Hemispheric Asymmetry in Cortical Auditory Processing: The Interactive Effects of Attention and Background Noise.

Background: Dichotic listening (DL) technique is a behavioral non-invasive tool which is used in studying hemispheric lateralization. Previous studies using behavioral DL have hypothesized that individuals with learning disabilities (LD) exhibit a lack of cortical specialization for processing speech stimulus. However, there is no event related potential (ERP) evidence, hence the main objective of the study is to explore hemispheric asymmetry using cortical auditory evoked potential (CAEPs) in normal hearing adults and also to compare the same in children with LD and healthy controls. Methods: CAEPs were recorded in 16 normal hearing young adults, eight right-handed children with LD and their age matched controls. Two stop constants (/Pa/ – voiceless, bilabial, stop: /Ta/ - voiceless, alveolar, stop) were chosen for this experiment and presented in each ear and dichotically in two different orders (/pa-ta/, /ta-pa/). ERPs were processed using a standard pipeline, and electrodes readings over the left and right hemispheres were averaged to create left and right regions of interest (ROI). The CAEPs were analyzed for mean amplitude and peak latency of P1-N1-P2 components. Results: The current study results suggest no statistically significant difference between the two stimulus in monaural condition and absence of order effect in dichotic condition. In healthy controls the CAEP latencies were shorter over the left hemisphere in both monaural and dichotic conditions in adults and control children. However, it was very evident that such a difference was lacking in children with LD. Conclusions: Hemispheric asymmetry can be detected using CAEPs for speech stimulus. The measures are consistent and void of stimulus or order effect. Taken together, the findings of current study, both monaural and dichotic condition illustrates the hemispheric differences in processing speech stimuli in normal hearers. Absence of latency differences between hemispheres in children with LD indicate a lack of hemispheric asymmetry.

Background: Dichotic listening (DL) technique is a behavioral non-invasive tool which is used in studying hemispheric lateralization. Previous studies using behavioral DL have hypothesized that individuals with learning disabilities (LD) exhibit a lack of cortical specialization for processing speech stimulus. However, there is no event related potential (ERP) evidence, hence the main objective of the study is to explore hemispheric asymmetry using cortical auditory evoked potential (CAEPs) in normal hearing adults and also to compare the same in children with LD and healthy controls. Methods: CAEPs were recorded in 16 normal hearing young adults, eight right-handed children with LD and their age matched controls. Two stop constants (/Pa/ - voiceless, bilabial, stop: /Ta/ - voiceless, alveolar, stop) were chosen for this experiment and presented in each ear and dichotically in two different orders (/pa-ta/, /ta-pa/). ERPs were processed using a standard pipeline, and electrodes readings over the left and right hemispheres were averaged to create left and right regions of interest (ROI). The CAEPs were analyzed for mean amplitude and peak latency of P1-N1-P2 components. Results: The current study results suggest no statistically significant difference between the two stimulus in monaural condition and absence of order effect in dichotic condition. In healthy controls the CAEP latencies were shorter over the left hemisphere in both monaural and dichotic conditions in adults and control children. However, it was very evident that such a difference was lacking in children with LD. Conclusions: Hemispheric asymmetry can be detected using CAEPs for speech stimulus. The measures are consistent and void of stimulus or order effect. Taken together, the findings of current study, both monaural and dichotic condition illustrates the hemispheric differences in processing speech stimuli in normal hearers. Absence of latency differences between hemispheres in children with LD indicate a lack of hemispheric asymmetry.

The study aimed to explore the effect of sensorineural hearing loss on the central auditory processing of signals in noise using cortical auditory evoked potentials (CAEPs) in a cohort of older adults. Three groups of individuals participated in the study. Each group included 33 older adults with normal hearing, those with mild hearing loss and those with moderate hearing loss. N1-P2 peaks of CAEPs by speech stimuli in silent conditions and with varying sound pressure levels of background noise were recorded. CAEP latencies, amplitudes and relative changes in CAEP amplitudes as a function of decreasing signal-to-noise ratios (SNR) in three groups were analyzed using the mixed analysis of variance method. There was a significant main effect of SNR on all CAEP components, as well as significant main effects of hearing status on N1 latencies, amplitudes and relative changes in N1 amplitudes. A significant interaction was found between hearing status and SNR for relative changes in N1 amplitudes. The normal hearing group differed from both the mild and moderate hearing loss groups in terms of relative changes in N1 amplitudes at SNR 10 dB. The results showed decreased amplitudes and increased latencies for N1-P2 response as the SNR of CAEP stimuli was lowered. The degree of reduction in the N1 amplitudes of the older people with normal hearing resulting from the increase in the background noise level was greater than those in their sensorineural hearing-impaired counterparts, providing evidence for decreased central inhibition for individuals with age-related hearing loss.

The functional asymmetry of the human brain hemispheres (motor, sensory, and mental) reflects the differences in the distribution of neuro-psychic functions between the left and right hemispheres. The left hemisphere is responsible for the brain's abstract-logical, inductive thinking, and verbal-analytical functions. The right hemisphere provides visual-figurative, deductive thinking. The dominance of the left hemisphere determines left-hemispheric thinking, while the dominance of the right hemisphere determines right-hemispheric thinking. The synchronous functioning of both hemispheres indicates balanced-hemispheric thinking. According to this distribution, different styles and effectiveness of students' cognitive activities will be observed. Therefore, our goal was to investigate and compare the types of cerebral hemisphere dominance in students of a physics and mathematics lyceum studying in classes with physics-mathematics and chemistry-biology specializations. We found that 84.4% of students of both genders, regardless of their chosen specialization, had left-hemisphere dominance with an average level of functional asymmetry. Among students of the chemistry-biology specialization who actively participate in Olympiads, there are representatives with left hemispheric (high, medium, and low asymmetry coefficients), right hemispheric, and balanced-hemispheric functional organization of the brain. Among students of the physics-mathematics specialization involved in Olympiads, there were children with left-hemispheric thinking (low and medium asymmetry coefficients). Among 14 students who participated in Olympiads, 86% (12) were right-handed, and 14% (2) were left-handed. This indicates that the type of interhemispheric asymmetry is not a factor that causes learning difficulties or vice versa. The article summarizes the necessity of considering the individual psychophysiological characteristics of students in the educational process, particularly their functional asymmetry of the cerebral hemispheres. It emphasizes the need to implement appropriate forms, methods, and teaching techniques in lessons that align with specific types of thinking to activate the potential of both cerebral hemispheres in students of a physics and mathematics lyceum with mathematical and biological specializations.

Background noise can enhance cortical auditory evoked potentials under certain conditions

Speech perception in background noise is difficult for many individuals, and there is considerable performance variability across listeners. The combination of physiological and behavioral measures may help to understand sources of this variability for individuals and groups and prove useful clinically with hard-to-test populations. The purpose of this study was threefold: (1) determine the effect of signal-to-noise ratio (SNR) and signal level on cortical auditory evoked potentials (CAEPs) and sentence-level perception in older normal-hearing (ONH) and older hearing-impaired (OHI) individuals, (2) determine the effects of hearing impairment and age on CAEPs and perception, and (3) explore how well CAEPs correlate with and predict speech perception in noise. Two groups of older participants (15 ONH and 15 OHI) were tested using speech-in-noise stimuli to measure CAEPs and sentence-level perception of speech. The syllable /ba/, used to evoke CAEPs, and sentences were presented in speech-spectrum background noise at four signal levels (50, 60, 70, and 80 dB SPL) and up to seven SNRs (-10, -5, 0, 5, 15, 25, and 35 dB). These data were compared between groups to reveal the hearing impairment effect and then combined with previously published data for 15 young normal-hearing individuals to determine the aging effect. Robust effects of SNR were found for perception and CAEPs. Small but significant effects of signal level were found for perception, primarily at poor SNRs and high signal levels, and in some limited instances for CAEPs. Significant effects of age were seen for both CAEPs and perception, while hearing impairment effects were only found with perception measures. CAEPs correlate well with perception and can predict SNR50s to within 2 dB for ONH. However, prediction error is much larger for OHI and varies widely (from 6 to 12 dB) depending on the model that was used for prediction. When background noise is present, SNR dominates both perception-in-noise testing and cortical electrophysiological testing, with smaller and sometimes significant contributions from signal level. A mismatch between behavioral and electrophysiological results was found (hearing impairment effects were primarily only seen for behavioral data), illustrating the possible contributions of higher order cognitive processes on behavior. It is interesting that the hearing impairment effect size was more than five times larger than the aging effect size for CAEPs and perception. Sentence-level perception can be predicted well in normal-hearing individuals; however, additional research is needed to explore improved prediction methods for older individuals with hearing impairment.

This article discusses the connection of hemispheric control over audioverbal perception processes and such individual features as “leading hand” (right-handedness and lefthandedness). We present a literature review and description of our research to provide evidence of the complexity and ambiguity of this connection. The method of dichotic listening was used for diagnosing audioverbal perception lateralization. This method allows estimation of the right-ear coefficient (REC), the efficiency coefficient (EC), and the effectiveness ratio (ER) of different aspects of audioverbal perception. Our research involved 47 persons with a leading right hand (mean age, 29.04±9.97 years) and 32 persons with a leading left hand (mean age, 29.41±10.34 years). Different hypotheses about the mechanisms of hemispheric control over audioverbal and motor processes were assessed. The research showed that both the leftand right-handers’ audioverbal perception characteristics depended mainly on right-hemisphere activity. The most dynamic and sensitive index of the functioning of the two hemispheres during dichotic listening was the efficiency coefficient of stimuli reproduction through the left ear (EC of the left ear). It turns out that this index depends on the coincidence/noncoincidence of the leading hemispheres in speech and motor processes. The highest efficiency of audioverbal perception revealed itself in the left-handers with a leading left ear (the hemispheric-control coincidence), and the lowest efficiency was in the left-handers with a leading right ear (the hemispheric-control divergence). The right-handers were characterized by less variation in values, although the influence of the coincidence/noncoincidence of the leading hemispheres in speech and motor processes also revealed itself as a tendency. This consistent pattern points out the necessity for further research on asymmetries of the different modalities that takes into account their probable interaction. The results of our study comport with scientific data showing genotypic left-handers with subzero right-ear coefficient (REC) values to be more efficient than left-handed persons who display high REC values.

Language processing from the cochlea to auditory association cortices shows side-dependent specificities with an apparent left hemispheric dominance. The aim of this article was to propose to nonspeech specialists a didactic review of two complementary theories about hemispheric asymmetry in speech processing. Starting from anatomico-physiological and clinical observations of auditory asymmetry and interhemispheric connections, this review then exposes behavioral (dichotic listening paradigm) as well as functional (functional magnetic resonance imaging and positron emission tomography) experiments that assessed hemispheric specialization for speech processing. Even though speech at an early phonological level is regarded as being processed bilaterally, a left-hemispheric dominance exists for higher-level processing. This asymmetry may arise from a segregation of the speech signal, broken apart within nonprimary auditory areas in two distinct temporal integration windows--a fast one on the left and a slower one on the right--modeled through the asymmetric sampling in time theory or a spectro-temporal trade-off, with a higher temporal resolution in the left hemisphere and a higher spectral resolution in the right hemisphere, modeled through the spectral/temporal resolution trade-off theory. Both theories deal with the concept that lower-order tuning principles for acoustic signal might drive higher-order organization for speech processing. However, the precise nature, mechanisms, and origin of speech processing asymmetry are still being debated. Finally, an example of hemispheric asymmetry alteration, which has direct clinical implications, is given through the case of auditory aging that mixes peripheral disorder and modifications of central processing.

Harmonization of the Activity of the Left and Right Cerebral Hemispheres - an Important Component of the Spiritual and Mental Health of Individual and Humanity

Objective:To investigate the correlation between Mandarin acceptable noise level （M-ANL） and cortical auditory evoked potential （CAEP）, and to explore the possible mechanism leading to individual differences in M-ANL values. Methods:Thirty listeners aged 22-33 years with normal hearing were selected as the study subjects, and the M-ANL test and CAEP test were performed respectively. The most comfortable level （MCL）, maximum background noise level （BNL）, M-ANL and CAEP values of each subject were recorded. The latency of each wave of P1, N1, P2, N2, P300 and the amplitude of P1-N1, P2-N2, P300 in CAEP were recorded for each subject. SPSS 25.0 was used for statistical analysis to explore the correlation between the MCL value, BNL value and M-ANL values and the latency of P1, N1, P2, N2, P300 and P1-N1, P2-N2, P300 amplitudes of CAEP. Results:①The MCL value and M-ANL value were positively correlated with the P2 latency of CAEP, and the correlation coefficients were 0.404 and 0.400, respectively, and the differences were statistically significant （P<0.05）. There was no correlation with P1, N1, N2, and P300 latencies of CAEP （P>0.05）. ②The MCL value, BNL value and M-ANL value had no significant difference with the CAEP wave amplitudes of P1-N1, P2-N2, and P300 （P>0.05）. Conclusion:There was a certain correlation between M-ANL and CAEP in young adults with normal hearing, suggesting that the central auditory cortex might play a potential regulatory role in the background noise tolerance. Individuals with a greater background noise acceptance might have stronger central efferent mechanisms and/or less active central afferent mechanisms.

Objective: To investigate speech stimuli and background-noise-dependent changes in cortical auditory-evoked potentials (CAEPs) in unaided and aided conditions, and determine amplification effects on CAEPs. Design: CAEPs to naturally produced syllables in quiet and in multi-talker babble were recorded, with and without a hearing aid in the right ear. At least 300 artifact-free trials for each participant were required to measure latencies and amplitudes of CAEPs. Acoustic characteristics of the hearing-aid-transduced stimuli were measured using in-the-canal probe microphone measurements to determine unaided versus aided SNR and to compare stimulus acoustic characteristics to CAEP findings. Study sample: Ten participants with normal hearing, aged 19 to 35 years. Results: CAEP latencies and amplitudes showed significant effects of speech contrast, background noise, and amplification. N1 and P2 components varied differently across conditions. In general, cortical processing in noise was influenced by SNR and the spectrum of the speech stimuli. Hearing-aid-induced spectral and temporal changes to the speech stimuli affected P1-N1-P2 components. Amplification produced complex effects on latencies and amplitudes across speech stimuli and CAEP components, and for quiet versus noise conditions. Conclusion: CAEP components reflect spectral and temporal characteristics of speech stimuli and acoustic changes induced by background noise and amplification.

Cortical auditory evoked potentials (CAEP) throughout a language task is beneficial during psychophysiological evaluation to advance identification of language disorders. So as to better comprehend human communication and to provide additional elements for neuropsychological examinations we aimed to (1) examine the influence of language tasks on cortical auditory processing and vagal control of heart rate and (2) to verify a possible association between the parasympathetic cardiac regulation and cortical auditory processing in language tasks. This study was completed with 49 women. The subjects were separated into two groups: (1) phonological language tasks (N = 21) and (2) semantic (N = 21) language tasks. Heart rate variability (HRV) and CAEP were evaluated before and after the tests. HRV reduced (small effect size) and P3 wave latency increased after the phonological task. Identical variables were significantly correlated after the phonological task and linear regression indicated significant interaction between pNN50 (percentage of adjacent RR intervals with a difference of duration greater than 50 milliseconds) and P3 latency (16.9%). In conclusion, phonological language tasks slightly reduced parasympathetic control of HR and increased cognitive effort. The association between HRV and CAEP are anticipated to be involved in this mechanism.

Identification and discrimination of speech sounds in noisy environments is challenging for adults and even more so for infants and children. Behavioral studies consistently report maturational differences in the influence that signal to noise ratio (SNR) and masker type have on speech processing; however, few studies have investigated the neural mechanisms underlying these differences at the level of the auditory cortex. In the present study, we investigated the effect of different SNRs on speech-evoked cortical auditory-evoked potentials (CAEPs) in infants and adults with normal hearing. A total of 10 adults (mean age 24.1 years) and 15 infants (mean age 30.7 weeks), all with normal hearing, were included in the data analyses. CAEPs were evoked to /m/ and /t/ speech stimuli (duration: 79 ms) presented at 75 dB SPL in the sound field with a jittered interstimulus interval of 1000-1200 ms. Each of the stimuli were presented in quiet and in the presence of white noise (SNRs of 10, 15, and 20 dB). Amplitude and latency measures were compared for P1, N1, and P2 for adults and for the large positivity (P) and following negativity (N: N250 and/or N450) for infants elicited in quiet and across SNR conditions. Infant P-N responses to /t/ showed no statistically significant amplitude and latency effects across SNR conditions; in contrast, infant CAEPs to /m/ were greatly reduced in amplitude and delayed in latency. Responses were more frequently absent for SNRs of 20 dB or less. Adult P1-N1-P2 responses were present for all SNRs for /t/ and most SNRs for /m/ (two adults had no responses to /m/ for SNR 10); significant effects of SNR were found for P1, N1, and P2 amplitude and latencies. The findings of the present study support that SNR effects on CAEP amplitudes and latencies in infants cannot be generalized across different types of speech stimuli and cannot be predicted from adult data. These findings also suggest that factors other than energetic masking are contributing to the immaturities in the SNR effects for infants. How these CAEP findings relate to an infant's capacity to process speech-in-noise perceptually has yet to be established; however, we can be confident that the presence of CAEPs to a speech stimulus in noise means that the stimulus is detected at the level of the auditory cortex. The absence of a response should be interpreted with caution as further studies are needed to investigate a range of different speech stimuli and SNRs, in conjunction with behavioral measures, to confirm that infant CAEPs do indeed reflect functional auditory capacity to process speech stimuli in noise.

Event Abstract Back to Event Hemispheric asymmetries in the resting-sate functional connectivity patterns of the brain regions critical for language comprehension And U. Turken1* and Nina F. Dronkers2 1 Veterans Affairs Northern California Health Care System, United States 2 UC Davis, Neurology Department, United States Introduction. We recently investigated the structural and functional connectivity profiles of five left hemisphere brain regions that support language comprehension (Turken & Dronkers, 2011). These regions were previously identified in a voxel-based lesion-symptom mapping (VLSM) investigation of auditory sentence comprehension deficits in aphasic patients with left hemisphere brain lesions due to stroke (Dronkers et al., 2004, Figure A). Lesion analysis findings highlighted as being critical for language comprehension the posterior middle temporal gyrus (MTG, yellow), anterior section of the superior temporal gyrus and Brodmann’s area 22 (ant. STG/BA22, red), Brodmann’s area 47 in the orbital section of the inferior frontal gyrus (IFGorb, BA47, blue), a part of Brodmann’s area 46 in middle frontal gyrus (BA46, brown) and a region extending from the superior temporal sulcus (STS) to parts of Brodmann’s area 39 (STS/BA39, green). Our subsequent analysis of structural and functional connectivity of these regions in a group of healthy subjects showed that these regions are part of a large network of brain regions that support language, interconnected by six major pathways and extending in the two hemispheres (Turken & Dronkers, 2011). The left posterior MTG showed a particularly extensive structural and functional connectivity pattern (Figure C), suggesting a key role in language comprehension. In order to gain further insights into the neural architecture of the language network, we examined here the hemispheric asymmetries in the functional connectivity patterns of these five regions. Methods. Whole-brain functional connectivity patterns of each of the five regions and their right hemisphere homologues were assessed and compared between the two hemispheres using resting-state functional MRI data from 25 healthy subjects (1000 Functional Connectomes database, http://www.nitrc.org/projects/fcon_1000, NYU test-retest reliability dataset, Shehzad et al., 2009; 3T EPI, full cerebral coverage, 2 second TR, 6 minute runs in three separate session). The Functional Connectivity Toolbox (http://www.nitrc.org/projects/conn) for SPM8 was used for deriving the functional connectivity maps for each region of interest (ROI) defined in Montreal Neurological Institute (MNI) space. Hemispheric asymmetries were assessed using contrasts comparing at each voxel the strength of the coupling between that voxel and the left and right hemisphere homologues of each ROI. Group level analysis were conducted with voxel-wise t-tests (p < 0.05, Bonferroni correction, cluster extent > 25 voxels). Results & Discussion. Hemispheric asymmetries in the resting-state functional connectivity patterns of the left and right posterior MTG were found for the angular gyrus, the orbital part of the inferior frontal gyrus (BA47), dorso-medial frontal cortex and the medial orbitofrontal cortex (Figure C, D). In each case, functional connectivity within the left hemisphere was stronger than in the right hemisphere. The anterior BA/BA22 did not show any significant asymmetries. The connectivity between BA47 and the angular gyrus as well as superior frontal gyrus was stronger in the left than in the right hemisphere. STS/BA39 showed stronger functional connectivity in the left hemisphere with IFGorb (BA 47) and dorso-medial frontal cortex. Overall, the results indicate stronger intrahemispheric coupling among the left hemisphere regions involved in language comprehension than between the homologous regions in the right hemisphere. The most notable functional connectivity asymmetries, involving the MTG, the angular gyrus and the orbital section of the IFG could be associated with structural asymmetries in the pathways connecting these regions, in particular, the middle longitudinal fasciculus and the inferior occipito-frontal fasciculus/extreme capsule fiber systems. Turken, A. U., Dronkers, N. F. (2011). The neural architecture of the language comprehension network: converging evidence from lesion and connectivity analyses. Frontiers in Systems Neuroscience, 5, 1:20. Dronkers, N.F., Wilkins, D.P., Van Valin, R.D., Jr., Redfern, B.B., Jaeger, J.J., 2004. Lesion analysis of the brain areas involved in language comprehension. Cognition 92, 145-177. Shehzad, Z., Kelly, A.M., Reiss, P.T., Gee, D.G., Gotimer, K., Uddin, L.Q., Lee, S.H., Margulies, D.S., Roy, A.K., Biswal, B.B., Petkova, E., Castellanos, F.X., Milham, M.P., 2009. The resting brain: unconstrained yet reliable. Cereb Cortex 19, 2209-2229. Figure 1 Keywords: Neuroimaging Conference: 4th INCF Congress of Neuroinformatics, Boston, United States, 4 Sep - 6 Sep, 2011. Presentation Type: Poster Presentation Topic: Neuroimaging Citation: Turken A and Dronkers N (2011). Hemispheric asymmetries in the resting-sate functional connectivity patterns of the brain regions critical for language comprehension. Front. Neuroinform. Conference Abstract: 4th INCF Congress of Neuroinformatics. doi: 10.3389/conf.fninf.2011.08.00044 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 17 Oct 2011; Published Online: 19 Oct 2011. * Correspondence: Dr. And U. Turken, Veterans Affairs Northern California Health Care System, Martinez, United States, andturken@ebire.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers And U. Turken Nina F. Dronkers Google And U. Turken Nina F. Dronkers Google Scholar And U. Turken Nina F. Dronkers PubMed And U. Turken Nina F. 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P1-244: Frequency of hemispheric metabolic asymmetry in probable Alzheimer's disease