Abstract: Consciousness has become a challenging question in life sciences. The viewpo int that consciousness is the processing of information at various levels of awareness is being widely accepted. It is inevitable to deal with unconscious or automatic p rocessing for explicating consciousness. The main concern is how consciousness i s converted into unconsciousness, how unconsciousness is done into consciousness , and the potential brain mechanisms of the conversion, including involvements o f anatomical and functional structure, synaptic connections in the neural networ ks and so on. The study of unconsciousness is of great benefit to untie the myst ery of consciousness that has been coming into focus by contemporary neuroscienc e. Recent progress of the study on the mechanisms of unconscious processing was reviewed from the points of cognitive neuroscience at different levels: the cogn itive profile of unconsciousness, the correlation between unconsciousness and br ain structures, and the interplay of synaptic connections. Contemporary research in cognitive psychology revealed that unconscious processing could even reach s emantic level, including unconscious processing of image, character and figure. In addition, unconscious processing was different from conscious processing in n ature and was distributed widely across the processing system of the brain, rath er than localized in any particular unit. Recently, cognitive neuroscience has g ot lots of findings on perceptual unconscious processing with functional magneti c resonance imaging (fMRI), positron emission tomography (PET), electroencephalo gram (EEG) etc. Various regions of the brain were involved in perceptual unconsc ious processing. Both the higher-and lower-order cortical areas had computation al power to make inferences about specific features of complex objects. The mech anism of synchronous neural activation of cortex was likely to bind together var ious features that belonged to each object and separate them from features of ot her objects. Evidence from neural networks and synapse also indicated that synch ronous neural activation of the cortex was an important mechanism of information processing. Finally, some potential perspectives of how to study unconsciousnes s and consciousness in cognitive neuroscience were presented.

Key words: brain, perception, unconsciousness, awareness