Study Notes on Chapter 10: Principles of Neocortical Function
A Hierarchy of Function
Brain plasticity allows large portions to be removed without significant behavioral impact.
Behavior can be influenced across numerous neural levels:
Spinal cord
Brainstem
Subcortical structures
Cortex
General Functionality: Lower levels govern basic movements; higher levels offer precision and flexibility.
Subcortical structures can manage complex behaviors, but the cortex mediates the initiation and combination of these behaviors.
Central Nervous System Hierarchy
Hierarchical control of behaviors from spinal reflexes to complex cortical functions:
Spinal (spinal cord):
Controls reflex responses to sensory inputs (e.g., stretching, withdrawal).
Low Decerebrate (hindbrain):
Executes basic postural support and motor actions (mouth movements).
High Decerebrate (midbrain):
Facilitates spontaneous movements in response to stimuli and automatic behaviors (grooming).
Diencephalic (hypothalamus, thalamus):
Links voluntary actions and automatic processes for self-maintenance (eating/drinking).
Decorticate (basal ganglia):
Organizes sequences of movement and interacts with sensory stimulus to process emotional values.
Typical (cortex):
Integrates emotion and cognitive maps to execute voluntary, organized movements.
Structure of the Cortex
Brain mapping has changed due to varying criteria:
Cell structure or timing of myelination are significant factors.
Brodmann's Cytoarchitectonic Map:
Remains a key tool based on cellular structure.
MRI and newer staining techniques have revealed about 200 cortical areas, expanding from the original 50 of Brodmann's map.
Brodmann's Map
Displays different areas of the brain, providing a visual representation of cortical regions, including:
Lateral and medial views show specific regions identified by numbers (e.g., 4, 6, 3, etc.).
Cortical Cells
Neurons in the cortex are categorized by dendritic spine presence:
Spiny Neurons:
Possess dendritic spines, increase surface area, generally excitatory.
Aspiny Neurons:
Lack spines, generally inhibitory.
Neocortical Cells and Layers
Layers possess specific structures:
Columnar Organization:
Consists of various types of cells such as pyramidal and spiny stellate cells.
Different functional roles of cortical layers and their corresponding afferents/efferents:
Layer IV: Input zone of the cortex receiving sensory information.
Cortical Spots and Stripes
Various cortical structures identified, such as:
Ocular Dominance Columns: Area 17
Blobs: Area 17
Stripes: Area 18
Barrels: Area SI
Multiple Representations: Mapping Reality
Multiple representations exist for various sensory areas (e.g., motor, somatosensory):
Dozens of maps in each sensory modality capture different features of stimuli.
Sensory Integration in the Cortex
The multimodal cortex amalgamates inputs from diverse sensory modalities.
Multimodal processing is widespread in the cortex, showcasing parallel systems for perceiving and interacting with the environment.
Mapping Reality Through the Cortex
Our perception of reality correlates with the extent and type of cortical maps.
Increased maps equate to enriched representations and interactions with existence.
Cortical Systems
Important connections emerge from cortical areas to several regions, modulating behavior significantly:
Frontal lobes.
Paralimbic cortex.
Multimodal cortex.
Subcortical connections and loops.
Cortical Connections
Gestalt Perception: The unified perception of the world as a whole.
Binding Problem: The dilemma surrounding how the brain integrates multiple stimulus information into a coherent perception.
Proposed Solutions:
One high-order cortical area to integrate stimuli (no such area identified).
Interconnections among sensory areas for information sharing (less than half connections identified).
Functional Organization of the Cortex
A hierarchical model of cortical functions proposes:
Anterior cortex (frontal lobe) formulates intentions and executes motor plans.
Units of area categorized as primary, secondary, and tertiary with increasing functional complexity.
Sensory information flows from primary to tertiary areas for processing.
Information travels from the tertiary sensory area to the tertiary motor area for movement planning.
Functional Units of the Cortex
Sensory Unit:
Sensory input flows from primary to secondary areas, evolving from sensation to symbolic processes.
Motor Unit:
These processes transform into intentions in tertiary motor zones.
Output translated into action patterns across secondary and primary motor zones.
Contemporary Model of Cortical Function
A distributed hierarchical model showcases the brain's operation through interactions of numerous modules.
Areas are not isolated processing centers but comprise a cohesive part of an extended neural network supporting cognitive functions.
Cerebral Cortical Networks
Analysis of cerebral networks among 1000 participants indicates significant individual differences in network architecture.
Default Mode Network
Challenges previous notions that the brain is inactive during rest, revealing active networks during non-directed tasks.
The default network remains engaged during active tasks, not solely during rest periods.
Do Human Brains Possess Unique Properties?
The human brain is postulated to have distinct capabilities including:
Use of grammatical language enabling structured communication.
Phonological imagery allows for thought representation via language.
Theory of mind: understanding others’ mental states.
Specific intelligence types, e.g., intuition.
Brain organization shows function-based, connectivity-focused, and topographical divisions.
Variations exist in the number of regions between species, with a noted increase in association area quantity in frontal, parietal, and temporal lobes in humans.
Von Economo Neurons: Exclusive to humans and certain other species, possibly linked to theory of mind.