Does stimulus preceding negativity reflect predictions in a somatosensory roving paradigm?

The mismatch negativity (MMN) has since decades become one of the most prominent phenomena in cognitive neuroscience, recognised as a brain response indexing automatic change-detection. While substantial work has characterized post-stimulus mismatch responses (MMRs), comparatively little is known about how prior information is represented before stimulus onset. 34 healthy human volunteers (12 females) underwent a somatosensory roving paradigm with EEG to investigate whether anticipatory brain activity reflects stimulus history accumulation. Post-stimulus analyses revealed canonical somatosensory MMRs, corresponding to a modulation of the N140 component (MMN), source localised in secondary somatosensory cortex, and a P300 MMR. Both were parametrically modulated by train length, with opposing direction for standard and deviant trials, decreasing over the course of the experiment. Pre-stimulus analyses revealed a stimulus-preceding negativity (SPN) that systematically varied as a function of stimulus history; longer trains of stimulus repetitions were associated with reduced anticipatory negativity. The SPN did not vary throughout the experiment, but its relationship with post-stimulus responses evolved, showing an initially negative correlation with the N140 that diminished over time, and an opposite pattern for the P300. Source reconstruction localized the SPN to a network involving inferior frontal, fronto-polar, and somatosensory cortices, suggesting a possible role in top-down gain modulation of upcoming sensory stimuli. These findings indicate that learning of statistical regularities is not only observable in the post-stimulus phase following violation of statistical regularities (i.e., prediction error signals), but also in neural activity preceding sensory inputs, thereby providing new avenues for investigating endogenous predictive processes. Significance Statement Research on unexpected sensory events has focused on post-stimulus neuronal responses, leaving the pre-stimulus representation of predictive information largely unexplored. Using a somatosensory roving paradigm, we show that stimulus history modulates pre-stimulus brain activity in addition to post-stimulus mismatch responses. The amplitude of the stimulus-preceding negativity (SPN) varies systematically with the number of preceding repetitions, indicating that anticipatory neural activity reflects the accumulation of prior information. These results provide evidence that endogenous predictive processes can be observed before sensory input arrives, complementing post-stimulus accounts of mismatch responses and advancing our understanding of anticipatory mechanisms in sensory processing.