Oscillatory Event-Related Brain Dynamics (Nato Science Series A:, 271)

How does the brain code and process incoming information, how does it recog­ nize a certain object, how does a certain Gestalt come into our awareness? One of the key issues to conscious realization of an object, of a Gestalt is the attention de­ voted to the corresponding sensory input which evokes the neural pattern underly­ ing the Gestalt. This requires that the attention be devoted to one set of objects at a time. However, the attention may be switched quickly between different objects or ongoing input processes. It is to be expected that such mechanisms are reflected in the neural dynamics: Neurons or neuronal assemblies which pertain to one object may fire, possibly in rapid bursts at a time. Such firing bursts may enhance the synaptic strength in the corresponding cell assembly and thereby form the substrate of short-term memory. However, we may well become aware of two different objects at a time. How can we avoid that the firing patterns which may relate to say a certain type of move­ ment (columns in V5) or to a color (V 4) of one object do not become mixed with those of another object? Such a blend may only happen if the presentation times be­ come very short (below 20-30 ms). One possibility is that neurons pertaining to one cell assembly fire syn­ chronously. Then different cell assemblies firing at different rates may code different information.