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End Notes: The Chemical Limitation of the Cortex
Observation: Signal Paths In the brain
In conversation with a psychiatrist, I was once presented with a useful contrast:
the nervous system communicates through electrochemical impulses, while the brain integrates those signals mainly through chemical modulation. This prompted a deeper question — what mechanisms shape the way our brains operate?
Most sensory inputs link to the brain through the brainstem, connecting to the older, more primitive parts of the brain:
- Hearing
- Touch
- Motion (balance and acceleration)
- Taste
These channels converge in the brainstem and project upward into the limbic system, particularly the amygdala.
Smell takes a more direct route, passing through the olfactory bulb and piriform cortex straight to the amygdala — explaining its unusually strong influence on mood and memory.
The amygdala acts as an early-warning and emotional-processing centre. When it detects something significant — a sudden sound, a threatening movement, or a pleasant taste — it triggers the release of neurochemicals such as adrenaline, dopamine, or cortisol throughout the brain and body.
Vision follows a distinct path: light travels via the optic nerve, crosses at the optic chiasm, continues to the lateral geniculate nucleus (LGN) of the thalamus, and then to the visual cortex, which performs most pattern recognition.
Depending on what the cortex recognises, it sends feedback to the limbic system (especially the amygdala, hippocampus, and hypothalamus) to adjust mood and prepare an appropriate emotional response.
Observation: Interaction Between the Cortex and the Old Brain
When something is recognised — whether a sound, an image, or even a thought — it activates a network in the cortex linked to an abstract sense or learned skill. These networks communicate through rapid electrical impulses between neurons, forming dynamic patterns that represent recognition, reasoning, or memory.
Such activity can be detected indirectly with functional MRI (fMRI), which measures local changes in blood flow associated with neural activity.
Once active, the cortical network sends signals to the limbic system, the emotional core of the brain. The limbic system translates these signals into chemical language, releasing neurotransmitters and hormones such as dopamine, serotonin, adrenaline, and cortisol.
These chemicals modulate the responsiveness of neurons across the brain, subtly shifting the system’s overall tone — what we experience as mood.
This chemical state influences the “old brain” — the deeper structures responsible for instinct, motivation, and visceral reactions — producing sensations often described as gut feeling or intuition. The cortex then reads this feedback, interpreting and moderating it, which can either amplify the feeling or restore balance.
A mood persists only while this circuit remains active — while the limbic system maintains chemical release and cortical networks stay engaged. When the stimulus fades, the chemicals are reabsorbed or broken down, and the emotional state gradually returns to baseline.
When the cortex overlays a mood with thought, memory, or imagination, a feeling becomes an emotion.
The chemistry of the old brain provides the background tone; the cortex shapes it into experience. Together they form the bridge between instinct and consciousness — the place where reflex becomes reflection.
To work, an emotion must be switched on or off. Though this is an oversimplification of brain circuitry, it highlights the mechanical basis of emotional bias — how emotions are triggered, maintained, and eventually reset.
Observation: Training Abstract Skill, Abstract Senses, and Emotion
Abstract skills, abstract senses, and emotional control are trained and reinforced in the young, plastic brain. This happens during childhood, guided by peers and anchored by the example and protection of family. How we are taught to regulate emotion and interpret the world sets the bias patterns that shape much of adult thought.
Consequence Drawn: Signal Paths in the Brain
The limbic system — particularly the amygdala — evolved to set mood and prepare the body for action. Humans still experience these physiological echoes of emotion: butterflies in the stomach, a gut feeling, or blood boiling. Such sensations reveal how intuition links body and mind — how a subtle physical response accompanies every internal emotion.
Consequence Drawn: Interaction Between the Cortex and the Old Brain
The limbic system works with a limited palette of neurochemicals — dopamine, serotonin, adrenaline, cortisol, and a few others — to set the brain’s basic mood tone. Because this palette is ancient and shared across vertebrates, the range of fundamental moods is small. What distinguishes human emotion is the cortex, which adds context, meaning, and interpretation.
A stimulus can switch an emotion on. The trigger might come from the external world — a sound, sight, or event — or from within, as one abstract sense or skill activates another through memory or imagination.
Once engaged, the limbic system remains active, sustained by continuous input from the stimulated network. As long as the signal — external or internal — continues to fire, the associated emotion will persist.
Yet once an emotion is invoked, it rarely remains isolated. It spreads through related memories and associations, activating other cortical circuits. This can amplify the emotion and sustain it long after the original trigger has passed.
To moderate emotion requires deliberate cognitive effort from the prefrontal cortex, the part of the brain responsible for reflection and regulation. Without this intervention, chemical activity in the limbic system can linger for hours or even days, quietly shaping perception, judgment, and decision-making.
Recognizing this chemical inertia helps explain why emotions, once triggered, so easily bias our thinking — and why conscious correction takes deliberate effort.
Consequence Drawn: Training Abstract Skill, Abstract Senses, and Emotion
How well we master the abstract side of the brain depends on what we carry forward from our families and peers. Much of this learning involves how we are shown — consciously or unconsciously — to set the biases of our emotions: what to fear, what to value, and what to ignore. These lessons form the foundation of adult emotional balance and the stability of judgment.
Action
The brain is most plastic in our early years. Once habits — good or bad — settle into our abstract thinking, they become difficult, but not impossible, to change. This is not a Hollywood “Mission Impossible”; it’s a real-world challenge of patience and persistence.
With openness and determination, self-improvement becomes an invigorating adventure. Along the way, advice and criticism will come from many directions. The key skill is to listen carefully and discriminate between the useful and the misleading.
Understanding the chemistry of emotion gives us a choice:
to be ruled by our moods, or to learn to recalibrate them —a small act of self-awareness that changes everything else.
📖 Series Roadmap
- Forward: A Little Background
- Introduction: Action, Reaction, and the Human Paradox (16.09.2025)
- Looking Back in Time: The Development of the Human Brain (23.09.2025)
- Abstract Senses: Enhancing the way we see the world outside (30.09.2025)
- Bias as a Concept & Climbing the Stairs: Pattern Recognition & Everyday Tasks (07.10.2025)
- Abstract Feelings and Abstract Senses (14.10.2025)
- Motivation (04.11.2025)
- The Social Knowledge Base (11.11.2025)
- Potential (18.11.2025)
- The Subliminal Way We Go Through Life (26.11.2025)
- Taking Responsibility (02.12.2025)
- Fishing for Complements (22.12.2025)
- Peter and Fermi (22.12.2025)
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End Notes: The Chemical Limitation of the Cortex
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