Unit 1: Biological Bases of Behavior

Measuring Brain Function

EEG (Electroencephalogram): Measures electrical activity (“brain waves”) via electrodes on the scalp.
• Used to study sleep patterns, seizures, and neural activity.
• Specific stimulus responses are called evoked potentials.

PET (Positron Emission Tomography): Uses radioactive glucose to show areas of high metabolic activity.

fMRI (Functional MRI): Tracks changes in blood oxygen to measure brain activity at higher resolution than PET.
• Example: seeing which areas activate while solving math problems.

MSI (Magnetic Source Imaging), via Magnetoencephalography (MEG): Detects faint magnetic fields from brain activity; useful for precise timing and localization.

Organization of the Nervous System

Central Nervous System (CNS): Brain and spinal cord — main processing hub.

Peripheral Nervous System (PNS): Connects CNS to the rest of the body.
It is divided into:

Somatic Nervous System: Controls voluntary movements via skeletal muscles.

Autonomic Nervous System: Controls involuntary functions (heartbeat, digestion).

Sympathetic Nervous System: Activates “fight or flight.” Increases heart rate, dilates pupils, releases adrenaline.

Parasympathetic Nervous System: Calms the body (“rest and digest”). Slows heartbeat, restores digestion, returns pupils to normal size.

Spinal Cord: Protected by meninges; relays messages between the brain and body.

The Brain

Triune Brain Model: Three evolutionary layers.

Reptilian Brain: Brainstem (medulla, pons, cerebellum). Controls survival functions like breathing, balance, and reflexes.

Old Mammalian Brain: Limbic system (hippocampus, amygdala, hypothalamus, thalamus). Regulates emotion, memory, and drives.

New Mammalian Brain: Neocortex (cerebral cortex). Higher-order cognition: judgment, decision-making, foresight, and language.

Localization: Specific brain areas control specific functions.

Localization and Lateralization of Brain Function

Association Areas: Parts of the cerebral cortex not tied to primary motor or sensory functions but involved in thinking, planning, and remembering.

Medulla Oblongata: Controls vital functions (i.e., heartbeat, breathing, digestion)

Pons: Helps regulate arousal, sleep, and communication between brain regions.

Cerebellum: Coordinates balance, posture, and movement.

Basal Ganglia: Controls movement initiation and implicit memory (i.e., riding a bike).

Thalamus: Relay center — directs sensory information to the appropriate cortex areas.

Hypothalamus: Maintains homeostasis; regulates hunger, thirst, body temperature, and links nervous and endocrine systems.

Hippocampus: Forms new long-term memories.

Cerebral Cortex: Handles high-level processing, judgment, and voluntary actions.

Frontal Lobe: responsible for higher-order thinking, planning, decision making, problem solving, personality, and voluntary motor movements. It plays a central role in executive functioning and self-control.

Parietal Lobe: processes sensory information related to touch, pressure, temperature, and pain. It also plays a role in spatial orientation and body awareness.

Occipital Lobe: primarily devoted to vision, interpreting visual information such as color, shape, and motion. Damage to this area can cause visual impairments or blindness.

Brain Stem connects the brain to the spinal cord and controls vital life functions. It houses centers that regulate breathing, heart rate, digestion, and arousal.

Temporal Lobe processes auditory information and is essential for understanding language. It also plays a role in memory, learning, and emotional responses.

Corpus Callosum is a thick band of nerve fibers connecting the left and right hemispheres of the brain, allowing them to communicate and share information.

Plasticity: The brain’s ability to reorganize and form new connections after injury.

Structure and Function of the Neuron

Glial Cells: Support neurons by providing nutrients, cleaning waste, and insulating axons (myelin sheath).

Neuron: The fundamental unit of the nervous system.

Dendrites: Receive messages.

Cell Body (Soma): Contains the nucleus.

Axon: Sends electrical impulses away from the cell body.

Myelin Sheath: Speeds up neural transmission.

Terminal Buttons: Release neurotransmitters into the synapse.

Synapse: Gap between neurons where chemical messages are transmitted.

The cell body (or soma) contains the cytoplasm and nucleus, directing the synthesis of neurotransmitters. From it extend dendrites, which are branching processes that receive information. Emerging from the soma is the axon, a long conducting fiber that ends in terminal buttons or axon terminals. The axon is typically covered by a myelin sheath, formed by glial cells, which insulates and speeds signal transmission.

Throughout life, the brain can generate new neurons through neurogenesis. Communication occurs through neurotransmitters, chemical messengers stored in vesicles within the terminal buttons. Key neurotransmitters include dopamine, which influences movement and alertness; glutamate, a major excitatory transmitter essential for memory formation; serotonin, linked to mood, attention, and sleep; opioid peptides like endorphins, which relieve pain; GABA, which inhibits neural firing; and norepinephrine, tied to alertness and arousal. Drugs can act as agonists, mimicking neurotransmitters, or antagonists, blocking their effects.

Neuron Functions

Neurons communicate using electrical impulses. At rest, a neuron has a negative charge inside the cell membrane compared to outside, known as its resting potential. When stimulated beyond a threshold, sodium ions rush into the cell, producing an action potential, a rapid electrical change across the membrane. This follows the all-or-none principle: the neuron either fires completely or not at all.

As the impulse travels, depolarization and repolarization occur along the axon. Gaps between myelin segments, called nodes of Ranvier, allow impulses to jump in a process called saltatory conduction, which speeds transmission. At the synapse, neurotransmitters may have an excitatory effect, increasing the likelihood of the next neuron firing, or an inhibitory effect, reducing the chance of firing.

Reflex Action

A reflex is a rapid, automatic response involving a short pathway called a reflex arc. Sensory or afferent neurons carry impulses from receptors to the spinal cord, where interneurons relay the message to motor (efferent) neurons. These then activate muscles or glands, known as effectors, to produce a response without the need for conscious brain involvement.

The Endocrine System

The endocrine system consists of glands that secrete hormones into the bloodstream, regulating processes such as growth, metabolism, and reproduction. The pineal gland produces melatonin, regulating circadian rhythms. The hypothalamus links the nervous and endocrine systems, controlling hormone release from the pituitary gland, which produces hormones like thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), antidiuretic hormone (ADH), and human growth hormone (HGH). The thyroid gland regulates metabolism through thyroxine, while the parathyroids maintain calcium levels. The adrenal glands release adrenaline and cortisol during stress. The pancreas secretes insulin and glucagon to regulate blood sugar. The ovaries and testes produce sex hormones critical for reproduction and development.

Genetics and Evolutionary Psychology

The nature-nurture controversy explores how both heredity and environment shape behavior. Evolutionary psychologists study how natural selection favored traits and behaviors that increased survival and reproduction. Behavioral geneticists investigate how genes and environment interact to influence personality, intelligence, and temperament. Research on twins reveals that identical twins, who share 100% of their genes, often display more similarities than fraternal twins, who share about 50%. Heritability measures the degree to which differences among individuals in a population are due to genetic variation.

Transmission of Hereditary Characteristics

Genes, located on chromosomes, determine traits. Humans typically have 46 chromosomes, or 23 pairs, with eggs and sperm carrying 23 each. Genetic disorders may arise from chromosomal abnormalities. For example, Down syndrome is caused by an extra chromosome 21. The genetic code of an individual is their genotype, while the observable traits are their phenotype. Some genetic disorders include Tay-Sachs disease, which causes progressive nervous system degeneration; albinism, due to pigment synthesis failure; phenylketonuria (PKU), which can cause severe brain damage without dietary intervention; Huntington’s disease, a dominant disorder causing nervous system degeneration; and some forms of Alzheimer’s disease, linked to chromosome 21.

Levels of Consciousness

Consciousness is a spectrum of awareness. The preconscious stores memories and feelings easily brought to awareness. The nonconscious governs bodily functions like blood flow and hormone release without awareness. The unconscious (sometimes called the subconscious) contains hidden desires and thoughts not readily available to awareness. Dual processing describes how the brain can handle conscious and unconscious information simultaneously. Unconsciousness is a state of non-responsiveness caused by trauma, anesthesia, or disease.

Sleep and Dreams

The hypothalamus regulates changes in body temperature, hormones, and activity levels across the day, helping control the circadian rhythm, the body’s internal 24-hour clock. Circadian rhythms influence when we feel awake or sleepy, responding to cues like light and darkness. Sleep itself involves varying levels of consciousness and arousal, measured using EEGs (Electroencephalograms), which record brain activity through electrodes placed on the scalp.

When you begin to fall asleep, you enter the hypnagogic state, a relaxed state in which you may fail to respond to outside stimuli. The first stage of sleep, known as NREM-1, shows theta waves on an EEG, which are higher in amplitude and lower in frequency than alpha waves of wakefulness. As you transition into NREM-2, your EEG reveals bursts of high-frequency activity called sleep spindles and larger waves called K-complexes. Deeper sleep occurs in NREM-3, where very high-amplitude, low-frequency delta waves dominate. About ninety minutes after falling asleep, you typically enter REM sleep (Rapid Eye Movement), a stage associated with vivid dreaming and heightened brain activity. During REM, frightening dreams may occur as nightmares, while lucid dreaming allows awareness and sometimes control of dreams, often used therapeutically to reduce distress from recurring nightmares.

Interpretation of Dreams

Sigmund Freud suggested that dreams reveal unconscious desires and fears. He distinguished between the manifest content, or the remembered storyline of the dream, and the latent content, the hidden psychological meaning. More modern approaches include the activation-synthesis theory, proposed by Robert McCarley and J. Alan Hobson, which argues that dreams are the brain’s attempt to make sense of random neural activity during sleep. The pons plays a key role in generating bursts of action potentials that activate the forebrain, leading to dream activity.

Sleep Disorders

Several disorders interfere with healthy sleep. Insomnia is the difficulty in falling or staying asleep. Narcolepsy involves sudden and uncontrollable sleep attacks, often leading directly into REM sleep. Sleep apnea is marked by repeated cessations of breathing during sleep, often causing frequent awakenings. Night terrors, most common in childhood, occur during deep NREM-3 sleep and involve intense fear, screaming, and physical movement. Sleepwalking, or somnambulism, also occurs during NREM-3 and involves walking or engaging in activities while still asleep.

Hypnosis

Hypnosis is an altered state of consciousness characterized by deep relaxation and increased suggestibility. Individuals under hypnosis may experience altered perception, such as feeling their body float, losing a sense of pain, or believing they are reliving past events. According to the dissociation theory, hypnosis divides streams of consciousness, allowing part of the mind to follow suggestions while the other remains aware.

Meditation

Meditation involves techniques that focus concentration away from distracting thoughts and emotions, fostering calmness and inner peace. It is commonly practiced in traditions such as Zen Buddhism. EEGs of meditators often display alpha waves, reflecting a state of relaxed alertness. Benefits of meditation include reduced stress, improved focus, and enhanced emotional regulation.

Drugs and Consciousness

Psychoactive drugs alter perception, mood, and behavior by passing through the blood-brain barrier and influencing neurotransmitter systems. Psychological dependence occurs when a person craves the drug’s effects despite negative consequences, while physiological dependence involves physical changes in the brain that create tolerance and withdrawal symptoms. Tolerance means the user requires more of the drug to achieve the same effect. Withdrawal symptoms include discomfort and craving when the drug is absent.

Depressants, such as alcohol, barbiturates, and tranquilizers, slow down nervous system activity, inducing relaxation and sleepiness. Stimulants, including caffeine, nicotine, and amphetamines, increase alertness and energy by boosting neurotransmitters like dopamine and norepinephrine. Hallucinogens, also called psychedelics, distort perception and evoke vivid sensory experiences in the absence of actual stimuli. These drug classes vary widely in their effects on consciousness, but all demonstrate how external substances can alter brain chemistry and behavior.