MCAT Behavioral Science Notes

Sensory Perception

• Visual Cues

  • Binocular Cues: Retinal disparity, Convergence.

  • Monocular Cues: Relative size, interposition, relative height, shading and contour, motion parallax.

  • Constancy: Perception of object doesn’t change even if it looks different on retina.

• Sensory Adaptation: Downregulation of a sensory receptor to a constant stimulus.

• Weber’s Law

  • Just noticeable difference (JND): The threshold at which you’re able to notice a change in any sensation.

  • \frac{\Delta I}{I} = k (Weber’s Law).

• Absolute threshold of sensation: The minimum intensity of stimulus needed to detect a particular stimulus 50% of the time.

• Subliminal stimuli: Stimuli below the absolute threshold.

• The Vestibular System: Balance and spatial orientation.

  • Semicircular canals filled with endolymph detect head rotation.

  • Otolithic organs (utricle and saccule) detect linear acceleration and head positioning.

• Signal Detection Theory: Decision-making under uncertainty.

  • d': Strength of a signal

  • c: Strategy – conservative or liberal.

• Bottom-Up Processing: Processing sensory information.

• Top-Down Processing: Driven by cognition.

• Gestalt Principles: Similarity, Pragnanz, Proximity, Continuity, Closure.

Sight (Vision)

• Structure of the Eye: Conjunctiva, Cornea, Anterior chamber (aqueous humour), Pupil, Lens, Suspensory ligaments, Ciliary muscle( ciliary body- secretes aqueous humor), Posterior chamber (aqueous humor), Vitreous chamber (vitreous humour), Choroid, Sclera, Retina( Macula & Fovea).

• Phototransduction Cascade: Light converts 11-cis retinal to 11-trans retinal, activating rhodopsin, then transducin, then phosphodiesterase (PDE), which reduces cGMP, closing Na+ channels and hyperpolarizing the rod.

• Photoreceptors: Rods (night vision, rhodopsin) and Cones (color vision, photopsin).

  • Rods: 120 million, sensitive to light, slow recovery time.

  • Cones: 6 million, concentrated in fovea, detect color, fast recovery time (60% Red, 30% Green, 10% Blue).

Sound (Audition)

• Requires pressurized sound wave and hair cell.

• Auditory Structure: Pinna -> External auditory meatus (auditory canal) -> Tympanic membrane (Eardrum) -> Malleus, Incus, and Stapes -> Oval window (elliptical window) -> Cochlea -> Round window -> Organ of Corti (basilar and the tectorial membrane).

• Hair cells: Kinocilium filaments connected by tip links, which are attached to gate of K+ channel.

  • When sound pushes the hair cells back and forth they stretch and allows K+ to flow inside the cell.

  • Ca2+ cells get activated when K+ is inside, so Ca2+ also gets activated, and causes AP in a spiral ganglion cell which then activates the auditory nerve.

• Auditory Processing: Basilar tuning (hair cells at base of cochlea activated by high frequency sounds, and those at apex by low frequency sounds).

  • Primary auditory cortex with tonotypical mapping distinguishes different frequencies.

Somatosensation

• Types: Temperature (thermoception), pressure (mechanoception), pain (nociception), and position (proprioception).

• Timing: Non-adapting, slow-adapting, fast-adapting.

• Location: Location-specific nerves to brain.

• Adaptation: Downregulation.

• Amplification: Upregulation.

• Somatosensory Homunculus: Topological map of body in the cortex.

• Proprioception: Cognitive awareness of body in space, sensors in muscles sensitive to stretching.

• Kinaesthesia: Movement of the body, doesn't include sense of balance.

• Pain and Temperature: TrypV1 receptor sensitive to temperature and pain. Activated by heat or molecule binding.

  • Fibers: A-beta (fast, thick, myelinated), A-delta (small diameter, less myelin), C fibres (small diameter, unmyelinated).

Taste and Smell

• Olfaction: Olfactory epithelium -> cribriform plate -> olfactory bulb -> glomerulus -> mitral/tufted cell -> brain.

  • Molecules bind to GPCR receptor, G-protein dissociates causing cascade of events, binds to ion channel which opens and triggers an AP.

• Pheromones: Chemical signal released by 1 member of the species and sensed by another species to trigger an innate response.

  • Accessory olfactory epithelium -> accessory olfactory bulb -> amygdala.

• Gustation: Taste buds (fungiform, foliate, and circumvallate), labelled lines model.

  • Sweet, umami, and bitter cells: GPCR receptors.

  • Sour and salty: Ion channels.

Sleep and Consciousness

• States of Consciousness: Alertness, daydreaming, drowsiness, sleep.

  • Brainwaves: Beta (awake/concentration), Alpha (daydreaming), Theta (drowsiness), Delta (deep sleep/coma).

• Sleep Stages: N1 -> N2 -> N3 -> N2 -> REM.

  • N1: Theta waves, hypnagonic hallucinations, Tetris effect, hypnic jerks.

  • N2: Theta waves, sleep spindles, K-complexes.

  • N3: Delta waves, sleepwalking/talking.

  • REM: Alpha, beta, and desynchronous waves, paradoxical sleep.

• Dreaming: Occurs during REM sleep, decreased prefrontal cortex activity.

• Circadian Rhythms: Controlled by melatonin, produced in the pineal gland.

• Dream Theories: Freud (unconscious desires), Activation Synthesis Hypothesis (brain's attempt to find meaning from random brain activity).

• Sleep Disorders: Insomnia, narcolepsy, sleep apnea, sleepwalking/sleep talking.

• Hypnosis: More alpha waves, dissociation theory, social influence theory.

• Meditation: More alpha waves (light meditation), increased theta waves (deep meditation).

Drug Dependence

• Psychoactive Drugs: Depressants, opiates, stimulants, hallucinogens.

• Depressants: Lower body's basic functions and neural activity (alcohol, barbiturates, benzodiazepines).

• Opiates: Act at body’s receptor sites for endorphins (heroin, morphine).

• Stimulants: Intensity neural activity/bodily functions (caffeine, nicotine, cocaine, amphetamines, methamphetamines, ecstasy).

• Hallucinogens: Cause hallucinations, altered perception (ecstasy, LSD, marijuana).

• Drug Dependence and Homeostasis: Body tries to counteract drugs to maintain homeostasis.

• Routes of Drug Entry: Oral, inhalation, injection, transdermal, intramuscular.

• Reward Pathway in the Brain: VTA sends dopamine to amygdala, nucleus accumbens, prefrontal cortex, hippocampus.

• Tolerance and Withdrawal: Need more drug to achieve same effect; withdrawal symptoms when drug is stopped.

• Substance Use Disorders: Intoxication, withdrawal, substance-induced disorders, substance use disorders.

Attention

• Divided Attention: Switching between tasks.

• Selective Attention: Reacting to certain stimuli selectively.

  • Exogenous cues: don’t have to tell ourselves to look for them (“pop-out effect”).

  • Endogenous cues: require internal knowledge to understand the cue (cocktail party effect).

• Inattentional Blindness: We aren’t aware of things not in our visual field when our attention is directed elsewhere in that field.

• Change Blindness: Fail to notice changes in environment.

• Theories of Selective Attention: Broadbent's Early Selection Theory, Deutch & Deutch's Late Selection Theory, Treisman's Attenuation Theory.

• The Spotlight Model of Attention: Selective attention from 5 senses.

• Resource model of attention: We have limited resources in attention.

Memory

• Information Processing Model: Sensory memory -> working memory -> long-term memory.

  • Sensory Memory: Iconic (visual, < 1/2 second) and echoic (auditory, 3-4 seconds).

• Working Memory: Phonological loop (verbal), visuo-spatial sketchpad (visual + spatial), central executive (coordinates).

  • Magic number 7 +/- 2

• Long-Term Memory: Explicit (declarative - semantic & episodic) and implicit (non-declarative - procedural & priming).

• Encoding Strategies: Rote rehearsal, chunking, mnemonic devices, self-referencing, spacing.

• Retrieval Cues: Priming, context, state-dependent memory.

• Retrieval Cues: Free Recall, Cued Recall, and Recognition.

  • Serial position curve/effect (primacy & recency)

• Memory Reconstruction: Based on schemas, false information, misleading information, source monitoring error.

• Long Term Potentiation and Synaptic Plasticity: Connections between neurons strengthen with repeated stimulation.

• Decay and Interference: Retroactive and Proactive.

• Aging and Cognitive Abilities: Stable (implicit memory, recognition), Improve (semantic memories, crystallized IQ, emotional reasoning), Decline (recall, episodic memories, processing speed, divided attention, prospective memory).

• Alzheimer’s Disease: Neurons die off over time, amyloid plaques and neurofibrillary tangles in brain.

• Korsakoff’s Syndrome: Caused by lack of vitamin B1 or thiamine, damages certain brain areas, leading to severe memory loss and confabulation. Retrograde/anterograde amnesia.

Cognition

• Piaget’s Stages of Cognitive Development: Sensorimotor (0-2 years), Preoperational (2-7 years), Concrete operational (7-11 years), Formal operational (12+).

• Problem Solving: Trial + error, algorithm, heuristics, intuition.

• Decision Making: Availability method, representativeness, biases.

• Semantic Networks and Spreading Activation: Concepts organized in mind in terms of connected ideas, modified semantic network with spreading activation.

• Intelligence (IQ is Intelligence Quotient): Analytical, practical, creative, fluid, crystallized. Heredity.

Emotion

• Emotions: Limbic System: Hypothalamus, amygdala, thalamus, and hippocampus.

• Cerebral Hemispheres and Prefrontal Cortex: Positive emotions (left side), negative emotions (right side).

• Autonomic Nervous System (ANS): Sympathetic (fight or flight) and parasympathetic (rest and digest).

• Three Components of Emotion: Physiological, behavioural, and cognitive.

• Universal Emotions: Happiness, sadness, fear, disgust, anger and surprise.

• James-Lange Theory: Physiological -> emotion.

• Cannon-Bard Theory: Physiological = emotion.

• Schachter-Singer Theory: Physiological + cognitive -> emotion.

• Lazarus Theory: Cognitive -> emotion + physiological.

• Yerkes-Dodson Law: People perform best when moderately aroused.

Stress

• What is Stress?: Strain experienced when an organism’s equilibrium is disrupted.

• Appraisal Theory of Stress: Primary appraisal (irrelevant, benign, stressful) and secondary appraisal (harm, threat, challenge).

• Responding to Stress: Sympathetic nervous system, endocrine response (epinephrine, norepinephrine, and cortisol), tend and befriend response (oxytocin).

• General Adaptation Syndrome: Alarm, resistance, exhaustion.

• Physical Effects of Stress: Heart, metabolism, reproductive, immune function.

• Behavioral Effects of Stress: Hippocampus and frontal cortex atrophy, depression, learned helplessness, anger, anxiety, addiction.

• Stress Management: Perceived control, optimism, social support, exercise, meditation, religious beliefs/faith, cognitive flexibility.

Behavior

• Structure of the Nervous System: CNS (brain & spinal cord) and PNS (cranial + spinal nerves).

• Functions of the Nervous System: Motor, sensory, automatic, cognition, emotions, and consciousness.

• Motor Unit: Lower motor neurons (efferent neurons of the PNS, abnormalities cause atrophy, fasciculations, hypotonia, hyporeflexia).

• Peripheral Somatosensation: Position sense, vibration, touch (mechanoreceptors), pain (nociceptors), temperature (thermoreceptors).

• Muscle Stretch Reflex: Somatosensory neurons (afferent) in muscle spindles form excitatory synapse in spinal cord with another neuron in the spinal cord, which sends axon out back to same muscle that was stretched, and excite skeletal muscle cells to contract – lower motor neurons(efferent).

• Gray and White Matter: Gray matter (neuron somas) and white matter (myelinated axons) - spinal cord vs brain arrangement.

• Upper Motor Neurons: Control LMNs, originate in cerebral cortex, corticospinal & corticobulbar tracts. Upper motor signs - Hyperreflixia, clonus, hypertonia extensor plantar response.

• Somatosensory Tracts: Position sense/vibration sense/fine touch vs. pain/temperature/gross touch.

• Functions of the Cerebral Cortex: Frontal lobe (motor, prefrontal, Broca’s area), Parietal lobe (somatosensory cortex, spatial manipulation), Occipital lobe (vision), Temporal cortex (sound, Wernicke’s area).

• Cerebellum: Coordinates movement (motor plan info, position sense information, feedback to motor cortex).

• Brainstem: Midbrain, pons, medulla. Reticular formation controls autonomic functions and respiration.

• Cranial nerves: 12 pairs, attached to the brainstem.

• Subcortical Cerebrum: Internal capsule, corpus collosum, basal ganglia, thalamus, hypothalamus.

• Neurotransmitter Anatomy: Glutamate (excitatory), GABA (brain) and Glycine (spinal cord) (inhibitory), Acetylcholine (basilis and septal nuclei), Histamine (hypothalamus), Norepinephrine (pons), Serotonin (raphe nuclei), Dopamine (VTA and substantia nigra).

• Lesion Studies and Experimental Ablation: Tissue removal, radiofrequency lesions, neurochemical lesions, cortical cooling (cryogenic blockade).

• Modern Ways of Studying the Brain: CAT scans, MRI, EEG, MEG, fMRI, PET scans.

Behavior and Genetics

• Temperament, Heredity, and Genes: Temperament (characteristic emotional reactivity, sociability). Heredity (passing traits from parents/ancestors to offspring through genes).

• Twin Studies and Adoption Studies: Monozygotic vs. dizygotic. If genes largely contribute to phenotype the Monozygotic (identical) should be nearly identical on that phenotype. If environment plays stronger role Fraternal should be virtually as identical

• Heritability: Variability of traits can be attributed to differences in genes.

• Gene-Environment Interaction: Nature vs. nurture. Attractive baby vs hideous baby etc..

• Regulatory Genes: Epigenetics - changes to gene expression other than to gene. Addition of methyl groups to the gene, which make it more difficult for TFs to come in and activate gene.

• Adaptive Value of Behavioral Traits: Behavior is coordinated internal and external response of organisms to their environment, aka adaptation.

  • Ethology focuses on the observation of animal behaviours, call these overt behaviours (not necessarily obvious, just means observable), Innate, learned, and complex behaviours

Motivation theories

• 5 schools of thought: Evolutionary Drive Reduction Theory, Optimum Arousal Theory, Cognitive, Maslow’s Hierarchy of Needs food