Delta(but not theta)-band cortical entrainment involves speech-specific processing

First published: 28 December 2017Cortical oscillations phase-align to the quasi-rhythmic structure of the speech envelope. This speech-brain entrainment has been reported in two frequency bands, that is both in the theta band (4-8 Hz) and in the delta band (<4 Hz). However, it is not clear if these two phenomena reflect passive synchronization of the auditory cortex to the acoustics of the speech input, or if they reflect higher processes involved in actively parsing speech information. Here, we report two magnetoencephalography experiments in which we contrasted cortical entrainment to natural speech compared to qualitative different control conditions (Experiment 1: amplitude-modulated white-noise; Experiment 2: spectrally rotated speech). We computed the coherence between the oscillatory brain activity and the envelope of the auditory stimuli. At the sensor-level, we observed increased coherence for the delta and the theta band for all conditions in bilateral brain regions. However, only in the delta band (but not theta), speech entrainment was stronger than either of the control auditory inputs. Source reconstruction in the delta band showed that speech, compared to the control conditions, elicited larger coherence in the right superior temporal and left inferior frontal regions. In the theta band, no differential effects were observed for the speech compared to the control conditions. These results suggest that whereas theta entrainment mainly reflects perceptual processing of the auditory signal, delta entrainment involves additional higher-order computations in the service of language processing.This work was partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO), the Agencia Estatal de Investigaci on (AEI) and the Fondo Europeo de Desarrollo Regional FEDER) (grant PSI2015-65694- P, ‘Severo Ochoa’ programme SEV-2015-490 for Centres of Excellence in R&D), the Basque Government (grant PI_2016_1_0014), the ANR-10- LABX-0087 IEC and the ANR-10-IDEX-0001-02 PSL*. Further support was provided by the AThEME project funded by the European Commission 7th Framework Programme, the ERC-2011-ADG-295362 from the European Research Council. We would like to thank Margaret Gillon-Dowens and Sara Guediche for comments on previous versions of this article and Mathieu Bourguignon for useful advice on the present project. We would like to thank the whole BCBL research centre for the constant support for our research

Contributions of local speech encoding and functional connectivity to audio-visual speech perception

Seeing a speaker’s face enhances speech intelligibility in adverse environments. We investigated the underlying network mechanisms by quantifying local speech representations and directed connectivity in MEG data obtained while human participants listened to speech of varying acoustic SNR and visual context. During high acoustic SNR speech encoding by temporally entrained brain activity was strong in temporal and inferior frontal cortex, while during low SNR strong entrainment emerged in premotor and superior frontal cortex. These changes in local encoding were accompanied by changes in directed connectivity along the ventral stream and the auditory-premotor axis. Importantly, the behavioral benefit arising from seeing the speaker’s face was not predicted by changes in local encoding but rather by enhanced functional connectivity between temporal and inferior frontal cortex. Our results demonstrate a role of auditory-frontal interactions in visual speech representations and suggest that functional connectivity along the ventral pathway facilitates speech comprehension in multisensory environments

Dual-stream accounts bridge the gap between monkey audition and human language processing:Comment on "Towards a Computational Comparative Neuroprimatology: Framing the language-ready brain" by Michael Arbib

No abstract available

Tuning of Human Modulation Filters Is Carrier-Frequency Dependent

Licensed under the Creative Commons Attribution License

Lip movements entrain the observers’ low-frequency brain oscillations to facilitate speech intelligibility

During continuous speech, lip movements provide visual temporal signals that facilitate speech processing. Here, using MEG we directly investigated how these visual signals interact with rhythmic brain activity in participants listening to and seeing the speaker. First, we investigated coherence between oscillatory brain activity and speaker's lip movements and demonstrated significant entrainment in visual cortex. We then used partial coherence to remove contributions of the coherent auditory speech signal from the lip-brain coherence. Comparing this synchronization between different attention conditions revealed that attending visual speech enhances the coherence between activity in visual cortex and the speaker's lips. Further, we identified a significant partial coherence between left motor cortex and lip movements and this partial coherence directly predicted comprehension accuracy. Our results emphasize the importance of visually entrained and attention-modulated rhythmic brain activity for the enhancement of audiovisual speech processing

Transcranial alternating current stimulation (tACS) at 40 Hz enhances face and object perception

Neurophysiological evidence suggests that face and object recognition relies on the coordinated activity of neural populations (i.e., neural oscillations) in the gamma-band range (> 30 Hz) over the occipito-temporal cortex. To test the causal effect of gamma-band oscillations on face and object perception we applied transcranial Alternating Current Stimulation (tACS) in healthy volunteers (N = 60). In this single-blind, sham-controlled study, we examined whether the administration of offline tACS at gamma-frequency (40 Hz) over the right occipital cortex enhances performance of perception and memory of face and object stimuli. We hypothesized that gamma tACS would enhance the perception of both categories of visual stimuli. Results, in line with our hypothesis, show that 40 Hz tACS enhanced both face and object perception. This effect is process-specific (i.e., it does not affect memory), frequency-specific (i.e., stimulation at 5 Hz did not cause any behavioural change), and site-specific (i.e., stimulation of the sensory-motor cortex did not affect performance). Our findings show that high-frequency tACS modulates human visual perception, and it is in line with neurophysiological studies showing that the perception of visual stimuli (i.e., faces and objects) is mediated by oscillations in the gamma-band range. Furthermore, this study adds insight about the design of effective neuromodulation protocols that might have implications for interventions in clinical settings

Opportunities and Limitations of Mobile Neuroimaging Technologies in Educational Neuroscience.

Funder: European Association for Research on Learning and InstructionFunder: Jacobs Foundation; Id: http://dx.doi.org/10.13039/501100003986As the field of educational neuroscience continues to grow, questions have emerged regarding the ecological validity and applicability of this research to educational practice. Recent advances in mobile neuroimaging technologies have made it possible to conduct neuroscientific studies directly in naturalistic learning environments. We propose that embedding mobile neuroimaging research in a cycle (Matusz, Dikker, Huth, & Perrodin, 2019), involving lab-based, seminaturalistic, and fully naturalistic experiments, is well suited for addressing educational questions. With this review, we take a cautious approach, by discussing the valuable insights that can be gained from mobile neuroimaging technology, including electroencephalography and functional near-infrared spectroscopy, as well as the challenges posed by bringing neuroscientific methods into the classroom. Research paradigms used alongside mobile neuroimaging technology vary considerably. To illustrate this point, studies are discussed with increasingly naturalistic designs. We conclude with several ethical considerations that should be taken into account in this unique area of research