Cognitive processes of the executive function
In much of popular self-help literature, YouTube wisdom, and social media chivalry, living the good life involves us seizing control of destiny, wrestling it into submission and compelling life to cough up the goodies. In neuroscience, the bravado, thus language, is much more measured.
All individuals must be able to adapt to ever-changing environments in order to survive. The ability to adapt by regulating reflexive reactions to current salient stimuli so that goals requiring complex behaviours can be attained has been labeled executive function. Executive function is theorised to be a group of higher order cognitive abilities that enable individuals to orient towards the future, demonstrate self-control, and successfully complete goal directed behaviour. - Logue & Gould
Executive function comprises of behaviours such as controlling impulse, inhibiting responses, decision-making, planning, judging, paying attention; behaviours that are required and expected in many of life’s settings. These behaviours are severely compromised if the prefrontal lobes are injured or the individual is suffering psychiatric disorders. Beyond such afflictions, would the rest of us also be liable to “lose it” at various points of time in various circumstances? Perhaps in euphoria, stress, or old age? Would such losses be potentially permanent?
I got curious because I caught myself wondering what if I do not want to control my impulse and inhibit my reflexive response? I just want to be a jerk because I can’t be bothered to be civil anymore. Does that mean that deep down, I’m actually not civil and probably never was? What if I never will be? Is it possible that for some (hopefully more) people, rather than rudeness and malevolence, their reflexive response and impulse are that of civility and benevolence? That, should they lose their executive function they will still be the sweetest people on earth?
Executive function
...be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God. For I say, through the grace given unto me, to every man that is among you, not to think of himself more highly than he ought to think; but to think soberly, according as God hath dealt to every man the measure of faith. - Romans 12:2-3
The executive function consists of four cognitive processes: response inhibition, attention, set-shifting, and reversal learning; the latter two characterise cognitive flexibility.
Set-shifting is the higher-level cognitive ability that enables an individual to shift attention or response patterns based on different rules and changing contexts. It involves the more specific processes of rule selection and strategy switching.
Learned response is a reflexive behaviour, often Pavlovian, which occurs upon encountering a set of stimulus. Reversal learning is a measure of an individual’s ability to actively suppress the learned response and disengage from ongoing behaviour. It involves the more specific processes of perseveration and strategy switching.
Research have been able to establish how the dopamine, serotonin, norepinephrine, and acetylcholine transmitter systems affects set-shifting, attention, response inhibition, and reversal learning through their regulation of the pre-frontal cortex.
Dopamine
We have previously explored dopamine in great details - its role in neuroplasticity and reward management. It is not surprising that executive function is regulated by the dopaminergic system which drives motivation. Higher levels of dopamine is associated with optimal performance in set-shifting and attention, go responses.
Norepinephrine
Norepinephrine, also known as noradrenaline, is chemically very similar to adrenaline which we are probably more familiar with. Norepinephrine can be released from the adrenal medulla into blood circulation or from noradrenergic neurons in the locus ceruleus into the central and sympathetic nervous systems. It has significant impact on all four cognitive processes of set-shifting, attention, response inhibition, and reversal learning. This may be attributable to the role of norepinephrine in regulating an individual's overall level of arousal.
Serotonin
Unlike dopamine which modulates motivation and anticipation of reward (hence more forward driving), serotonin is associated with calmness and a sense of satisfaction (hence stillness). It is found that low levels of serotonin is associated with poor response inhibition and deficits in reversal learning, no-go responses. It almost seems like serotonin is the complementary neurotransmitter to dopamine.
Acetylcholine
Acetylcholine is a neurotransmitter that is associated with focus and is one of the key neurotransmitters in neuroplasticity. In executive function, acetylcholine appears to have a coordinating role through the modulation of the levels of dopamine, norepinephrine, and serotonin.
Be ye transformed by the renewing of your mind
It is perhaps no surprise that the neurotransmitters responsible for executive function are very much the same ones responsible for neuroplasticity and habit formation. So, going back to where I began in today's article, I asked what if I do not want to control my impulse and inhibit my reflexive response? What if I know what I'm doing is wrong but I do not want to stop (response inhibition)? What if I need to make an improvement but I cannot bring myself to action (set-shifting)? What if I know what I'm doing is not getting me the desired results but I keep doing it nonetheless (reversal learning)? What if I just can't be bothered (attention)? I suppose then that my executive function is running low, a phenomenon that has been termed ego depletion. Ego depletion was popular in the late 1990s but subsequent research seem to suggest that it might not be a thing after all. Or is it? That's the teaser for the next post.
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