Different responses of spontaneous and stimulus‐related alpha activity to ambient luminance changes

Abstract

Alpha oscillations are particularly important in determining our percepts and have been implicated in fundamental brain functions. Oscillatory activity can be spontaneous or stimulus-related. Furthermore, stimulus-related responses can be phase- or non-phase-locked to the stimulus. Non-phase-locked (induced) activity can be identified as the average amplitude changes in response to a stimulation, while phase-locked activity can be measured via reverse-correlation techniques (echo function). However, the mechanisms and the functional roles of these oscillations are far from clear. Here, we investigated the effect of ambient luminance changes, known to dramatically modulate neural oscillations, on spontaneous and stimulus-related alpha. We investigated the effect of ambient luminance on EEG alpha during spontaneous human brain activity at rest (experiment 1) and during visual stimulation (experiment 2). Results show that spontaneous alpha amplitude increased by decreasing ambient luminance, while alpha frequency remained unaffected. In the second experiment, we found that under low-luminance viewing, the stimulus-related alpha amplitude was lower, and its frequency was slightly faster. These effects were evident in the phase-locked part of the alpha response (echo function), but weaker or absent in the induced (non-phase-locked) alpha responses. Finally, we explored the possible behavioural correlates of these modulations in a monocular critical flicker frequency task (experiment 3), finding that dark adaptation in the left eye decreased the temporal threshold of the right eye. Overall, we found that ambient luminance changes impact differently on spontaneous and stimulus-related alpha expression. We suggest that stimulus-related alpha activity is crucial in determining human temporal segmentation abilities.

Visual Modulation of Resting State α Oscillations

“…For example, Cohen (2014) noted that ␣ peak frequency increased with increasing luminance of a contralateral stimulus during an infrequent time-coordinated stimulus localization task. However, a study by Benedetto et al (2018) found the opposite effect under task conditions: when the luminance of a covertly attended disk was altered, phase-locked ␣ peak frequency increased in low ambient luminance conditions, whereas spontaneous ␣ was unaffected. Furthermore, ambient luminance was found to have no effect on spontaneous ␣ frequency under resting conditions.…”

“…The differences in results between these two studies and the present one may be due to several factors. Differences in the task between the Cohen (2014) and Benedetto et al (2018) studies, especially task difficulty and task-relevance of the luminancechanging stimulus, may account for the different effects of luminance on ␣ frequency. Furthermore, only the luminance of a relatively small square stimulus was manipulated in the Cohen (2014) study, whereas ambient luminance was also manipulated in the Benedetto et al (2018) study, as in the present study.…”

“…However, these sensory effects are unclear and may be influenced by task and/or stimulus parameters. For example, some studies indicate that under task conditions, ␣ peak frequency increases with increasing luminance of a peripheral stimulus (Cohen, 2014), while others indicate that peak frequency decreases or stays the same (Benedetto et al, 2018). Conversely, under resting conditions, ␣ power, but not peak frequency, increases with reduced luminance (Benedetto et al, 2018).…”

Oscillations, criticality and responsiveness in complex brain networks

“…The amplitude and phase of alpha waves (8-13Hz) are associated with sensory stimuli processing, especially in regard to visual perception [5][6][7][8][9][10][11][12][13][14]. Stimulation at lower amplitudes and at a phase near the trough of an alpha wave show increased target detectability [6,[8][9][10][11]13,37].…”

“…In the conscious state, perceptual responses to sensory stimuli are associated with ongoing brain activity at the moment when the stimulus is applied. In visual perception tasks, for example, target detectability is dependent on the power and phase of ongoing alpha oscillations (~10Hz) [5][6][7][8][9][10][11][12][13][14]. Recent repetitive TMS (rTMS) studies have suggested that the instantaneous phase of the sensorimotor -rhythm in the alpha band ) is an important factor in determining the stimulation effect [15,16].…”