Brain Theories and Composition

Brain Composition

• The cerebrum contains 16 billion neurons
• The cerebellum contains 69 billion neurons

Historical Brain Theories

• Aristotle believed sensation originated in the heart
• Aristotle thought the brain's purpose was to cool blood heated by passion before sending it back to the heart
• Galen (150-200 AD) theorized the existence of "3 minds"
• Galen believed the brain was the rational soul, the heart, the passionate soul, and the liver the appetitive soul, responsible for hunger
• Galen thought thinking occurred in ventricles and signals were sent through the spinal cord
• Galen believed the body contained blood, black and yellow bile
• Andreas Vesalius (1500-1540) identified the brain as the center for thought, feeling, and action

Advancements in Understanding Brain Function

• Luigi Galvani (1737-1798) discovered the brain uses electricity to function
• Galvani found electricity could be tracked and replicated
• Neurons in the brain can communicate with each other
• Franz Gall (1758-1828) developed phrenology

Localization of Brain Function

• Different brain areas have different functions, which cause growth and bumps on the skull
• Different parts of the brain performing different things can cause a bump to grow like a muscle
• Localization of brain function is correct; however, the original functions associated with areas were wrong
• Early localization theories incorrectly linked brain function to skull shape, justifying racism
• Phineas Gage's case demonstrated different parts of the brain having different functions, as damage led to personality changes
• Pierre Paul Broca (1824-1880) studied a patient who lost the ability to speak after a stroke
• Broca went public, his research showed consistent findings that language is localized in the brain

Philosophy of Mind

• Dualism posits the brain and mind/soul are separate entities
  • Descartes supported Dualism
• Monism/materialism suggests the brain and mind are two manifestations of the same thing
  • Monism states the brain is what the mind does
• Functionalism states the mind carries out functions implemented by the brain
  • Communication is an example of a mind function

Emergence of Psychology

• Wilhelm Wundt established the first psychology lab in 1879 to study thought
• Hermann Ebbinghaus conducted the first memory studies in 1885
• William James authored the first psychology textbooks in 1890

Brain Activity

• The default mode network is where mind-wandering/internally focusing occurs
• Angelo Mosso (1846-1910) and Marie Curie (1867-1934) first recognized brain/radio activity, which allowed visualizing brain activity using MRI
• Active brain areas have a larger volume of blood flow, indicating higher activity, energy use, and blood demand

Brain Lesions and Animal Studies

• Methods to manipulate the brain include brain damage, drugs, and genetic manipulations
• Advantages of studying brain damage is learning the function of specific brain areas
• Limitations of studying brain damage include:
  • Lesions are large and affect multiple brain areas
  • It's difficult to find people with the same brain lesions, leading to inconsistency between cases
  • H.M.'s hippocampus removal to treat epilepsy altered his memory, and he could not form new memories, but retained old ones
• Animal studies overcome limitations using electrolytic lesions
• Electrolytic lesions kill cells and fibers in the targeted area
• Animal studies overcome these limitations using local electrolytic lesions or chemical lesions which is a solution

Stimulation and Imaging Techniques

• Direct brain stimulation (electrical or magnetic) can activate brain regions
  • A limitation is that complicated surgeries are required and performed only when medication fails
• Transcranial magnetic stimulation (TMS) uses low-level neuronal excitation or high-level neuronal inhabitation
  • TMS has a limitation and can only reach 2-3 cm deep, activating all cells rather than specific ones
• Common imaging techniques include EEG, fMRI, PET, and microscopy
• Microscopic imaging cannot be performed on live animals

Electrical Imaging (EEG)

• EEG is mostly conducted on the skull
  • Advantages of EEG include being fast, having high resolution (as fast as cells fire), and measuring multiple regions simultaneously
  • Limitations include measuring the average activity of millions of neurons, mainly in cortical regions

Magnetic Imaging (MRI)

• Structural MRI is mainly based on measuring hydrogen
  • Useful for good resolution, contrast, and detecting structural changes
• Functional MRI measures functional activity based on the amount of BOLD (blood oxygen level dependent)
  • Functional MRI shows more oxygen when the brain is more active and always compares two conditions
    • Limitations include time consumption and that it shows correlations, but not functional explanations Connectivity between brain regions is critical for behavior, like in autism

Brain Hemisphere Specialization and Synaptic Connections

• Roger Sperry (1913-1994) studied differences between the left and right sides of the brain
• Sperry split the sides of the brain in epilepsy patients to slow the spread of seizures
• Rita Levi-Montalcini (1909-2012) was critical for understanding how synapse connections are being formed through chemical reactions
• Post-mitotic neurons can only die, not multiply

Brain Development

• During development, edges fold over to create a tube, with bulges forming into the heart and spinal cord
• The brain develops in three main sections: hindbrain, midbrain, and forebrain
• Development starts around 3 weeks gestation
• At birth, the brain weighs 300 grams, and neurons are not yet fully developed
• By 1 year, the brain weighs 1000 grams, which is almost adult size
• The sensory system develops before integrative and motor systems
  • Spinal cord activity can drive muscle movement before the brain motor system develops
• Neurogenesis, or the formation of new neurons, occurs at birth
• Synaptic pruning strengthens useful synapses and disconnects those that are not
• Brain development can be altered during pregnancy

Neurotransmitters and Axon Guidance

• Serotonin affects mood
• Cell bodies send axons from the cell body to the optical lobe
• The location on the retina corresponds to a specific location in the brain
  • The front of the eye maps to the back of the brain, and the top of the eye maps to the bottom of the tectum
• Cells of origin in the eye guide axons to their destinations during development

Axon Pathfinding and Adult Plasticity

• Axons follow chemical trails to reach their final destinations
• Initially, many axons are formed and move towards the target
  • The target releases nerve growth factor (NGF) to strengthen the axon, released from the post-synaptic cell, strengthens the connection
  • If the target releases NGF, the axon degenerates, and the cell dies via apoptosis
• Adult plasticity involves:
  • Dendrites and spines continually grow and retract
  • Learning and memory can increase their size and connections - Chronic stress can decrease their size and connections

Brain Adaptation and Damage

• The prefrontal cortex is the last structure to fully develop with myelination completed around age 20
• Neurons are post-mitotic, so they cannot divide or replicate after damage
• New stem cells are formed in brain structures like, the hippocampus and striatum
• These new cells are related to learning and memory, not recovery
• Stroke is a temporary dysregulation of blood flow to the brain

Ischemia and Brain Damage Repair

• Ischemia is the loss of blood, oxygen, and glucose
• Hemorrhage can also damage brain cells due to excess blood, oxygen, and CA2+
• Ischemia and Hemorrhage both impair the Na+/K+ pump, leading to excess Na+ inside the cell
• Increased Na+ leads to enhanced glutamate release, which can ultimately kill cells
• Increased activity around the lesion can compensate for loss of cells
• Treatment for stroke:
  • TPA (tissue plasminogen activator) breaks up the blood clot and has to be administered quickly, within 4.5 hours
  • Reducing Ca2+ entry into the cell can reduce glutamate transmission

Plasticity After Brain Damage

• Compensation can occur through increased activity in surrounding areas
• To compensate, other brain regions with damaged neurons project to and increase activity in the surrounding areas
  • Peripheral axons can grow back, but axons in the CNS cannot
  • Collateral sprouting can occur due to the release of neurotrophic factors, leading to denervation (receptor) super sensitivity
• Amputation can cause phantom limbs due to the reorganization of the somatosensory cortex
• Axonal sprouting allows denervated areas to be invaded by other regions, sometimes from far away

Genetics and Heredity

• Genes enhance the chance of mental illness but are not causations
• Gregor Mendel (1822-1884): radically changed genetics
• Mendel found heredity by shifting studies from monkeys to peas
• Mendel explained the structure of DNA

Mendel's Genetics

• Symbol blending theory believes characteristics are from grandparents or mothers, an untrue statement
• Mendel studied plants (green or yellow pods)
• If you mix two species and they are generally infertile, luck is required at the 2nd generation
• The blending theory for how traits are passed down is wrong because then flowers should have a 50/50 chance of being white or red
• Every organism inherits two heredities
  • There are 2 elements of heredity
• Individuals inherit one element from each parent
• One element can dominate the other, with the latter referred to as the recessive element
• Elements are called alleles
  • When both alleles are identical = homozygous
  • When both alleles are different = heterozygous

Chromosomes and DNA

• Genes are located in chromosomes
• Humans have 24 chromosomes
• DNA is comprised of sugar, phosphate, and bases
  • DNA 4 bases (nucleotides): A, T, C, G

DNA, RNA, and Protein Synthesis

• DNA can self-replicate, producing two identical copies and is very stable
• DNA is transcribed into RNA, using 4 bases: A, U, C, G
• RNA translates into proteins Proteins are made of amino acids, with the type of amino acid determined by sequences of 3 bases
• It takes 3 bases to form a code for 1 amino acid Transcription is DNA to RNA, translation is RNA to protein T is replaced with U during transcription of DNA to RNA and slightly changes the sugar
• A single change in the DNA code can lead to a change in an amino acid

Mutations and Epigenetics

• Simple mutations can affect behavior COMT is a protein that breaks down dopamine and consists of a chain of amino acids Epigenetics: All cells contain the same DNA, yet brain cells are fundamentally different from kidney cells All cells contain the same DNA, every cell type makes its own RNA Epigenetics relates to how tightly DNA is rolled up in the cell nucleus Environmental challenges can change the binding of DNA to histones and lead to increases or decreases in DNA This effect can last for a long time and can continue to be transmitted to the next generation
• Mutation is a change in the base sequence of DNA
• Epigenetic change can also occur, it either makes DNA more open or closed, so cells can make more or less proteins Heritability Twin studies (mono vs dizygotic) and Adoption studies

Evolutionary Psychology

• Some behaviors that seem odd today were once important for survival Goose bumps and grasp reflexes Altruism
  • Evolution vs kin selection, reciprocal altruism, group selection