Activation/suppression balances in rat Superior Colliculus encode the visual continuity illusion

The continuity illusion occurs when visual stimuli are presented at a sufficiently high frequency, thereby triggering a shift from the static to the dynamic vision mode. This facilitates perception of continuous and moving objects, which is key for interactions with the surrounding environment. However, how the continuity illusion is encoded along the entire visual pathway remains poorly understood, with disparate Flicker Fusion Frequency (FFF) measured at the retinal, cortical, and behavioural levels. Here, we combine a behavioural paradigm, functional–MRI (fMRI), and electrophysiological validation for studying the mechanisms underlying the encoding of the continuity illusion effect in the rat. Our behavioural measurements reported a Flicker Fusion Frequency (FFF) of 18±2 Hz. Remarkably, whole–pathway fMRI revealed marked zero–crossings from positive to negative fMRI signal regimes at the FF in the superior colliculus (SC) – an important visual saliency detector – but not in higher cortical or thalamic visual areas. Our electrophysiological recordings in SC explained the sources of these observations as arising from strong neuronal suppression when the continuity illusion is achieved. Combined, our data suggests that activation and suppression balances in SC play a critical role in encoding the continuity illusion effect. ### Competing Interest Statement The authors have declared no competing interest.