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The Brain · Chapter 2 of 7
The word on the tip of her tongue. The thread of a sentence she dropped and could not find. A fog that took an hour to lift. A neurologist tested every piece of the cerebrumThe largest part of the brain, responsible for thought, memory, and voluntary movements. he could reach from a chair and found nothing focal — which was true, and was also the clue. This chapter puts addresses on function: five lobes, the sulcus that splits motor from sensory, four motor areas and eight sensory ones, two homunculi, the association cortex where meaning is made, and the two hemispheres that are not mirror images.
The question you will answer
“Nothing focal” is a precise statement about the cerebrum: no single cortex was failing. So where does a fog live? Before you can answer, you need the map the neurologist was using — lobes, primary cortices, association areasBrain regions that integrate sensory input and coordinate responses., lateralization — and the rule that no area acts alone.
Opener · Nothing Focal · about 1¾ minutes
The opener is the same narrated animation you will watch in Scene 1.
Watch the opener first. It sets the question; the chapter answers it.
1
Read the chart
Patient chart · Stina
2017–2020 · ages 42–45 · the exam that found nothing
2017 · 42
Neurologist (“Ten folders”): cranial nervesNerves that arise from the brain and control head and neck functions., strength, reflexesAutomatic responses to stimuli., sensation, gait, finger-to-nose, three-word recall — all normal. “Nothing focal.” Tension-type headache.
2017–20
The private list: tip-of-the-tongue words, dropped threads, the extra morning hour. Teaching planned around the period and the fevers; the fog worst the week of a flare. Never charted.
2020 · 45
MRI: spots in the white matterThe outer portion of the spinal cord made of myelinated nerve fibers that transmit signals. — the cables between regions — not in any cortex.
Standing
Handedness right; language left (assumed, as in nine of ten). No seizures, no weakness, no visual loss, no aphasia — ever.
Chart clues this module: #10 — A few white spots, more than expected for age
Before you go on · your prediction
Word-finding stalls, dropped threads and a slow morning, with a normal neurological exam. The best first reading is…
Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.
Early damage to the language cortex — Broca’s or Wernicke’s area
Ask what an aphasia looks like at the bedside, and whether a stalled word that eventually arrives is the same as a word that is gone.
Stress, poor sleep and being busy — the cortex is fine
Ask whether “nothing focal” means “nothing wrong,” and what the exam can and cannot reach.
The regions are intact; the connections between them are slow
Ask what joins Wernicke’s to Broca’s, what joins the prefrontal cortex to everything else, and what tissue those joins are made of.
From Stina’s diary
2
The story
Three short movements: the case, the anatomyThe study of the structure of the human body. and physiologyThe study of how the body functions., then the tie back to Stina. Each links to the scene where you’ll see it move.
I · The exam that found nothing
The neurologist in 2017 was thorough. He shone a light in each eye, watched her follow his finger, had her smile and stick out her tongue, tapped her knees and ankles, pricked her shins, walked her heel-to-toe along the floor, had her touch his finger and then her nose, and asked her to remember three words and name them five minutes later. Every station passed. He wrote “nothing focal,” which was true, and “tension-type headache; stress,” which was a guess. She took it as permission to stop mentioning the rest: the word on the tip of her tongue that would not come and then did, the thread of a sentence she dropped mid-lecture and had to walk back for, the extra hour each morning before the fog lifted. She called it getting older. She called it being tired. Her own mini-lecture on the cerebrum says it in another voice: “I had a friend in high school. She suffered a frontal lobeThe brain region responsible for decision-making, personality, and voluntary movements. injury from a car accident. She was a completely different person afterwards.” That is what a focal lesion does — it changes one thing. Nothing about Stina had changed in one place. Everything had slowed a little everywhere.
See it move: Scene 1 · Nothing Focal · Scene 4 · Where Meaning Is Made
II · Addresses for function
The cerebrum is roughly forty percent of the brain, split by the longitudinal fissureA deep groove separating the left and right hemispheres of the brain. into two hemispheres that look like mirror images and are not. The coarse map is the five lobes — frontalForehead bone; forms the front part of the skull and roof of the orbits. Smooth and curved., parietal, temporal, occipitalPosterior and base of the skull; curves under to form the back of the head., named for the bones over them, and the insulaA deep brain region involved in taste, emotions, and visceral functions. buried in the floor of the lateralAway from the midline of the body. sulcus. The useful map is finer. The <strong>central sulcus</strong> divides the hemisphere front from back and by job: motor in front, sensory behind — the same rule as the spinal cordThe central nervous system structure that relays signals between the brain and body.. The <strong>precentral gyrus</strong> is the primary motor cortex, last stop before the corticospinal tractA descending motor pathway controlling voluntary movements., with enormous representation for face, hands and tongue (the motor homunculusA map of sensory or motor control in the brain, representing different body parts.); in front of it the premotor cortex holds learned patterns, Broca’s area (left side only) runs speech, and the frontal eye field moves the eyes. The <strong>postcentral gyrus</strong> is the primary somatosensory cortexA region in the postcentral gyrus that processes touch and sensation., which does spatial discrimination — where did that come from — and has a homunculus of its own with lips and fingertips the size of continents. Seven more sensory areas follow the same pattern of a cortex that registers and a cortex next door that interprets: somatosensory association (“change in your pocket”), primary visual and visual association in the occipital lobeThe brain region responsible for visual processing. (spatial and facial recognition), auditory (pitch, loudness, location) and its association area (whisper versus scream), olfactory on the medialToward the midline of the body temporal lobeThe brain region responsible for processing sound and memory. (the piriform lobe, the rhinencephalon), gustatory in the insula, visceral sensorySensory input from internal organs to the CNS., and vestibular. Beyond them lies most of the surface: the multimodal association areas — prefrontal (intellect, judgment, personality, planning; it matures late, which is why four-year-olds lie badly), posterior (patterns, faces, written and spoken language — Wernicke’s area for comprehension), and limbic (the emotional weight). Their jobs are the packet’s four: understand, form memories, make associations, decide. And the hemispheres divide the work — cerebral dominance is set by language, left in about ninety percent, with the right leading on intuition, emotion, art and music — and talk to each other through white matter.
See it move: Scene 2 · The Sulcus That Splits the Jobs · Scene 3 · Eight Ways to Feel · Scene 4 · Where Meaning Is Made · Scene 5 · Two Hemispheres, Not Two Brains
III · Where a fog lives
An aphasia is focal. Damage Broca’s area and speech is halting and effortful while understanding is intact; damage Wernicke’s and speech is fluent, well-shaped and meaningless, and the patient often does not know it. Stina had neither. Her words arrived — late. Her threads could be found — by walking back. Her mornings cleared — in an hour. Every region passed its test because every region was working; what was slow was the traffic between them, and the traffic runs on white matter: the bundle that joins Wernicke’s to Broca’s, the long association fibers that join the prefrontal cortex to the posterior lobes, the corpus callosumThe large bundle of nerve fibers connecting the two cerebral hemispheres. that joins the hemispheres. “Nothing focal” was the right finding. It just was not the same as “nothing wrong.” The scan three years later put the spots exactly where this chapter says the fog should live — in the cables, not the cortex — and that is the next chapter’s subject.
See it move: Scene 4 · Where Meaning Is Made · Scene 5 · Two Hemispheres, Not Two Brains
3
Watch · explore · think · check
5 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.
How to read the scenes
- Animation (dark teal) — a short animated explainer, one idea each
- Slide (dark teal) — a still to study: a micrograph, a diagram or a map
- Explore (purple) — something to push on while you watch
- Game (purple) — a quick challenge
- Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
- Check (gold) — a quick H5P that scores itself
Scene 1 of 5
Nothing Focal
A neurologist tested every address he could reach from a chair; all of them answered.
Animation · in production · 1 min 40 s
Nothing Focal
The exam as a tour of the cerebrum; every station green; then the fog dims everything a little rather than one place a lot. Caption: nothing focal — because the problem was not in a region.
Prefer the full lecture? Lobes of the Cerebrum (original video on the site)
Explore · in production
Run the exam
Eight bedside tests on cards (reflexes, finger-to-nose, smile, follow my finger, name three objects, repeat this phrase, heel-to-toe, pinprick). For each, drag it to the part of the nervous systemThe organ system that controls body functions using electrical and chemical signals. it mainly tests — a cortex, the cerebellumThe brain region responsible for balance, coordination, and fine motor control., the brainstemThe lower part of the brain that connects to the spinal cord and controls vital functions., the cord — before the reveal. Then a second deck: five patients’ complaints (a word that will not come but does; speech that is fluent nonsense; a weak right hand; a wide staggering gait; a slow morning everywhere). Sort each as <em>focal</em> or <em>diffuse</em> and say which test would catch it. Reveal: the one complaint no bedside test catches.
Think · not graded
“Nothing focal” and “nothing wrong” sound alike and are not. What does a normal neurological exam actually rule out, and what kind of injury could pass every station on it?
The true/false spot-check for this prompt is in production.
Check · Drag the Words
Lobes and jobs.
This self-scoring check is in production.
Evidence card 1
Add it to your evidence board
Every region passed its test in 2017 — a true “nothing focal” that was mistaken for “nothing wrong.”
Scene 2 of 5
The Sulcus That Splits the Jobs
Motor in front, sensory behind — the cord’s rule, one floor up — and four motor areas in the frontal lobe.
Animation · in production · 1 min 50 s
Four Motor Areas
The central sulcusA groove separating the frontal and parietal lobes. draws itself across a hemisphere; the precentral gyrusThe area of the frontal lobe responsible for voluntary movements. in front turns red, the postcentral behind turns blue. The motor homunculus drapes over the precentral gyrus — huge hands, lips, tongue; a thin trunk. Three more motor areas light in turn: premotor (a child tying a shoe, the pattern assembling), Broca’s (left side only — a mouthThe opening of the digestive tract where food enters and mastication begins. shaping a word), the frontal eye field (eyes tracking). A corticospinal axon drops from the primary motor cortex down through the brainstem. Caption: this cortex decides nothing; it is the last stop.
Prefer the full lecture? Cerebral Cortices (original video on the site)
Explore · in production
Scale the homunculus
A blank body outline and a slider for each part — hands, lips, tongue, trunk, legs, feet. Before the reveal, set each part’s size to how much motor cortex you think it gets. The reveal overlays Marieb’s motor homunculus and scores the guesses. Then flip to the sensory side and do it again — and read the one rule both maps obey: cortex is allocated by precision, not by bulk. Last: predict which of Stina’s symptomsSubjective experiences reported by the patient (e.g., nausea, fatigue). a lesion in the precentral gyrus would have caused — and tick that she never had it.
Think · not graded
The primary motor cortex “decides nothing” — it is the last stop before the corticospinal tract. Then where is a movementA fundamental property of life involving motion of the body or its parts. decided, and why does damage to the primary motor cortex cost you voluntary control but not reflexes or tone?
The true/false spot-check for this prompt is in production.
Check · Flip Cards
Four motor areas — front and back.
This self-scoring check is in production.
Evidence card 2
Add it to your evidence board
Her hands, face and tongue never weakened and her speech never halted — the precentral gyrus and Broca’s area were never the problem.
Scene 3 of 5
Eight Ways to Feel
A cortex that registers, and a cortex next door that interprets — eight times over.
Slide · in production
Register, Then Interpret
Eight sensory areas on one hemisphere, each paired register/interpret where it has a partner; the sensory homunculus beside the postcentral gyrusThe area of the parietal lobe responsible for processing sensory input..
Prefer the full lecture? Cerebral Cortices (original video on the site)
Explore · in production
Sensation or perception
Twelve short sentences (“your skinThe body’s largest organ, providing protection and regulation. is hot” / “it’s hot because I’m wearing a sweater in the sun” / “a whisper” / “that sound is a whisper, not a scream” / “a face” / “that is my sister”…). Drag each to <em>sensation (primary cortex)</em> or <em>perception (association cortex)</em>, and then to its lobe. Reveal names the pair every time. Then one bedside puzzle: a dust mote on the eyelid is placed to the inner, middle or outer third, but a scratch on the back cannot be — click the two body parts and read why from the homunculus.
Think · not graded
The sensory homunculus is “not a picture of your body; it is a picture of how much cortex your body gets.” What decides the allocation — and why would the lips and fingertips, rather than the back, be where that decision was made?
The true/false spot-check for this prompt is in production.
Check · Multiple Choice
Which pairing is wrong?
This self-scoring check is in production.
Evidence card 3
Add it to your evidence board
Sensation is registered in one cortex and understood in the next; her senses registered and were understood — the fog was never a sensory loss.
Scene 4 of 5
Where Meaning Is Made
Most of the surface is association cortex — and language is the clearest place to watch it work.
Animation · in production · 2 min 00 s
Wernicke to Broca
A word is heard: the primary auditory cortex lights; the signal moves to Wernicke’s area at the temporal-parietal junction — understanding; then along a bundle of association fibers to Broca’s area in the frontal lobe — assembly; then to the premotor and primary motor cortex — the mouth. Two breaks play: cut Broca’s and speech stutters while understanding stays; cut Wernicke’s and speech flows, well-shaped and empty. Then the three multimodal areas shade in — prefrontal, posterior, limbic — with the packet’s four jobs: understand, remember, associate, decide. Caption: raw signal in, perception out, and a decision relayed to the premotor cortex.
Prefer the full lecture? Cerebral Cortices (original video on the site)
Explore · in production
Break the circuit
A language circuit on screen — ear, primary auditory cortex, Wernicke’s, the connecting bundle, Broca’s, motor cortex, mouth. Click any station to break it, then predict before the playback how a patient would speak and understand. The reveal plays the speech pattern as text. Three breaks are classic (Broca’s, Wernicke’s, the bundle); the fourth is a slowed bundle rather than a cut — and the student must say which of the four matches “the word that would not come, and then did.”
Think · not graded
The prefrontal cortex “matures late” — hence lying in four-year-olds. If the association cortex is where understanding, memoryThe ability to store and recall information., association and decision happen, what do you expect a diffuse slowing of its connections to feel like from the inside — a loss, or a delay?
The true/false spot-check for this prompt is in production.
Check · Single Choice
Which area does which?
This self-scoring check is in production.
Evidence card 4
Add it to your evidence board
Comprehension and speech each have an address and both were intact; what carried the word between them was slow.
Scene 5 of 5
Two Hemispheres, Not Two Brains
Dominance is set by language; neither side is better at everything; and they talk through white matter.
Slide · in production
Split Screen
A brain from above split by the longitudinal fissureA deep groove in the brain’s surface., each side’s specialties listed, the corpus callosum drawn as the bridge; the airport-bookshop claims crossed out.
Prefer the full lecture? Introduction to the Cerebrum (original video on the site)
Explore · in production
Left or right
Ten tasks (naming a face, solving an equation, humming a tune, reading aloud, judging a mood, packing a trunk…). Before the reveal, drag each to the hemisphere that usually leads it, then flip a switch — “left-handed, right-dominant” — and watch which cards move. A second round: a right-hand weakness, a left-field visual loss, a lost melody — click the hemisphere, and say whether the lesion is on the same side as the symptom. Last: the myth-buster — three airport-bookshop claims to mark true or false.
Think · not graded
Contralateral control: the left hemisphere runs the right hand. Where does the crossing happen, and what structure lets the two hemispheres share what each one knows?
The true/false spot-check for this prompt is in production.
Check · Drag the Words
Lateralization, by the numbers.
This self-scoring check is in production.
Evidence card 5
Add it to your evidence board
Two hemispheres divide the work and confer constantly — through white matter, which is where her spots were.
4
Your evidence board
Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: Intact regions, slowed connections, Neither on its own, or A focal cortical lesion, or nothing at all. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.
Evidence board · drag and drop · in production
The sorting board for this chapter’s cards is being built. Until it arrives, sort your evidence cards on paper into the three columns above.
5
Your verdict
Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.
Look back at your prediction
Word-finding stalls, dropped threads and a slow morning, with a normal neurological exam — the reading that fits best is…
Find the one you chose at the top. Does the evidence support it, refute it, or revise it?
- Early damage to the language cortex — Broca’s or Wernicke’s area
- Stress, poor sleep and being busy — the cortex is fine
- The regions are intact; the connections between them are slow
Build your verdict · no writing
Choose the statement that holds in each set. The ones you keep become your argument.
This activity is in production.
6
The finding
Finding · the hat
Nothing Focal, Everything Slow
A full neurological exam in 2017 found every cortical address working — motor, sensory, language, memory, coordination. Chart entry: her complaints were delays, not losses; the association cortex and the hemispheres were intact and the traffic between them was slow. Held open: traffic runs on white matter, and in 2020 the spots appeared there.
Next · Chapter 3
Cables and Islands
The cables between the regions have names and routes — association, commissural, projection — and islands of gray sit among them running the start and stop of every movement. The spots were in the cables; the next chapter opens them.
Reliable information on rare diseases
NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation
Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.
Hop to:
← Familial Mediterranean Fever — case home
All pages for Module 10 — The Brain
10.0 Module Overview
10.1 Spots on the Scan
10.2 The Big Brain Hat
10.3 Cables and Islands
10.4 The Thermostat and the Relay
10.5 The Stalk and the Little Brain
10.6 Cushions and Currents
10.7 The Wall and the Tide
10.8 Conclusion and Assessment
10.9 Evidence Behind the Case
All Modules
- Anatomical Language, Membranes & Homeostasis
- Just Enough Chemistry
- The Cell & Its Transport
- Making Cells & Proteins
- The Integumentary System
- The Skeletal System
- The Muscular System
- Nervous Tissue & the Senses
- The Spinal Cord
- The Brain & the Blood–Brain Barrier
- The Autonomic Nervous System
- Special Senses (in developmentThe process of growth and differentiation.)
- The Endocrine System
- Blood
- The Heart
- Blood Vessels
- The Digestive System
- The Respiratory System
- The Urinary System
- Fluids, Electrolytes & Acid–Base Balance
- The Reproductive System
- The Immune System
List of terms
- cerebrum
- association areas
- cranial nerves
- reflexes
- white matter
- anatomy
- physiology
- frontal lobe
- longitudinal fissure
- frontal
- occipital
- insula
- lateral
- spinal cord
- corticospinal tract
- homunculus
- primary somatosensory cortex
- occipital lobe
- medial
- temporal lobe
- visceral sensory
- corpus callosum
- nervous system
- cerebellum
- brainstem
- central sulcus
- precentral gyrus
- mouth
- symptoms
- movement
- postcentral gyrus
- skin
- memory
- fissure
- development