Recent new approaches for studying consciousness
Brain functional imaging provides a powerful tool to investigate possible neuronal mechanisms for consciousness in healthy humans. By designing different visual/sensory/auditory sensory stimulation cues, one can compare brain imaging to detect which brain regions are specially related to consciousness or self-recognition (Gu et al. , 2013; Scheinin et al. , 2021; Mashour, 2022). In addition, it is also possible to perform the same study in patients with disorders of consciousness (DOC), and such studies with a comparison with human subjects certainly reveal brain areas or brain connectivity that contribute to consciousness (Qinet al. , 2010).
Animal research using anesthesia combined with brain stimulation, recent studies have revealed several key pathways that are able to wake animals from anesthesia, an indirect way to approach consciousness (Redinbaughet al. , 2020; Afrasiabi et al. , 2021; Redinbaugh et al. , 2022). For example, in primates, Tasserie et al (2022) reported that deep brain stimulation of the thalamus restored consciousness during anesthesia (Tasserie et al. , 2022). Interestingly, Redinbaugh et al (2022) found that thalamic deep brain stimulation using multi-microelectrode could reduce the level of consciousness during anesthesia, indicating that thalamus-related activity may be able to produce biphasic modulation of the consciousness. These works provide clear evidence that animal experiments during anesthesia may help us to understand the basic mechanism of brain circuits to consciousness.
Cellular and synaptic studies in cortical and related circuits have found that glutamate is the major transmitter in the circuits. Optogenetic, whole-cell patch, and molecular approaches can provide detailed synaptic mechanisms (Bliss et al. , 2016; Zhuo, 2016b). Thus, these projection systems are not grey boxes anymore. By using optogenetic and virus approaches, one can investigate the neuronal mechanism for transmission and modulation of consciousness.