Chapter 2
Brain and Behavior

Gateway question: What are the major divisions of the nervous system?

• Everything you sense, think, feel, and do comes from activity in your nervous system. It has roughly 100 billion neurons.
• Central nervous system (CNS) = brain + spinal cord. The brain does most of the "computing." The spinal cord is a column of nerves carrying information between the brain and the PNS.
• Peripheral nervous system (PNS) = everything outside the brain and spinal cord.
• A neuron is a single cell that transmits information. A nerve is a big bundle of neuron axons. Neurons are microscopic; nerves you can see.

Somatic nervous system (SNS)

• Carries messages from the sense organs and to the skeletal muscles. Controls voluntary behavior and sensory input.
• Example: clapping your hands or dancing.
• Transmits commands for voluntary movement from the CNS to the muscles, and brings sensory input back to the CNS.
• 31 pairs of spinal nerves serve the torso and limbs. They exit between the bones of the vertebrae.
• 12 pairs of cranial nerves serve the head, neck, and some internal organs. They connect straight to the brain without going through the spinal cord.

Autonomic nervous system (ANS)

• Controls internal organs and glands. Autonomic means "self-governing."
• Examples: heart rate, digestion, perspiration, the pancreas releasing insulin after you eat a cookie.
• Sympathetic branch: activates the body. Fight or flight. Dilates pupils, raises heart rate and breathing, activates sweat glands, releases adrenaline, inhibits digestion.
• Parasympathetic branch: quiets the body. Rest and digest. Constricts pupils, slows heart rate, stimulates digestion and salivation.
• Both are always active. How relaxed or aroused you are is their combined balance (homeostasis).

SNS + ANS working together (haunted house)

• You voluntarily walk along the pathway. That's the SNS.
• Something jumps out, your breathing and heart rate spike and you startle. That's the ANS, sympathetic.
• You leave and calm your breathing back down. That's the ANS, parasympathetic.

Gateway question: How do neurons operate and communicate with each other?

Parts of a neuron

• Dendrites (DETECT!): branches from the cell body that receive input from other neurons. Neurotransmitters from the sending neuron bind to receptors on these dendrites.
• Cell body (soma): contains the nucleus; also receives messages.
• Axon (ANNOUNCE!): the branch that transmits information away from the cell body to other neurons. Some are 0.1 mm, some are several feet long.
• Axon terminals: bulb-shaped ends containing synaptic vesicles, which hold the neurotransmitters.
• Metaphor: a line of people holding hands. Left hand = dendrites, you = soma, right arm = axon, right hand = axon terminals.

Neural communication is a two-step process

• Step 1: electrical signaling. Starts at the junction of the cell body and axon. The neuron generates an action potential that travels the length of the axon to its terminal.
• Step 2: chemical signaling. The action potential arriving at the axon terminal triggers the release of neurotransmitters. They float across the extracellular fluid between the two neurons. If influenced enough, the second neuron fires its own action potential and passes the message along.

Action potentials

• When a neuron is not processing information it is at resting potential: the interior is negatively charged relative to the exterior (about −60 to −70 millivolts). Every neuron is a tiny biological battery.
• Incoming chemical signals can make a neuron depolarized (more likely to fire) or hyperpolarized (less likely to fire).
• Enough depolarization and it reaches threshold (around −50 mV), which reliably produces an action potential.
• The size and shape of action potentials are always the same. Either it fires or the cell stays at rest, no middle ground. This is all-or-none, like a light switch.
• During it, ion channels open and sodium ions (Na+) rush in, gate after gate down the axon. Afterward potassium (K+) flows out and the charge dips below resting level: the negative after-potential.

Propagation and myelin

• Propagation is the duplication of the electrical signal down the length of the axon to the terminal. It works differently in myelinated and unmyelinated axons.
• Unmyelinated axon: action potentials occur step by step, from one small section of the axon to the next.
• Myelinated axon: potentials form only at the gaps between myelin segments, called nodes of Ranvier. The signal "skips" the myelin-covered sections, which is fast and efficient. This jumping is saltatory conduction.
• Once the action potential reaches the axon terminal, the system switches from an electrical signal to a chemical one.

The synapse

• Synapse: the microscopic gap between two neurons (about one-millionth of an inch).
• Receptors are special channels on the receiving dendrite that "catch" neurotransmitters. Think locks and keys.
• Neurotransmitters don't stay bound for long. They drift away from the gap, get broken down by enzymes, or return to the axon terminal that released them in a process called reuptake.
• They don't force firing. They make it more likely (excitatory) or less likely (inhibitory).

Neurotransmitters

• Any chemical released by a neuron that alters activity in other neurons. Over 100 exist.
• Key ones: acetylcholine (movement, memory; deficiency linked to Alzheimer's), dopamine (motivation and reward; low = Parkinson's, excess linked to schizophrenia), GABA (main inhibitory; deficiency = anxiety), glutamate (main excitatory; learning and memory), norepinephrine (arousal, vigilance, mood), serotonin (mood, appetite, sleep; deficiency linked to depression).
• Drugs can mimic, duplicate, or block neurotransmitters. Cocaine is chemically close to dopamine and triggers a dopamine increase, but in the long run disturbs dopamine functioning (addiction).
• Curare blocks acetylcholine receptors on muscles and causes paralysis.

Neural regulators

• Neuropeptides don't carry messages. They regulate the activity of other neurons.
• Enkephalins and endorphins both relieve pain and reduce stress.
• Endorphins also improve mood and sense of well-being, and help regulate body weight. Enkephalins help regulate feeding behavior.
• May explain how placebo medications work: they raise endorphins.
• Endorphins are related to runner's high, masochism, acupuncture, and skydiving. You can get "addicted" to that feeling.

Neural networks and the reflex arc

• A neural network is an interlinked collection of neurons that processes information. Your brain has 100 trillion+ synapses.
• A reflex arc occurs when a stimulus provokes an automatic response, like stepping on a nail. Reflexes are initiated by the spinal cord without the assistance of the brain.
• Path: sensory neuron carries the pain from the foot to the CNS → interneuron links them inside the cord → motor neuron carries the command from CNS to muscle → the muscle contracts and lifts the foot.
• A neuron sums up hundreds or thousands of excitatory (+) and inhibitory (−) inputs before "deciding" to fire. Each one is a tiny biocomputer.

Glial cells and the blood-brain barrier

• Glial cells form the framework that holds neurons in place.
• They create tight connections with the blood vessels serving the brain, forming the blood-brain barrier.
• They clean up debris where neurons have been damaged, and they generate myelin.
• Neurons are the grey matter of the brain; myelin is the white matter (lighter because of the myelin coating).
• Myelin in the brain and spinal cord forms scar tissue when damaged, interfering with transmission. Myelin in the rest of the nervous system does not.

Gateway question: How does the nervous system change and grow?

• Neuroplasticity: our nervous system changes in response to experience. The brain isn't programmed. It learns.
• New synaptic connections can be made, existing connections can be strengthened, and inactive connections may weaken and die.
• The younger the individual, the more plasticity there is.
• Hebb's rule: neurons that "fire together, wire together." Repeatedly activating a synapse strengthens the connection.
• Long-term potentiation (LTP) is the strengthening of those connections through repeated use.
• Neurogenesis: the production of new brain cells. We used to think you're born with all you'll ever get. Thousands of new cells form deep in the brain each day and join the circuitry, probably serving learning, memory, and adaptation.
• London taxi drivers who memorize thousands of streets have enlarged brain areas for that learning. Nico and Brooke had large portions of their brains removed as infants and their brains rewired themselves.
• PNS nerves can regrow. CNS damage was long thought permanent, though repair of spinal cord neurons is now progressing.
• CTE (chronic traumatic encephalopathy) has poor recovery prospects because head trauma triggers ongoing damage long after the hits stop.

Gateway question: How are different parts of the brain identified, and what do they do?

• Biopsychology: the study of how biological processes, especially in the nervous system, relate to behavior.
• Localization of function: investigating which areas of the brain control which mental or behavioral functions, where they are localized, and how brain areas are connected.

Imaging the brain

• CT scan (computed tomographic): X-rays taken from many different angles, formed into an image by a computer. Reveals brain structure: strokes, injuries, tumors. Can expose patients to unhealthy doses of radioactivity with multiple scans.
• MRI (magnetic resonance imaging): the body is placed inside a strong magnetic field, creating a 3-D image that can be displayed in "slices." Structure only, no known side effects.
• fMRI (functional MRI): uses MRI technology to make activity visible. May be able to detect when someone is lying, which raises the question of whether it should be used in court during testimony.
• PET (positron emission tomography): detects positrons emitted by weakly radioactive glucose as the brain consumes it. Higher energy use = higher activity. Creates a moving color video of brain activity, so you can watch as someone hears, sees, or speaks.
• EEG (electroencephalography): electrodes on the scalp measure waves of electrical activity near the brain's surface. Patterns can detect tumors, epilepsy, and other diseases, and show different activity during sleep, daydreaming, and hypnosis.

Clinical studies of the brain

• Electrical stimulation of the brain (ESB): a thin insulated wire (an electrode) is used to "turn on" the surface of the brain. Done during brain surgery to see the effects. The brain has no pain receptors, so patients are awake.
• Ablation: surgical removal of parts of the brain, then observing the effect on behavior.
• Deep lesioning: destroying or removing tissue below the surface with an electrode.
• Case studies of injury or disease (Phineas Gage). Neurological soft signs are behavioral hints of dysfunction: clumsiness, awkward gait, poor hand-eye coordination.
• Myth: we use only 10 percent of our brains. False. Scans show all parts are active during waking hours.

Studying the brain: summary table

Quick rule: CT and MRI show structure. EEG, PET, and fMRI show activity.

Gateway question: How do the left and right hemispheres of the cerebral cortex differ?

• Above the brainstem sit the two large cerebral hemispheres.
• The corpus callosum is a large bundle of axons connecting the two hemispheres.
• The cerebral cortex is the thin (about 3 mm) wrinkled layer of cells covering the outer surface of the hemispheres, where high-level processing happens. It holds about 70 percent of all CNS neurons.
• The cerebrum, hypothalamus, and thalamus together are called the forebrain.
• Human intelligence isn't from brain size (whales have bigger brains). It's from corticalization: the increase in size and wrinkling of the cortex.
• The ventricles generate cerebrospinal fluid, which cushions the brain and spinal cord.

Lateralization and contralateral organization

• Lateralization: the specialization of the abilities of the left and right hemispheres.
• Contralateral organization: the left hemisphere controls the right side of the body, and vice versa.
• Spatial neglect: damage to one hemisphere makes patients act as though they can't see half of a display. They won't eat food from half of the plate, or draw only half a figure.
• Dominant hemisphere: usually the side that produces language. Over 90 percent of everyone uses the left brain for language.

The split brain

• Split-brain operation: the corpus callosum is cut to control severe epilepsy. Tests then reveal how each hemisphere handles information on its own.
• Usually, in normal processing, one half overrides the other.
• Flash a dollar sign to the right brain and a question mark to the left: the left hand draws the dollar sign, but the right hand points to the question mark. One hemisphere doesn't know what the other saw.
• Roger Sperry won a Nobel Prize in 1981 for this work.

What each side does better

• Left: 95 percent of us use it for language (speaking, writing, understanding). Also math, judging time and rhythm, and coordinating the order of complex movements such as speech. Processes analytically and sequentially; focus is local (details).
• Right: simple words and numbers. Good at pattern recognition, faces, melodies, puzzles, drawing pictures, expressing and detecting emotion, and getting jokes, irony, sarcasm, implications, and metaphors. Processes holistically and simultaneously; focus is global (big picture).
• "Left-brained" and "right-brained" people is an oversimplification. Normal people use both sides constantly and share the work.

White matter vs grey matter

• Grey matter = cell bodies (darker).
• White matter = neural fibers, lighter in color because of their myelin coating.

Gateway question: What are the different functions of the lobes of the cerebral cortex?

Frontal lobe: movement, planning, sense of self

• Home of the primary motor cortex, which directs the body's muscles. The map is proportional to dexterity, not size. The hands get far more area than the feet.
• Prefrontal cortex: the most forward portion of each frontal lobe. Involved with planning of behavior, attention, and judgment, plus executive functions: the higher-level processes that regulate and coordinate our own thinking.
• Orbitofrontal cortex: part of the prefrontal cortex located just behind the bony orbits protecting the eyes. Plays an important role in our emotional lives.
• Broca's area: speech center in the left frontal association area, responsible for speech production (speaking or writing). Damage causes motor (expressive) aphasia: slow, labored speech. The famous patient could only say "Tan."
• Aphasia is any speech disorder resulting from brain damage.
• Mirror neurons fire both when you perform an action and when you watch someone else perform it. Possibly the basis of imitation and empathy; the "broken mirrors" hypothesis links damaged mirror systems to autism spectrum disorder. Still hypotheses awaiting confirmation.

Parietal lobe: bodily sensation

• Home to the primary somatosensory cortex, which helps localize touch, pain, skin temperature, and body position.
• Processes input about taste, and like the temporal lobe does some complex processing of vision.
• The map is distorted by sensitivity: lips and hands are huge, the back and trunk are small.

Temporal lobe: hearing and language comprehension

• Home to the primary auditory cortex, which processes incoming sounds.
• Handles some higher visual tasks including recognizing objects and the faces of familiar people.
• Wernicke's area: responsible for receptive language. Damage makes it difficult to understand speech, particularly the meaning of words. Speech stays fluent but meaning is lost, shown a picture of a chair, a patient might confidently say "truck."

Occipital lobe: vision

• Located at the back of the brain, home to the primary visual cortex.
• Two important pathways link it to the rest of the brain: one to the temporal lobe lets us recognize objects we see, and one to the parietal lobe lets us process the movement of objects.
• Visual agnosia: an inability to identify seen objects. A patient can see a candle, describe it, and draw it, but not name it until it's placed in their hand.
• Facial agnosia (prosopagnosia): the inability to perceive familiar faces. Linked to the fusiform gyrus.

Association areas

• Association areas are all the cortex that isn't primarily sensory or motor. They combine and process information, connecting the sight of a rose with memories so you recognize and name it.

Gateway question: What are the major parts of the subcortex?

• Subcortex: all brain structures below the cerebral cortex. You could survive without the cortex, but not without this. Serious damage means coma or death.
• Three layers: hindbrain (medulla, pons, reticular formation, cerebellum), midbrain (connects hindbrain to forebrain), forebrain (limbic system, thalamus, hypothalamus, and the cortex).

Hindbrain / brainstem

• Medulla: merges with the spinal cord. Contains large bundles of axons traveling to and from higher levels of the brain. Manages essential functions such as heart rate and blood pressure. Damage usually results in quick death.
• Pons: sits above the medulla. Involved in the management of sleep, arousal, and facial expressions. Connects the cerebellum to the rest of the brain.
• Cerebellum: essential for balance and motor coordination (posture, muscle tone). Stores memories related to skills and habits. Athletes have larger cerebellums. One of the first brain structures affected by alcohol. Recent research suggests it's also involved in language, cognition, and perception.
• Reticular formation (RF): runs the length of the brainstem's core from the upper medulla into the midbrain. Participates in the control of mood, arousal, sleep, and attention. Handles reflexes involving breathing, sneezing, coughing, and vomiting.
• Midbrain: sits above the pons; contains structures involved in sensory reflexes, movement, and pain.

The limbic system

• Early anatomists grouped some subcortical structures into the limbic system, sometimes called the "emotional brain." That term is losing popularity as the full range of functions becomes better understood: emotion, memory, motivation, and social processing.
• Thalamus: the relay hub for sensory systems (vision, hearing, touch, taste). Also involved with memory and states of consciousness. Every sense except smell passes through it.
• Basal ganglia: voluntary movement, motor control, motor learning, executive functioning, emotions. Degeneration can cause Parkinson's disease, which makes initiating voluntary movement extremely difficult. Possibly involved in OCD and ADHD.
• Amygdala: identifying, remembering, and responding to fear and aggression. Emotion processing, connected to memory and the senses. Gives a fast primitive path to the cortex, so you can react to danger before you consciously know what's happening.
• Hypothalamus: a collection of structures involved with motivation and homeostasis: regulating temperature, thirst, hunger, biological rhythms, and sexual activity. Directs the autonomic nervous system and the endocrine system.
• Hippocampus: essential to the formation of long-term memories, and involved in the storage and retrieval of memories located elsewhere in the brain.
• Cingulate cortex: the forward two-thirds (anterior cingulate cortex, ACC) works with the hypothalamus to control the ANS, and matters for decision making, emotion, anticipation of reward, and empathy. The rear third (posterior cingulate cortex, PCC) participates in memory and visual processing.
• The limbic system contains reward/pleasure pathways. Cocaine, amphetamine, heroin, nicotine, cannabis, and alcohol all activate them, and so does "thrilling" music.

Three cautions

• Glial cells outnumber neurons about 9 to 1 and aren't silent servants: they support, insulate, remove waste, provide nutrients, and communicate with neurons.
• Assigning one function per brain part is only partly true. Information scatters all over the brain and reconverges.
• You know what you're reading but have no awareness of how. Only objective methods can reveal that.

Gateway question: How does the endocrine system affect behavior?

• Endocrine system: a number of glands that release chemical messengers called hormones into the bloodstream to communicate with other body parts.
• It responds to input from the nervous system, and from the hypothalamus in particular.
• Especially involved with arousal, metabolism, growth, and sex. It's a slower parallel communication system to the nervous system.

Major glands

• Pituitary gland: the "master gland." Produces hormones that control other endocrine glands and regulate growth, metabolism, and reproduction. But the master has a master: the hypothalamus directs it.
  • Anterior pituitary hormones: human growth hormone (HGH), prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH).
  • Posterior pituitary hormones: antidiuretic hormone (ADH, also called vasopressin) and oxytocin.
• Thyroid gland (neck): produces hormones that regulate metabolism and control the body's energy level. Hyperthyroidism → thin, tense, excitable. Hypothyroidism → inactive, sleepy, slow.
• Adrenal glands (on top of the kidneys): produce hormones that regulate the body's response to stress and help control blood pressure. The adrenal medulla releases epinephrine and norepinephrine; the adrenal cortex produces corticoids that regulate salt balance and help the body adjust to stress.
• Pancreas: produces hormones including insulin that regulate blood sugar levels and aid digestion.
• Parathyroid glands: regulate the levels of calcium in the blood.
• Pineal gland: produces melatonin, which regulates sleep patterns, in response to daily cycles of light and dark.
• Ovaries (females) and testes (males): produce hormones that regulate the reproductive system, including the production of eggs and sperm.

Sex hormones

• In males, the major reproductive glands are the testes, which secrete testosterone. It influences sexual function and plays a critical role in puberty.
• In females, the major reproductive glands are the ovaries, which secrete estrogen. It influences sexual function, plays a critical role in puberty, and is one of the major hormones of the menstrual cycle.
• Anabolic steroids are synthetic testosterone used to bulk up. Side effects include voice deepening or baldness in women, shrunken testicles or breast enlargement in men, "roid rage," heart attack and stroke risk, liver damage, and stunted growth in adolescents.

Important hormones to know

Memory hook: Epinephrine = fEar. Norepinephrine = anger.

Gateway question: How can self-regulation help me in my personal and professional life?

• Self-regulation: the ability to consciously exert self-control. Rooted in the frontal lobes, especially the prefrontal cortex.
• Walter Mischel's Marshmallow Test: children choose one marshmallow now or two later. Better self-regulators later showed better health, more professional success, and greater financial stability.
• The Dunedin study in New Zealand followed over 1,000 children into their thirties. Higher childhood self-regulation predicted better health, fewer substance abuse problems, better finances, and less criminal activity.
• Executive functions are the foundation: they let us set goals, make plans, control attention and emotion, and monitor progress. Like an air traffic control system coordinating flights.
• Self-regulation is partly genetic but shaped by environment and action. Mischel says it's a skill anyone can develop.

Hot vs cool systems

• Hot emotional system: wants what you want right now. Tied to the limbic system.
• Cool cognitive system: reflects on long-term consequences. Tied to the prefrontal cortex. Essential to self-regulation.

Strategies

• Selective attention: change what you pay attention to, focusing away from the temptation.
• Cognitive reappraisal: reframe the situation ("I don't need an extra gym trip to work off that beer").
• Bring long-term consequences to mind. Picture your future self suffering the consequences.
• Choose or change your environment so the temptation isn't there.
• And when all else fails, plain old self-control: just say no.