Ch. 2 - Brain Overview & Function

main anatomical axes of the brain

Brain Structure

Hindbrain (life support)

  • medulla oblongata (bottom of brain stem) - respiration, BP, coughing, sneezing, vomiting, heart rate

  • pons (middle of brain stem) - bridge between cerebrum and cerebellum; balance, sleep, arousal

    • reticular formation (also part of midbrain!) - main job is consciousness & wakefulness

  • cerebellum - muscle coordination, balance, general motor behavior


Midbrain (top of brain stem)

  • bridge between lower brain stem & forebrain; relays visual/auditory signals

  • has superior & inferior colliculi (4 bumps on the back of midbrain)


Forebrain

  • thalamus - relays info to cerebral cortex (w/ a little bit of preprocessing)

  • hypothalamus - controls pituitary gland (controls endocrine system) & homeostatic behaviors (e.g. temp. control, eating, drinking, sleep etc.)

  • hippocampus - long term memory

  • amygdala - emotional learning/memories

  • basal ganglia - voluntary motor behavior

  • cerebrum - brain’s largest part

    • white matter - inner layer of brain (at brain stem, it is outer); carries info between brain structures

    • cerebral cortex (grey matter) - outer layer of brain; processes information

      • frontal lobe

        • motor cortex - fine motor movements

        • prefrontal cortex (PFC) - planning, decision making, inhibitory control; last to develop in brain, first to decline in age

        • parietal lobe - has the somatosensory cortex which processes sensory info (e.g. pain, pressure, touch, temp.)

        • temporal lobe - in the area of the hippocampus & amygdala

        • occipital lobe - visual information processing

  • corpus callosum - major bridge between left & right hemisphere

  • anterior commissure - below and in front of corpus callosum; bridges temporal lobes


Localization of Function

early ideas: different brain areas control different mental abilities (franz gall), phrenology (now discredited) - bumps on skull = ability strength/personality traits (gall’s student spurzheim)

current idea: different brain regions have specialized functions !!


aphasias (disruption of expressive language)

  • language disorder caused by damage to language areas in left side of brain, affecting expression/understanding of language + reading/writing

    • broca’s area (non-fluent aphasia) - damage to left frontal lobe → impaired speech production

      • “walk dog” “book book two table”

    • wernicke’s area (fluent aphasia) - damage to superior posterior temporal lobe → impaired language understanding

      • “you know the smoodle pinkered, and that i want to get him round and take care of him like you want before”


homunculus (body map)

  • areas with more sensory input (e.g. hands, tongue, face)


kluver-bucy syndrome (KBS)

  • neurological/psychiatric disorder caused by damage to both temporal lobes, specifically in the amygdala

  • first described in 1939 after observing dramatic behavioral changes in monkeys following surgical removal of both temporal lobes

    • symptoms: hyperorality, hypersexuality, visual agnosia, hyperphagia, memory loss, emotional “flattening”, reduced fear and aggression


limits of localization -

  • not all brain functions can be neatly mapped to specific regions

  • ablation (removal of parts of the brain) showed that memory deficits depended on the amount, not location, of the cortex removed

  • brain = reorganizes, some regions can take over lost functions (equipotentiality), especially in young brains (more plasticity)


Lateralization of Function

referring to how 2 cerebral hemispheres play different roles in cognitive functioning

→ left - language specialization (about 95%) though a few can be bilateralized or right hemisphered dominant

→ right - spatial processing, musical ability & other cognitive activities

analytic-synthetic theory: 2 basic thinking modes; analytic in the left (computerlike info processing) & synthetic in the right (gestalts)


split-brain patients: those whose corpus callosum were surgically severed (happened in some epilepsy cases to prevent seizure spread)

  • resulted in:

    • left hand able to pick up objects but can’t describe/name it

    • information on the left could be identified by touch without seeing, while right hand can’t


Methods for Brain Study

computerized [axial] tomography (CAT/CT)

  • uses x-rays (radiation; invasive) from different angles to create images of the body

  • scans allow us to see “slices” of a living brain, which helps with diagnosing brain injury

magnetic resonance imaging (MRI)

  • uses strong magnetic field + radio waves to make images

    • radio waves make molecules in body line up, before returning to normal and sending signals, which show different tissues of body

  • better contrast resolution & no radiation

positron emission tomography (PET)

  • injects radioactively labeled compound, measuring blood flow to different regions of the brain

  • uses radiation (invasive) → scans show “slices” of living brain

single-photon emission computed tomography (SPECT)

  • nuclear medicine scan using a radioactive tracer, creating 3D images of organ function, involving radiation exposure (invasive)

  • commonly used for cardiac perfusion/stress testing & brain disorders

  • lower contrast/spatial resolution but cheaper than PET scan

functional magnetic resonance imaging (fMRI)

  • examines brain function by evaluating blood flow across different brain regions

    • occurs when a part of the brain becomes more active → more blood flow → more oxygen → more MRI signal in that region


electrical recording methods

electroencephalography (EEG)

  • measures brain activity using scalp electrodes, detecting different states of consciousness

  • excellent temporal resolution (timing accuracy)

  • limited spatial detail

magnetoencephalography (MEG)

  • measures magnetic field from brain activity

  • precise location of brain function + timing accuracy

  • better spatial resolution

  • often used with MRI (more expensive than EEG)

event-related potential (ERP)

  • measures brain responses to specific events via EEG before, during and after stimulus

transcranial magnetic stimulation (TMS)

  • studies specific brain circuit activity via magnetic coil near scalp to excite/inhibit targeted brain areas

  • used in research/clinic


Brain Training

neuroplasticity: brain’s ability to adapt by changing its structure and function

  • enriched environments → better brain development + dendritic fields

  • brain games → improved cognitive skills (perhaps in memory/processing speed) but limited to trained stacks, lack broad/lasting benefits (doesn’t prevent major declines like alzheimer’s), and no studies yet meet the highest research standards

  • physical exercise + social activities = stronger health benefits (than only brain training)