Cerebral Cortex

Introduction to the Cerebral Cortex

  • Highly complex network comprised of 25 billion neurons and 10^14 synapses.

  • Thickness: Only a few millimeters, but it accounts for nearly half the weight of the brain.

  • Critical functions it mediates:

    • Voluntary motor control

    • Sensory perception

    • Learning

    • Memory

    • Language functions

    • Affective processes

Histology of the Cortex

  • The neocortex is the newest part of human brain, located superficially.

  • Composed of six layers arranged parallel to the cortical surface.

  • Localization of function: Specific patches of cortex are specialized to process certain types of information, which means functions are localized to specific cortical areas.

    • The brain's plasticity allows it to take on new/functions under appropriate conditions.

  • Different cortical areas can be mapped based on their structure and function, as recognized by Korbinian Brodmann starting in the early 1900s.

    • Brodmann's areas: Each region assigns numbers (1-44).

Division of the Cortex

  1. Primary Sensory Cortex

    • Detects sensory stimuli; receives input from thalamus.

    • Has reduced occupation of cortical surface through evolution.

  2. Primary Motor Cortex

    • Initiates voluntary action; contributes to corticospinal/corticobulbar tracts.

    • Similar to sensory cortex, has decreased space over evolution.

  3. Association Cortex

    • Handles higher-order information processing; occupies most of human cortex.

  4. Limbic Cortex

    • Often referred to as the emotional brain.

Primary Sensory and Motor Cortex

Primary Somatosensory Cortex (S1; Brodmann’s areas 3, 2, & 1)

  • Located in the postcentral gyrus of the parietal lobe.

  • Impairment: Affects ability to discriminate intensity or localize sensations contralaterally.

  • Occupations affected: Safety in cooking with heat sources.

Primary Visual Cortex (V1; Brodmann’s area 17)

  • Located in the occipital lobe.

  • Impairment: Leads to cortical blindness in contralateral visual field.

  • Occupations affected: Daily activities (ADLs) involving mobility.

Primary Auditory Cortex (A1; Brodmann’s area 41)

  • Located in the transverse temporal gyri.

  • Impairment: Loss of ability to localize sound; minor hearing loss contralaterally.

  • Occupations affected: Listening to music.

Primary Motor Cortex (M1; Brodmann’s area 4)

  • Located in the precentral gyrus of the frontal lobe.

  • Impairment: Results in contralateral paresis.

  • Occupations affected: Basic self-care tasks such as bathing.

  • Topographical organization characterizes primary sensory and motor areas, mapping body surfaces onto cortical areas with distorted representations for sensitive/control regions (e.g., fingers).

Association Cortex

Unimodal Association Cortex

  • Processes higher-order functions for a single sensory/motor modality, often adjacent to primary areas.

  • Impairments lead to agnosia: sensation without perception.

Somatosensory Association Cortex

  • Responsible for interpreting somatosensation.

    • Impairment: Astereognosis (inability to recognize objects by touch).

    • Occupations affected: Finding keys in a purse.

Visual Association Cortex

  • Processes and interprets visual information.

    • Impairment: Visual agnosia.

    • Occupations affected: Grooming tasks.

Auditory Association Cortex

  • Interprets auditory information.

    • Impairment: Auditory agnosia. Includes Wernicke’s area for language comprehension (found in superior temporal gyrus).

Multimodal Association Cortex

  • Integrates multiple sensory/motor functions.

Posterior Multimodal Association Area

  • Located at the intersection of parietal, occipital, and temporal lobes.

  • Integrates sensory information for overall perception.

    • Impairments might result in contralateral neglect, predominantly from right hemisphere damage.

Anterior Multimodal Association Area (Prefrontal Cortex)

  • Responsible for executive functions:

    • Planning, insight, foresight, personality elements.

  • Contains two sub-areas:

    • Dorsolateral prefrontal cortex: Integrates sensory data for executive functions, essential for working memory.

    • Ventromedial prefrontal cortex: Integrates emotions for decision-making.

    • Associated impairments include:

      • Apathy

      • Lack of initiative/goals

      • Difficulty with working memory/planning

      • Disinhibition of emotional/behavioral control.

Right vs. Left Brain Functions and Disorders

  • No evidence of people being strictly "right-brained" or "left-brained".

  • Evidence of lateralization of brain function:

    • Language processing is predominantly left-brained.

    • Attention is primarily a right-brained function.

Aphasia

  • Refers to the inability to use language, associated with left hemisphere damage. Types include:

  • Nonfluent aphasia (Broca’s aphasia): Difficulty producing words but can comprehend.

  • Fluent aphasia (Wernicke’s aphasia): Produces grammatical sentences that lack meaning.

    • Paraphasia: Word substitution;

    • Neologisms: New, meaningless words;

    • Jargon aphasia: Incoherent strings of words.

  • Global aphasia: Involves damage to both Broca's and Wernicke's areas.

Consciousness

  • Defined as a state of self-awareness allowing attention direction and abstract manipulation.

    • Content and Level: Ranges from alertness to drowsiness.

  • Emerges from neuron interactions rather than a specific structure.

States of Unconsciousness

  • Coma: No arousal, awareness, or responsiveness.

  • Vegetative state: Arousal is present, but neither awareness nor responsiveness exists.

  • Minimally conscious state: Arousal with emerging responsiveness/awareness.

Sleep

  • A naturally occurring state of unconsciousness with an active process.

  • The hippocampus is believed to play a role in memory consolidation during sleep.