Modality-specific tracking of attention and sensory statistics in the human electrophysiological spectral exponent

Abstract

A hallmark of electrophysiological brain activity is its 1/f-like spectrum – power decreases with increasing frequency. The steepness of this “roll-off” is approximated by the spectral exponent, which in invasively recorded neural populations reflects the balance of excitatory to inhibitory neural activity (E:I balance). Here, we first demonstrate that the spectral exponent of non-invasive electroencephalography (EEG) recordings is highly sensitive to general, anaesthesia-driven as well as specific, attention-driven changes in E:I balance. We then present results from an EEG experiment during which participants detected faint target stimuli in streams of simultaneously presented auditory and visual noise. EEG spectral exponents over auditory and visual sensory cortices tracked stimulus spectral exponents of the corresponding domain, while evoked responses remained unchanged. Crucially, the degree of this stimulus–brain spectral-exponent coupling was positively linked to behavioural performance. Our results highlight the relevance of neural 1/f-like activity and enable the study of neural processes previously thought to be inaccessible in non-invasive human recordings.