Updated: Sep 23
The following model is a simple way to describe the relationships between primary brain processes and how brain operations impact behavioral expression and decision-making.
Given the brain has 100-ish billion neurons, over 100-ish trillion synapses, and has evolved over hundreds of millennia, this model is about as reductive as you get. [i] I forced myself to put it on a single slide. By the way, the most important takeaway from this model is that the brain is highly interactive and dynamic. While there are distinct functional centers, in order to realize how a single brain function operates, one must understand how it relates to the whole. [ii]
Table of Contents:
How the emotion tag gets built
Brain Pathway Examples
My ability to specify this model has evolved as informed by the thinking of others. Thanks to work by Daniel Kahneman, Iain McGilchrist, Albert Einstein, Jill Bolte Taylor, George Dyson, Charles Darwin, Richard Dawkins, Robert Sapolsky, Douglas Hofstadter, and others. Also, a particular mention goes to Jill Bolte Taylor. She is the only brain scientist I'm aware that actually traveled into their brain as an explorer. Dr. Jill did this as a result of a stroke. Her first-hand account of her journey is extraordinary. Her book is called My Stroke Of Insight.
This model uses a concept known as an “emotion tag.” Think of an emotion tag as additional information added to ”flat” sensory input. The degree of intensity generally guides the mental processing path. That is, a high-emotion tag triggers the cognitive path via the right hemisphere. Whereas a low emotion tag triggers the cognitive path via the left hemisphere. The tagging concept is consistent with decision research found in the notes section. [iii] Also, it is appropriate to think of the sensory input traveling different mental pathways as a matter of degree or probability. Certain tags will trigger a higher or lower degree to which it travels these different cognitive pathways. However, all pathways are generally engaged at least to some degree. That is why people may be predisposed to present certain behaviors, but no behavior is guaranteed.
2. How the emotion tag gets built
Before discussing the brain pathway cognitive process, the essential building blocks are explored. The neuron count is a feature of the human genome. Except in rare circumstances, all humans are endowed with an astounding number of neurons at birth and in the earliest stages of our childhood. Each neuron is connected by about 1,000 or even more synapses. The volume of synapses may reach above 100 TRILLION for each person. Synapses are a little different than neurons from a numbers standpoint. Where the neuron count is more of a genetic given, our volume of synapses is more flexible as to our environment. Our synapses are very dynamic. Synapses both grow and are pruned depending on environmental demand. Think of neurons as the learning basis passed down from our ancestors. Our genome legacy contains the genomic blueprint to start a life tuned for survival fitness. Think of synapses as the learning basis to adapt to your current life, also needed for survival fitness. [iv]
The human brain, including neurons and synapses, is one of the most complex systems known to man... and it is going on in our own heads! There are 3 main parts of each neuron:
The nucleus produces the bioelectrical signal for its neighbor neurons.
The axon originates the signal from its nucleus to be sent to the next neuron.
The dendrite receives the signal from the last neuron for its nucleus.
The neuron is a simple binary switch. Its complexity comes from the astounding volume of neurons and their connecting synapses.
In the axon, the vesicle will release a cascade of different neurotransmitters into the neuron connecting synapse. On the other side of the synapse is the dendrite of the neighbor neuron. The dendrite hosts receptors. Think of the receptors as locks and the neurotransmitters as keys. The neurotransmitters must fit the receptor to be used. The neurotransmitters that don’t fit the receptors will be discarded. Think of the receptor as a control point. In general, people produce more neurotransmitters of all kinds than they will ever use. It is the receptor lock that needs to be opened. If the receptor lock is opened by the neurotransmitter key, the brain’s learning path continues. If the neurotransmitter key does not fit, then that learning signal does not fire in the receiving neuron. Thus, someone with more dopamine receptors will find extroversion-based rewards easier to achieve. Conversely, someone with more acetylcholine receptors will find introversion-based rewards easier to achieve. Plus, we have both receptors but do tend to skew with more of one or the other.
In addition, as the learning is reinforced by environmental feedback, the pre and post-synaptic connections involved in the learning will increase in size and numbers. More neurotransmitters and receptors will become available to accommodate the demanded dominant neurotransmitter. Conversely, if learning is not reinforced, the synapses will weaken and likely be pruned over time. This will make more room for new synaptic connections demanded for other reinforced learnings.
The neurotransmitter and receptor key-and-lock fit continues our thought, learning, and action path.
3. Brain Pathway Examples
To add some dynamism to this model, please consider two contrasting cases. The following cases are extreme examples to demonstrate the brain's different pathways. [v] Remember, the brain is incredibly dynamic, even in these extreme cases, the brain is still fully engaged, just more in certain functions than others. Next, I will describe each case. Immediately following, I will show each case with a highlighted pathway overlay. These pathway examples are simplistic. The actual path exhibits more feedback loops and interaction.
1) The high emotion tag & low language case - Imagine being chased by a lion. You see the lion and you are in a dangerous situation. The next moment, you are running at full speed, probably the fastest you have ever run. You will not likely recall a decision to run. It just happened. See the model below, this is a shaded version of the earlier model, with the pathways highlighted. Your eyes provide sensory input. Immediately your sensory memory is activated and a high-intensity fear tag is placed on the sensory input. [vi] Immediately it is routed directly to your right hemisphere. It has no language, but it is fast. Immediately a signal is given to your legs to run. Your brain will also signal hormone production to enhance your body's physical reaction. Your brain, via the neurotransmitter tagging process, likely releases hormones to enhance your fear reaction physical performance. Hormones like adrenaline, endorphins, and cortisol will likely be released in a stressful situation.
This case is the result of many millennia of evolution. In the context of natural selection, our genome evolved to pass on the genetic code most likely to enable human survival. Running from lions was high on the natural selection list! In the next section, we discuss cognitive biases and other challenges associated with our evolved cognitive state.
This is also the brain case targeted by social media. Social media engages people via emotion and often with augmentation via the addiction-forming dopamine neurotransmitter. Social media may elicit a right hemisphere-oriented response. A person may act without control from the left hemisphere or related executive functions.
The nature of the emotion tag matters as well. Fear, anxiety, and other negative emotions have nuanced impacts as compared to happiness, fulfillment, and other positive emotions. We provide more context in the article The anatomy of choice - learning from a brain explorer.
Our executive control functions are found in our prefrontal cortex and are associated with left hemispheric processing. Our executive control functions do not fully mature until the mid-twenties, on average.
As such, anyone under 25 should be very careful making big decisions.
It has always been a bit of a head-scratcher that (U.S.-based) children are able to get driver’s licenses at 16 and are able to commit to potentially massive, life-altering college debt at 17! Have you ever noticed car insurers have higher insurance premiums for those under 25? Car insurers seem to understand the implications of executive control function maturation and neuroanatomy!
2) The low emotion tag & high language case - You are reading about neuroscience. You are studying the different neurotransmitters as they are produced in the brain's limbic system. You have learned that neurotransmitters are like color hues, they are mixed with just a few primary neurotransmitters to create an almost infinite number of combinations. You think about how these mixes affected you in the past and could affect you in the future. You are calm and satisfied with the learning. See the model below, this is a shaded version of the earlier model, with the pathways highlighted. Your eyes provide sensory input. Your long-term, declarative memory is activated and either no or a very low-intensity emotional tag is placed on the sensory input. It is routed directly to your left hemisphere. This is where the connections are made to the past and the future. This is where cognitive-based analysis is processed. It has significant language but is relatively slow. The signal of your learning could take days or longer to fully process. Sleep also affects your ability to process and remember.
4. Cognitive Bias
A cognitive bias is a systematic error in thinking that occurs when people are processing and interpreting information in the world around them and affects the decisions and judgments that they make. The difference between the fast high emotion tag & low language-based brain decisions and more modern low emotion tag & high language-based complex decisions present as cognitive biases. There is a rich literature base on our many cognitive biases. Daniel Kahneman and Amos Tversky's classic Judgement Under Uncertainty comes to mind. Also, it is cognitive biases that present challenges to our everyday life. For example, cognitive biases impacting saving and investing, are:
Time Discounting Bias - preferring immediate gratification over long-term financial goals
Procrastination Bias - delay in completing an important task
Confirmation Bias - retaining selective information that confirms existing beliefs
Availability Bias - over-weighting immediate, easy-to-perceive information at the expense of under-weighting longer-term, harder-to-perceive information
It is no wonder then why 1) savings must be intentional, and 2) the U.S. has a very low retirement saving rate! Our own brains are naturally NOT wired for long-term savings.
5. Brain Travel
The next passage is from Jill Bolte Taylor’s book. At this point, she is experiencing the stroke and is aware of the unique nature of her Brain’s Right Hemisphere as her Left Hemisphere is intermittently on and offline as per the stroke originating in her left hemisphere.
“Imagine, if you will, what it would feel like to have each of your natural faculties systematically peeled away from your consciousness. First, imagine you lose your ability to make sense of sound coming in through your ears. You are not deaf, you simply hear all sound as chaos and noise. Second, remove your ability to see the defined forms of any objects in your space. You are not blind, you simply cannot see three-dimensionally, or identify color. You have no ability to track an object in motion or distinguish clear boundaries between objects. In addition, common smells become so amplified that they overwhelm you, making it difficult for you to catch your breath. No longer capable of perceiving temperature, vibration, pain, or proprioception (position of your limbs), your awareness of your physical boundaries shift. The essence of your energy expands as it blends with the energy around you, and you sense that you are as big as the universe. Those little voices inside your head, reminding you of who you are and where you live, become silent. You lose memory connection to your old emotional self and the richness of this moment, right here, right now, captivates your perception. Everything, including the life force you are, radiates pure energy. With childlike curiosity, your heart soars in peace and your mind explores new ways of swimming in a sea of euphoria. Then ask yourself, how motivated would you be to come back to a highly structured routine?”
Dr. Taylor also makes the following observation:
“... many of us may think of ourselves as thinking creatures that feel, biologically we are feeling creatures that think”
As the model suggests, the emotion-based limbic system receives information via our nervous system (and brain stem). It is our emotions that first react to sensory information. Our cerebral cortex, in either the left or right hemisphere, regulates and processes limbic-based information.
In the Pulitzer Prize-winning book, Goedel, Escher, Bach; the author, Douglas Hofstadter, makes the comment:
“Apparently the master wants to get across the idea that (Zen) enlightened state is one where the borderlines between self and the rest of the universe are dissolved."
Jill Bolte Taylor’s experience validates the notion of enlightenment as a right hemisphere endeavor and as necessary to quiet the left hemisphere. This could represent the paradoxical "dualism" of enlightenment, that is, "learning without learning" or "thinking without thinking."
[i] Literature reviews suggest the number of neurons in the human brain is reasonably well known, at approximately 100 Billion. The number of synapses is less well-known. 100 Trillion seems to be a starting number, with some estimates suggesting well into the quadrillion. Part of the challenge of measuring synapses is agreeing upon what a synapse actually is!
To provide relative size context for your neurons and synapses. Let’s say you could rent the synapses found in your brain for $1 / synapse. How much would it cost to rent all the synapses found in your brain? It would cost about 1.5x the annual economic output of the entire earth (2017, nominal GDP in US$).
[ii] As Hofstadter says in his book Godel, Escher, Bach “the most naive assumption that there is a fixed group of neurons for each concept (functional center)-is almost certainly false.” Steven Rose in The Conscious Brain and in reference to neurologist Karl Lashley‘s memory experiments: “So far as memory was concerned, the cortex appeared to be equipotential, that is, with all regions of equal possible utility.”
[iii] Finucane et al., The Affect Heuristic in Judgments of Risks and Benefits, Journal of Behavioral Decision Making, 13, no. 1 (2000): 1-17.
Finucane describes tagging as:
“The basic tenet in this paper is that images, marked by positive and negative affective feelings, guide judgment and decision making. Specifically, we propose that people use an affect heuristic to make judgments. That is, representations of objects and events in people's minds are tagged to varying degrees with affect.”
[iv] I do want to qualify the observation that "neurons are for 'nature' as handed down by our ancestors" and "synapses are for 'nurture' as generated within our lives." As usual, when it comes to the brain, this is a practical simplification that is correct on average, but certainly has nuance and exceptions.
Neurogenesis (the creation of neurons after we are born) does happen sometimes. Also, synaptic self-assembling occurs within our brains, when we are in the womb or after our birth, are the result of our legacy genomic blueprint. Thus, the "nature vs. nurture" line is gray when it comes to neurons and synapses. However, neurons ARE certainly a powerful legacy of natural selection occurring from our ancestors. Synapses DO help us update learning within our lives.
[v] Neurotransmitter reward pathways are also associated with personality typing. In general, introverts favor the acetylcholine-based pathway associated with the "The low emotion tag & high language case." Extroverts favor the dopamine-based pathway associated with the "The high emotion tag & low language case."
Hulett, Creativity - For Both Introverts and Extroverts, The Curiosity Vine, 2022: Please see section 2 "Neurotransmitters and Personality."
[vi] Camina, Guell,The Neuroanatomical, Neurophysiological and Psychological Basis of Memory: Current Models and Their Origins, Frontiers in Pharmacology, 2017
Hulett, Dreams are a window to our memories and healthy thinking, The Curiosity Vine, 2022
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