The brain stem is the brain’s life-support hub. Located where the spinal cord meets the brain, it includes the medulla and midbrain structures and controls basic, automatic functions you don’t think about—breathing, heart rate, swallowing, and blood pressure (CED 1.4.A.1). It’s also the main highway for neural signals between the body and the cortex and houses the reticular activating system (RAS), which helps regulate arousal, wakefulness, and attention (CED 1.4.A.2). Because these functions are essential for survival, damage to the brain stem can be life-threatening or cause coma. For AP Psych, you should be able to name the medulla, explain basic life functions, and link the RAS to arousal—these concepts show up in Unit 1 items (15–25% of the exam). For a quick Topic 1.4 review, check the Fiveable study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU).

Chunk them + use a few strong mnemonics. Group the limbic pieces and one-line functions you must know for the CED: thalamus = sensory relay, hypothalamus = homeostasis (hunger, thirst, temp), pituitary = hormone master gland, hippocampus = memory/episodic memory, amygdala = emotion (especially fear), nucleus accumbens = reward/motivation. Mnemonic: “THiP HAM N” (T = Thalamus, Hi = Hypothalamus, P = Pituitary, H A M = Hippocampus, Amygdala, N = Nucleus accumbens)—or make your own sentence: “The Hungry Pig Hides Almonds Nicely.” Flashcards with picture + function, 30–60 sec recall each, then spaced review (distributed practice) works best for the exam. For FRQs, practice describing each structure’s behavior link (e.g., hippocampus → impaired episodic memory after damage). Review the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and drill 1000+ practice items (https://library.fiveable.me/practice/ap-psych-new) so you can quickly ID functions on multiple-choice and explain them on free-response.

Short answer: the cerebellum is a subcortical structure that mainly coordinates movement, balance, and some procedural learning, while the cerebral cortex is the brain’s outer layer responsible for higher-order thinking, perception, language, and complex voluntary behavior. More detail: the cerebellum (near the brainstem) fine-tunes motor commands so your movements are smooth and balanced and helps with motor skills you do without thinking (procedural memory)—CED 1.4.A.3. The cerebral cortex is divided into two hemispheres and includes the limbic structures, corpus callosum, and the four lobes (occipital = vision, temporal = hearing/language, parietal = somatosensory/association, frontal = executive function and motor cortex)—CED 1.4.A.4 and 1.4.A.4.i–iv. Damage to the cerebellum affects coordination; damage to cortical areas affects perception, language, executive functions, or voluntary movement depending on the lobe. For quick review, check the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU), unit overview (https://library.fiveable.me/ap-psych-new/unit-1), and practice questions (https://library.fiveable.me/practice/ap-psych-new). The Biological Bases unit is tested ~15–25% on the AP exam, so know these distinctions.

They act “weird” because cutting the corpus callosum (split-brain surgery) stops the two hemispheres from sharing information, so each half can only report what it directly receives. In most people the left hemisphere handles language (Broca’s/Wernicke’s areas), while the right is better at visuo-spatial tasks. In experiments researchers flash an image to one visual field (which projects to the opposite hemisphere). If the picture goes to the right hemisphere, the person can’t name it because the left (language) side didn’t get the info—so they might pick up the object with their left hand instead. The left hemisphere often invents a plausible explanation for odd actions (confabulation), which looks strange. This is classic Topic 1.4 content (corpus callosum, hemispheric specialization) you should know for the AP exam. For a quick review, check the Topic 1.4 study guide on Fiveable (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU).

Short answer: sort of—but not “completely.” Brain plasticity (CED 1.4.A.6) means the brain can modify existing connections and form new ones so other regions can sometimes take over functions (like after a stroke). Younger brains are more plastic, and processes like synaptic pruning, long-term potentiation, and limited adult neurogenesis help change wiring. That doesn’t mean every part can fully rewire for any lost function (e.g., brain stem roles like breathing are hard to reassign), and recovery depends on age, severity, and which structures (hippocampus, prefrontal cortex, motor cortex, etc.) are involved. For the AP exam, know the definition in the CED and examples (e.g., damaged part’s function assumed by another area). Want to review this topic more? Check the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and practice questions (https://library.fiveable.me/practice/ap-psych-new).

If you damage Broca’s area (left frontal lobe) you get Broca’s aphasia: speech production is impaired. People understand spoken language pretty well but speak slowly, with effort, missing grammar and function words (nonfluent/expressive aphasia). Writing can be affected too because it’s a language-production problem. Damage to Wernicke’s area (left temporal lobe) gives Wernicke’s aphasia: speech is fluent but often nonsensical and full of made-up or irrelevant words, and comprehension is poor (receptive aphasia). People often aren’t aware their speech doesn’t make sense. Both are classically left-hemisphere language areas per the CED (1.4.A.5.i). Recovery can improve over time because of brain plasticity (1.4.A.6). Want to review this topic more? Check the AP Psych Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and practice questions (https://library.fiveable.me/practice/ap-psych-new).

Scientists study the brain mostly without hurting people by using noninvasive methods, careful case studies, and ethically approved medical procedures. Common noninvasive tools include EEG (records electrical activity) and fMRI (shows active brain areas) so researchers can link structures—like the hippocampus or prefrontal cortex—to memory, emotion, or executive functioning (CED 1.4.A.4–1.4.A.4.iv; 1.4.A.6). Case studies (e.g., split-brain patients) and naturally occurring lesions let scientists learn what damage to Broca’s or Wernicke’s areas does without creating harm. When surgical or lesion data exist, it’s usually from medical treatment (e.g., epilepsy surgery) and studied afterward. All human research follows ethical rules (informed consent, minimal harm), and experiments avoid intentionally injuring participants (CED 1.4.A.7). If you want a compact review of these methods for AP Psych, check the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and try practice problems (https://library.fiveable.me/practice/ap-psych-new).

Short answer: know what each lobe does and one quick mnemonic. - Frontal lobe (behind forehead): higher-order thinking, executive functions (prefrontal cortex), language production, motor cortex at its rear controls voluntary skeletal movement—think planning, decisions, speech (Broca’s area nearby). - Parietal lobe (top/back crown): association areas that process/organize info and the somatosensory cortex—touch, spatial sense. - Temporal lobe (sides): auditory and language processing (Wernicke’s area = comprehension), memory-related processing. - Occipital lobe (rear): visual information processing. Mnemonic: “F.P.T.O.—Frank’s Pretty Terrific Optics” or map them on your head: forehead = frontal, crown/top = parietal, ears = temporal, back = occipital. Add limbic reminders (hippocampus, amygdala, thalamus, hypothalamus) for memory/emotion/relay. Study tip: sketch a brain, label lobes + motor/somatosensory strips, and quiz with practice questions (AP topics test 1.4.A skills). For the topic study guide and tons of practice, check the AP Psych brain study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and practice bank (https://library.fiveable.me/practice/ap-psych-new).

The corpus callosum is a thick bundle of neural fibers (white matter) that connects the left and right cerebral hemispheres, letting them share information (so sensory, motor, and higher-order signals travel between sides). Doctors sometimes surgically sever it—a procedure called a corpus callosotomy—to treat severe, medication-resistant epilepsy. Cutting the callosum limits the spread of seizure activity from one hemisphere to the other, reducing the frequency and severity of generalized seizures. Split-brain research (from these patients) also shows hemisphere specialization: language is usually left-lateralized (Broca’s/Wernicke’s areas), so when connection is cut, information shown to one visual field may not be reported verbally. This topic maps to AP CED 1.4.A.4–1.4.A.5 (cerebral cortex & split-brain findings). For a quick review on brain structures and split-brain studies, see the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU).

fMRI (functional magnetic resonance imaging) measures brain activity indirectly by detecting changes in blood flow and oxygenation—the BOLD signal (blood-oxygen-level–dependent). When a brain area works harder (e.g., visual cortex during a sight task), it needs more oxygen, local blood flow increases, and the fMRI picks up that change. So fMRI shows which brain regions are more active during tasks or rest (good spatial detail: millimeter-level), but it’s an indirect, correlative measure with poor temporal resolution (seconds), so it can’t tell you individual neurons firing or prove causation. Researchers combine fMRI with methods like EEG (better millisecond timing) or lesion studies to link structure and function (CED Topic 1.4 and 1.4.A.4). For AP review, know fMRI vs. EEG strengths/limits and that brain imaging is used for research (CED 1.4.A.7). Want more examples and practice? Check the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and practice problems (https://library.fiveable.me/practice/ap-psych-new).

Because language functions—speech production and comprehension—are usually lateralized to the left hemisphere in most people, that side is often described as “more important” for language. Classic evidence comes from Broca’s area (left frontal lobe) —damage causes difficulty producing speech (Broca’s aphasia)—and Wernicke’s area (left temporal lobe) —damage causes poor comprehension (Wernicke’s aphasia). Split-brain studies (severed corpus callosum) and lesion/case studies show that when language input is presented to the right visual field (processed by the left hemisphere), patients can name it; when shown to the left visual field, they often can’t. That pattern plus brain imaging (EEG, fMRI) and the brain’s contralateral organization support left-hemisphere specialization. Remember: plasticity (1.4.A.6) means language can sometimes shift after damage. If you want a quick CED-aligned review, check the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and try practice problems (https://library.fiveable.me/practice/ap-psych-new) for exam prep.

The reticular activating system (RAS) is a network in the brainstem that regulates arousal, alertness, and attention—basically your “wakefulness switch.” It filters incoming sensory info so your cortex isn’t overloaded (so you notice important stuff and ignore background noise), helps control sleep–wake cycles, and supports sustained attention. Per the CED, it also plays a role in some voluntary movement, eye movement, and in types of learning, cognition, and emotion (1.4.A.2). Damage or dysfunction can make someone very sleepy, hard to focus, or affect basic arousal. On the AP exam, expect RAS questions tied to brainstem functions and how arousal/attention affect behavior (Topic 1.4). For a quick review and practice items on this topic, check the Topic 1.4 study guide on Fiveable (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU).

The motor cortex and the somatosensory cortex are neighbors but do different jobs. The motor cortex sits at the rear of the frontal lobe (precentral gyrus) and controls voluntary skeletal movement—sending signals out to muscles. The somatosensory cortex sits in the front of the parietal lobe (postcentral gyrus) and processes incoming touch information like pressure, temperature, and body position. Both show contralateral organization (left cortex → right side of body) and are mapped topographically (the “homunculus”) so different body parts take up different amounts of cortex. Damage to the motor cortex → weakness or paralysis; damage to somatosensory cortex → loss of touch or proprioception. These details map to CED 1.4.A.4.iii–iv and show up on the AP exam’s Unit 1 questions. Want a quick review or practice Qs? Check the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU) and practice problems (https://library.fiveable.me/practice/ap-psych-new).

Damage to one brain area usually produces deficits tied to that area’s function—e.g., damage to Broca’s area causes trouble producing speech (aphasia), occipital lobe damage impairs vision, cerebellar damage hurts coordination (CED 1.4.A.4–1.4.A.4.i–iii). How much behavior changes depends on location, size, and severity. The brain can often “take over” through plasticity: surviving neurons form new connections or other regions assume some functions, especially in younger people and with rehabilitation (CED 1.4.A.6). But plasticity has limits—complex skills (like language) may not fully recover if critical areas are extensively damaged or if intervention is late. Split-brain and lateralization research also show specialization of hemispheres, so transfer isn’t always complete (CED 1.4.A.5). For review, see the Topic 1.4 study guide (https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU). For broader unit review and practice problems, use (https://library.fiveable.me/ap-psych-new/unit-1) and (https://library.fiveable.me/practice/ap-psych-new). On the exam expect to explain specific structure-function links and plasticity.

You need split-brain research because it’s the clearest evidence that the two cerebral hemispheres can specialize in different functions—a CED-level point (1.4.A.5). When the corpus callosum is severed (treatment for severe epilepsy), researchers use contralateral visual-field tests to show the left hemisphere usually handles language (Broca’s/Wernicke’s areas) while the right handles spatial/face tasks. That matters for AP items: you’ll be asked to identify lateralization, explain results of split-brain experiments, and link structure (corpus callosum) to behavior—skills tested in multiple-choice and FRQs in Unit 1 (15–25% of the exam). Review the Topic 1.4 study guide for concrete examples and practice how researchers present stimuli to one visual field (see: https://library.fiveable.me/ap-psych-new/unit-2/4-the-brain/study-guide/zffu0vU5m7HwEMsU). For extra practice, try the AP-style questions at (https://library.fiveable.me/practice/ap-psych-new).