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Psychology Unit 1: Biological bases of behavior

Behavior and mental processes come from the interaction of genes, neurons, neurotransmitters, hormones and the brain.

Covers: Research methods, heredity and environment, the nervous system and neurons, neurotransmitters and hormones, the brain, sleep, sensation

Study guide

Psychology is the scientific study of behavior and mental processes. It relies on research methods: experiments manipulate an independent variable and measure a dependent variable, using random assignment to control confounding variables, so they can show cause and effect. Correlational studies show relationships but not causation. Other methods include case studies, naturalistic observation and surveys, and good research follows ethical guidelines like informed consent. Psychologists study how heredity and environment interact, using twin and adoption studies.

The nervous system has a central division (brain and spinal cord) and a peripheral division, which includes the somatic system (voluntary movement) and the autonomic system, split into the sympathetic (fight or flight) and parasympathetic (rest and digest) branches. Neurons communicate through action potentials, which follow the all-or-none principle, and neurotransmitters released across the synapse. Key neurotransmitters include dopamine (reward and movement), serotonin (mood), acetylcholine (muscles and memory), GABA (inhibition), glutamate (excitation) and endorphins (pain relief). Drugs act as agonists (mimicking neurotransmitters) or antagonists (blocking them). The endocrine system sends slower messages through hormones like adrenaline, oxytocin and melatonin.

The brain's regions specialize. The brainstem (medulla) controls breathing and heart rate, the cerebellum coordinates movement, and the limbic system includes the hippocampus (memory), amygdala (fear) and hypothalamus (drives). The cerebral cortex has frontal (planning, Broca's area for speech production), parietal (touch), occipital (vision) and temporal (hearing, Wernicke's area for comprehension) lobes. Neuroplasticity lets the brain reorganize after injury. Sleep cycles through NREM stages and REM sleep (dreaming) about every 90 minutes, regulated by circadian rhythms. Sensation begins when receptors convert energy into neural signals (transduction); concepts include absolute and difference thresholds, sensory adaptation, and how vision, hearing and other senses work.

Researchers summarize data with measures of central tendency (mean, median, mode) and variation (range and standard deviation, where a larger SD means scores are more spread out). A correlation coefficient runs from −1 to +1 and is shown on a scatterplot. A statistically significant result is one unlikely to be due to chance, while a nonsignificant difference may just be chance. A percentile rank tells what percent of scores fall at or below a given score. An operational definition states exactly how a variable will be measured, for example "number of times the dog looked at the person in 30 seconds." Random sampling picks participants so the sample represents the population. It is different from random assignment, which places participants into groups. Results generalize only to populations like the sample, so judge generalizability from who the participants were, not just how many there were.

In a within-subjects design every participant experiences all conditions, while in a between-subjects design each group gets one condition. Placebo and single- or double-blind procedures control participant and experimenter bias. Key ethical guidelines are informed consent (or assent for minors), protection from harm, confidentiality, minimal and justified deception, debriefing, and review by an institutional review board. Animal research must also minimize harm. A neuron receives signals through its dendrites, passes them along the axon (sped up by the myelin sheath) and releases neurotransmitters from terminal buttons into the synapse, where reuptake later recycles them. Sensory (afferent) neurons carry information to the CNS, interneurons process it, and motor (efferent) neurons carry commands to muscles and glands. A reflex arc can run through the spinal cord without the brain.

Light passes to the retina, where rods (dim light) and cones (color and detail, packed in the fovea) send signals through bipolar and ganglion cells to the optic nerve. The point where the optic nerve leaves the eye is the blind spot. Color is explained by trichromatic theory (three cone types) and opponent-process theory (paired opposites, which explains afterimages). Hubel and Wiesel found feature-detector cells in the visual cortex that respond to specific edges and angles. Pitch depends on a sound wave's frequency and loudness on its amplitude, and the semicircular canals and vestibular sacs in the inner ear sense balance. Psychoactive drugs are grouped as stimulants (caffeine, cocaine), depressants (alcohol), hallucinogens (LSD, marijuana) and opioids (heroin). Repeated use builds tolerance, so a person needs more of the drug for the same effect, and stopping can cause withdrawal symptoms.

Sleep disorders include insomnia (trouble falling or staying asleep), narcolepsy (sudden sleep attacks, sometimes treated with stimulants), sleep apnea (breathing stops during sleep), somnambulism or sleepwalking (during NREM stage 3), and REM sleep behavior disorder (acting out dreams). EEG records the brain's electrical activity and is good for timing. CT and MRI show structure, while fMRI and PET show activity; PET does this by tracking a radioactive glucose tracer. Lesion and split-brain studies show which functions depend on particular regions or on the corpus callosum linking the hemispheres.

Key ideas

• Only experiments with random assignment can show cause and effect.
• Neurons communicate through action potentials and neurotransmitters.
• The autonomic system's sympathetic and parasympathetic branches balance arousal.
• Brain regions specialize, but the brain can reorganize (neuroplasticity).
• Sensation transduces physical energy into neural signals.

Formulas and rules

Common mistakes

• Saying correlation proves causation.
• Mixing up Broca's area (producing speech) and Wernicke's area (understanding it).

Words to know

Independent variable

The factor manipulated in an experiment.

Dependent variable

The outcome measured in an experiment.

Random assignment

Placing participants in groups by chance to control differences.

Confounding variable

A factor other than the independent variable that could affect results.

Correlation coefficient

A number from −1 to 1 showing the strength and direction of a relationship.

Informed consent

Participants agree to a study after learning what it involves.

Central nervous system

The brain and spinal cord.

Sympathetic nervous system

Arouses the body for fight or flight.

Parasympathetic nervous system

Calms the body (rest and digest).

Action potential

A neural impulse traveling down an axon.

All-or-none principle

A neuron either fires fully or not at all.

Dopamine

A neurotransmitter for reward and movement.

Serotonin

A neurotransmitter linked to mood, hunger and sleep.

Agonist

A drug that mimics a neurotransmitter.

Antagonist

A drug that blocks a neurotransmitter.

Amygdala

A limbic structure involved in fear and emotion.

Hippocampus

A limbic structure that forms new memories.

Broca's area

A frontal lobe region for producing speech.

Neuroplasticity

The brain's ability to reorganize after damage or experience.

REM sleep

The sleep stage with rapid eye movements and vivid dreams.

Transduction

Converting physical energy into neural signals.

Absolute threshold

The minimum stimulation detected 50% of the time.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.