaluate the source localization and brain activity. Results of VEF source
localization show a typical brain waves. Brain activity of the occipital lobe demonstrate low activation in the ipsilateral
to the tumour. However, result shows the activation on the contralateral hemisphere was high and bigger in activation
volume. AEF result shows an identical source localization and both side of the temporal lobe are activated. This result
suggests that there is a positive plasticity in auditory cortex and slow-growing tumour can induce functional reorganization
and alteration to the brain.
Heschl’s gyrus (HG) is known to interact with other auditory related areas of the same hemisphere during the performance
of an auditory cognitive task. However, the information about how it interacts with the opposite HG is still lacking.
The aim of this study was to investigate the psychophysiologic interaction (PPI) between the bilateral HG during a
simple arithmetic addition task and to verify the role of noise as an experimental factor that would modulate the PPI.
Functional magnetic resonance imaging (fMRI) scans were performed on eighteen healthy participants, in which a
single-digit addition task were solved during in-quiet (AIQ) and in-noise (AIN) conditions. The fMRI data were analysed
using Statistical Parametric Mapping (SPM8). The interaction between the bilateral HG was investigated using PPI
analysis. The response in right HG was found to be linearly influenced by the activity in left HG, vice-versa, for both
in-quiet and in-noise conditions. The connectivity from right to left HG in noisy condition seemed to be modulated
by noise, while the modulation is relatively small oppositely, indicating a non-reciprocal behavior. A two-way PPI
model between right and left HG is suggested. The connectivity from right to left HG during a simple addition task in
noise is driven by a higher ability of right HG to perceive the stimuli in a noisy condition. Both the bilateral HGs took
part in the cognitive processes of arithmetic addition from which the interactions between the two were found to be
different in noise.
A functional magnetic resonance imaging (fMRI) study was conducted on 4 healthy male and female subjects to investigate brain activation during passive and active listening. Two different experimental conditions were separately used in this study. The first condition requires the subjects to listen to a simple arithmetic instruction (e.g. one-plus-two-plus-three-plus-four) - passive listening. In the second condition, the subjects were given the same series of arithmetic instruction and were required to listen and perform the calculation - active listening. The data were then analysed using the Statistical Parametric Mapping (SPM5) and the MATLAB 7.4 (R2007a) programming softwares. The results obtained from the fixed (FFX) and random effects analyses (RFX) show that the active-state signal intensity was significantly higher (p < 0.05) than the resting-state signal intensity for both conditions. The results also indicate significant differences (p < 0.001) in brain activation between passive and active listening. The activated cortical regions during passive listening, as obtained from the FFX of the first condition is symmetrical in the left and right temporal and frontal lobes covering the cortical auditory areas. However, for the second condition, which was active listening, more activation occurs in the left hemisphere with a reduction in the number of activated voxels and their signal intensity in the right hemisphere. Activation mainly occurs in the middle temporal gyrus, precentral gyrus, middle frontal gyrus, superior temporal gyrus and several other areas in the frontal lobes. The point of maximum signal intensity has been shifted to a new coordinates during active listening. It is also observed that the magnetic resonance signal intensity and the number of activated voxel in the right and left superior temporal lobes for the second condition have been reduced as compared to that of the first condition. The results obtained strongly suggest the existence of functional specialisation. The results also indicate different networks for the two conditions. These networks clearly pertain to the existence of functional connectivity between activation areas during listening and listening while performing a simple arithmetic task.
In this study, functional magnetic resonance imaging (fMRI) is used to investigate func-tional specialisation in human auditory cortices during listening. A silent fMRI paradigm was used to reduce the scanner sound artefacts on functional images. The subject was instructed to pay attention to the white noise stimulus binaurally given at an inten-sity level of 70 dB higher than the hearing level for normal people. Functional speciali-sation was studied using the Matlab-based Statistical Parametric Mapping (SPM5) software by means of fixed effects (FFX), random effects (RFX) and conjunction analyses. Individual analyses on all subjects indicated asymmetrical bilateral activation of the left and right hemispheres in Brodmann areas (BA) 22, 41 and 42, involving the primary and secondary auditory cortices. The percentage of signal change is larger in the BA22, 41 and 42 on the right as compared to the ones on the left (p>0.05). The average number of activated voxels in all the respective Brodmann areas are higher in the right hemisphere than in the left (p>0.05). FFX results showed that the point of maximum intensity was in the right BA41 whereby 599±1 activated voxels were ob-served in the right temporal lobe as compared to 485±1 in the left temporal lobe. The RFX results were consistent with that of FFX. The analysis of conjunction which fol-lowed, showed that the right BA41 and left BA22 as the common activated areas in all subjects. The results confirmed the specialisation of the right auditory cortices in pro-cessing non verbal stimuli.
This study was carried out to investigate the effects of noisy background on brain activation during a working memory task. Fourteen healthy male subjects underwent silent functional Magnetic Resonance Imaging (fMRI) scans while listening to words presented verbally against quiet (WIS) and noisy (WIN) backgrounds. The stimuli were binaurally presented to the subjects at 70 dB sound pressure level (SPL) in both conditions. Group results indicated significant (p < 0.001) bilateral widespread of brain activations in the primary auditory cortex, superior temporal gyrus, inferior frontal gyrus, supramarginal gyrus and inferior parietal lobes during WIS. Additional significant activation was observed in the middle cingulate cortex and anterior cingulate cortex during WIN, suggesting the involvement of cingulate cortex in working memory processing against a noisy background. The mean percentage of signal change in all regions was higher during WIN as compared to WIS. Right hemispheric predominance was observed for both conditions in primary auditory cortex and middle frontal gyrus and this could be attributed to the increased difficulty of the tasks. The results obtained from this study demonstrated that background noise increased task demand and difficulty. Task demand was found to play an important role in determining the activation magnitude in the brain areas during working memory task.
The purpose of this study was to determine the effects of noise type, signal-to-noise ratio (SNR), age, and hearing status on cortical auditory evoked potentials (CAEPs) to speech sounds. This helps to explain the hearing-in-noise difficulties often seen in the aging and hearing impaired population. Continuous, modulated, and babble noise types were presented at varying SNRs to 30 individuals divided into three groups according to age and hearing status. Significant main effects of noise type, SNR, and group were found. Interaction effects revealed that the SNR effect varies as a function of noise type and is most systematic for continuous noise. Effects of age and hearing loss were limited to CAEP latency and were differentially modulated by energetic and informational-like masking. It is clear that the spectrotemporal characteristics of signals and noises play an important role in determining the morphology of neural responses. Participant factors such as age and hearing status, also play an important role in determining the brain's response to complex auditory stimuli and contribute to the ability to listen in noise.
In animal models, exposure to high noise levels can cause permanent damage to hair-cell synapses (cochlear synaptopathy) for high-threshold auditory nerve fibers without affecting sensitivity to quiet sounds. This has been confirmed in several mammalian species, but the hypothesis that lifetime noise exposure affects auditory function in humans with normal audiometric thresholds remains unconfirmed and current evidence from human electrophysiology is contradictory. Here we report the auditory brainstem response (ABR), and both transient (stimulus onset and offset) and sustained functional magnetic resonance imaging (fMRI) responses throughout the human central auditory pathway across lifetime noise exposure. Healthy young individuals aged 25-40 years were recruited into high (n = 32) and low (n = 30) lifetime noise exposure groups, stratified for age, and balanced for audiometric threshold up to 16 kHz fMRI demonstrated robust broadband noise-related activity throughout the auditory pathway (cochlear nucleus, superior olivary complex, nucleus of the lateral lemniscus, inferior colliculus, medial geniculate body and auditory cortex). fMRI responses in the auditory pathway to broadband noise onset were significantly enhanced in the high noise exposure group relative to the low exposure group, differences in sustained fMRI responses did not reach significance, and no significant group differences were found in the click-evoked ABR. Exploratory analyses found no significant relationships between the neural responses and self-reported tinnitus or reduced sound-level tolerance (symptoms associated with synaptopathy). In summary, although a small effect, these fMRI results suggest that lifetime noise exposure may be associated with central hyperactivity in young adults with normal hearing thresholds.