Unit 3B: The Brain
  1. Introduction
    1. There’s little doubt that what makes you yourself and me myself resides in our brains.
    2. The mind is somehow a combination of body plus brain.
  2. The tools of discovery: having our head examined
    1. Early on, there were no tools to “map” the brain. Damages to the brain and resulting symptoms enabled researchers to build a rough “brain map”.
    2. Today, we have several techniques to measure brain activity.
      1. Areas of animals brains can be destroyed and the results analyzed. Or, brain areas can be stimulated and the results analyzed.
      2. An EEG (electroencephalogram) is a read-out of electrical brain activity.
      3. A PET scan (positron emission topography) shows the brain's "hot-spots" of action by measuring its consumption of sugar glucose, the brain's fuel.
      4. An MRI (magnetic resonance imaging) provides a picture of the brain’s soft tissue. MRI’s have shown brain differences in things such as people who have perfect pitch or schizophrenia.
      5. An fMRI (functional MRI) can show the brain’s structure and function. An fMRI measures blood-flow to and within the brain and therefore can show brain activity.
  3. Older brain structures
    1. Brain size-to-body weight ratio is important to an animal’s intelligence, but it isn’t the only factor of intelligence.
    2. Simple animals, like sharks, have brains that are concerned with survival—breathing, resting, eating. In mammals and especially in humans, higher order brain functions emerge, like emotion and memory.
      1. Thus, we have two brain functions: “old brain functions” dealing with survival and more complex brain functions dealing with thought.
    3. The brainstem is the oldest brain region.
      1. The brainstem begins as the spinal cord enters the brain it swells in width. This section is called the medulla. The medulla controls heartbeat and breathing.
      2. Above the medulla is the pons. It helps to coordinate movements.
      3. The reticular formation is inside the brainstem. It looks a bit like folded fingers and relays incoming stimuli to other areas of the brain (also regulates autonomic functions, such as arousal.)
    4. Atop the brainstem is the thalamus. It’s the hub that sends incoming sensory impulses (except for smell) to the higher brain areas.
    5. The cerebellum is at the back of the brain. It’s baseball size, is split into two parts, is wrinkled in appearance, and means “little brain” which is what it looks like.
      1. The cerebellum coordinates movement, manages emotions, and figures out sounds and textures.
    6. The limbic system sits between the older brain structures and the cerebral hemispheres (the two large halves of the brain).
      1. The hippocampus is critical because it processes memory.
      2. The amygdala is made up of two bean-size nerve bundles. The amygdale manages anger and fear. It also is involved with handling the emotions and memories involved here.
        1. It’s important to note something here—we like to categorize things, such as A does B, and X does Y exclusively. The brain, however, is far more complex. Several parts of the brain handle things like emotions, memories, learning, movement, etc.
      3. The hypothalamus (“hypo” meaning below) is below the thalamus. The hypothalamus is important in hunger, thirst, body temperature, and sexual behavior.
        1. As an example, thinking about sex in the cerebral cortex activates the hypothalamus. It emits hormones that affect the pituitary (the master gland) which affects other hormones to. These hormones influence brain activity. Remember the chain: Brain->Pituitary->Other glands->Hormones->Brain
        2. As another example, a chance discovery had two scientists implant an electrode in a rat’s “reward” or “pleasure center” of the brain—the hypothalamus. This spawned experiments. Rats would similarly press a lever to give a reward to its brain, up to 7,000 times/hour, until it stopped from exhaustion.
          1. Later rats were essentially driven, remote controlled, to turn left or right by pleasure impulses to their hypothalamuses.
        3. Animal research shows a release of dopamine within pleasure areas of eating, drinking, and sex.
        4. People have shown mild, but not the same, frenzied results as the rats.
  4. The cerebral cortex
    1. Whereas the older brain parts carry out survival functions and less voluntary things, the newer brain parts deal with more voluntary functions, like perception, thinking, and speaking. The cerebral cortex is the largest section of the brain, about 85% of its weight. It’s the gnarled “bark” that encompasses the rest of the brain.
    2. Being wrinkly, the cerebral cortex looks like a giant walnut. It has about 20 to 23 billion nerve cells linked together by 300 trillion synapses.
      1. These nerve cells are supported by 9 times as many glial cells. These cells feed and insulate the nerve cells.
    3. The cerebral cortex is divided into four lobes, separated by fissures, and each with their own specialties…
      1. The frontal lobe is in the front, behind the forehead.
      2. The parietal lobe is at the top and to the back of the brain.
      3. The occipital lobe is at the back and bottom of the brain.
      4. And the temporal lobe is near the temples, on the side.
    4. The cerebral cortex has different functions centered on different areas.
      1. The motor cortex is a strip roughly between the frontal and parietal lobes. It handles our movements and motions by sending impulses from the brain to the body. Tests where electrical stimulation to this part of the brain would make animals or people move in various ways.
        1. The question then became, “Could a person or animal control a machine (like a computer mouse) using his brain?” The answer seems to be, “Yes.” A monkey was “wired up” to control a mouse with only his motor cortex.
        2. Researchers are trying to use this technique with a paralyzed person who cannot speak. The idea is to “wire up” the cortex to a machine, the person thinks of the word, and the machine speaks for him.
        3. The FDA gave the okay for a “neural prosthetic” in 2004. With a computer chip implanted in his motor cortex, the man could control a TV, draw shapes on a computer, and play video games.
      2. Sensory functions
        1. The sensory cortex receives input from the senses to the brain (the opposite direction from the motor cortex). The sensory cortex is a strip just behind the motor cortex, at the front of the parietal lobe.
          1. The more sensitive the area of the body (like the sensitive lips), the larger that area of the sensory cortex.
        2. The occipital lobe processes vision. Being bonked in the back of the head can literally have you “see stars” or flashes because the lobe gets jarred.
        3. Sounds are processed in the auditory cortex in the temporal lobe (appropriately, just above the ear).
      3. The areas described thus far in the cerebral cortex make up only about ¼ of its size. The other ¾ of the cortex is harder to pin down and label, but seems that it’s for thinking. It’s generally called association areas. These areas piece parts together and make sense of things.
        1. For instance, seeing a stick of dynamite and a lit match side-by-side mean nothing until they’re associated with one another. The logical conclusion – danger!
        2. The frontal lobe handles judgment, planning, and new memories.
          1. It also impacts personality. Phineas Gage was famously injured in a railroad accident in 1848 when a iron spike drove through his skull. It injured his frontal lobe. He was largely okay, but his personality had changed completely from friendly and mild-mannered to profane, cranky, and dishonest.
        3. The parietal lobe seems to handle math and spatial reasoning (Einstein’s were large) as well as recognize faces.
        4. Despite these hot spots, the brain’s “map” really isn’t written in stone and we should be careful to not think that it is.
      4. The brain has a measure of plasticity, that is its ability to change itself after being damaged.
        1. Whereas something like skin can “grow back” or “heal over,” neurons don’t regenerate themselves. A severed spinal cord stays severed. But the brain seems able to reorganize or reassign jobs and functions.
        2. Children’s brains are amazingly plastic.
        3. People seem to heal fastest when their “good hand is tied behind their back” and are forced to use their “bad hand.” This forces the brain to reorganize.
        4. There are many examples…
          1. Blind people who read Braille have increased sensitivity in their fingertip.
          2. Deaf people’s hearing area of the brain turns toward visual stimulation.
          3. A lost finger’s area of the brain will take on the nearby fingers’ sensation.
        5. Contrary to popular belief, we do grow new brain cells in a process called neurogenesis. Naturally, this is promoted by exercise, sleep, and non-stressful but stimulating environments.
  5. Our divided brain
    1. We’ve known for over 100 years that the two sides of the brain have different purposes. Damage to the left hemisphere resulted in problems with reading, writing, speaking, math, and reasoning. Around 1960, it was discovered that the right hemisphere had its specialties as well.
    2. In 1961, patients with severe epileptic seizures had their corpus callosum cut. The corpus callosum links the two hemispheres. The seizures stopped and the patients were very normal afterwards.
      1. These patients were then subject to experiments. The patient stared at the center of a screen and words or images were sent displayed to each side and thus were sent to one half of their brain. For example…
      2. HE . ART was flashed while staring at the center dot. HE went to the right brain, ART to the left brain. When asked what he saw, he said “ART” (left brain talking). Then he pointed to HE with his left hand (right brain controlling).
    3. Left brain – right brain research can get very confusing with its criss-crossing nature, but the overall conclusions were…
      1. The left brain handles rational, logical thought, speech and words. Think of Mr. Left, a boring, methodical, math teacher who carefully works through complicated problems step-by-step and always gets the correct answer.
      2. The right brain handles images, emotions, intuition, and drawing inferences. Think of Mrs. Right, a flaky, unpredictable art teacher who can instantly tell when you’re having a down day.
  6. Right-left differences of the intact brain
    1. For nearly all people (those who don’t have a severed corpus callosum) the hemispheres “talk” to one another instantly. Still, the halves have their specialties.
      1. A sedative to patients that goes to the left brain will leave the person’s right arm limp and they can’t speak.
      2. A sedative to patients that goes to the right brain will leave the person’s left arm limp but they can still speak.
      3. Sign language is also dominated by the left hemisphere. One might think the right hemisphere would handle this (being more spatial and visual in nature), but not so. Language is language regardless of how it is conveyed.
      4. The right hemisphere handles our sense of self – who we are and how we look.
    2. 90% of people are right-handed. 96% of these folks process speech in the left hemisphere. But, only 70% of left-handers process speech in the left hemisphere.
      1. Left or right handedness seems to be genetic in some way.
      2. Left-handers have more reading disabilities, allergies, and migraines. But they seem better than righties at music, math, and art.
    3. These facts illustrate the overall theme of this chapter – biology influences everything psychological.

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