Functional Organization and Cortical Areas

Functional Organization: Broca's and Wernicke's Areas

  • Broca’s Area

    • Located in the left hemisphere (typically in right-handed individuals).
    • The corresponding area in the right hemisphere is linked to emotional responses to language.
    • Historical Context:
    • Louis Leborgne (Tan): A patient of Paul Broca who could only utter the word "Tan."
    • He had language production deficits, despite intact comprehension.
    • Broca’s aphasia (Expressive Aphasia):
    • Impairment in language production.

  • Wernicke’s Area

    • Located in the left hemisphere of both right-handed and left-handed individuals.
    • Responsible for language cognition.
    • Wernicke’s Aphasia (Receptive/Fluent Aphasia):
    • Patients can produce words but struggle with comprehension.

Wernicke-Lichtheim-Geschwind Model

  • A model describing language processing in the brain.
  • Arcuate Fasciculus:
    • A bundle of nerve fibers connecting Broca’s area and Wernicke’s area.
  • Language Processing Steps:
    • Spoken word reception:
    • Occurs in Area 41 (where the ear is located).
    • Cognition:
    • Begins in Wernicke’s area.
    • Signal transmission:
    • Wernicke's area sends signals to Broca's area for language production.
    • Written word reception:
    • Occurs in Area 17, located in the occipital lobe.
  • Angular Gyrus:
    • Part of the inferior parietal gyrus.
    • Involved in language and number processing, as well as memory and reasoning.
  • BA:
    • Brodmann Area.

The Corpus Callosum & Cortex Overview

  • The Corpus Callosum

    • Largest bundle of nerve fibers connecting the brain's hemispheres.
    • Contains approximately 200 million axons.

  • The Cortex Structure

    • Cortex: The outer surface of the brain.
    • Composed of three main structures:
    • Gyri: Surface elevations.
    • Sulci: Grooves.
    • Fissures: Deep grooves.

The Cortex Function

  • Functions of the Cortex:
    • Consciousness:
    • Primarily managed in the Reticular Formation (Brainstem - Cerebral cortex).
    • Sensory Perception
    • Skilled Movement
    • Emotions and Motivation:
    • Located in the Limbic System (Diencephalon and Brainstem).
    • High Mental Functions:
    • Memory, thinking, and language.

PET Scan (Positron Emission Tomography)

  • Positron Emission Tomography (PET):
    • A medical imaging technique using a radioactive substance.
    • Allows visualization and measurement of metabolic processes, especially in the brain.

Motor and Sensory Cortices

  • Primary Motor Cortex (Precentral Gyrus):
    • Located in the posterior part of the frontal lobe.
    • Anterior to the central sulcus.
    • Function:
    • Generates signals to initiate and control movements.
    • Provides precise movement with appropriate strength and direction.
    • Damage:
    • Causes contralateral hemiparesis (weakness on the opposite side of the trauma).

Pyramidal Cells in Primary Motor Cortex

  • Pyramidal Cells:
    • Key neurons in the primary motor cortex.
    • Specialized neurons with a pyramid-like shape and long axons.
    • Form the Corticospinal Tract.
  • Premotor Cortex
    • Anterior to the Precentral Gyrus (Primary Motor Cortex).
    • Responsible for repetitious and simultaneous movements.
    • Relies on sensory feedback.
    • Supplementary Motor Area (SMA):
    • Located on the dorsomedial part of the premotor cortex.
    • Programs complex movements.
    • Responsible for bilateral movements and planning and executing planned moves.

Sensory Areas

  • Sensory Areas (Located posterior of the brain):
    • Visual Area:
    • Vision; located in the Occipital Lobe.
    • Auditory area:
    • Hearing; located anterior to Wernicke’s area.
    • Vestibular area:
    • Equilibrium.
    • Gustatory area:
    • Taste; located posterior to Broca’s area.
    • Olfactory area:
    • Smell.
    • Primary Somatosensory Cortex (Postcentral Gyrus):
    • Somatosensory: Senses during consciousness (Somatic).
    • Receives sensory information from skin and muscles.
    • Responsible for Spatial Discrimination.
    • Represents body parts with a high degree of sensitivity.
    • Stimulation produces numbness and tingling.

2 Functions of the Cerebral Cortex: Sensory and Motor

  • Precentral Gyrus:
    • Primary Motor Cortex.
  • Postcentral Gyrus:
    • Primary Sensory Gyrus.
  • Motor areas:
    • Premotor Cortex:
    • Planning movement.
    • Primary Motor Cortex:
    • Generation of movement (special regions: Frontal eye & Broca’s area).
  • Sensory areas:
    • Primary Sensory Cortex:
    • Sensation.
    • Association Areas:
    • Add context and meaning to sensation.
    • Multimodal Association Cortex:
    • Association between multiple sensory stimuli.

Prefrontal Cortex

  • Anterior Association Area (Prefrontal Cortex)
    • Functions:
    • Intellect / Cognition / Recall (memory) / Personality.
    • Contains memory needed for:
    • Judgement / Reasoning / Persistence / Conscience Development.
    • Relies on feedback from the Social Environment.