Long-term variability in visual processing versus perceptual stability

Our brain is in constant change due to neural plasticity, but, still, our experience of the world feels relatively stable to us. Focusing on visual processing, we hypothesise that brain responses to stimuli may change over long periods of time, but in a way that is orthogonal to the dimensions that are relevant to stimulus category discrimination. To test this hypothesis, we acquired and analysed a MEG dataset containing recordings from one female adult participant, with several scanning days spanning over six months. The participant passively attended to visual stimuli with the same stimulus presented within each session. We demonstrate that, the specific scanning day can be predicted from the brain responses in simple passive viewing paradigm, suggesting continuous temporal changes in neural activity over long time scales. However, information from one scanning day could be used to robustly decode the animacy of objects on a different scanning day, and importantly, decoding accuracy did not suffer with increasing time intervals between scans. That is, cross-decoding accuracy remained stable over months, despite between-scanning-day variability. These findings suggest that while processing of visual stimuli shows variability over long time scales, the core neural structure underlying object recognition remains stable and non-stimulus specific. The results were validated in the open-access THINGS-MEG dataset, which employs a similar paradigm but covers a shorter longitudinal timespan. We find similar results across the four additional participants. Significance statement While prior research has shown that neural responses to the same stimuli can change over short timescales (seconds to days), it remains unknown whether such changes impact higher-level representations, such as object categories, over longer periods. Using longitudinal MEG data collected from a single individual across six months, we show that responses to repeated visual stimuli drift over time, yet category-level representations remain robust. These findings demonstrate that the brain maintains stable perceptual representations despite gradually changing sensory responses, with implications for theories of neural variability, long-term decoding, and individual-level brain tracking.