We have performed a set of experiments that correlate EEG spectral parameters with cognitive functions. The tasks (visual perception, supramodal object recognition, short-term memory) were chosen so that the cortical area involved extended over different length scales. The extent of the cognitive neuronal assemblies correlated inversely with the frequency where EEG synchronization was found. This provides a further relation between experiment and the theory put forward in the Nunez target article.

Recent experimental work suggests that the concept of contextual fields should be generalized to allow the modulation of local information extraction by both external and internal context. The external context relates to the coherent information of the stimulus; the internal context refers to the parts of this information which are relevant for behavior. This dual interaction, present at every level of the hierarchy, requires a fundamental unit of processing more complex than a single neuron appears today. We argue that the cortical column supplies the required mechanisms for a separate top-down and bottom-up processing and allows for interaction without destructive cross-talk. This flexibility might explain why the same basic architecture of a cortical column is used in the whole isocortex.