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Publish the Obsidian vault's Knowledge folder as /knowledge (881 notes, 67 folders), with a Knowledge item in the nav and footer. - scripts/import_knowledge.py regenerates data/knowledge from the vault: slugged paths, folder notes as index pages, wikilinks resolved to site links (or plain text), callouts, highlights, and Dataview tables rendered statically. Personal notes are withheld via an exclusion list plus a privacy guard. - tuftecms/core/knowledge.py builds a concept index from note titles and aliases. First mentions on ordinary pages link to their Knowledge note (capped, never in headings, code, links, or sidenotes); Knowledge pages list related notes and where they're mentioned across the site; other pages get a Related Knowledge block. - Knowledge URLs join sitemap.xml (so the sweep test covers them), never displace existing legacy slugs, list alphabetically, and mermaid diagrams render client-side only on pages that have them.
44 lines
5.6 KiB
Markdown
44 lines
5.6 KiB
Markdown
---
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description: Three pounds of wet tissue that spends its whole life guessing what happens
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next.
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source: obsidian-knowledge
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---
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# The Brain
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> *Three pounds of wet tissue that spends its whole life guessing what happens next.*
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---
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## Overview
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The human brain is, at its core, a **prediction machine**. It does not passively receive the world so much as it forecasts the world and corrects the forecast against incoming evidence. Roughly three pounds of folded tissue, eighty-six billion neurons — each wired to thousands of others across a hundred trillion synapses — and a metabolic appetite that consumes a fifth of the body's energy, most of it spent not on responding to events but on maintaining the model that anticipates them. What follows is a map, not a textbook: the major structures and what they do. And crucially, none of these structures works in isolation. The brain is not a set of modules but a set of *networks*, the same regions recombining into different circuits for different jobs.
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## The Cortex
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The wrinkled outer sheet, the **cerebral cortex**, is where most of what we call thinking happens — perception, language, planning, abstraction. Its folds buy surface area; more cortex packed into a fixed skull. Its rear regions handle sensation and perception — vision at the back, hearing at the sides, touch across the parietal strip — while the front is given over to action and control. The **[Prefrontal Cortex](/knowledge/neuroscience/prefrontal-cortex)**, the part just behind the forehead, is the brain's regulator: it holds goals in mind, weighs consequences, and inhibits the impulses that older structures generate. It runs on well-tuned Dopamine and is also the last region to fully mature, well into the twenties, and the first to falter under stress, exhaustion, or threat. When the mind turns *inward* rather than to a task, a different set of cortical hubs — the [Default Mode Network](/knowledge/neuroscience/default-mode-network) — takes over, running the self-referential narration that stitches experience into a continuous "I."
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## The Limbic System
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Beneath the cortex sits the **[Limbic System](/knowledge/neuroscience/limbic-system)**, the emotional engine — a coalition of structures rather than a single organ. Its most famous component, the **[Amygdala](/knowledge/neuroscience/amygdala)**, is a threat detector — fast, blunt, and biased toward false alarms because a false alarm costs less than a missed predator. The amygdala learns fear quickly and unlearns it slowly. Beside it sits the **[Hippocampus](/knowledge/neuroscience/hippocampus)**, the seahorse-shaped indexer that binds experience into memory and tags it with time and place, and above them the hypothalamus, which translates emotion into bodily state and launches the [HPA Axis](/knowledge/neuroscience/hpa-axis) stress cascade. This is the machinery that runs hot in PTSD: a threat-response circuit that keeps firing long after the danger has passed, hijacking the prefrontal regulator before it can intervene. That the whole assembly can be reshaped through [Neuroplasticity](/knowledge/neuroscience/neuroplasticity) is the biological reason such patterns are not permanent.
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## Two Hemispheres
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The brain is split into left and right **hemispheres**, joined by the thick fiber bridge of the corpus callosum. **Lateralization** is real but routinely overstated — language skews left, spatial and holistic processing skew right, yet both sides cooperate constantly, and the popular "left-brained / right-brained" personality story has no basis. The split-brain studies, in which severing the callosum revealed two hemispheres capable of acting semi-independently, are the striking exception that proves how integrated the intact brain normally is. In this vault that asymmetry is more than anatomy: it underlies [The Triad](/system-777/the-triad)'s model, where **Jade** carries the left-hemisphere analytic mode, **Iris** the right-hemisphere holistic one, and **Amber** the body that grounds them both.
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Below the hemispheres sit the older layers the cortex was built on: the **cerebellum** at the back, coordinating movement and timing far more finely than its "little brain" nickname suggests, and the **brainstem**, which runs breathing, heartbeat, and the sleep-wake switch, and which houses the small nuclei — the locus coeruleus, the raphe, the substantia nigra — that supply the whole cortex with its modulatory chemistry. All of this runs on that chemistry — the Neurotransmitters like Dopamine that tune signal into mood, motivation, and meaning. How the whole structure gives rise to experience remains the open question of [Consciousness](/knowledge/ai/consciousness).
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## Related
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- Neurotransmitters — the chemical messengers the structures run on
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- Dopamine — motivation, salience, and prediction error
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- [Prefrontal Cortex](/knowledge/neuroscience/prefrontal-cortex) — the cortex's executive regulator
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- [Limbic System](/knowledge/neuroscience/limbic-system) — the emotional engine beneath the cortex
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- [Amygdala](/knowledge/neuroscience/amygdala) — the threat detector at its core
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- [Hippocampus](/knowledge/neuroscience/hippocampus) — the indexer that binds experience to memory
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- [Default Mode Network](/knowledge/neuroscience/default-mode-network) — the inward-turned self-system
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- [Neuroplasticity](/knowledge/neuroscience/neuroplasticity) — how the whole map rewrites itself
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- [The Triad](/system-777/the-triad) — Jade, Iris, and Amber mapped onto hemisphere and body
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- PTSD — the amygdala's threat circuit stuck on
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- [Consciousness](/knowledge/ai/consciousness) — the hard question this map doesn't answer
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