Revealing the distinction between perception and cognition through intra-individual variability of visual evoked responses

Searching for a method to objectively detect the cognitive activity of the brain, the variability of visual evoked responses (ER) was analysed in 75 human subjects and 10 animals. The individual ERs of a normal subject were found typically very scattered in the first approx. 120 ms after stimulation, converging at 160–220 ms and then diverging again progressively. This variability pattern (VP) is event-related and is not attributable to background noise. On the other hand, statistically significant correlation showed that in most patients, with anatomically intact visual structures but with pronounced mental troubles, the VP is absent and the ERs are randomly scattered. Based on these results we consider that the event-related variability reflects the cognition function of the subjects and that it is instrumental in evidencing the distinction between cognitive and perceptive processes. The results are further consistent with the idea that cognition implies the chaotic activity of certain neural populations and that the VP reflects this chaotic, non-repetitive, non-linear and impredictable but effective neural activity.