Collection · COL-13

The Brain

Wiring, neurochemistry and emotion: the connections and chemistry behind how you think and feel.

11 case files · 22 quiz questions · Science, People, Tech

11 case files in this collection

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Free PDF: every quick fact with its ID, the write-ups, sources and a quiz with an answer key.

What Is in The Brain?

11 case files on how the brain is wired and the circuits and chemicals behind your feelings: its roughly 86 billion neurons and their trillions of connections, then happiness, sadness, anger, disgust, surprise and fear, one at a time, plus the antidepressants that act on serotonin. The locus coeruleus is the brain's main source of noradrenaline. DD-747 SSRIs work by inhibiting the serotonin transporter, SERT. DD-749

The Case Files, in Order

  1. 01
    DID YOU
    KNOW?    ConnectedDD-635

    DD-635Science

    Connected

    86 billion neurons, trillions of links.

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  2. 02
    DID YOU
    KNOW?    HappinessDD-743

    DD-743Science

    Happiness

    Why there's no single 'happy chemical'.

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  3. 03
    DID YOU
    KNOW?    SadnessDD-744

    DD-744Science

    Sadness

    What changes in the brain when we feel sad.

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  4. 04
    DID YOU
    KNOW?    AngerDD-745

    DD-745Science

    Anger

    The brain circuits behind a flash of anger.

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  5. 05
    DID YOU
    KNOW?    DisgustDD-746

    DD-746Science

    Disgust

    The emotion built to keep contamination out.

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  6. 06
    DID YOU
    KNOW?    SurpriseDD-747

    DD-747Science

    Surprise

    What happens in the brain when expectations break.

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  7. 07
    DID YOU
    KNOW?    FearDD-748

    DD-748Science

    Fear

    What your brain and body do when danger appears.

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  8. 08
    DID YOU
    KNOW?    SSRIsDD-749

    DD-749Science

    SSRIs

    How a common class of antidepressants works.

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  9. 09
    DID YOU
    KNOW?    Synaptic TransmissionDD-275

    DD-275Science+ People

    Synaptic Transmission

    Neurons pass signals across a gap called the synaptic cleft.

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  10. 10
    DID YOU
    KNOW?    Seems FamiliarDD-429

    DD-429Science

    Seems Familiar

    Scientists build virtual worlds for mice running on treadmills.

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  11. 11
    DID YOU
    KNOW?    NeuralinkDD-527

    DD-527Tech+ Science

    Neuralink

    Neuralink implants a coin-sized chip with thin threads into the brain.

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Collection Quiz

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22 questions from all 11 case files in The Brain. Test Your Knowledge: answers are revealed instantly.

  1. About how many neurons are in the human brain?

    1. 86 billion
    2. 8.6 million
    3. 860 billion
    4. 86 trillion
    Show the answer

    Answer: A. 86 billion Now You Know: About 86 billion, per a 2009 study. Source: DD-635 · Connected · Write-up · Exhibit A (Where 86 billion comes from) · Azevedo et al. (2009): Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain, J. Comp. Neurol. (PubMed)

  2. What figure did the 86 billion estimate replace?

    1. 100 billion
    2. 10 billion
    3. 1 trillion
    4. 50 billion
    Show the answer

    Answer: A. 100 billion Now You Know: The textbook 100 billion. Source: DD-635 · Connected · Write-up · Exhibit A (Where 86 billion comes from) · Azevedo et al. (2009): Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain, J. Comp. Neurol. (PubMed)

  3. According to Berridge, dopamine is mainly linked to...

    1. 'Liking'
    2. 'Wanting'
    3. Vision
    4. Bone strength
    Show the answer

    Answer: B. 'Wanting' Now You Know: Dopamine supports incentive 'wanting' and reward learning. Source: DD-743 · Happiness · Write-up · Exhibit B (Wanting versus liking) · Berridge & Kringelbach (2015), Pleasure systems in the brain, Neuron (PMC)

  4. Where are 'hedonic hotspots' found?

    1. Nucleus accumbens and ventral pallidum
    2. Fingertips
    3. Liver
    4. Retina
    Show the answer

    Answer: A. Nucleus accumbens and ventral pallidum Now You Know: Small hotspots there amplify pleasure. Source: DD-743 · Happiness · Write-up · Exhibit C (Hedonic hotspots) · Berridge & Kringelbach (2015), Pleasure systems in the brain, Neuron (PMC); Kringelbach & Berridge (2010), The Functional Neuroanatomy of Pleasure and Happiness (PMC)

  5. Is everyday sadness the same as clinical depression?

    1. Yes
    2. No, it's a normal emotion distinct from depression
    3. Only in winter
    4. Only in children
    Show the answer

    Answer: B. No, it's a normal emotion distinct from depression Now You Know: Sadness is a normal emotion; depression is a clinical condition. Source: DD-744 · Sadness · Write-up · Exhibit A (A normal emotion) · Arias et al. (2020), The neuroscience of sadness: A multidisciplinary synthesis and collaborative review, Neuroscience & Biobehavioral Reviews; Wikipedia: Sadness

  6. Which brain region does the 2020 review link to sadness?

    1. Subgenual anterior cingulate cortex
    2. Cerebellar vermis only
    3. Olfactory bulb
    4. Retina
    Show the answer

    Answer: A. Subgenual anterior cingulate cortex Now You Know: It also links the dorsal periaqueductal gray and frontal changes. Source: DD-744 · Sadness · Write-up · Exhibit B (Distributed circuitry) · Arias et al. (2020), The neuroscience of sadness: A multidisciplinary synthesis and collaborative review, Neuroscience & Biobehavioral Reviews

  7. Which structure completes the amygdala-hypothalamus threat circuit?

    1. Periaqueductal gray
    2. Cerebellum
    3. Retina
    4. Olfactory bulb
    Show the answer

    Answer: A. Periaqueductal gray Now You Know: The basic threat system runs from the amygdala through the hypothalamus to the PAG. Source: DD-745 · Anger · Write-up · Exhibit A (A threat circuit) · Blair (2012), Considering anger from a cognitive neuroscience perspective, WIREs Cognitive Science (PMC); Understanding Brain Mechanisms of Reactive Aggression (2020, PMC)

  8. Which brain area helps regulate reactive aggression?

    1. Ventromedial prefrontal cortex
    2. Visual cortex
    3. Medulla only
    4. Spinal cord
    Show the answer

    Answer: A. Ventromedial prefrontal cortex Now You Know: Ventromedial and orbital frontal regions help regulate the response. Source: DD-745 · Anger · Write-up · Exhibit B (Prefrontal regulation) · Blair (2012), Considering anger from a cognitive neuroscience perspective, WIREs Cognitive Science (PMC); Understanding Brain Mechanisms of Reactive Aggression (2020, PMC)

  9. Which brain region is most consistently linked to disgust?

    1. Anterior insula
    2. Cerebellum
    3. Visual cortex alone
    4. Spinal cord
    Show the answer

    Answer: A. Anterior insula Now You Know: Felt disgust correlates with anterior insula activity. Source: DD-746 · Disgust · Write-up · Exhibit A (Feeling disgust) · Harrison et al. (2010), The Embodiment of Emotional Feelings in the Brain, Journal of Neuroscience

  10. Is the insula disgust-specific?

    1. Yes, only disgust
    2. No, it represents the body's internal state in many emotions
    3. It only processes vision
    4. It only controls movement
    Show the answer

    Answer: B. No, it represents the body's internal state in many emotions Now You Know: The insula is involved in interoception broadly. Source: DD-746 · Disgust · Write-up · Exhibit E (The body's state) · Harrison et al. (2010), The Embodiment of Emotional Feelings in the Brain, Journal of Neuroscience; Wikipedia: Disgust

  11. Where is the locus coeruleus?

    1. Brainstem
    2. Retina
    3. Spinal cord base
    4. Frontal lobe surface
    Show the answer

    Answer: A. Brainstem Now You Know: It is a small nucleus in the brainstem's pons. Source: DD-747 · Surprise · Write-up · Exhibit A (The locus coeruleus) · Wikipedia: Locus coeruleus

  12. Which chemical does the locus coeruleus mainly release?

    1. Dopamine
    2. Noradrenaline (norepinephrine)
    3. Insulin
    4. Serotonin
    Show the answer

    Answer: B. Noradrenaline (norepinephrine) Now You Know: It is the brain's main source of noradrenaline. Source: DD-747 · Surprise · Write-up · Exhibit A (The locus coeruleus) · Wikipedia: Locus coeruleus

  13. Which brain region sends the first distress signal to the hypothalamus?

    1. Cerebellum
    2. Amygdala
    3. Hippocampus
    4. Occipital lobe
    Show the answer

    Answer: B. Amygdala Now You Know: The amygdala signals the hypothalamus when it perceives danger. Source: DD-748 · Fear · Write-up · Exhibit A (The alarm) · Harvard Health: Understanding the stress response

  14. Which hormone causes the fast surge in heart rate?

    1. Insulin
    2. Epinephrine (adrenaline)
    3. Melatonin
    4. Oxytocin
    Show the answer

    Answer: B. Epinephrine (adrenaline) Now You Know: The adrenal glands pump epinephrine into the blood. Source: DD-748 · Fear · Write-up · Exhibit B (The fast wave) · Harvard Health: Understanding the stress response

  15. What do SSRIs block?

    1. The dopamine receptor
    2. The serotonin transporter (SERT)
    3. Serotonin production
    4. The blood-brain barrier
    Show the answer

    Answer: B. The serotonin transporter (SERT) Now You Know: They inhibit SERT, so serotonin stays in the synaptic cleft longer. Source: DD-749 · SSRIs · Write-up · Exhibit A (The mechanism) · StatPearls (NCBI Bookshelf): Selective Serotonin Reuptake Inhibitors

  16. What does the 'S' for selective refer to?

    1. Little effect on dopamine or norepinephrine
    2. Prescription only
    3. Taken once a day
    4. Made in a lab
    Show the answer

    Answer: A. Little effect on dopamine or norepinephrine Now You Know: SSRIs act mainly on serotonin reuptake. Source: DD-749 · SSRIs · Write-up · Exhibit A (The mechanism) · StatPearls (NCBI Bookshelf): Selective Serotonin Reuptake Inhibitors

  17. Where do neurons communicate?

    1. At synapses
    2. In bones
    3. In blood
    4. In skin
    Show the answer

    Answer: A. At synapses Now You Know: Junctions. Source: DD-275 · Synaptic Transmission · Write-up · Exhibit A (Synapse) · Wikipedia: Chemical synapse

  18. What triggers release?

    1. An action potential
    2. Light
    3. Heat
    4. Sound
    Show the answer

    Answer: A. An action potential Now You Know: An electrical impulse. Source: DD-275 · Synaptic Transmission · Write-up · Exhibit B (Vesicles) · Wikipedia: Chemical synapse

  19. What does the mouse run on?

    1. A treadmill or ball
    2. A wheel only
    3. Sand
    4. Water
    Show the answer

    Answer: A. A treadmill or ball Now You Know: Stays in place. Source: DD-429 · Seems Familiar · Write-up · Exhibit A (Setup) · Wikipedia: Virtual reality

  20. Why VR?

    1. To record the brain
    2. For fun
    3. To exercise
    4. To sell
    Show the answer

    Answer: A. To record the brain Now You Know: Neuroscience. Source: DD-429 · Seems Familiar · Write-up · Exhibit B (Screens) · Wikipedia: Virtual reality

  21. Founded?

    1. 2016
    2. 2002
    3. 2020
    4. 2010
    Show the answer

    Answer: A. 2016 Now You Know: Musk. Source: DD-527 · Neuralink · Write-up · Exhibit A (Founded) · Wikipedia: Neuralink

  22. BCI means?

    1. Brain-computer interface
    2. Basic chip input
    3. Bionic cell implant
    4. None
    Show the answer

    Answer: A. Brain-computer interface Now You Know: Tech. Source: DD-527 · Neuralink · Write-up · Exhibit B (Device) · Wikipedia: Neuralink