Cerebral Cortex Functions and Pathologies

Cerebral Cortex Overview

  • Functionality:
    • The cerebral cortex is termed the brain's "executive suite" responsible for conscious mind activities including awareness, sensory perception, voluntary motor initiation, communication, memory storage, and understanding.
    • Layers: It consists of a thin (2–4 mm) layer of gray matter, composed of neuron cell bodies, dendrites, glial cells, and blood vessels, lacking axons.
    • Proportion: Accounts for 40% of total brain mass.

Neocortex Structure and Layers

  • Variability exists in each cell layer across the cortex.
    • Sensory Areas: Prominent internal granular layer (layer IV) for sensory input (e.g., primary visual cortex).
    • Motor Areas: Have a smaller layer IV, with more robust output layers (i.e. layer V).
  • Brodmann's Areas: Developed in 1909, this classic subdivision of the cortex is based on observations from a single human brain.

Functional Areas of the Cortex

  • Four General Considerations:
    1. Types of Areas:
    • Motor Areas: control voluntary movement.
    • Sensory Areas: consciousness of sensation.
    • Association Areas: integrate diverse information.
    1. Each hemisphere is responsible for the opposite side of the body.
    2. Lateralization can occur in one hemisphere.
    3. Conscious behavior activates the entire cortex in various manners.

Motor Areas of the Cortex

  • Location: Frontal lobe; responsible for controlling voluntary movement.
    • Components:
    • Primary Motor Cortex: Located in the precentral gyrus; includes large pyramidal cells enabling precise muscle movements via pyramidal (corticospinal) tracts.
    • Somatotopy: Mapping from primary cortex areas to body muscles reflected as a motor homunculus.

Sensory Areas of the Cortex

  • Definition: Concerned with conscious sensory awareness.
  • Main Areas: Includes primary somatosensory cortex, visual areas, auditory areas, etc.
    • Primary Somatosensory Cortex:
    • Located in the postcentral gyrus of the parietal lobe; it processes general sensory information from skin and proprioceptors; features a somatosensory homunculus for sensory input mapping.
    • Visual Areas:
    • Includes the primary visual cortex (occipital lobe) receiving retinal information, and the visual association area interpreting stimuli.
    • Auditory Areas:
    • Primary auditory cortex processes sound information, while the auditory association area retains sound memories.
    • Vestibular and Gustatory Areas:
    • Responsible for balance awareness and taste perception, respectively.
    • Olfactory Area: Involved in the awareness of odors, stemming from the primitive rhinencephalon region that covers part of the limbic system.

Association Areas

  • Multimodal Functions:
    • Integrate inputs from multiple sensory areas for understanding and memory.
    • They are divided into three parts:
    • Anterior Association Area: (Prefrontal Cortex) linked to intellect and personality development.
    • Posterior Association Area: Recognizes patterns and spatial localization, involved in language understanding.
    • Limbic Association Area: Supports emotional significance in memory formation.

Techniques to Study Brain Function

  • fMRI (Functional Magnetic Resonance Imaging): Measures blood flow and can identify active functional regions.
  • PET (Positron Emission Tomography): Visualizes brain activity and localizes motor and sensory functions.
  • EEG (Electroencephalogram): Records electrical activity reflecting higher mental functions, useful for diagnosing conditions like epilepsy.

Brain Waves and EEG Patterns

  • Types of Waves:
    • Alpha Waves: (8–13 Hz) associated with resting state.
    • Beta Waves: (14–30 Hz) indicative of alert states.
    • Theta Waves: (4–7 Hz) seen in children and present in drowsy adults.
    • Delta Waves: (below 4 Hz) typical of deep sleep (high amplitude).

Higher Mental Functions

  • Language:
    • Involves Broca’s area (speech production) and Wernicke’s area (language comprehension).
  • Memory:
    • Types of memory include declarative (facts) and procedural (skills).
    • Memory consolidation involves transferring short-term memory (STM) to long-term memory (LTM) influenced by emotional states and rehearsal.
  • Consciousness:
    • Encompasses perception, movement control, and higher-order processing, defined on a continuum

Sleep Cycles

  • Sleep Definition: Partially unconscious state; includes REM and non-REM sleep phases.
  • Cyclical Nature: Controlled by the circadian rhythm governed by the hypothalamus.
  • Importance: Aids in memory consolidation and physiological restoration.

Clinical Issues and Disorders

  • Cerebrovascular Accidents (CVAs): Refers to strokes; involve ischemia leading to potential paralysis.
  • Neurodegenerative Disorders: Includes Alzheimer’s disease (caused by misfolding proteins leading to dementia) and Parkinson’s disease (caused by depletion of dopamine).
  • Brain Injuries: Include concussions and contusions with varying degrees of impact on functionality.