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Module 11 Notes: Studying the Brain, Older Brain Structures, and the Limbic System

Techniques for Studying Brain–Behavior Relationships

  • How scientists study the brain in general
    • Lesion studies: brain tissue is destroyed or damaged, and researchers study the resulting impact on functioning.
    • Stimulation studies: brain regions are stimulated electrically, chemically, or magnetically to observe resulting changes in behavior or function.
    • This combination of lesioning and stimulation revealed causal links between brain regions and behaviors.

Imaging Modalities: Structure vs. Function

  • Electroencephalography (EEG):
    • Recording of the waves of electrical activity across the brain’s surface.
    • Measured by electrodes placed on the scalp.
  • Magnetoencephalography (MEG):
    • Measures magnetic fields generated by the brain’s natural electrical activity.
    • Provides temporal information about brain activity.
  • Computed Tomography (CT/CAT):
    • X-ray photographs taken from different angles and combined by a computer to show a slice of the brain’s structure.
    • Primarily shows structural damage.
  • Positron Emission Tomography (PET):
    • Visual display of brain activity that detects where radioactive glucose goes while the brain performs a task.
    • Indicates functional activity.

Imaging Modalities: Structure vs. Function (continued)

  • Magnetic Resonance Imaging (MRI):
    • Uses magnetic fields and radio waves to produce detailed images of brain anatomy.
    • More detailed than CT for structural information.
  • Functional MRI (fMRI):
    • Measures blood flow and brain activity by comparing successive MRI scans.
    • Can show brain function as well as structure; used to infer regions activated during tasks.

Which Techniques Show Structure vs. Function?

  • Structure:
    • CT (CAT), MRI, and (to a degree) fMRI provide structural information.
  • Function:
    • EEG, MEG, PET, and fMRI provide functional information (activity).
  • Note: fMRI spans both structure and function.

How Do the Imaging Techniques Compare? (Summary)

  • EEG:
    • How it works: Electrodes placed on the scalp measure electrical activity in neurons.
    • Example insight: records real-time electrical activity;
    • Strength: excellent temporal resolution.
  • MEG:
    • How it works: A head coil records magnetic fields from the brain’s currents.
    • Strength: good temporal resolution, less distortion than EEG.
  • CT:
    • How it works: X-rays create images of head structure to locate damage.
    • Strength: fast, good for acute injury.
  • PET:
    • How it works: Tracks a temporarily radioactive form of glucose to map metabolic activity.
    • Strength: shows functional activity patterns during tasks;
    • Limitation: involves radioactive tracer.
  • MRI:
    • How it works: Magnetic fields and radio waves produce detailed images of anatomy.
    • Strength: high spatial resolution for structure.
  • fMRI:
    • How it works: Detects blood flow changes associated with neural activity.
    • Strength: combines structure and function; maps functional activation.

Example Findings (Research Highlights)

  • Depression or anxiety correlates with increased activity in the right frontal lobe (associated with withdrawal and negative emotion): Thibodeau et al., $2006$.
  • PTSD: stronger magnetic fields in the visual cortex when viewing trauma-related images: Todd et al., $2015$.
  • Children’s brain injuries seen on CT scans predict impairments in intelligence and memory processing: Königs et al., $2017$.
  • Anxious temperament in monkeys shows higher glucose use in fear/memory/punishment areas: Fox et al., $2015$.
  • History of violence linked to smaller frontal lobes, especially regions involved in moral judgment and self-control: Glenn & Raine, $2014$.
  • Survivors of trauma (e.g., plane crash) show greater activation in fear, memory, and visual centers when viewing trauma-related material compared to other materials (e.g., 9/11 footage): Palombo et al., $2015$.

AP Exam Tip

  • Knowing which brain imaging technique is used to show activity vs. structure is often tested on the AP Exam.
  • Pay close attention to the chart and understand which method yields structural vs. functional information.

Practice Questions and Answers

  • Question 1 (Page 9): Which scanning technique measures glucose consumption as an indicator of brain activity?
    • A. CT B. MRI C. fMRI D. PET
    • Answer: D) PET.
  • Question 2 (Page 15): Damage to which brain structure puts a person’s life in the most danger because it may cause breathing to stop?
    • A. amygdala B. thalamus C. medulla D. hippocampus
    • Answer: C) medulla.
  • Question 3 (Page 24): Damage to which brain structure would affect the processing of new explicit memories?
    • A. cerebral cortex B. medulla C. corpus callosum D. hippocampus
    • Answer: D) hippocampus.
  • Question 4 (Page 25): Thomas fell and hit his head. How would CT, MRI, and fMRI differently inform doctors about the injury?
    • CT: rapid structural imaging to detect acute bleeding or fractures.
    • MRI: detailed anatomy, better for soft tissue differences and non-acute lesions.
    • fMRI: assesses functional consequences; may show active changes during tasks or at rest; can help map affected networks.

Brainstem Overview

  • Structures making up the brainstem (as listed in the module):
    • Thalamus
    • Reticular formation
    • Pons
    • Medulla
    • Note: Brainstem is responsible for automatic survival functions.
  • Medulla
    • Location: at the base of the brainstem.
    • Functions: controls heartbeat and breathing.
  • Pons
    • Location: just above the medulla.
    • Functions: coordinates movements and helps regulate sleep.
  • Reticular Formation
    • Description: nerve network that travels through the brainstem into the thalamus.
    • Function: helps control arousal and filters incoming sensory stimuli.
  • Thalamus
    • Location: at the top of the brainstem.
    • Function: relay station for incoming and outgoing sensory information (except smell).
  • Cerebellum
    • Location: at the rear of the brainstem.
    • Functions: processes sensory information to coordinate movement and balance; involved in nonverbal learning and memory.

The Limbic System: Structures and Functions

  • Structures: Hypothalamus, Amygdala, Hippocampus
  • Amygdala
    • Description: two Lima-bean-sized neural clusters.
    • Functions: linked to emotion, fear, and aggression.
    • Research highlights:
    • Math anxiety associated with hyperactivity in the right amygdala (Young et al., $2012$).
    • Some studies link criminal behavior with amygdala dysfunction (Boccardi et al., $2011$; Ermer et al., $2012$).
    • Angry vs. happy faces: only the angry ones increase amygdala activity (Mende-Siedlecki et al., $2013$).
  • Hypothalamus
    • Location: below (hypo) the thalamus.
    • Functions: directs eating, drinking, body temperature; helps govern the endocrine system via the pituitary gland; linked to emotion and reward.
    • Research highlights:
    • Stimulating reward centers of the hypothalamus motivates a rat to cross an electrified grid to obtain more stimulation (reward-driven behavior).
  • Hippocampus
    • Structure: small with two arms that wrap around the thalamus.
    • Functions: helps process and store explicit (conscious) memories of facts and events.
    • Research highlights:
    • Humans who lose their hippocampus (surgery or injury) lose the ability to form new memories of facts/events (Clark & Maguire, $2016$).
    • Childhood hippocampal brain tumor survivors may struggle to remember new information in adulthood (Jayakar et al., $2015$).
    • Concussions in NFL players linked to shrinkage of the hippocampus and memory issues (Strain et al., $2015$).
  • Pituitary Gland
    • Role: the “master gland” that controls the hypothalamus by stimulating it to release hormones.

Review: Learning Targets 11-1 to 11-3

  • Learning Target 11-1: Techniques for studying the brain’s connections to behavior and mind
    • Key methods: case studies and lesioning revealed general effects of brain damage.
    • Imaging shows: anatomy via CT and MRI; function via EEG, MEG, PET, and fMRI (functional MRI).
  • Learning Target 11-2: Brainstem, thalamus, reticular formation, cerebellum
    • Brainstem: automatic survival functions.
    • Medulla: heartbeat and breathing.
    • Pons: coordinate movements; sleep.
    • Reticular formation: arousal and sensory filtering.
    • Thalamus: sensory control center.
    • Cerebellum: coordination, balance; sensory processing; nonverbal learning and memory.
  • Learning Target 11-3: Limbic system structures and functions
    • Limbic system: emotions, memory, drives.
    • Amygdala: emotion, fear, aggression.
    • Hypothalamus: maintenance functions; reward; endocrine control via pituitary.
    • Hippocampus: explicit memories; conscious recall.
    • Pituitary: master gland controlling other endocrine glands via hormonal release.

Real-World Relevance and Connections

  • The techniques map closely to foundational neuroscience principles:
    • Localization of function: specific brain regions support specific functions (e.g., amygdala and fear, hippocampus and memory).
    • Structure–function relationships: how anatomy (CT/MRI) relates to activity (EEG/MEG/PET/fMRI).
    • Neuroendocrine integration: hypothalamus–pituitary axis links brain processes with hormonal regulation.
  • Practical implications:
    • Imaging choice depends on whether the question concerns structure, function, or both.
    • Understanding brain injuries and disorders relies on integrating anatomical imaging with functional data.
  • Ethical and safety considerations (implied by imaging methods):
    • CT uses ionizing radiation; PET involves radioactive tracers; MRI/fMRI avoid ionizing radiation but require participant stillness and certain contraindications.