Study Guide for SLH/LIN 350(C): Language and the Brain


Introduction

  • Name of TA: Gabriel Gallinate

  • Academic level: Third-year PhD student in the Linguistics Department at UT Austin.

  • Origin: Bolivia, residing at 4000km above sea level.

  • Research focus: How humans express the concept of motion and space; Current project involves documenting and describing motion, path, and orientation in Ese Ejja, a language spoken by about 1000 people in the Amazon.

Debunking Some Brain Myths

  1. Neurons in the Brain - The human brain has approximately 80 billion neurons, contrary to the common belief of 100 billion.

  2. Using 10% of Our Brain - Myth that we only use 10% of our brains; significant brain activity occurs across various regions.

  3. Bigger Brains Do Better - The size of the brain does not directly correlate with intelligence or capability; Haller’s rule on allometric scaling indicates variations across species.

Counting Neurons

  • Suzana Herculano’s method for counting neurons involves: 1. Slicing the brain into smaller pieces. 2. Dissolving brain tissue in Triton X-100 detergent. 3. Shaking the mixture for 20 minutes. 4. Adding DNA-binding fluorescent dye (DAPI) to visualize cells.

  • Final neuron count in a human brain: around 80 billion.

Brain Functionality Myths

We Only Use 10% of Our Brain?

  • Huth et al. (2016) discussed that in multiple brain regions, about 10% of neurons fire during many activities, leading to the myth. In fact, most neurons are excitatory, making 100% activation hazardous and counterproductive (e.g., triggering seizures).

Do Bigger Brains Perform Better?

  • Haller's rule states that brain mass scaling follows an exponential function.

  • Brain mass does not directly translate to functionality or cognition since the number of neurons per unit mass varies across species.

Types of Neurons

  • Overview of neuron types includes: 1. Pyramidal Neuron 2. Stellate Neuron 3. Granule Neuron 4. Oval Neuron 5. Basket Neuron 6. Chandelier Neuron

Neuronal Communication

  • Mechanism: Neurons use electro-chemical signals for communication, where voltage changes result in neurotransmitter release.

  • Communication through: - Molecule Release - Ligand binds to receptor, initiating signaling pathways. - Local imprecise communication compared to more coordinated electrical signals.

Electrical Communication in Neurons

  • Importance of Electrochemical Signals: - Travel long distances efficiently, outperforming mere chemical methods which only work short distances. - Neural communication relies on the fast signaling afforded by electrical signals occurring in a saline medium (the brain).

The Axon Revolution

  • Enables distal and precise communication within the brain.

  • Signal speed varies based on axon properties (length and thickness) - e.g., sciatic nerve signals travel at 42 m/s in humans and 70 m/s in elephants.

  • Myelination increases conduction speed; nodes of Ranvier amplify signals at these nodes.

Axonal Arborization

  • In neurons, axons can bifurcate, sending collateral signals to numerous neurons, yet many of these signals lack successful transmission due to constraints in neuronal connections.

Synapses: Connection Points Between Neurons

  • Neurons connect at synapses through various types of junctions: 1. Axodendritic: from axon to dendrites; most common. 2. Axosomatic: from axon to soma. 3. Axoaxonic: from axon to axon; influences neurotransmitter release directly.

Glial Cells

Microglia

  • First responders in the brain's immune response.

  • Perform phagocytosis to remove dying cells and pathogens.

Macroglia

  • Overseers of the nervous tissue, including: - Oligodendrocytes: Produce myelin, increasing signal conductivity. - Astrocytes: Support neurons in various ways: - Surround synapses to regulate neurotransmitter release. - Form the blood-brain barrier. - Prune excess synapses as development matures; influent critical periods of learning.

Behavioral and Cognitive Correlates of Glia

  • Example: Einstein had a higher density of astrocytes in specific brain areas compared to other individuals, highlighting potential links between glial cell counts and cognitive ability.

Myelin and Multiple Sclerosis

  • Effect of Demyelination: Multiple sclerosis leads to visual and mobility declines as myelin deteriorates, particularly evident in optic and sciatic nerves. Symptoms manifest due to impaired neural transmission.

The Neuron Doctrine

Historical Foundations

  • The Neuron Doctrine explains that: - Neurons communicate through contact (Cajal) vs. continuity (Golgi). - Various staining techniques like Golgi and Nissl stains visualize different aspects of neurons.

Action and Graded Potentials

Action Potential Discovery

  • Action potentials (spikes) were first recorded by Julius Bernstein around 1865; these discoveries predate the identification of neural components like the sodium-potassium pump.

Characteristics of Action Potentials

  • All or None Principle: Neural spikes are identical in shape and function, significantly influencing models of processing in modern computing.

Neuromodulation

Concepts in Modulation

  • Distinction made between mediation (neural circuitry) and modulation (performance).

  • Electronical and biochemical modulators play roles in neurotransmitter action.

  • Terminology: - Agonist: activates receptors. - Antagonist: blocks receptors.

Neurotransmitter Classes

  • Major Classes: - Amino Acids: Glutamate and GABA. - Amine Neurotransmitters: Dopamine, norepinephrine, serotonin, and acetylcholine. - Nonclassical: Neuropeptides and gases. - Functionality differs across neurotransmitter types based on systemic roles (motility, emotional response, etc.).

Advanced Neuroanatomy

  • Cerebral Regions: Discusses relative roles of various brain structures in cognitive function, motor control, emotional regulation, and sensory processing.

  • Modern Techniques: Usage of fMRI, EEG, MEG for mapping real-time brain activity to comprehend deeper cognitive processes.

Brain Rhythms and their Significance

  • Brain rhythms (gamma, beta, alpha, theta, delta) indicate various cognitive and emotional states.

  • Significance noted in pathological states, such as schizophrenia or ADHD, related to disruptions in normal rhythmic activity.

Neural Bases of Language and Communication

Language Localization

  • Key studies focused on Broca’s area (speech production) and Wernicke’s area (comprehension) elucidating the modular aspects of language in the brain.

Lexical Concepts and Word Meaning Processing

  • Exploration of how brains categorize and differentiate meanings based on linguistic context and neuroanatomical structures.

Neuroplasticity and Critical Periods

  • Critical for understanding language acquisition; involves brain adaptability during formative years.

Major Experiments and Observational Studies

  • Different methodologies—longitudinal studies, modeling experiments that uncover how distinct neural systems communicate, process language, and produce speech.

  • Social Implications: Categorization and conceptualization in non-clinical and clinical populations enhance understanding relevant to language recovery strategies post-brain injury.


Overview of Imaging Technologies

  1. Functional Magnetic Resonance Imaging (fMRI)    - Purpose: Measures brain activity by detecting changes associated with blood flow.    - Mechanism: Exploits the fact that cerebral blood flow and neuronal activation are coupled; areas of the brain that are more active receive more blood.    - Resolution: Provides high spatial resolution (millimeters) and moderate temporal resolution (seconds).    - Applications: Used for understanding brain functions, identifying regions involved in cognitive processes, and detecting abnormalities such as tumors.

  2. Electroencephalography (EEG)    - Purpose: Records electrical activity in the brain through electrodes placed on the scalp.    - Mechanism: Captures the electrical impulses produced by neuron activity, allowing for measurement of brain waves.    - Resolution: High temporal resolution (milliseconds) but low spatial resolution.    - Applications: Useful for studying sleep disorders, epilepsy, and cognitive processes like attention and memory.

  3. Magnetoencephalography (MEG)    - Purpose: Measures the magnetic fields produced by neural activity.    - Mechanism: Detects the magnetic fields generated by the electrical currents in neurons, providing a non-invasive means to study brain function.    - Resolution: High temporal resolution (milliseconds) and better spatial resolution than EEG.    - Applications: Often used in mapping brain functions before surgery, studying sensory processing, and cognitive research.

  4. Positron Emission Tomography (PET)    - Purpose: Visualizes metabolic processes in the body, including the brain.    - Mechanism: Involves injecting a radioactive tracer that emits positrons; the emitted radiation is detected to create images of brain activity.    - Resolution: Moderate spatial resolution but low temporal resolution.    - Applications: Used in diagnosing conditions like Alzheimer’s disease, understanding brain metabolism, and tracking tumor activity.

  5. Computed Tomography (CT)    - Purpose: Imaging technique for creating detailed images of internal bodily structures, including the brain.    - Mechanism: Combines multiple X-ray images taken from different angles to create cross-sectional views of the brain.    - Resolution: Good spatial resolution but not typically used for functional studies.    - Applications: Commonly used in emergency settings to detect bleeding, fractures, or lesions in the brain.

  6. Diffusion Tensor Imaging (DTI)    - Purpose: A type of MRI that specifically maps the diffusion of water molecules in brain tissue.    - Mechanism: Focuses on the diffusion process in myelinated axons to visualize white matter tracts in the brain, revealing connectivity.    - Resolution: High spatial resolution, more specialized for studying the brain's white matter pathways.    - Applications: Useful for studying brain development, mapping white matter integrity, and understanding various neurological disorders.