Joos, E. | bioRxiv Science

bioRxiv2025

Subthreshold violations of trajectory predictions are sensitive to TMS of Cerebellum CRUS I/II

Temporal prediction can help to follow a trajectory. In case of an error, the prediction can be adjusted. However, processing the error and adjusting the prediction can take time. What happens immediately after a prediction error, and can the processing of the prediction be modulated? We use a newly found illusion based on moving squares and requiring trajectory regularity to be elicited. We examined the conscious consequences of a sub-threshold manipulation of the square trajectories, and transcranial magnetic stimulation (TMS) on the cerebellum (right CRUS I/II) to study the modulation of the processing of the trajectory manipulations. The TMS was a typical intermittent theta-burst stimulation, but only one sequence of around 3 minutes, compared with a placebo stimulation. The trajectory manipulation had a reliable effect on the illusion, even though the illusion emerged within less than 100 ms after the trajectory manipulation. The results suggest that the prediction is temporarily stopped after the trajectory change. The illusion was accompanied by EEG signals whose amplitude was modulated by TMS on the cerebellum, at least in those participants who received verum TMS after having performed the task three times. Those EEG signals resembled a late LPP (Late Positive Potential). As LPP spontaneously decreased over time, the results suggest the effect of TMS may represent a reinstation of the EEG consequences of the prediction error, i.e., a modulation of its significance.

neuroscience↗

bioRxiv2023

Spontaneous Necker-Cube Reversals are not that Spontaneous

During observation of the ambiguous Necker cube, our perception suddenly reverses between two about equally possible 3D interpretations. During passive observation, perceptual reversals seem to be sudden and spontaneous. A number of theoretical approaches postulate destabilization of neural representations as a precondition for spontaneous reversals of ambiguous figures. In the current study, we focused on possible EEG correlates of perceptual destabilization, that may allow to predict an upcoming perceptual reversal. We presented ambiguous Necker cube stimuli in an onset-paradigm and investigated the neural processes underlying endogenous reversals as compared to perceptual stability across two consecutive stimulus presentations. In a separate experimental condition, disambiguated cube variants were alternated randomly, to exogenously induce perceptual reversals. We compared the EEG immediately before and during endogenous Necker cube reversals with corresponding time windows during exogenously induced perceptual reversals of disambiguated cube variants. For the ambiguous Necker cube stimuli, we found the earliest differences in the EEG between reversal trials and stability trials already one second before a reversal occurred, at bilateral parietal electrodes. The traces remained similar until approximately 1100 ms before a perceived reversal, became maximally different at around 890 ms (p=7.59*10-6, Cohens d=1.35) and remained different until shortly before offset of the stimulus preceding the reversal. No such patterns were found in the case of disambiguated cube variants. The identified EEG effects may reflect destabilized states of neural representations, related to destabilized perceptual states preceding a perceptual reversal. They further indicate that spontaneous Necker cube reversals are most probably not as spontaneous as generally thought. Rather, the destabilization may occur over a longer time scale, at least one second before a reversal event.

neuroscience↗