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).