see also:

• brain evolution and development
• cerebrospinal fluid (CSF)
• stroke (CVA)
• neurology
• the comatose patient
• Youtube: an excellent talk on consciousness and also why AI is unlikely to gain true consciousness by Anil Seth March 2024

• clinicians take a rather simplistic approach to the concept of consciousness and conscious states without really defining consciousness but instead relying upon other measures such as state of alertness and state of cognition as tested in measures such as the Glasgow Coma Scale
• the actual definition of consciousness however still plagues philosophers and neuroscientists alike as does the concept of which organisms display consciousness
• furthermore, the actual neural physiology for consciousness is still to be elucidated although, at least for higher levels of consciousness, it most likely requires a top-down neural activity such as from cortical areas, in particular, prefrontal cortex, frontal cortex, anterior cingulate and/or temporal lobe cortex
  • NB. sensory stimuli may reach primary cortical sensory processing areas but these may not be perceived and hence not enter into the consciousness - an extreme example would be cortical blindness or patients with sensory neglect after stroke
• a broader definition could suggest nearly all living organisms have a degree of consciousness if they can respond to their self's homeostatic needs, particularly if the mechanism is via some form of neural network
  • can plants feel pain? do trees have consciousness given they have such enormous interconnected networks?
  • are all vertebrates and many invertebrates sentient beings given they all have the anatomic neural structures for emotion and have approach/avoidance emotions such as fear and generally have a nurturing capacity for their offspring or social group - albeit not as well developed as in mammals?

• the level of alertness is determined by:
  • activity of the reticular formation (eg. locus caerulus and connections)
  • sleep-wake cycles (see physiology of sleep )
  • neuronal function
    • adequacy of energy supply in the form of glucose
    • adequacy of oxygen supply
    • presence of drugs / toxins
    • neuronal cell health - viral infections, other pathophysiology, etc
    • neuronal cell death
• sentience
  • having the capacity to have feelings as well as being self-aware and to have awareness and empathy for others
• sapience
  • the capacity to reason, plan for the future, and act with “wisdom” - evolved with societal groups / extended families (includes apes, whales, dolphins)

• what is perceived is based largely on past experience perceptions (Bayesian priors) which is then combined with new sensory data (which form Bayesian likelihoods) with the result being our real time perception which equates to a Bayesian Posterior prediction probability state as evidenced by many psycho-physiologic phenomena such as illusions, seeing familiar patterns when they are not there, etc.
• our perceptions then could be seen as being controlled hallucinations or representations of what we predict is real
• hence our priors can create self-fulfilling outcomes - we perceive what we want or think we should perceive

• there are components to this, each being controlled hallucinations:
  • bodily self
    • your awareness of your body, being alive, feeling emotions, etc
    • interoception
      • the continual awareness, control and regulation of our homeostatic processes to keep us alive (many of which occur on a sub-conscious level such that we are not aware of them)
      • this is probably the evolutionary driver for consciousness - as consciousness is on a separate domain axis to intelligence - language and intelligence are not necessary for most forms of life but consciousness of self homeostasis is.
      • this probably underlies the perception of emotion and also the placebo effect and self-fulfilling prophecies as the brain primarily works as a prediction machine to control the body and can create actions which perpetuates the predictions to reduce perceptual surprises
    • this can become distorted such as by the rubber hand experiment which creates transient cognitive dissonance especially if a person is hypnotizable as these people have higher demand characteristics where the prior probabilities are held strongly so that the brain predicts an incorrect prediction
    • “2nd order consciousness” - awareness of awareness - ability to reflect on its own ability to be aware
  • perspectival self - how you are able to act in the perceived world
    • purposely selectively attend and respond to the environment
    • a human newborn has sensory awareness, is able to differentiate from non-self touch and self touch, express emotions, can recognize faces, imitate, have preferential gaze, and show signs of shared feelings but is unreflective, present oriented, does not have concept of self, while short term memory for vision only lasts a few seconds, and thus have “basic consciousness” when awake
  • volitional self - free will
  • narrative self - what you perceive of yourself - personal identity
    • introspect thoughts
    • access memories
    • be self-aware physically and/or mentally
      • NB. physical mirror self-awareness has been demonstrated in humans older than 18 months, great apes, bottlenose dolphins, orcas, pigeons, European magpies and elephants
  • social self - what you perceive that others perceive of you

• although showing movements, facial expression, etc, these are generally preprogrammed movements are from subcortical origin, and the in utero fetus is essentially “unconscious” and in a persistent sleep state until birth due to¹⁾:
  • low oxygen levels
  • pregnanolone (an anaesthetic)
  • placental prostaglandin D2
• by 16th wk can respond to low frequency sounds, can habituate to repetitive stimuli by 22-23wks, but cortical hearing occurs after 26th wk
• by 19th wk, reflex withdrawal reflexes to painful stimuli are evident and by 20th wk, they can smell
• after 24 wk, thalamocortical axons grow into the somatosensory, auditory, visual, and frontal cortices and the pathways mediating pain perception become functional around the 29-30 wks
• well-defined REM sleep states appear by 32wks
• fetuses born before 26wks have closed eyes and appear to be constantly sleeping whereas older pre-term infants do open their eyes and establish at least minimal eye contact