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.