High-level stimulus template modulates neuronal response at the earlier processing stages

There is ample evidence that the brain matches sensory information with internal templates, but the details of this mechanism remain unknown. Here we consider the processing of repeatedly presented ambiguous stimuli with high ambiguity (HA) and low ambiguity (LA) and analyze how the processing depends on the ambiguity of the previous stimulus. On the behavioral level, we report a faster response to the HA stimulus after HA stimuli and a faster response to the LA stimulus after LA stimuli. The EEG analysis reveals that when HA stimulus follows LA stimuli, the neuronal activity in the sensory areas attenuates at the early processing stage but enhances during the latter stages. It evidences the hierarchical processing organization where low levels process the stimulus details, and high levels represent its interpretation. It also confirms that on low levels, HA and LA stimuli processing is similar due to their similar morphology. Therefore, the brain uses the LA stimulus template on the low levels to reduce the demands when processing the HA stimulus details. When LA stimulus follows HA stimuli, the attenuated response in the sensory regions accompanies high response in the frontal cortex. Namely, we observe high{theta} power in the medial frontal cortex and high {beta} power in the right inferior frontal cortex. It shows activation of the top-down cognitive control functions detecting the mismatch between the LA stimulus and the HA stimulus template and transfer this template to the low processing levels. Significance statementThe brain attenuates its response to repeatedly presented similar stimuli. When an ambiguous visual stimulus follows unambiguous stimuli with the same morphology, the neuronal response in sensory areas decreases at the early processing stage but enhances during the latter stages. It evidences hierarchical processing organization where low levels process the details, and high levels represent the interpretation. It also confirms that the brain uses templates on different levels to reduce the processing demands. When an unambiguous stimulus follows ambiguous stimuli, a low response in the sensory regions accompanies high response in the frontal cortex. It manifests activation of the top-down mechanisms to detect the mismatch between an unambiguous stimulus and an ambiguous template and transfer this template to low levels.