Conscious Awareness and the Brain Processing.

The study of consciousness has been limited primarily to philosophical domain. There are a number of conceptual and methodological issues that have prevented scientific investigation of conscious experience. We began the investigation by exploring its cognitive components. Since awareness is an important component, we used neuroimaging techniques to study the brain processing of awareness using memory as a model. It is known that in the tests of 'nonconscious memory' subjects retrieve studied items without becoming consciously aware of retrieval. In contrast, they are fully aware in conscious memory tests. Spatial and temporal patterns of cortical activities observed during the two forms of memory were analyzed to understand neural network that might be associated with the awareness of retrieval. It appears that during conscious recollection, studied items are first retrieved nonconsciously. Thereafter, a reentrant signaling loop is activated between the extrastriate area and frontal cortex. Experiments suggest that this loop may be responsible for the awareness of nonconsciously retrieved information. Further characterization of the extrastriate-frontal connectivity may help explain the neural mechanism of conscious experience.