Key thalamus-cortical network
The thalamus-cortex network is well known for transferring peripheral
sensory information to the cortex, including gentle touch, pain itching,
and visual and auditory signals. Cumulative evidence suggests that this
sensory information including nociceptive information is not diffusely
distributed in the cortex. For example, for painful information or
unpleasant information, it has been demonstrated that ACC and the
insular cortex (IC) play vital roles in the coding of unpleasantness or
pain (Zhuo, 2008; 2014; Bliss et al. , 2016; Zhuo, 2016a). It has
been proposed that the thalamus-cortex networks play critical roles in
consciousness (Llinas et al. , 1998; Roy & Llinas, 2008).
Interestingly, in a key milestone article of neural science by Albright
et al (2000), both cortical regions have been suggested to contribute to
consciousness. It has to be pointed out that there are different aspects
of consciousness including awareness of the environment by sensory
stimuli, and volition, the voluntary control of thoughts and feelings
(Albright et al. , 2000). To understand synaptic and molecular
mechanisms of consciousness, it is highly possible that the very first
component of consciousness can be tackled at the present time and
consciousness of different forms of pain is a key indicator for
consciousness (Ambron, 2023).
By using human brain imaging and non-human primate studies, it becomes
clear that the thalamus and its related cortical areas play important
roles in consciousness (Redinbaugh et al. , 2020; Afrasiabiet al. , 2021; Scheinin et al. , 2021; Mashour, 2022). It is
generally accepted that the thalamus-cortex projections play key roles
in consciousness, and inhibition or disruption of such projections will
lead to loss of consciousness, and activation of this system can
facilitate the recovery from unconsciousness. Based on these
observations, I would like to propose a possible network for
consciousness, especially for the awareness component of consciousness.
As shown in Figure 1, the projection from the thalamus to the prefrontal
cortex including ACC serves as a core network circuit for consciousness.
Callosal projections link two sides of the cortical network together to
add the flexibility and complexity of these consciousness circuits. The
other indirect links with subcortical regions and cortical areas serve
as possible loops to maintain the excitability of these core circuits.
Thus, a lesion of one side of the brain or regions will only affect or
reduce the level of consciousness, and will not completely block the
consciousness (Figure 1).