This is the follow-up to how bi-hemispherical morphology seemingly has little, to no bearing on the superiority of human cognition. What is responsible for human cognition and by extension — consciousness?

This is a summation of key notes I’ve made over the past few days that I think are worth sharing.

Two ideas…

  1. Hemispherectomy
  2. Anaesthetic

…lead me to more questions.

A hemispherectomy is used for patients with extreme seizures — where pharmacological and previous surgical attempts have failed. Ablation of the localised hemisphere cures 80%+ patients. Such an intrusive procedure is usually performed on children that are under the age of three.

The consequence of a hemispherectomy: the contralateral side of the body with respect to the ablated hemisphere, shows restricted skeletal-muscular tone and control — a consequence of the primary motor neurons in the respective pre-central gyrus being removed. No memory deficits, no personality or mood irregularities, no diminished executive function and no changes to IQ or related intelligence-indicators.

And then anaesthetic. With a bit of research you’re left asking…does repeated exposure to Sevoflurane, Propofol and Ketamine reduce neurological development during childhood?

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From this 2018 study, it suggests there can be a correlation which corroborates the FDA’s warning in 2016 that children under the age of 4 when repeatedly exposed to general anaesthetic are at a higher risk of developing a learning disability and behavioural disorders.

Question: How can repeated usage of general anaesthetic have a greater impact on behaviour and intellectual ability than removing half the brain?

The behaviour of anaesthetic isn’t clear-cut. 1/1000–2000 patients experience a sense of consciousness when they’re sedated and studies with the isolated forearm technique (a tourniquet is applied to the arm before paralysis is induced), show that patients under general anaesthesia can sometimes carry on a conversation using hand signals, but post-operatively deny ever being awake.

Real world experience reveals how consciousness isn’t a binary system. From states of drunkenness, to the dissociative effects of anesthetics like ketamine which at high-doses can cause the face to take on a disconnected blank-stare, there clearly exists a spectrum of expressions to reflect discrete states of consciousness.

A “spectrum” always sounds like a catch-all attempt but it’s worth examining the uniqueness of the human brain. The Allen Institute mapped gene expressions within the brains of 8 individuals and produced the following histogram.

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Whole brain with no highlighted regions

The x-axis and y-axis are cerebral regions, beginning with the frontal cortex (top-left) and when diagonally-descending through the graph towards the bottom-right, we posteriorly traverse the brain till we lastly reach the medulla in the brain-stem. Blue indicates strong similarity across all 8-brains, and orange is the inverse.

What we find is a homogeneity that suggests the cerebral cortex is canonically similar between the frontal lobe to cingulate gyrus. Interestingly, the arrangement of the primary visual cortex appears highly individualised as seen by the streaks of yellow cutting the x and y axes.

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Primary Visual Cortex is highlighted

Across the brain there appears two primary structures that are uncompromisingly homogenous: the amygdala and cerebellum.

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Amygdala is highlighted
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Cerebellum is highlighted

So what does this show? Our brains are highly similar in some regions, but highly impressionable in others. Mainly, where our primitive behaviour is triggered (amygdala) and motor functions (cerebellum), appear similarly expressed in each other’s brains. However, the regions that process personal experiences, such as the visual cortex, show distinct design.

Question: How does personal experience change the design of our brains?

Individuality has to be transcribed somewhere which has to consequently affect our senses of consciousness. By derivative, what stimulates one person, can be non-stimulating to another.

It’s possible to slip out of an attentive state while conscious. 8am lectures on electromagnetic fields, un-relatable conversations with lab-partners while you watch them build a voltage divider, and then finally the train-trip home which somehow “happened” but you just can’t remember how.

Attention seems to be like a spotlight that requires work, just like any other mechanical force. Unsurprisingly, it’s easy to lose grip of attention when we’re tired or bored — unstimulated by either choice or consequence of depleted energy resources.

Question: If two people always brought their own attention onto the same “ideas” or stimuli as the other, and given an infinite timeline, could they eventually become behaviourally indifferent to one another?

The most consistent symptom of unconsciousness precipitated by anesthetics is reduction of thalamic metabolism and blood-flow. Could the thalamus be a cognitive switch? Midline thalamic damage leads to vegetative states and conversely, respective recoveries have necessitated a restoration of functional connectivity between the cingulate cortex and thalamus.

Alternatively, many anaesthetics deactivate or disconnect the lateral temporo-parieto-occipital complex of multimodal associative areas centred on the inferior parietal cortex. Lesions within this region and the delivery of localised anaesthetic are mutually supportive: no signs of perceptual experience despite a flurry of undirected motor activity.

It appears that consciousness and its derivative, cognition, is a function of information integration.

Over the past few days I’ve been looking into how these impact consciousness, which by extension I’ve associated with cognition. I think it’s reasonable to assume that to perform higher-mental functions, the individual needs to be conscious — not necessarily responsive though. For instance, patients in vegetative states can be conscious but unresponsive.

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Here’s some (incomplete) thoughts for now…

  1. Do neurons possess an internalised nervous system, akin to the large nervous systems across the central and peripheral regions? When a neuron is activated, an internalised nervous system could in theory become aware of its own activation. You can’t become conscious of an experience if it doesn’t happen. Such as, feeling scared when you’re sitting on a beach with no visible threats around you highlights a disconnect from your reality. This isn’t to say you can’t emulate a sensation.
  2. Emulating sensations presumably derive from reactivating memories. The mind can’t “imagine” without any prompts. Children raised in isolation are unable to learn speech or perform higher-mental activities that we would associate with normal cognition. However, procedural memories such as skills and general actions can be learnt. This wouldn’t appear to be a complex ability given more primitive species such as dogs and mice can be classically or instrumentally conditioned. If anything, conditioning is the construction of a reflex-arc.
  3. Anaesthetic seems to deactivate synapses around the parietal lobe. Mammalian brains appeared to grow outward (hence the development of the neocortex), but that doesn’t necessarily mean the neurons within maintained their associations to their respective lobes. If the occipital lobe (where visual sensation is primarily received) neighbours the parietal lobe, could the neurons used for visual processing have mutated and migrated towards the parietal lobe?
  4. The brain is a soup of shifting chemical gradients. Mood abnormalities and disorders seem to derive from chemical imbalances. Ketamine at low-doses causes depersonalisation, out of body experiences, forgetfulness and loss of motivation to follow commands. The recognition of such information appears to be correlated with chemical states.
  5. Neuronal firing patterns don’t constitute consciousness. While flat electroencephalogram (EEG) is an indicator of brain death, convulsive seizures show a loss of consciousness despite highly active and synchronised neural activity.
  6. Consequently, action potentials (AP) seem to be a force that exploits an already pre-existing conscious state.
  7. Conscious states seem to be forcibly changed by blocking synaptic connections. That is, when the rate of change in synaptic activity is 0, patients become unconscious.
  8. Sleep demonstrates the only time when healthy humans regularly lose consciousness. Sleep however is regulated by melatonin which is secreted by the interventricular zone in the hypothalamus. This is the same region that manages the autonomic nervous system. In 2017 the Nobel Prize for Physiology or Medicine was awarded to a trio of scientists that uncovered the biological mechanisms that described the Circadian rhythm. In short — two proteins, PER and TIM, build up in cells overnight before degrading by daytime. This cycle took 24-hours…the perfect body-clock. This is just a reminder but an important one to ground my ideas — chemistry informs behaviour.
  9. If chemistry informs behaviour then perhaps chemistry informs consciousness. If consciousness is consequently directed by the internal state of the mind, rather than an individual’s sense of controlled-thought, then consciousness would be akin to being ridden throughout the mind rather than exploring it for ourselves.
  10. This is the key idea — consciousness might not be controllable. We might not get to choose what we think. Instead, we might be exploring pre-constructed chemical gradients that are shaped by action potentials (the neural activity measured in EEGs). If this is the case, consciousness is a consequence of chemical interpretation — so where in a neuron is this “interpreter”? It sounds like what an internalised nervous system in a neuron would be reacting to…
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I clearly have a lot more to think about.

I’ll let you know what I come up with,

Thanks for reading :)

Written by

Electrical engineering/Neuroscience at University of Sydney. Aspiring neuro-trauma surgeon with a few software/hardware goals.

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