Higher Cortical Functions Notes

Higher Cortical Functions

I. Overview of Cortical Structure

  • Cerebrum: The cerebrum is the largest and most complex part of the brain, characterized by its outer gray matter. It encompasses two hemispheres (left and right) that communicate with each other through the corpus callosum, a thick band of neural fibers.

    • The cortex is highly convoluted, with a surface area measuring approximately 4,000 cm², allowing for increased surface area for neural processing.

    • It is subdivided into 47 distinct areas of Brodmann

    • The cerebrum contains an estimated 10 to 30 billion neurons. The supporting cells, commonly known as glia, greatly outnumber neurons with a ratio of about 5:1, supporting the intricate networks formed by trillions of synapses.

II. Functional Areas of the Cortex

  • Primary Cortices: primary motor or sensory functions

  • Association Cortices: These areas are crucial for complex cognitive functions as they integrate information from multiple sensory modalities and interact with various other brain regions, enabling advanced behaviors such as decision-making and problem-solving.

III. Major Association Cortices (PAT)

  • Parietal Association Cortex: Plays a vital role in attending to stimuli from both external and internal environments, integrating sensory information to form a coherent perception of the body’s position in space.

  • Temporal Association Cortex: Critical for processing auditory and visual stimuli (nature of stimuli) and understanding their meanings, which is essential for language and recognition tasks.

  • Frontal Association Cortex: Engages in high-level cognitive functions, including planning, decision-making, and regulating emotions—functions that are critical for social interactions and adaptive behaviors.

IV. Under the Microscope

  1. Heterotypical cortex - association cortices

  2. Homotypical cortex - primary areas; granular or agranular neurons predominate

  • Pyramidal cells - precentral gyrus (BA 4 and 6)

  • Granular cells - Postcentral gyrus (BA 3, 1, and 2), Calcarine sulcus (BA 17), Heschel’s gyrus (BA 41 and 42)

V. Frontal Lobe Features

  • The frontal lobe accounts for approximately 30% of the cerebrum (4, 6a, 6b, 8, 9-12, 44-45, 45-47)

    • Primary Motor Cortex (BA 4): Directly involved in controlling individual muscle movements.

    • Premotor Area (BA 6a): Involved in the planning and coordination of movements.

    • Supplementary motor Area (BA 6b)

    • Frontal gaze (BA 8)

    • Broca’s Area (BA 44, 45): Essential for language production and speech function, critical for communication skills.

    • Prefrontal Area (BA 9-12, BA 45-47): Engaged in complex cognitive processes such as planning, reasoning, and decision-making in unpredictable situations.

  • Five Major Circuits Governing its Functions: (MODOA)

    1. Motor Circuit: Involved in executing planned movements.

    2. Oculomotor Circuit: Responsible for controlling eye movements.

    3. Dorsolateral Prefrontal Circuit: Associated with executive functions, including working memory and attention.

      • input: medial and lateral parieto-occipital cortex, caudal superior temporal gyrus

      • lesions: executive dysfunction syndrome - poor organizational strategies, reduced inhibitions, lack of planning, and motor programming deficits

    4. Orbitofrontal Circuit: behavior

      • input: ventral or object processing visual stream, taste, olfactory, and somatosensory inputs

      • lesions: acquired sociopathy - orbitofrontal syndrome (personality changes, emotional lability, irritability, outspokenness, reduced concerns/worries, imitation/utilization behaviors)

    5. Anterior Cingulate Circuit: motivated behavior, reversal learning, reward process and evaluation, adjustments in cognitive control


VI. Temporal Lobe Functions

  • The temporal lobe integrates sensory experiences related to emotions and memory, playing a significant role in forming cohesive representations. Key structures within this lobe include:

    • Primary Auditory Cortex (Areas 41, 42): Processes auditory information and plays a key role in the perception of sounds.

    • Wernicke's Area: Critical for understanding spoken and written language, and its damage can lead to language comprehension disorders.

    • Functions include sensor integration, language comprehension, memory formation, and providing emotional context to experiences, which is vital for social interactions.

VII. Parietal Lobe Functions

  • The posterior parietal lobe is fundamental in various cognitive functions, such as:

    • Perception and Attention: Involved in localizing and orienting towards objects in the environment.

    • Discriminative Senses: Such as graphesthesia (identifying writing on the skin), stereognosis (recognizing objects by touch), and texture discrimination, which are vital for tactile perception.

    • Understanding Spatial Relationships: Particularly through the right inferior parietal lobule, important for spatial reasoning and navigation.

  • Associated disorders include agnosia (the inability to recognize familiar objects), apraxia (difficulty with motor planning), and various visual disorders, which can impact daily living activities.

VIII. Occipital Lobe Functions

  • The occipital lobe is essential for visual perception and recognition; the primary visual cortex is localized in the calcarine fissure (Area 17) and is the first area to process visual input received from the retina.

  • Associated clinical phenomena include:

    • Visual Field Defects: Such as homonymous hemianopia, where half of the visual field is missing.

    • Cortical Blindness: A condition where the eyes are functional but visual information is not processed due to brain damage.

    • Anton’s Syndrome: A rare condition where an individual does not recognize their blindness and may confabulate explanations for the lack of visual input.

  • Dorsal and Ventral Streams: The dorsal stream, often referred to as the "where" pathway, is associated with spatial awareness and movement, while the ventral stream, or "what" pathway, is critical for object recognition and identifying the characteristics of what we see.