The synaptic hypothesis of consciousness
Based on brain imaging and network studies, I would like to propose that the thalamus-cortex serves as a key component in consciousness. Among cortical areas, ACC may be one of the key harbors for it, although alternative cortical areas may be able to compensate for the loss of such function when ACC activity is lost. Recent network studies reveal that ACC forms multiple connections with other cortical areas, and ACC-ACC connections may well serve as an alternative center to maintain consciousness. For example, in case of loss of one side of the ACC function, the other ACC may take over. It is also likely that this network is complex, and has multiple feedback systems. Thus, a lesion of any component will not lead to a loss of consciousness completely. Figure 1 proposes some initial models for such loops.
Based on this hypothesis, it is well predicted that external stimulation can recall consciousness from unconsciousness. Furthermore, due to the rich expression of plastic excitatory synapses among these circuits, it is like that consciousness can be trained and enriched. I would suggest that consciousness can be categorized into three basic levels, basic, normal, and high level. Learning will lead to a high consciousness level, at least to the related environment or sensory inputs. Humans and animals are highly sensitive to contextual information and novel subjects. This environment information will process through the hippocampus and hippocampus-related structures.
For consciousness, it maybe it is the status of electrical flow to keep the circuits to be active. It is thus not precisely located in several nuclei or neurons. It is consistent with networks that have multiple layers in order to be constantly or not easily affected by lesions or interruption. However, it is sensitive enough to synaptic activity with circuits that can have a range of levels to be operated. Inhibition or overexcitation can lead to loss of consciousness, if appropriate information can not be recalled, such as names, visual identification sensory, etc. Since ACC neurons are likely activated and contribute to many key brain functions, it is likely that consciousness can not be stored or carried out by the soma of pyramidal cells; instead, I propose that consciousness is processed by certain synapses that form specific connections with other cortical and subcortical areas. In order to effectively recall updated consciousness information, these synapses are likely to be trained and learned. Thus, the same groups of neurons may carry out different tasks through these highly diversified synapses. Consciousness is a result of neuronal activities of a subset of the brain network. It is unlikely processed by selective regions or nuclei. Selectivity is not coded by action potentials but by the firing of certain groups of neuronal networks.