There is strong consensus that for mental and higher functions of the cortex comprise a necessary, although not sufficient, condition to sustain states of phenomenal consciousness. However, it is well known that an intact corpus callosum and, correspondingly, interhemispheric communication is not essential for consciousness. One possible explanation for the preserved consciousness of split-brain patients is that each hemisphere’s thalamo-cortical connections remain intact following commissurotomy. Conversely, the cerebellum does not appear to be necessary for being in a conscious state1.
Source: https://en.wikipedia.org/wiki/Thalamocortical_radiations2
Recent breakthroughs in the study of cellular and circuit level aspects of consciousness have led to the conclusion that cortical pyramidal neurons have a central role in states of consciousness. The discovery that general anaesthesia separates the two different parts of the pyramidal neurons in the cerebral cortex suggests that there is a way to understand consciousness from the bottom-up (ie, from cellular mechanisms to cognitive properties of conscious processing)3.
Lack or loss of consciousness is a serious urgency in medicine. Assessing the immediate causes of a patient unconsciousness is one of the first tasks of a medical intervention. Generic causes of pathological loss of consciousness include lack of oxygen, some form of poisoning, or acute trauma to the brain. Lack of oxygen affects the very survival of neurons and is a common cause of acute loss of consciousness following a stroke. Excessive doses of some medications may lead to loss of consciousness. For examples, overdoses of sleeping or tranquilliser pills. Ingestion of natural toxic substances that affect the nervous system can lead to loss of consciousness, for example, eating some poisonous mushrooms. Concussion of the brain or acute lesions of specific parts of the brain can also lead to loss of consciousness. Brainstem injuries can lead to coma or a vegetative state, where the patient exhibits a lack of consciousness and basic motor responses. In all these conditions the generic term of coma is used.
The increasing understanding of the mechanisms underlying coma gives a clear perspective of the brain structures which are involved in maintaining a state of awareness4.
- ME Hatten (2020): Adding cognitive connections to the cerebellum. Science 370, 1411-1412. ↩︎
- FC Yeh et al (2018): Population-averaged atlas of the macroscale human structural connectome and its network topology. NeuroImage, 178, 57-68. ↩︎
- J Aru et al (2020): Cellular mechanisms of conscious processing. Trends in Cognitive Science 24, 814–825. ↩︎
- J Parvizi & A Damasio (2003): Neuroanatomical correlates of brainstem coma. Brain 126, 1524–1536. ↩︎