The Brain: Structure, Function, and Study
Introduction to the Brain
Why study the brain? The brain is considered the basic machinery that defines who we are.
What is the brain?
It contains approximately 40 ext{-}80 ext{ billion} neurons.
It weighs about 1.3 ext{ kgs}.
It is divided into numerous regions and subregions.
A primary division separates the brain into "older" and "newer" sections.
For the purpose of these notes, the limbic system is categorized as part of the "old brain."
Biopsychology and the Old Brain
What is the old brain?
It comprises parts of our brain and systems that are found in older evolutionary species.
Almost all plants and animals possess hormones (with the exception of single-celled organisms).
Almost all animals have neurons (sea sponges like Spongebob Squarepants are an exception).
All vertebrates share spinal cords and fundamental brain structures similar to humans.
Important Areas to Know (Old Brain/Limbic System):
Hippocampus: Primarily associated with conscious memory.
Amygdala: Functions as a threat register, linked to emotion.
Hypothalamus: Acts as a reward center; stimulation of the hypothalamus can have significant effects on fundamental drives and emotions. It also controls maintenance functions like eating, helps govern the endocrine system, and is linked to emotion and reward circuitry.
Thalamus: Relays messages between lower brain centers and the cerebral cortex.
Pituitary Gland: Known as the master endocrine gland, controlled by the hypothalamus.
Reticular Formation: Plays a role in controlling arousal and wakefulness.
Medulla: Controls vital autonomic functions such as heartbeat and breathing.
Spinal Cord: Serves as the pathway for neural fibers traveling to and from the brain and controls simple reflexes.
Cerebellum: Coordinates voluntary movement and balance.
The New Brain: Cerebral Cortex
Characteristics of the "New Brain":
Found exclusively in creatures with a similar evolutionary history to humans.
Mainly refers to the Cerebral Cortex.
Cerebral Cortex:
A thin, outer layer of the brain (the term "cortex" means "bark" in Latin).
The deeper part is largely composed of "white matter."
Enables capabilities unique to humans (and some other advanced animals):
Use of language.
Application of logic and complex reasoning to solve problems.
Development of a sophisticated concept of the "self."
It is the ultimate control and information-processing center.
It has specialized areas for different functions.
Historical Perspectives on Brain Study
Phrenology (Early 1800s):
An early method for studying biopsychology and understanding brain structure.
Aimed to understand psychological traits by examining bumps and the shape of the skull.
Certain skull regions were associated with specific psychological faculties (e.g., morality, perception, language).
Popularity and Flaws:
Was very popular despite its scientific inaccuracies.
The central premise was incorrect: there is no relationship between skull shape and brain skills, and the skull does not even precisely follow the shape of the brain.
Philosophical Significance: Despite its empirical failures, phrenology was philosophically on the right track by positing that different parts of the brain are associated with different functions. It merely erred in its measurement methodology.
Studying Brain Function: Case Studies
Phineas Gage (1848):
A famous case study that provided significant insights into the functions of the frontal lobe.
Gage, a railway worker, suffered an accident where an explosion drove a tamping iron through his brain, specifically impacting his frontal lobe.
Remarkably, he survived the injury.
Consequences and Intellectual Capacity After Accident:
While his core intellectual capacities (reasoning, logical problem-solving, language, general intelligence) remained largely intact, his personality and social behavior profoundly changed.
Difficulties in containing emotions.
Increased emotionality and sensitivity.
Impaired decision-making in everyday life.
Loss of ability to conduct himself according to social rules and norms.
Brain Damage and Understanding Brain Function:
Much understanding of cerebral cortex functions came from studying patients with brain damage.
Significant advances in this area occurred after World War I due to the prevalence of head injuries.
Cerebral Cortex Lobes:
Composed of four distinct lobes, each with its own primary functions.
These lobes interact extensively with each other.
Understanding each lobe and its respective functions is crucial.
Advanced Tools for Brain Study
Cognitive Neuroscience: The field that directly studies the brain using various advanced tools.
Electroencephalogram (EEG):
Measures electrical signals on the scalp, which are generated by firing neurons.
Provides excellent temporal resolution (when brain activity occurs).
Positron Emission Tomography (PET) Scan:
Involves injecting a person with radioactive glucose.
The scan detects areas where glucose is being consumed in the brain, indicating active brain regions.
Magnetic Resonance Imaging (MRI):
Uses strong magnetic fields to create detailed images of soft tissues, including the brain.
Offers improved spatial resolution (where brain activity occurs) compared to EEG.
Can be used to image all body parts, not just the brain.
Allows for visualization of brain structures (e.g., going back to front or side to side).
Functional MRI (fMRI):
A specialized type of MRI that provides information about brain function in addition to structure.
Uses a rapid succession of MRI images to detect blood flow in active areas of the brain.
Reflects neuronal activity indirectly by measuring changes in blood oxygenation.
NYUAD possesses a dedicated fMRI scanner.
Magnetoencephalogram (MEG):
Measures magnetic waves produced by brain activity, similar to a sophisticated EEG.
Can be configured for upright or flat positions.
NYUAD is rare among universities without a medical school to have an upright MEG scanner.
Brain Specialization and Hemispheres
Cross-Laterality:
Different halves of the body are primarily controlled by different halves of the brain.
The left side of your brain largely controls the right side of your body, and the right side of your brain largely controls the left side of your body.
Similarly, perception in the left visual field is processed in the right brain, and vice versa.
Class Exercise Example: Trying to move the right hand and right ankle in opposite directions simultaneously is difficult, illustrating the coordinated control within one hemisphere. Doing it with the left hand and right ankle (controlled by different hemispheres) is much easier.
Left Hemisphere Specialization:
Speech and language (most people are right-handed, linked to left-hemisphere dominance for language).
Reasoning.
Calculation.
Right Hemisphere Specialization:
Nonverbal information processing.
Visual-spatial information processing.
Emotion (perceiving and portraying emotional expressions like faces).
Intuition and insight.
Creativity.
Illustrative Example: "Happier Face" Illusion: When presented with two mirror images of the same face, most people perceive the left-sided image (processed by the right hemisphere, which specializes in emotion) as happier.
Corpus Callosum:
A thick band of axon fibers connecting the two cerebral hemispheres.
Allows the brain to function seamlessly by facilitating communication between the specialized halves.
Despite hemispheric specialization, the corpus callosum ensures integrated brain function.
Split-Brain Patients:
In some medical cases (e.g., severe epileptic seizures), the corpus callosum may be surgically severed.
Studying "split-brain" patients provides profound insights into normal brain processing and the distinct functions of each hemisphere operating independently.
Further Functional Specialization
Brain specialization extends beyond the left/right hemispheres to specific localized regions:
Fusiform Face Area (FFA): More highly activated when processing faces compared to other stimuli.
Parahippocampal Place Area (PPA): Shows greater activation for places than for other types of stimuli.
Extrastriate Body Area (EBA): Primarily activated by body parts.
Visual Word Form Area (VWFA): More activated by words than by other visual stimuli.
Key Discussion Points from Biopsychology
Importance of Biological Psychology: It is crucial to specifically study biological psychology to understand the neural and biological bases of human behavior, thought, and emotion. This approach differs from merely applying general biological principles, as it focuses on the unique complexities of the human brain and its systems in relation to psychological phenomena.
Role of Animal Models in Neuroscience: Despite advances in neuroimaging techniques, the question remains whether animal use is still necessary for understanding human behavior.
Arguments for continued use: Animal models often allow for invasive studies or manipulations that are ethically impossible in humans, providing fundamental insights into brain circuits, genetic influences, and early developmental processes. They can also provide models for complex disorders that cannot be fully replicated or understood through imaging alone.
Arguments for reducing/replacing animal use: Neuroimaging offers non-invasive ways to study complex human cognition and behavior directly. Ethical concerns regarding animal welfare drive the development of alternatives, and the limitations of generalizing findings from animal brains to the highly complex human brain are recognized. The goal is often to refine, reduce, and replace animal use where possible, leveraging human-specific data from neuroimaging.
The balance lies in using the most appropriate tools for specific questions, combining insights from animal models with human imaging and clinical studies to build a comprehensive understanding. The question implies a nuanced discussion that balances ethical considerations with scientific necessity and technological capability. The advent of neuroimaging complements rather than entirely replaces other methods.