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Left hemispheric dominance during auditory processing in a noisy environment.

Okamoto H, Stracke H, Ross B, Kakigi R, Pantev C - BMC Biol. (2007)

Bottom Line: We observed significant decrements of auditory evoked responses and a significant inter-hemispheric difference for the N1m response during both ipsi- and contra-lateral masking.The decrements of auditory evoked neural activities during simultaneous masking can be explained by neural interactions evoked by masker and test stimulus in peripheral and central auditory systems.The inter-hemispheric differences of N1m decrements during ipsi- and contra-lateral masking reflect a basic hemispheric specialization contributing to the processing of complex auditory stimuli such as speech signals in noisy environments.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Biomagnetism and Biosignalanalysis, University of Muenster, Muenster, Germany. okamotoh@uni-muenster.de

ABSTRACT

Background: In daily life, we are exposed to different sound inputs simultaneously. During neural encoding in the auditory pathway, neural activities elicited by these different sounds interact with each other. In the present study, we investigated neural interactions elicited by masker and amplitude-modulated test stimulus in primary and non-primary human auditory cortex during ipsi-lateral and contra-lateral masking by means of magnetoencephalography (MEG).

Results: We observed significant decrements of auditory evoked responses and a significant inter-hemispheric difference for the N1m response during both ipsi- and contra-lateral masking.

Conclusion: The decrements of auditory evoked neural activities during simultaneous masking can be explained by neural interactions evoked by masker and test stimulus in peripheral and central auditory systems. The inter-hemispheric differences of N1m decrements during ipsi- and contra-lateral masking reflect a basic hemispheric specialization contributing to the processing of complex auditory stimuli such as speech signals in noisy environments.

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Representative single subject results. (A) Overlay of individual magnetic field waveforms of all channels (30 Hz low-pass filtered). (B) The contour map of the magnetic field distribution for the maximal N1m response at the latency of 0.118 s. (C) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms in (A). Blue and red lines represent the source strengths in the left and right hemispheres, respectively. (D) Overlay of individual magnetic field waveforms of all channels representing the auditory steady state response (ASSR; band-pass filtered between 30 to 50 Hz). (E) The contour map of the magnetic field distribution at the maximum field distribution at the latency of 0.337 s. (F) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms (D).
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Figure 1: Representative single subject results. (A) Overlay of individual magnetic field waveforms of all channels (30 Hz low-pass filtered). (B) The contour map of the magnetic field distribution for the maximal N1m response at the latency of 0.118 s. (C) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms in (A). Blue and red lines represent the source strengths in the left and right hemispheres, respectively. (D) Overlay of individual magnetic field waveforms of all channels representing the auditory steady state response (ASSR; band-pass filtered between 30 to 50 Hz). (E) The contour map of the magnetic field distribution at the maximum field distribution at the latency of 0.337 s. (F) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms (D).

Mentions: An example of individual magnetic field waveforms (30 Hz low-pass filtered) for the no masking condition (Figure 1A) demonstrates the N1m response peaking approximately 100 ms after the onset of the test stimulus (TS) as most pronounced component of the auditory evoked fields. P1m waves (preceding the N1m) were also visible, but small and variable across subjects. Thus, in the present study, we focused on the N1m response. The source waveforms also exhibited the P1m-N1m response complex to the onset of the TS (Figure 1C). An example of individual magnetic field waveforms (same subject) for the ASSR (band-pass filtered between 30 to 50 Hz) for the no masking condition is displayed in Figure 1D. The signals exhibit the transient evoked gamma-band response and the development of the ASSR after TS onset (Figure 1D,F). The waveforms show clear polarity reversal. Even though the field amplitudes were smaller compared to the N1m, the iso-contour plots of the magnetic field distribution demonstrates a pattern typically resulting from dipolar sources (Figure 1B,E).


Left hemispheric dominance during auditory processing in a noisy environment.

Okamoto H, Stracke H, Ross B, Kakigi R, Pantev C - BMC Biol. (2007)

Representative single subject results. (A) Overlay of individual magnetic field waveforms of all channels (30 Hz low-pass filtered). (B) The contour map of the magnetic field distribution for the maximal N1m response at the latency of 0.118 s. (C) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms in (A). Blue and red lines represent the source strengths in the left and right hemispheres, respectively. (D) Overlay of individual magnetic field waveforms of all channels representing the auditory steady state response (ASSR; band-pass filtered between 30 to 50 Hz). (E) The contour map of the magnetic field distribution at the maximum field distribution at the latency of 0.337 s. (F) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2194668&req=5

Figure 1: Representative single subject results. (A) Overlay of individual magnetic field waveforms of all channels (30 Hz low-pass filtered). (B) The contour map of the magnetic field distribution for the maximal N1m response at the latency of 0.118 s. (C) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms in (A). Blue and red lines represent the source strengths in the left and right hemispheres, respectively. (D) Overlay of individual magnetic field waveforms of all channels representing the auditory steady state response (ASSR; band-pass filtered between 30 to 50 Hz). (E) The contour map of the magnetic field distribution at the maximum field distribution at the latency of 0.337 s. (F) The cortical source strength obtained from the source space projection approach applied to the magnetic field waveforms (D).
Mentions: An example of individual magnetic field waveforms (30 Hz low-pass filtered) for the no masking condition (Figure 1A) demonstrates the N1m response peaking approximately 100 ms after the onset of the test stimulus (TS) as most pronounced component of the auditory evoked fields. P1m waves (preceding the N1m) were also visible, but small and variable across subjects. Thus, in the present study, we focused on the N1m response. The source waveforms also exhibited the P1m-N1m response complex to the onset of the TS (Figure 1C). An example of individual magnetic field waveforms (same subject) for the ASSR (band-pass filtered between 30 to 50 Hz) for the no masking condition is displayed in Figure 1D. The signals exhibit the transient evoked gamma-band response and the development of the ASSR after TS onset (Figure 1D,F). The waveforms show clear polarity reversal. Even though the field amplitudes were smaller compared to the N1m, the iso-contour plots of the magnetic field distribution demonstrates a pattern typically resulting from dipolar sources (Figure 1B,E).

Bottom Line: We observed significant decrements of auditory evoked responses and a significant inter-hemispheric difference for the N1m response during both ipsi- and contra-lateral masking.The decrements of auditory evoked neural activities during simultaneous masking can be explained by neural interactions evoked by masker and test stimulus in peripheral and central auditory systems.The inter-hemispheric differences of N1m decrements during ipsi- and contra-lateral masking reflect a basic hemispheric specialization contributing to the processing of complex auditory stimuli such as speech signals in noisy environments.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute for Biomagnetism and Biosignalanalysis, University of Muenster, Muenster, Germany. okamotoh@uni-muenster.de

ABSTRACT

Background: In daily life, we are exposed to different sound inputs simultaneously. During neural encoding in the auditory pathway, neural activities elicited by these different sounds interact with each other. In the present study, we investigated neural interactions elicited by masker and amplitude-modulated test stimulus in primary and non-primary human auditory cortex during ipsi-lateral and contra-lateral masking by means of magnetoencephalography (MEG).

Results: We observed significant decrements of auditory evoked responses and a significant inter-hemispheric difference for the N1m response during both ipsi- and contra-lateral masking.

Conclusion: The decrements of auditory evoked neural activities during simultaneous masking can be explained by neural interactions evoked by masker and test stimulus in peripheral and central auditory systems. The inter-hemispheric differences of N1m decrements during ipsi- and contra-lateral masking reflect a basic hemispheric specialization contributing to the processing of complex auditory stimuli such as speech signals in noisy environments.

Show MeSH