Biological Approach to Psychology

One of psychology's largest and most highly contested debates is the nature versus nurture issue, arguing which plays a greater role in psychological traits or behaviors - genes and heredity or environment?

The biological approach to psychology focuses on how the body and brain enable emotions, memories, and sensory experiences and how our genes and heredity influence our individual differences. 

Everything psychological is biological. 

Breakdown of Genes & Heredity

• Chromosomes: threadlike structures made of DNA molecules that contain the genes

• DNA: a complex molecule containing the genetic information that makes up the chromosomes

• Genes: biochemical units of heredity that make up the chromosomes; segments of DNA capable of synthesizing proteins

• Genome: the complete instructions for making an organism, consisting of all the genetic material in that organism’s chromosomes

• Molecular genetics: the subfield of biology that studies the molecular structure and function of genes

• Heritability: the proportion of variation among individuals in a group that we can attribute to genes 

• Epigenetics: the study of environmental influences on gene expression that occur without DNA change
  
  

Behavior Genetics

If a musician's children grow up to be superstars, can we attribute their talent to genes or environment?

Behavior geneticists are those who study the relative power and limits of genetic and environmental influences on behavior.

• Heredity: the genetic transfer of characteristics from parents to offspring

• Environment: every nongenetic influence, from prenatal nutrition to the people and things around us

Behavior geneticists explore the genetic and environmental roots of human differences. Evolutionary psychologists, however, focus on what makes us alike as humans, primarily by exploring the principles established by Charles Darwin. 

• Natural selection: the principle that inherited traits that better enable an organism to survive and reproduce in a particular environment will (in competition with other trait variations) most likely be passed on to the succeeding generations

• Mutation: a random error in gene replication that leads to a change

Twin & Adoption Studies

Evolutionary psychologists presume all human behaviors reflect the influence of physical and psychological predispositions that helped human ancestors survive and reproduce. To study this, researchers observe twins.

Identical vs. Fraternal Twins

• Identical or monozygotic twins develop from a single fertilized egg that splits, meaning all the genes are the same.

• Fraternal or dizygotic twins develop from different eggs that were fertilized simultaneously, so they share the same genes as siblings but are not identical.

Twin studies are a favorite of psychologists because they provide the perfect opportunity to test the nature vs. nurture debate. Identical twins raised in the same household should be the same, right? Not always. Just as identical twins separated at birth and raised in different environments often have many similarities. 

Parts of the Brain

The oldest part of the brain is the brain stem, found at the base of the skull above the spinal cord. Often referred to as the "reptilian brain", the structures within the brain stem are responsible for automatic survival functions.

• Reticular Formation: a nerve network that travels through the brainstem into the thalamus and plays an important role in controlling arousal

  • If severed or damaged, you could be in a state of permanent sleep or wakefulness.

• Medulla: the base of the brainstem that controls breathing and heartbeat

  • If severed or damaged, you’ll most likely die or be on life support.

• Pons: Connects hindbrain, midbrain, forebrain together; involved in respiration and REM sleep, also serves as a communications and coordination center between the two hemispheres of the brain

Next to the brainstem is the cerebellum or “Little brain”, which coordinates movement and balance, processes sensory input, judgment of time, and enables nonverbal learning and memory. 

• • One of the first parts of the brain impacted by alcohol, thus explaining why people stagger and struggle to react quickly when intoxicated.

Above the brainstem is the thalamus, which serves as the sensory “switchboard”, directing messages to the sensory receiving areas in the cortex and transmitting replies to the cerebellum and medulla. 

• • Receives sensory information from all senses except smell

At the core of the brain is the limbic system, a series of structures associated with emotions and drives.

• • Amygdala: responsible for survival emotions of fear and aggression

  • Hippocampus: responsible for processing and storing explicit memories of facts and events

  • Hypothalamus: below the thalamus; direct several maintenance behaviors, like eating, drinking, and maintaining optimal body temperature, helps regulate the endocrine system via the pituitary gland, and is linked to emotion and reward

Connecting the two hemispheres together is the corpus callosum, a network of fibers allowing for communication between both sides of the brain and body.

• • Can be severed as a treatment for epilepsy, but has some interesting effects (see split-brain studies)

Any areas of the cerebral cortex that are not involved in primary motor or sensory functions, but are rather involved in higher mental functions such as learning, remembering, thinking, and speaking are known as association areas. These areas help us produce a meaningful perceptual experience of the world, enable us to interact effectively, and support abstract thinking and language. 

The cerebral cortex is the intricate fabric of interconnected neural cells covering the cerebral hemispheres that functions as the body’s ultimate control and information-processing center. It plays a key role in memory, attention, perceptual awareness, thinking, speaking, and consciousness, and is organized into lobes based on function:

• • Frontal

    1. Behind your forehead, largest lobe

    2. Involved in our executive functions: 

       1. Ability to recognize future consequences

       2. Making judgements 

       3. Planning & decision making

       4. Abstract thought

       5. Personality 

    3. Contains motor cortex: sends signals to our body controlling muscle movements.

    4. Contains Broca’s Area: responsible for controlling muscles that produce speech

       1. Broca’s Aphasia: problems with fluency in speech production due to damage

  • Parietal

    1. Top of the head

    2. Receives sensory input for touch sensations (pain, pressure, temperature) and body position

    3. Contains somatosensory cortex: specified area of the parietal lobe that takes in sensory input from corresponding body parts

    4. Angular gyrus: written language and number processing, spatial recognition, and elements of memory

  • Temporal

    1. Above the ears

    2. Includes auditory areas, each receiving input from the opposite ear (contralateral control) 

    3. Contains Wernicke’s Area: responsible for language comprehension

       1. Wernicke’s aphasia: problems with meaning of speech due to damage; the syntax and grammar jumbled

    4. Auditory cortex: organization and processing of auditory information

    5. Assists with memory

  • Occipital

    1. Back of the head, above the cerebellum 

       1. This is why a hit to the back of your head could make you “see stars” or temporarily blur your vision.

    2. Receives information from the visual fields of opposite eyes for visual processing (contralateral control)

    3. Visual cortex: organization and processing of visual information

Neurogenesis, Neuroplasticity, & Neurological Disorders

Your brain is not only sculpted by your genes but by your life. Your brain is constantly changing, reorganizing itself for your needs without your awareness. Neuroplasticity refers to the brain’s ability to change, build, and reorganize after damage or experience. This process is easier for children than it is for adults. The whole “you can’t teach an old dog new tricks” thing. 

Although the brain will try to mend itself by reorganizing existing tissue, it sometimes has to produce new neurons, a process known as neurogenesis.

Complications among brain structure/chemistry, damage to the nervous system, and genetic anomalies can lead to neurological disorders such as multiple sclerosis or myasthenia gravis. 

Case Study: Phineas Gage

While scientists have always been fascinated with studying the brain, a favorite case is that of railway worker Phineas Gage, who in the mid 1800s survived a major brain injury which caused several changes to his personality, behavior, and performance. There are mixed reports of how extensively this accident changed Phineas, but it did confirm different brain regions are responsible for different functions.

Viewing the Brain

Only in recent years have scientists had the ability to view the brain in an non-invasive and painless way. Prehistoric skulls show evidence of trephination, or drilling holes into the skull to “release evil spirits”. In some cases today, skulls will be drilled into and brain tissue destroyed (lesioned), but that is for the purpose of behavior modification and only as a last resort. Otherwise, research on the brain involves the following techniques:

• Electroencephalogram (EEG)

• Magnetoencephalography (MEG)

• Computed tomography (CT)

• Positron Emission tomography (PET)

• Magnetic resonance imaging (MRI)

  • Functional Magnetic Resonance Imaging (fMRI)

Split-Brain Studies

The lateralization of brain function is the tendency for some neural functions or cognitive processes to be specialized to one side of the brain or the other. 

Patients with severe epileptic seizures found treatment in the form of the split-brain procedure, where their corpus callosum was cut. It eliminated their seizures, but caused some difficulty in basic tasks as the two hemispheres couldn’t communicate with each other. 

In an early experiment, Gazzaniga asked split-brain patients to stare at a dot as he flashed HE·ART on a screen. Thus, HE appeared in their left visual field (which transmits to the right hemisphere) and ART in the right field (which transmits to the left hemisphere). When he then asked them to say what they had seen, the patients reported that they had seen ART. But when asked to point to the word they had seen, they were startled when their left hand (controlled by the right hemisphere) pointed to HE. Given an opportunity to express itself, each hemisphere indicated what it had seen. The right hemisphere (controlling the left hand) intuitively knew what it could not verbally report.

What is consciousness?

Most psychologists define consciousness as our subjective awareness of ourselves and our environment. The strengths and limitations of this awareness are largely debated, and can be altered by outside influences.

• Hypnosis

• Meditation

• Psychoactive Drugs

• Sleep & Dreams

Consciousness offers a reproductive advantage by helping us cope with novel situations, read the emotions of others, and follow through on long-term goals. Cognitive neuroscience is the study of the brain activity linked with cognition, including language, perception, memory, and thinking. 

At any moment, we are aware of little more than what is in our conscious awareness, but beneath the surface, unconscious information processing takes place simultaneously. This is known as dual processing. If you see a bird in flight, you’ll be consciously aware of which type of bird it is if you know, but unconsciously be taking in information about its color, size, movement, etc. Our ability to take in information about the look and movement of the bird simultaneously is known as parallel processing. 

This alternative to this is sequential processing, in which we process one aspect of a problem at a time. This is used for processing new information or solving difficult problems. Move your dominant foot in a counterclockwise direction while writing the number 3 repeatedly at the same time. This difficult task will often result in your foot going in the direction of the writing the number 3 or your hand drawing circles.

Blindsight is a condition in which a person can respond to a visual stimulus without consciously experiencing it. This is used to help explain how those without sight can sense objects in their environment.

Biological Rhythms

Sleep is a periodic, natural loss of consciousness - as distinct from unconsciousness resulting from a coma, general anesthesia, or hibernation. In other words, even in sleep, you still have some level of awareness, that’s why you don’t roll off the top bunk, the music from your headphones might end up in your dreams, or why that prank of putting a sleeping friend’s hand in warm water works. 

Why do we sleep?

• Protection

• Recuperation

• Restore/rebuild memory

• Feeds creative thinking

• Growth

What causes problems with sleep?

• Age

  • Newborns need 16 hours of sleep, teenagers need 9, while most adults can survive on 6.

• Genetics

• Environment

• Brain

  • Suprachiasmatic nucleus (SCN): a pair of cell clusters in the hypothalamus that control circadian rhythm 

  • Pineal gland: adjust melatonin levels

  • Reticular formation: monitors sleep and wake cycle

• Exposure to Light

Sleep is part of our circadian rhythm - our biological clock that regulates our mood, temperature, and arousal through a 24-hour cycle. As morning approaches, our body temperatures rise and we begin to wake up. Our temperature and arousal peak around midday, then start to dip as we approach dusk. This is why most people prefer to sleep in colder temperatures - it helps you fall asleep faster.

Circadian rhythms can be thrown off by a change of time zones (jetlag) or a certain work schedule. They can also vary by age and individual (night owls vs. morning larks).

• Other biological rhythms include:

• 90-minute sleep cycles

• 28-day menstrual cycles

• Annual → Hibernation/Migration

• Mating seasons

Sleep Cycles

About every 90 minus, we cycle through distinct sleep stages: NREM or non- rapid eye movement sleep and REM or rapid eye movement sleep.

• NREM-1: light sleep, easily awoken → alpha waves

  • Can experience hallucinations (false sensory experiences) and hypnagogic sensations (bizarre experiences such as jerking with a sensation of falling)

• NREM-2: fully asleep → theta waves with sleep spindles (random short bursts of activity) & k-complexes (random tall bursts of activity)

• NREM-3: deep sleep → delta waves

• REM: body relaxed as if paralyzed but brain as active as if it was awake (paradoxical sleep) → beta waves

  • Becomes longer & more frequent as night progresses

  • Vivid dreams occur

  • REM Rebound: If deprived of REM sleep, a person will spend more time in REM the next time they go to sleep. 

Effects of Sleep Loss & Deprivation

After oxygen, food, and water, the thing our body needs most is sleep. If we do not sleep, or do not get enough sleep, our body makes it known to us how badly it needs a break. Research shows that inadequate sleep can make you more likely to:

• Struggle with focus and concentration

• Gain weight

• Get sick

• Be irritable and/or depressed

• Feel old

  • Not-so-fun fact: Driving sleep deprived is as dangerous as driving drunk. 

Sleep Disorders

• Insomnia: recurring problems falling or staying asleep

• Narcolepsy: a sleep disorder characterized by uncontrollable sleep attacks; sufferer may lapse directly into REM sleep

• Sleep Apnea: a sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings 

• Night Terrors: a sleep disorder characterized by  high arousal and an appearance of being terrified; unlike nightmares, night terrors occur during NREM-3 sleep and are not remembered

• Somnambulism: sleepwalking

• Somniloquy: sleep talking

Nightmares, Night Terrors, & Dreams

Nightmares are emotional dreams, occurring during REM sleep with our bodies still and you are able to remember it. Night terrors affect the body very strongly, causing the heart to pound, breathing rate to increase, and blood pressure rises. You are unable to remember the event, able to move during the episode, and occurs in the first 3 hours of sleep. 

Dreams are sequences of images, emotions, and thoughts passing through a sleeping person’s mind. Although dreams can occur at any stage of sleep, they are most vivid during REM sleep. 

Why do we dream? 

• Wish-Fulfillment 

  1. Suggested by Sigmund Freud

  2. Dreams are simply ways we play out all of the things we want to do subconsciously-hidden wishes.

  3. Believed in two parts to dreams - manifest & latent content

     1. Manifest content: actual content of the dream

     2. Latent content: hidden or symbolic meaning of the dream

• Information Processing 

  1. A.k.a problem-solving theory

  2. The most widely accepted theory

  3. Dreams are a way to deal with/sort out the stresses of everyday life

  4. This theory states that we tend to dream more when we are more stressed

• Activation Synthesis 

  1. Developed by Allan Hobson and Robert McCarley.

  2. Limbic system becomes active as we are in REM and randomly fires

  3. Our cerebral cortex is trying to interpret random electrical activity we have while sleeping

  4. That is why dreams sometimes make no sense

  5. The brain's efforts to make sense out of meaningless patterns of firing in the brain as we sleep

• Physiological Function

  1. Dreams provide the sleeping brain with periodic stimulation to develop and preserve neural pathways. 

  2. Neural networks of newborns are quickly developing; therefore, they need more sleep.

  3. 
     

• Cognition 

  1. Dreams are the expression of a person's thoughts

  2. A dream is conceived as a pictorial representation of the dreamer's conceptions, usually about himself, other people, the world, impulses, prohibitions, penalties, and conflicts

  3. The reveal the structure of how we envision our lives

Common Dream Topics

• Negative Emotional Content: 8 out of 10 dreams have negative emotional content.

• Failure Dreams: People commonly dream about failure, being attacked, pursued, rejected, or struck with misfortune.

• Sexual Dreams: Contrary to our thinking, sexual dreams are rare. Sexual dreams in men are 1 in 10; and in women 1 in 30.

• Dreams of Gender: Women dream of men and women equally; men dream more about men(their buddies or co-workers) than women.

• Lucid dreaming: knowing that you are dreaming and occasionally being able to control aspects of your dream

• Sleep paralysis a feeling of being conscious but unable to move, occurring when a person passes between stages of wakefulness and sleep. During these transitions, you may be unable to move or speak for a few seconds up to a few minutes. 

Psychoactive Drugs

Psychoactive drugs are chemical substances that alter perceptions and moods. While some psychoactive drugs can be used in moderation to help with concentration or pain relief, others can lead to addiction and substance use disorder (a disorder characterized by continued substance craving and use despite significant life disruption and/or physical risk. 

When is drug use a disorder?

• Diminished control & social functioning

• More is needed to get the desired effect

• It is hazardous to use

Dependence/Addiction

• Many psychoactive drugs can be harmful to the body.

• Psychoactive drugs are particularly dangerous when a person develops an addiction or becomes  physically and/or psychologically dependent on the substance.

Factors related to addiction: 

• Tolerance: diminished psychoactive effects after repeated use

• Withdrawal: painful symptoms of the body re-adjusting to the absence of the drug.

• impact on daily life of substance use

• physical and psychological dependence

Types of Drugs:

• Stimulants - excite neural activity

  • Increase energy, decrease appetite, brief feelings of euphoria

  • Speed up (stimulate) bodily processes

  • Ex. caffeine, nicotine, cocaine, amphetamines (meth)

• Depressants - reduce neural activity

  • Increase relaxation and pain relief, decrease mood and arousal

  • Slow down (depress) bodily processes

  • Ex. alcohol, barbiturates, opiates (heroin)

• Hallucinogens - distort perception

  • Cause false sensory hallucinations, impair memory, feelings of relaxation and/or euphoria

  • Ex. marijuana, mushrooms, LSD, ecstasy/MDMA (also a stimulant)

How do drugs affect the body?

Psychoactive drugs primarily work by stimulating, inhibiting, or mimicking neurotransmitter activity. The prolonged and excessive use of alcohol (also known as alcoholism or alcohol use disorder) can shrink the brain, disrupt memory formation, reduce inhibitions, and slow functioning. 

Other States of Consciousness

Near Death Experiences

Another state of consciousness is a near-death experience, when individuals report strange sensations or vivid visions following a close brush with death (similar to drug-induced hallucinations). 

Hypnosis

Hypnosis is a social interaction in which one person (the hypnotist) suggests to another (the subject) that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur. Hypnosis is also described as a systematic procedure that typically produces a heightened state of suggestibility. 

In psychology, hypnosis has been used to unlock repressed memories, overcome traumatic experiences, treat phobias, and cure addiction. Some phenomena associated with hypnosis include:

• Analgesia: treatment of acute and chronic pain (used by dentists/doctors as a substitute for anesthetic)

• Sensory distortions and hallucinations: sensing things that are not present, or failing to sense things that are

• Disinhibition: effect of hypnosis that removes boundaries that would typically prevent subject from performing specific actions (social norms, illegal acts, etc.)

• Posthypnotic amnesia: supposed inability to recall what one experienced during hypnosis; induced by the hypnotist’s suggestion

• Posthypnotic suggestion: a suggestion, made during a hypnosis session, to be carried out after the subject is no longer hypnotized; used by some clinicians to control undesired symptoms or behaviors

Meditation

Meditation refers to a family of practices that train attention to heighten awareness and bring mental processes under greater voluntary control. There are two types of meditation:

• Focused attention: attention is concentrated on a specific object/image/sound/sensation

• Open monitoring: attention is directed to the contents of one’s moment-to-moment experience in a nonjudgmental and nonreactive way

Unit 1 Vocabulary

• absolute threshold: the minimum stimulation needed to detect a particular stimulus 50% of the time.

• accommodation: in vision, the process by which the lens of the eye shifts to focus on a particular object. 

• acetylcholine: A neurotransmitter involved in muscle activation, memory, and learning.

• action potential: a brief electrical charge that travels down the axon of a neuron, generated by the movement of positively charged atoms in and out of channels in the neuron's membrane.

• activation-synthesis theory: A theory of dreaming that suggests dreams are the brain's attempt to make sense of random neural activity.

• adaptation: the process by which a species becomes fitted to its environment through natural selection

• addiction: a complex condition characterized by compulsive drug use or behaviors despite harmful consequences.

• agonist: a drug or chemical that enhances the activity of neurotransmitters.

• alcohol: A depressant that slows down the central nervous system, impairing cognitive and motor functions.

• all-or-none response: the principle that a neuron either fires completely or does not fire at all.

• alpha waves: the relatively slow brain waves associated with relaxation and wakefulness.

• amplitude: The height of a wave, which determines the loudness of a sound.

• amygdala: the limbic system structure involved in processing emotions, particularly fear and aggression.

• antagonist: a drug or chemical that inhibits or blocks the action of neurotransmitters.

• aphasia: A condition characterized by the loss of ability to understand or express speech.

• association areas: areas of the cerebral cortex that are not involved in primary motor or sensory functions but are involved in higher mental functions such as learning, remembering, thinking, and speaking

• audition: the sense of hearing

• auditory Cortex: The part of the brain that processes auditory information.

• autonomic nervous system: the part of the peripheral nervous system that controls involuntary functions like heart rate, digestion, and glandular secretions

• axon: the extension of a neuron through which neural impulses are sent.

• barbiturates: a class of drugs that depress the activity of the central nervous system, reducing anxiety but impairing memory and judgment.

• behavior genetics: the study of the relative power and limits of genetic and environmental influences on behavior.

• biological psychology: a branch of psychology concerned with the links between biology and behavior.

• biopsychosocial approach: an integrated approach that incorporates biological, psychological, and social-cultural levels of analysis.

• blind spot: the point at which the optic nerve leaves the eye, creating a small gap in the field of vision.

• blindsight: condition in which a person can respond to visual stimuli without consciously experiencing them.

• bottom-up processing: analysis that begins with sensory receptors and works up to the brain's integration of sensory information.

• brainstem: the oldest part and central core of the brain, responsible for automatic survival functions.

• Broca's Area: A region in the frontal lobe of the brain associated with speech production.

• caffeine: A stimulant found in coffee, tea, and many soft drinks that increases alertness and reduces fatigue central nervous system: the brain and spinal cord, responsible for processing and coordinating information.

• cerebellum: structure in the hindbrain that helps coordinate voluntary movement and balance.

• cerebral cortex: the outer layer of the brain responsible for complex cognitive processes such as thinking, planning, and language.

• Charles Darwin: English naturalist who proposed the theory of evolution by natural selection.

• circadian rhythm: the biological clock; regular bodily rhythms that occur on a 24-hour cycle.

• cocaine: A powerful stimulant drug that increases levels of dopamine in the brain, leading to intense euphoria and increased energy.

• cochlea: coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses.

• cochlear implant: device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.

• cognitive neuroscience: the interdisciplinary study of the brain activity linked with cognition (including perception, thinking, memory, and language).

• computed tomography (CT): scanning technique using multiple X-rays to construct a 3D image of the brain's structure.

• conduction hearing loss: hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.

• cones: photoreceptor cells in the retina that are responsible for color vision and fine detail.

• consciousness: our awareness of ourselves and our environment.

• consolidation theory: The theory that sleep helps strengthen the neural connections that form our memories.

• contralateral control: The principle that each hemisphere of the brain controls the opposite side of the body.

• cornea: the transparent outer layer of the eye that covers the pupil and iris and helps focus incoming light.

• corpus callosum: the large band of neural fibers connecting the two brain hemispheres and carrying messages between them.

• David Hubel: Canadian neurophysiologist known for his work with Torsten Wiesel on the processing of visual information in the brain.

• delta waves: the large, slow brain waves associated with deep sleep.

• dendrites: branchlike extensions of a neuron that receive messages and conduct impulses toward the cell body.

• depolarization: The process by which a neuron's membrane potential becomes less negative, leading to the firing of an action potential.

• depressants: drugs that reduce neural activity and slow body functions.

• dichromatism: A type of color blindness where one of the three basic color mechanisms is absent or not functioning.

• difference threshold: the minimum difference between two stimuli required for detection 50% of the time; also known as just noticeable difference (JND).

• dopamine: A neurotransmitter involved in reward, motivation, and motor control.

• dream: sequence of images, emotions, and thoughts passing through a sleeping person's mind.

• dual processing: the idea that information is simultaneously processed on separate conscious and unconscious tracks.

• electroencephalogram (EEG): recording of the electrical waves sweeping across the brain's surface, measured by electrodes placed on the scalp.

• embodied cognition: the theory that cognition is influenced by the body's interactions with the environment.

• endocrine system: the body's slow chemical communication system, consisting of glands that secrete hormones into the bloodstream.

• endorphins: neurotransmitters that are natural painkillers produced by the brain.

• environment: every nongenetic influence, from prenatal nutrition to the people and things around us.

• epigenetics: the study of environmental influences on gene expression that occur without a DNA change.

• Ernst Weber: German physician credited with the formulation of Weber's law, which describes the relationship between the magnitude of a physical stimulus and the intensity of its perceived sensation.

• eugenics: A controversial and unethical movement aimed at improving the genetic quality of the human population.

• evolutionary psychology: the study of the evolution of behavior and the mind, using principles of natural selection.

• excitatory Neurotransmitter: A neurotransmitter that promotes the firing of neurons.

• farsightedness (Hyperopia): A condition where distant objects can be seen clearly, but close objects appear blurry.

• feature detectors: nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement.

• fMRI: technique for revealing blood flow and, therefore, brain activity by comparing successive MRI scans.

• forebrain: the largest and most prominent part of the brain, including the cerebral cortex and subcortical structures.

• fovea: the central focal point in the retina, around which the eye's cones cluster.

• fraternal (dizygotic) twins: twins who develop from separate eggs and are no more similar genetically than non-twin siblings.

• frequency: the number of complete wavelengths that pass a point in a given time.

• frequency theory: the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.

• frontal lobes: the portion of the cerebral cortex lying just behind the forehead, involved in planning and judgment.

• GABA (Gamma-Aminobutyric Acid): The main inhibitory neurotransmitter in the brain.

• ganglion cells: Neurons in the retina that relay information from the photoreceptors to the brain.

• gate-control theory: the theory that the spinal cord contains a neurological "gate" that blocks pain signals or allows them to pass on to the brain.

• genes: the biochemical units of heredity that make up the chromosomes; a segment of DNA capable of synthesizing a protein.

• genome: the complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes.

• glial cells: cells in the nervous system that support, nourish, and protect neurons, and play a role in learning and thinking.

• glutamate: The main excitatory neurotransmitter in the brain.

• gustation: the sense of taste

• Gustav Fechner: German psychologist known for his work in psychophysics, particularly his development of Weber's law and the concept of the just noticeable difference.

• hallucinations: perceptions that have no direct external cause, arising from disorders such as schizophrenia, sensory deprivation, or drug-induced states.

• hallucinogens: drugs that alter perception and cause hallucinations or profound distortions in a person's perceptions of reality.

• heredity: the genetic transmission of characteristics from parents to offspring.

• heroin: An opioid drug that produces intense euphoria and pain relief, highly addictive.

• hindbrain: the lower part of the brainstem, comprising the medulla, pons, and cerebellum, responsible for basic life functions.

• hippocampus: a neural center located in the limbic system that helps process explicit memories for storage.

• hormones: chemical messengers produced by the endocrine glands and circulated in the bloodstream, regulating the activity of target cells or organs.

• hue: the dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, etc.

• hypnagogic sensations: experiences during the transition from wakefulness to sleep, including hallucinations, muscle jerks, and sensations of falling.

• hypothalamus: a neural structure lying below the thalamus, regulating bodily functions such as hunger, thirst, body temperature, and sexual behavior, and controlling the pituitary gland.

• identical (monozygotic) twins: twins who develop from a single fertilized egg that splits in two, creating two genetically identical organisms.

• inhibitory neurotransmitter: A neurotransmitter that inhibits the firing of neurons.

• inner ear: the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs, involved in balance and hearing.

• insomnia: persistent problems falling asleep and/or staying asleep.

• intensity: the amount of energy in a light or sound wave, which we perceive as brightness or loudness.

• interneurons: neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs.

• iris: the colored ring of muscle that regulates the size of the pupil by controlling the amount of light entering the eye.

• jet lag: A temporary sleep disorder that occurs when a person's internal body clock is out of sync with the time zone they are in.

• just noticeable difference (JND: The minimum difference in stimulation that a person can detect 50% of the time.

• kinesthesis: the sense of the body's position and movement of body parts relative to each other.

• lens: the transparent structure behind the pupil that changes shape to help focus images on the retina.

• lesion: damage to body tissue, often caused by disease or injury, but can be used to modify behavior by destroying targeted areas of brain tissue

• limbic system: set of structures in the brain, including the amygdala, hypothalamus, and hippocampus, involved in emotion, motivation, and memory.

• magnetic resonance imaging (MRI): technique that uses magnetic fields and radio waves to produce detailed images of the brain's soft tissue.

• magnetoencephalography (MEG): brain imaging technique that measures magnetic fields generated by neuronal activity in the brain.

• marijuana: A drug containing THC that alters mood, perception, and cognitive function.

• medulla: the base of the brainstem, controlling heartbeat and breathing.

• Michael Gazzaniga: pioneering neuroscientist known for his split-brain research, which revealed insights into the functional differences between the brain's hemispheres.

• midbrain: small region of the brainstem involved in auditory and visual processing and regulation of motor movements.

• middle ear: the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea's oval window.

• monochromatism: Complete color blindness where only shades of grey are perceived, with no ability to distinguish colors.

• motor (efferent) neurons: neurons that carry outgoing information from the brain and spinal cord to the muscles and glands.

• motor cortex: an area at the rear of the frontal lobes that controls voluntary movements.

• multiple sclerosis: A disease in which the immune system attacks the protective covering of nerves, leading to communication problems between the brain and the rest of the body.

• mutation: a random error in gene replication that leads to a change.

• myasthenia gravis: An autoimmune disorder that affects communication between nerves and muscles, leading to muscle weakness.

• myelin: the fatty tissue layer that encases the axons of some neurons, speeding up the neural impulses.

• narcolepsy: a sleep disorder characterized by uncontrollable sleep attacks, often triggered by strong emotions.

• natural selection: the principle that heritable traits that better enable an organism to survive and reproduce in a particular environment will most likely be passed on to succeeding generations.

• nature-nurture issue: the debate over the relative contributions of genetic inheritance and environmental factors to human development.

• near-death experience: an altered state of consciousness reported after a close brush with death, often including out-of-body experiences and feelings of peace.

• nearsightedness (Myopia): A condition where close objects are seen clearly, but distant objects are blurry.

• nervous system: the body's speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems.

• neurogenesis: the formation of new neurons.

• neuron: nerve cell; the basic building block of the nervous system.

• neuroplasticity: the brain's ability to reorganize itself by forming new neural connections throughout life, particularly in response to learning, experience, or injury.

• neurotransmitters: chemical messengers that transmit signals across the synaptic gap between neurons.

• NREM sleep (Non-Rapid Eye Movement sleep): the sleep stages characterized by slow brain waves, relaxed muscles, and decreased heart rate and breathing.

• norepinephrine: A neurotransmitter and hormone involved in arousal and alertness.

• occipital lobes: regions of the cerebral cortex located at the back of the brain, responsible for processing visual information.

• oleogustus: A proposed sixth taste sensation for the taste of fat.

• olfaction: the sense of smell.

• opioids: a class of drugs that act on opioid receptors to produce morphine-like effects, including pain relief and feelings of euphoria.

• opponent-process theory: theory of color vision proposing that the brain processes color information in pairs of complementary colors (e.g., red-green, blue-yellow).

• optic nerve: the bundle of nerve fibers that carries visual information from the retina to the brain.

• parallel processing: the brain's ability to process multiple aspects of a problem or stimulus simultaneously.

• parasympathetic nervous system: the division of the autonomic nervous system that calms the body, conserving its energy and promoting rest and digestion.

• parietal lobes: regions of the cerebral cortex located at the top of the brain, responsible for processing sensory information such as touch and spatial awareness.

• perception: the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

• peripheral nervous system: the sensory and motor neurons that connect the central nervous system to the rest of the body, transmitting information to and from the brain and spinal cord.

• pheromones: Chemicals secreted by animals that influence the behavior or physiology of others of the same species.

• pitch: a tone's experienced highness or lowness; depends on frequency.

• pituitary gland: The "master gland" of the endocrine system that regulates other glands and controls various bodily functions.

• place theory: the theory that links the pitch we hear with the place where the cochlea's membrane is stimulated.

• plasticity: The brain's ability to change and adapt as a result of experience.

• positron resonance tomography (PET): a brain imaging technique that measures brain activity by detecting radioactive glucose uptake in active brain areas.

• priming: the activation of certain associations, thus predisposing one's perception, memory, or response.

• prosopagnosia: A neurological disorder characterized by the inability to recognize faces, also known as face blindness.

• psychoactive drug: a chemical substance that alters perception, mood, consciousness, cognition, or behavior.

• psychophysics: the study of the relationship between physical characteristics of stimuli and our psychological experience of them.

• pupil: the adjustable opening in the center of the eye through which light enters.

• reflex: a simple, automatic response to a sensory stimulus, such as the knee-jerk reflex.

• reflex arc: The neural pathway that controls a reflex action.

• refractory period: a brief period after a neuron has fired during which it cannot generate another action potential.

• REM rebound: the tendency for REM sleep to increase following REM sleep deprivation.

• REM sleep (Rapid Eye Movement sleep): a stage of sleep characterized by rapid eye movements, vivid dreams, and muscle paralysis.

• REM sleep behavior disorder: sleep disorder characterized by the acting out of violent or dramatic dreams during REM sleep.

• resting potential: The electrical charge of a neuron when it is not active.

• reticular activating system: A network of neurons in the brainstem involved in arousal and attention.

• reticular formation: a network of neurons running through the core of the brainstem, involved in controlling arousal and attention.

• retina: the light-sensitive inner surface of the eye, containing receptor cells (rods and cones) and layers of neurons that begin the processing of visual information.

• reuptake: the reabsorption of neurotransmitters by the sending neuron after they have been released into the synaptic gap.

• reuptake inhibitors: Medications that block the reabsorption of neurotransmitters into neurons, increasing their levels in the brain.

• rods: retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond.

• Roger Sperry: A neuropsychologist who won the Nobel Prize for his split-brain research, showing functional differences between the brain's hemispheres.

• semicircular canals: Structures in the inner ear involved in maintaining balance and detecting head movements.

• sensation: the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.

• sensorineural hearing loss: hearing loss caused by damage to the cochlea's hair cells or the auditory nerve.

• sensory (afferent) neurons: neurons that carry incoming information from the sensory receptors to the brain and spinal cord.

• sensory adaptation: diminished sensitivity to an unchanging stimulus over time.

• sensory interaction: the principle that one sense may influence another, as when the smell of food influences its taste.

• sensory receptors: specialized cells that detect sensory stimuli and convert them into neural impulses to be sent to the brain.

• sequential processing: the processing of one aspect of a stimulus at a time, used when we focus attention on new or complex tasks.

• serotonin: A neurotransmitter that affects mood, appetite, and sleep.

• signal detection theory: a theory predicting how and when we detect the presence of a faint stimulus amid background noise.

• Sigmund Freud: Austrian neurologist known as the founder of psychoanalysis, a clinical method for treating psychopathology through dialogue between a patient and a psychoanalyst.

• sleep: a natural state of rest for the body and mind, characterized by altered consciousness, reduced sensory activity, and inactivity of nearly all voluntary muscles.

• sleep apnea: a sleep disorder characterized by pauses in breathing or shallow breaths during sleep, leading to disrupted sleep and daytime fatigue.

• somatic nervous system: the division of the peripheral nervous system that controls the body's skeletal muscles and transmits sensory information to the central nervous system.

• somatosensory cortex: a brain region located in the parietal lobe that processes sensory information from the skin and internal body receptors for touch, temperature, and body position.

• somnambulism: A disorder in which a person walks or performs other complex behaviors while asleep.

• sound localization: The process by which the position of a sound source is determined.

• spinal Cord: The part of the central nervous system that transmits signals between the brain and the rest of the body.

• split brain procedure: a surgical procedure that involves severing the corpus callosum, the bundle of nerve fibers connecting the brain's hemispheres, typically done to treat severe epilepsy.

• stimulants: drugs that excite neural activity and speed up body functions, such as caffeine, nicotine, amphetamines, and cocaine.

• subliminal: below one's absolute threshold for conscious awareness.

• substance P: A neurotransmitter involved in the transmission of pain signals.

• substance use disorder: a condition characterized by continued use of a substance despite significant substance-related problems.

• supertasters: Individuals with heightened sensitivity to all tastes and mouth sensations.

• suprachiasmatic nucleus: a tiny region of the hypothalamus that acts as the body's internal clock, regulating circadian rhythms such as the sleep-wake cycle.

• sympathetic nervous system: the division of the autonomic nervous system that mobilizes the body's resources during stress and emergencies, preparing the body for "fight or flight" responses.

• synapse: the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron, where neurotransmitters are released.

• synesthesia: A condition in which one sense is simultaneously perceived as if by one or more additional senses.

• temporal lobes: the regions of the cerebral cortex located above the ears, responsible for processing auditory information and containing areas involved in memory, language comprehension, and emotion.

• thalamus: the brain's sensory control center, located on top of the brainstem, relaying sensory information (except for smell) to the appropriate areas of the cerebral cortex.

• threshold: the level of stimulation required to trigger a neural impulse.

• tolerance: the diminishing effect of a drug with regular use, requiring larger doses to achieve the same effect.

• top-down processing: information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations.

• Torsten Wiesel: Swedish neurophysiologist known for his collaborative work with David Hubel, elucidating the visual processing system and its role in perception.

• transduction: the process of converting one form of energy into another, such as sensory stimuli into neural impulses.

• umami: One of the five basic tastes, often described as savory or meaty.

• vestibular sense: the sense of body movement and position, including the sense of balance.

• visual accommodation: The process by which the eye's lens changes shape to focus on objects at different distances.

• visual cortex: The part of the brain that processes visual information.

• volley principle: A theory of hearing which states that groups of neurons respond to sound by firing action potentials slightly out of phase with one another.

• wavelength: the distance from the peak of one wave to the peak of the next wave, determining the wave's color (in vision) or pitch (in audition).

• Weber's Law: the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage rather than a constant amount.

• Wernicke's Area: A region in the temporal lobe of the brain associated with language comprehension.

• withdrawal: the discomfort and distress that follow discontinuing the use of an addictive drug or behavior.

• Young-Helmholtz (Trichromatic) Theory: the theory that the retina contains three different types of color receptors (cones)—red, green, and blue—that can produce any color by combining the three.