Attentional Modulation of the Auditory Steady-State Response across the Cortex

Abstract

Selective auditory attention allows us to focus on relevant sounds within noisy or complex auditory environments, and is essential for the processing of speech and music. The auditory steady-state response (ASSR) has been proposed as a neural measure for tracking selective auditory attention, even within continuous and complex soundscapes. However, the current literature is inconsistent on how the ASSR is influenced by selective attention, with findings based primarily on attention being directed to either ear rather than to sound content. In this experiment, a mixture of melody streams was presented to both ears identically (diotically) as we examined if selective auditory attention to sound content influences the ASSR. Using magnetoencephalography (MEG), we assessed the stream-specific ASSRs from three frequency-tagged melody streams when attention was directed between each melody stream, based on their respective pitch and timing. Our results showed that selective attention enhances the ASSR power of an attended melody stream by 15 % at a general sensor level. Furthermore, we explored the distribution of cortical ASSR sources and their respective attentional modulation. A novel finding using distributed source modelling revealed that the ASSR is modulated by attention in many areas across the cortex, with frontal regions experiencing the strongest enhancement of up to ~ 80 %. ASSRs in the temporal and parietal cortices were enhanced by approximately 20 -25 %. We also found a systematic right hemispheric bias of the ASSR attentional modulation. Overall, this study demonstrates that selective auditory attention to sound content increases the ASSR power of the attended stream according to a specific neural pattern involving the frontal, parietal and temporal cortices. This ability to readily capture attentional changes in a stimuliprecise manner makes the ASSR a useful tool for studying selective auditory attention, especially in complex auditory environments.In light of the brain's limited capacity to process simultaneous information, the ability to attend to one out of several 2 competing sounds is therefore essential, allowing one to extract and process the most important information amidst a complex 3 auditory environment. This phenomenon was first coined the "Cocktail party effect (CPE)" by Cherry in 1953 and is important 4 to functions such as speech recognition, musicianship and threat identification 1 . In music, selective auditory attention can 5 manifest as the ability to discern a single instrument amongst an orchestral performance, or a single voice in a choir. This 6 ability, measured both in terms of speech-in-noise performance 2 and robustness of neural patterns 3 , is positively correlated with 7 the listener's amount of musical training 2-3 , suggesting that selective attention capabilities may be improved through strategic 8 training regimes. While the relevance of the CPE for perception and performance is well documented, the neural mechanisms 9 underlying this phenomenon is still not complete...

Deficient auditory gamma-BOLD coupling in schizophrenia is related to sensory gating deficits

“…However, it is notable that we did not find reductions in gamma power in SZ during our paradigm. Since scanner sound is not task-relevant, given our resting-state instructions to maintain visual fixation, attentional effects might reduce entrained auditory power (Manting et al, 2020) which could be further impaired in SZ (Javitt and Sweet, 2015). Future studies might employ interleaved "silent" fMRI (Rondinoni et al, 2013) or EEG recordings of fMRI scanner stimuli (Pripfl et al, 2006) to disentangle relationships between evoked gamma, scanner sound and attentional orientation.…”

Tracking selective attention in a musical cocktail

“…This interpretation is supported by studies utilizing single-unit neurophysiology 43 as well as broad-scale neuroimaging methodologies 25-26, 39, 41-42 , is able to accommodate a wide range of stimuli (even within each neuroimaging and sensory modality), and appears to be applicable across sensory modalities including vision, audition, and touch 39,[41][42][44][45][46][47][48][49] . Attentional modulation of neural activity has been found in several regions across both cortical 33,[50][51][52] and sub-cortical 53 structures of the brain. Typically, the effect of selective attention manifests in the auditory cortex (AC) 26,54 , although its extent and precise location depend on specific experimental and stimulus parameters.…”

“…Frequency-tagging offers a simple, efficient and precise method to disentangle the processing of multiple sound streams presented simultaneously, since the neural ASSR activity corresponding to each stream can be distinguished by its unique fm during analysis 115,118 (see section 1.3.3 for further details on multiple ASSRs). Today, the ASSR has found itself useful in many applications ranging from hearing assessments [119][120][121] to attention research 13,51,99,122 and schizophrenia [123][124] . The origin of the ASSR is a topic that has sparked much debate between two main opposing camps.…”

“…At source level, most studies have shown that the attentional enhancement of ASSRs is manifested in the auditory cortices 13,99,122,144 . More recently, using complex musical stimuli, our group has demonstrated that the neural activity enhancement from intramodal selective auditory attention occurs also in regions beyond the temporal cortex, such as the parietal and frontal cortices, with regions in the pre-frontal cortex experiencing the largest degree of ASSR enhancement [51][52] . In addition, we also discovered that both the ASSR power itself and its degree of attentional modulation correlate with subjects' musicality 52 .…”

“…Many of these cross-experimental variations affect the signal-to-noise ratios for ASSRs and increase the minimum recording time needed to separate individual ASSRs or capture ASSR modulations across conditions, which may make it problematic or even infeasible to directly apply the use of the ASSR from one experimental setting to another, as in the case of comparing single-source to multi-source designs. These problems are further complicated by the fact that the ASSR is generated by an extensive collection of sources across the neural cortex [51][52] , which differ in strength as well as how they are modulated by behavioural and individual factors like selective attention and musicalit y respectively. Related to this point, our results build on ASSR sources generated by AM frequencies close to 40 Hz and may not be generalizable across ASSRs at other frequencies which have the tendency to display different source distribution patterns 249 .…”