Unit One. Biological Basis of Behavior
1.1. Interaction of Heredity and Environment
40 Studies Reading 3 (Twin Study)
The Tabula Rasa (think of a blank writing surface). This is an idea associated with John Locke, Rene Descartes, and other empiricist philosophers who assume everything we ever are to know or become depends entirely on our experiences—from childhood to adulthood. Who we are is determined entirely by our environment—our parents, teachers, friends and siblings, and all of the interactions we had with them. Why do some people become saints and others vicious criminals? They surely were not born that way. They learn to be what they are.
But is this all there is? Some children brought up in perfectly normal, respectable families turn out quite badly, and for no apparent reason. Others grow up in growling poverty and violence and become hardworking, honorable citizens. Why? And how could any sort of experiment determine whether our inherited natures or our experiences as babies, children, and young adults made us who we are?
The Minnesota Study of Twins Reared Apart (40 studies reading 3), provides us with one tool to explore the role of nature and nurture. The researcher, Thomas Bouchard, focused on monozygotic (i.e. identical) twins who had been reared apart for some reason and demonstrated that, while genetic influences are important, identical twins reared apart are only fifty percent similar. Even though they share DNA, identical twins are just as much unique individuals as they are twins.
Behavior Genetics: looking at the human genome to learn how genetic changes influence behavior and personality.
The Biopsychosocial Approach considers the way we learn to respond to the world influences our thought processes and behavior. Someone with a genetic tendency toward a trait like extroversion or introversion might be encouraged or discouraged in that direction by social pressures.
Gene Expression: Though we have genes that influence us in in one direction or another, not all genes are expressed. Some behaviors like smoking, drinking alcohol, and overeating might cause a preexisting gene to express itself in diabetes or cancer. Someone with the same genetic code who lives differently may never have to deal with the expression of those problematic genes. Or not. Following the rules of a healthy lifestyle will improve our chances of avoiding some diseases but guarantees nothing. There are heavy smokers who live into their nineties and marathon running non-smokers who do not live to see their grandchildren born.
1.2 Overview of the Nervous System
Central Nervous System (brain and spinal cord)
Peripheral Nervous System (connects sensory and motor neurons to the CNS.
Neural Networks
Reflex and automatic responses (neural pathways, interneurons)
PNS: autonomic nervous system and somatic nervous system
ANS: sympathetic nervous system and parasympathetic nervous system
Sympathetic: Fight or Flight
Parasympathetic: Rest and Digest
1.3. The Neuron and Neural Firing
a. Neural Communication and the Endocrine System
Sensory or afferent neurons
Efferent neurons
Interneurons
Neurons: Dendrites, soma, axon, myelin, terminal branches, neurotransmitters, synaptic gap, action potential. Depolarization, Electrical synapse, chemical synapse.
Neural Firing: Action Potential, threshold, stimulus, depolarization, depolarization, refractory period, resting state.
Terminal buttons, neurotransmitters, vesicles, synaptic gap, receptor sites, reuptake
Neurotransmitters: antagonist neurotransmitters, agonist neurotransmitters
b. Substance Use Disorders and Psychoactive Drugs
Some drugs and poisons work by blocking uptake (antagonist) and preventing neurotransmitters from communicating with the dendrite. Agonists might mimic the structure of specific neurotransmitters causing our brains to respond to the drug rather than the neurotransmitter. Opiates mimic the effects of endorphins, which eventually prevents the production of normal endorphins.
Neurotransmitters left floating around in the synaptic gap after threshold and firing will be taken back up into the vesicles of the terminal branches. This is called reuptake. Some psychoactive drugs inhibit reuptake (reuptake inhibitors) in order to increase the level of neurotransmission. Since a lack of serotonin plays a major role in depression, various selective serotonin reuptake inhibitors (SSRIs) have played a major role in improving the symptoms of depression.
The Endocrine System operates through the bloodstream rather than through the nerves, causing its messages to move more slowly but to stay around longer. If you receive a sudden fright (BOO!), your heart will continue racing long after you realize that there was nothing to be afraid of.
Pituitary Gland produces oxytocin: metabolism, emotion, sleep, blood pressure
Pineal Gland produces melatonin: circadian rhythm
Thyroid Gland produces thyroxine, metabolism
Adrenal Glands (adrenalin), fight or flight, heart rate and BP.
Pancreas produces insulin which turns blood sugar into energy
Testes and ovaries produce sex hormones estrogen and testosterone, promotes growth. . .
1.4. The Brain
a. Neuroplasticity and Tools of Discovery
EEG
PET
CT
MRI
fMRI
Case Studies
Split Brain Studies and the corpus callous (Roger Sperry)
Left and right hemispheres
Motor Cortex
Formation of neural pathways
Neurogenesis
b. Brain Regions and Structures
Brainstem
Midbrain
Pons
Medulla Oblongata (regulates heart rate, BP, respiration). The area postrema detects and regulates chemical messages in the blood, causes nausea and vomiting.
Thalamus (relays sensory input except for smell)
Cerebellum (balance)
Limbic System (emotions, drives, long term memory)
Amygdala (fear and aggression center)
Hippocampus (learning, long-term memory, spatial navigation)
Hypothalamus (Homeostasis and reward system: fight, flee, feed, mate)
Cerebral Cortex: frontal lobe, parietal lobe, temporal lobe, occipital lobe)
Association Areas (integrates information from other brain areas)
Wernike’s Area: language comprehension
Broca’s Area: speech production
Hemispheres connected by the corpus callosum.
Split brain experiments.
c. Brain Damage Response and Brain Hemispheres
Hemispheres connected by the corpus callosum.
Split brain experiments.
40 Studies, Readings 1, 2 (Split Brain, Experience)
1.5. Sleep
a. Consciousness:
b. Stages and Theories:
The Circadian Rhythm
Suprachiasmatic nucleus
Pineal Gland
Alpha waves and Beta Waves (EEG)
NREM 1
NREM 2 (sleep spindles)
NREM 3 (delta waves)
REM Sleep
c. Sleep Loss, Sleep Disorders, Dreams
Insomnia and Narcolepsy
Sleep apnea
Night terrors (NREM 3)
REM Rebound
Dreaming:
Freud, The Interpretation of Dreams: Manifest and Latent Content, wish fulfillment and unconscious drives.
Or, dreams may reveal nothing at all.
Hallucinations: perceiving sights, sounds, smells that are not “there.” Since perception happens in the brain, hallucinations seem no less real than things that are “really” there. Just because something is “just in your mind” does not make it less real, or does it?
Sleeping and Dreaming are states of consciousness. Someone who is unconscious cannot be awakened and has no perception of the passage of time. We experience different levels of consciousness throughout the day from first awakening to fully alert and engaged to day dreaming and drifting off to sleep again.
40 Studies, Readings 6. 7, 8 (Sleeping, Dreaming, Hypnotism)
1.6. Sensation:
a. Basic Concepts:
Our bodies are impacted by heat and cold, sunlight and cold winds, pointy things, scratchy things, noises, tastes and smells. Our sensory organs receive the sensations through our senses of sight, taste, smell, hearing, and touch and convert them into meaningful sensations. If a tree falls in the forest and no living creature is there to hear it, it may create vibrations in the air and in the ground, but it makes no “sound.” Sound requires sensory organs and functioning brains.
In addition to the five senses we have vestibular senses (Am I upright? Inside down?) and body position senses (where is my leg?).
Sensation becomes perception through top down and bottom up processing.
The sensory receptors associated with our different senses send messages to the appropriate brain structure which interprets them in bottom up processing.
Your brain constructs perception out of sensory information. This happens in sensory adaptation and sensory adaptation.
Gestalt Principles: our tendency to create whole images out of discrete parts. Our brains fill in the blanks and interpret a whole image out of a few parts.
Sensory Transduction: happens when sensory information is converted from one form of energy (sound or light waves, pressure on the skin, light in the eyes . . .) into the electrochemical messages of the nervous system which are interpreted by the brain.
The Absolute Threshold (Gustav Fechner): the minimum stimulation needed for detection. On a dark night, how far away can you detect a candle, how faint can a noise be for you to still hear it?
Some stimuli are subliminal: You are not consciously aware that you are receiving the stimuli though it may still influence your behavior.
Signal Detection Theory
Difference Threshold
b. Vision: Light presents itself as particles or as waves.
Corpuscular Theory: Isaac Newton proposed a theory of light as particle (which he called corpuscles but which modern physicists call photons). Photons have not mass and travel through a vacuum at 186, 282 miles per second. Since the sun is 93 million miles from the earth, it takes 8 minutes and 20 seconds for a photon fired from the sun to reach the earth. The most distant visible object in the universe (a galaxy called HD1) is 13.3 billion light years distant, which means that the photons reaching the Hubble Space telescope today left HD1 13.3 billion years ago and what we are seeing (through Hubble) is a picture from the early history of the universe—a long time ago in a galaxy far, far away.
Wave Theory: Light, and other forms of electromagnetic radiation can also act like waves rather than particles. Acting like particles, light travels at, literally, the speed of light. All kinds of radiation (X rays, radio signals. . . ) travels at the same speed. But light also travels in waves which are not at all like particles. If you drop a stone into a calm body of water, you will see waves radiating out from the point of impact. Sound does the same thing. If you examined the waves more carefully, you would notice that the waves travel in regular patterns of peaks and valleys as they spread across the water, bounce off the sides of the pool and interact with oncoming waves. The distance between the peaks of two waves is the wavelength. The hight of the waves is the amplitude. Within the spectrum of light waves that are visible to humans, wavelength determines the color we perceive. Amplitude determines the brightness. Lightwaves with relatively long wave lengths (and thus low frequency) are perceived as red. Lightwaves with relatively short wavelengths (and higher frequency) are perceived as blue and violet. Light waves beyond our ability to perceive are either infrared (below red, which we experience it as heat) or ultraviolet (above violet, which we tend not to perceive at all but which causes sunburn and, eventually, skin cancer).
Eyes have evolved to transduce a sliver of the electromagnetic spectrum—what we call visible light—into electrochemical signals that can be interpreted by the brain as meaningful shapes and colors. Some animals (birds, bees, and a few others) have eyes that permit them to see beyond the spectrum of colors visible to humans. Others (your dog, for example), have limited ability to perceive color but get along just fine in a world made up mostly of shades of grey. Some people are born with or have acquired color blindness which not only causes them to confuse blues and greens, but to be unable to see any colors beyond black, white, and shades of gray.
You are able to move your eyes with a set of small muscles that attach to the front of your eyeballs. Your eyes are protected by the conjunctiva which lines the outer front surface of the eye and the inner surface of the eyelid. Pinkeye is often an inflammation of the conjunctiva and is thus conjunctivitis.
The Cornea is the clear outer surface of the front of the eye through which light passes before entering the anterior chamber (which is filled with the aqueous humor) and then the pupil, the open space at the center of the iris (the colored part of the eye—essentially a sphincter muscle which closes and opens the pupil to adjust for different levels of ambient light.
Light passes from the pupil into the lens which is able to be focused at different distances. The lens focuses the incoming light onto the retina where the transduction of light into action potential takes place.
The Retina is made up of two types of photoeceptors, rods and cones.
Rods perceive motion and allow us to “see” in black and white, especially in low light situations. Rods are found throughout the retina.
Cones are concentrated in the macula, the central focal point at the back of the eye. Cones allow us to see in color and are concentrated around and in the fovea, a depression at the back of the eye where vision is sharpest. When you focus on bluebird singing in the distance, you are focusing the image of the bird (and the colors of the bird) onto your fovea.
The rods and cones are connected to the optic nerve by a series of ganglion and bipolar cells.
The point in the back of your eye where the optic nerve intersects the retina lacks any photoreceptor cells, creating a blindspot.
The outer covering of the eye is the sclera (the whites of your eyes). Between the sclera and the retina is the choroid which is made up of blood vessels and keeps the retina supplied with oxygen and nutrition.
The main body of the eye is inflated by the vitreous humor, a clear liquid with the consistency of Jello.
Theories: How do we see color?
Young-Helmholtz Trichromatic Theory: Posits three kinds of color receptors—RBG—which combine to create all of the colors we can see. This conveniently explains color blindness. If one is missing one or more of the color sensors, one will not be able to discern the full palette of colors.
Ewald Hering: Opponent-Process Theory. Some neurons are turned on by red and off by green. On by blue and off by yellow. On by black and off by white.
Seeing happens in the brain, but first the signals have to get from the photoreceptors in the retina to the visual cortex of the brain (which is located in the occipital lobe.
You have (presumably) two eyes. The visual receptors on the left sides of both eyes send their signals via the left optic nerve to the visual cortex of the left hemisphere. The visual receptors on the right sides of both eyes sends their signals to the visual cortex on the right hemisphere. If you see with only one eye, you are still engaging both hemispheres. The optic nerves cross over each other at the optic chiasm before reaching the lateral geniculate nucleus, a relay station of sorts within the thalamus. From the geniculate nucleus visual signals travel to the visual cortex along the optic radiation.
Seeing happens within the visual cortex which means that damage to the back of the head can impact our ability to interpret the signals coming into the brain from the retina. For example, patients with damage to the visual cortex might have perfect eyesight but be completely incapable of recognizing faces—even their own face staring at them from the mirror, a condition called prosopagnosia.
Visual Perception: Though our eyes might perceive light and color, we have not really seen something until our visual cortex has interpreted the signals received from our eyes and given them meaning. Visual meaning takes several key forms:
Form (or gestalts): Figure-ground
Group Principles: we group similar figures together (like players on a team)
Proximity: We group nearby figures together (thus, we create constellations from randomly distributed start which happen to be grouped together.
Continuity: we create continuous patterns out of discrete dots.
Closure: We fill in gaps to create whole objects (think of the Big Dipper in the night sky).
Connectedness: We perceive units that are uniform and linked as a single unit: Basketball huddled together form a single perceptual unit.
Depth Perception:
Monocular cues: relative height, relative size, interposition, motion parallax, linear perspective, light and shadow
Binocular cues: retinal disparity
Motion Perception (I couldn’t understand why the Frisbee kept getting bigger and then it hit me.)
Stroboscopic movement (like animated cartoons or flipbooks). Fewer than 24 frames per second makes an image look choppy. HDTV is able to run at much higher speed, which creates more realistic images.
c. Hearing (Audition):
Sound begins with sound waves (waves of compression, much like waves on the surface of a pond. Waves are measured by frequency (greater frequency —less distance between waves—produces a higher pitch). The amplitude of the sound waves (the distance from trough to crest) determines how loud the sound is that we are perceiving. Amplitude is measured in units called decibels (dB). As you breath normally, you are producing about ten dB. A passing ambulance with siren screaming produces about 120 dB. Prolonged exposure to sound levels over 85 dB or even brief exposure to sounds at 140 dB can cause irreversible hearing loss.
Parts of the Ear:
Outer Ear: The pinna, auditory canal, eardrum (tympanic membrane)
Middle Ear: hammer (malleus), anvil (incus) and stirrup (stapes)
Inner Ear: Cochlea.
Transduction takes place in the cochlea, a fluid filled, spiral shaped (kind of like a snail) body in the inner ear. Sound waves are transmitted to the cochlea through the bones of the middle ear. The shape of the cochlea causes different frequencies to be received by tiny groups of hair cells within the organ. As the hair cells vibrate the organ of Corti converts the movement of the hairs into action potential: messages which travel down the auditory nerve to the auditory cortex located in the temporal lobe.
d. Skin, Chemical, and Body Senses and Sensory Interaction
Chemical Senses include taste (gustation) and smell (olfaction)
Taste (which involves both taste and smell), is created when our taste buds (mostly on the tongue) encounter chemicals that are interpreted as having taste: salty, sweet, sour, bitter, and umami.
About a quarter of the population has a gene that causes them to taste bitter flavors at levels most people would not notice. This group is referred to as super tasters. If you hate broccoli spinach, brussels sprouts or turnips, you may be a super taster.
Messages from the taste receptors on the tongue pass through the thalamus to the gustatory cortex in the frontal lobe. The perception of taste is almost always influenced by olfaction.
Olfaction: Smell receptors are located in in the sinus cavity behind the nose. Humans have about four million smell receptors. Dogs—especially species like the bloodhound—have 300 million. Whenever we inhale airborne molecules from a bowl of fresh popcorn, a cup of coffee, or a dead skunk (anything with a smell) some of these molecules will connect with receptors specific to the molecule. If we do not have a receptor for a particular smell, we don’t smell it. The message from the olfactory receptors go first to the olfactory bulb and then to the amygdala and hippocampus.
Most smells are complex. A steak cooking on the grill produces a variety of airborne molecules that are received and interpreted within the Olfactory Cortex located very near the sinuses in the frontal cortex.
We remember and make associations with smells (the work of the amygdala) even when we are not able to put a name to the smell which is the basis of the multibillion dollar perfume industry.
One of the more distressing symptoms of long Covid is that the disease not only damages the sense of smell, it confuses it. A steak on the grill might smell like burning car tires. Coffee smells (and tastes) like kerosine.