Prestimulus Network Integration of Auditory Cortex Predisposes Near-Threshold Perception Independently of Local Excitability

Abstract

An ever-increasing number of studies are pointing to the importance of network properties of the brain for understanding behavior such as conscious perception. However, with regards to the influence of prestimulus brain states on perception, this network perspective has rarely been taken. Our recent framework predicts that brain regions crucial for a conscious percept are coupled prior to stimulus arrival, forming pre-established pathways of information flow and influencing perceptual awareness. Using magnetoencephalography (MEG) and graph theoretical measures, we investigated auditory conscious perception in a near-threshold (NT) task and found strong support for this framework. Relevant auditory regions showed an increased prestimulus interhemispheric connectivity. The left auditory cortex was characterized by a hub-like behavior and an enhanced integration into the brain functional network prior to perceptual awareness. Right auditory regions were decoupled from non-auditory regions, presumably forming an integrated information processing unit with the left auditory cortex. In addition, we show for the first time for the auditory modality that local excitability, measured by decreased alpha power in the auditory cortex, increases prior to conscious percepts. Importantly, we were able to show that connectivity states seem to be largely independent from local excitability states in the context of a NT paradigm.

A roadmap for the study of conscious audition and its neural basis

“…What has been done in more recent years has focused on how pre-stimulus brain states can affect whether subsequent nearthreshold acoustic events are consciously perceived [99][100][101][102][103]. Although the effects are subtle and multifaceted, the answer to this question seems to be 'yes'.…”

“…However, because these aspects of brain activity are measured before the arrival of an acoustic event in question, they are not likely to constitute true NCC A but rather putative prerequisites [16,29] that can impact subsequent stimulus-driven activity. In the subset of studies that reported post-stimulus activity [101][102][103], it is clear that hits elicited larger activity in AC than did misses. Although exact source topographies and response polarities are difficult to determine, the post-stimulus response from at least one study [103] appears consistent with the awareness-associated vertex negativity reported by Hillyard et al [23].…”

Dynamical Network States as Predisposition of Perception

“…The framework gained further empirical evidence in the auditory modality (Leske et al 2015). Within this study, the authors interrogated the prestimulus brain state that predisposed participants to perceive an NT auditory signal.…”

Pre-stimulus feedback connectivity biases the content of visual experiences

“…They help explain why repetitions of the same physical stimuli elicit different percepts and responses from trial to trial in both animals (1) and humans (2)(3)(4)(5). Both local excitability changes in task-relevant sensory regions (6,7) and neural network connectivity patterns have been shown to underlie trial-by-trial fluctuations in perception (8)(9)(10)(11).…”

“…The paradigms to study the impact of ongoing neural activity on perception typically involve near-threshold detection and discrimination tasks, in which pre-stimulus neural fluctuations influence the perceptual fate of stimuli, for example whether an object is seen ("Hit") or not ("Miss"; e.g. (8,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)). Beyond mere stimulus detection and discrimination, one of the visual system's essential functions is to identify and categorize objects and, in this way, construct the content of visual experiences (19)(20)(21).…”