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Questions and Answers
Which layer characteristic is unique to the neocortex compared to the archicortex and paleocortex?
Which layer characteristic is unique to the neocortex compared to the archicortex and paleocortex?
What is the primary role of the dorsolateral prefrontal cortex in the right hemisphere?
What is the primary role of the dorsolateral prefrontal cortex in the right hemisphere?
Brodmann’s areas were established primarily through what method?
Brodmann’s areas were established primarily through what method?
What cognitive function is primarily associated with the ventromedial prefrontal cortex?
What cognitive function is primarily associated with the ventromedial prefrontal cortex?
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At what stage does the prefrontal cortex reach functional maturation?
At what stage does the prefrontal cortex reach functional maturation?
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Which cell type is primarily responsible for receiving thalamic input within the neocortex?
Which cell type is primarily responsible for receiving thalamic input within the neocortex?
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What is the primary output target of layer 5/6 pyramidal cells in the neocortex?
What is the primary output target of layer 5/6 pyramidal cells in the neocortex?
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In the canonical organization of the neocortex, which type of connections inhibit the soma or axon hillock of principal cells?
In the canonical organization of the neocortex, which type of connections inhibit the soma or axon hillock of principal cells?
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Which statement best describes the vertical organization of cell columns, as observed in rat barrel cortex?
Which statement best describes the vertical organization of cell columns, as observed in rat barrel cortex?
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What role do hypercolumns in the primary visual cortex serve?
What role do hypercolumns in the primary visual cortex serve?
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What defines the majority of axonal outputs in the neocortex?
What defines the majority of axonal outputs in the neocortex?
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What is a characteristic of GABAergic cells within the neocortex?
What is a characteristic of GABAergic cells within the neocortex?
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In the cortical microcircuits, which type of neuron predominantly targets principal cells during feedback inhibition?
In the cortical microcircuits, which type of neuron predominantly targets principal cells during feedback inhibition?
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What significant change occurs in the prefrontal cortex (PFC) during the 7th/8th decade of life?
What significant change occurs in the prefrontal cortex (PFC) during the 7th/8th decade of life?
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Which region of the frontal lobes is associated with decision making and social skills impacted by Phineas Gage's injury?
Which region of the frontal lobes is associated with decision making and social skills impacted by Phineas Gage's injury?
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What is the domain specificity theory concerning prefrontal cortex function?
What is the domain specificity theory concerning prefrontal cortex function?
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Which layer of the neocortex is primarily composed of dendrites with few cell bodies?
Which layer of the neocortex is primarily composed of dendrites with few cell bodies?
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What role do principal cells in the neocortex primarily serve?
What role do principal cells in the neocortex primarily serve?
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What is a key characteristic of horizontal layers within the neocortex?
What is a key characteristic of horizontal layers within the neocortex?
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Which of the following statements about Phineas Gage's injury is correct?
Which of the following statements about Phineas Gage's injury is correct?
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What does persistent neural activity during memory tasks in the dlPFC indicate?
What does persistent neural activity during memory tasks in the dlPFC indicate?
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What was the significance of the computer graphics and neural imaging techniques used in 1994 regarding Phineas Gage?
What was the significance of the computer graphics and neural imaging techniques used in 1994 regarding Phineas Gage?
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What is primarily indicated by the existence of vertical, functional columns in the cortex?
What is primarily indicated by the existence of vertical, functional columns in the cortex?
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Why might columnar organization not be essential for information processing in certain mammals?
Why might columnar organization not be essential for information processing in certain mammals?
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What role do functional columns play in the activity of PFC neurons?
What role do functional columns play in the activity of PFC neurons?
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What type of neural mechanism can sustain persistent activity without external inputs?
What type of neural mechanism can sustain persistent activity without external inputs?
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What characteristic distinguishes Old World monkeys from New World monkeys in terms of neural structure?
What characteristic distinguishes Old World monkeys from New World monkeys in terms of neural structure?
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Which of the following best describes the overall processing architecture of the cortex?
Which of the following best describes the overall processing architecture of the cortex?
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What remains a significant question regarding the columnar structure in the cortex?
What remains a significant question regarding the columnar structure in the cortex?
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What physiological mechanism could explain a rapid on-off control of neural activity around 100ms?
What physiological mechanism could explain a rapid on-off control of neural activity around 100ms?
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How is persistent activity in PFC neurons exhibited based on selectivity and sensitivity?
How is persistent activity in PFC neurons exhibited based on selectivity and sensitivity?
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What characterizes the 'up' state in cortical slow oscillation?
What characterizes the 'up' state in cortical slow oscillation?
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In recurrent excitatory loops of the neocortex, which layer connects with itself?
In recurrent excitatory loops of the neocortex, which layer connects with itself?
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What does the canonical view of information processing indicate?
What does the canonical view of information processing indicate?
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What was the effect of pharmacological inactivation of Layer 4 on sensory-evoked synaptic input to Layer 5/6?
What was the effect of pharmacological inactivation of Layer 4 on sensory-evoked synaptic input to Layer 5/6?
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Which theory proposes that the stimulant identification can be dependent on a single neuron's activation?
Which theory proposes that the stimulant identification can be dependent on a single neuron's activation?
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What does the updated model of information processing suggest about Layer 6's connections?
What does the updated model of information processing suggest about Layer 6's connections?
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Which of the following is cited as a reason why the thalamus might activate separate strata of the cortex?
Which of the following is cited as a reason why the thalamus might activate separate strata of the cortex?
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In cortical processing, what can be implied by saying 'one layer is involved in more abstract/contextual representations than the other'?
In cortical processing, what can be implied by saying 'one layer is involved in more abstract/contextual representations than the other'?
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Which characteristic is a key feature of persistent cortical activity?
Which characteristic is a key feature of persistent cortical activity?
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What is a notable outcome of paired recordings from Layer 5/6 neurons and thalamic neurons in sedated rats?
What is a notable outcome of paired recordings from Layer 5/6 neurons and thalamic neurons in sedated rats?
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Study Notes
Neocortex: Synaptic Organization
- The neocortex has a distinctive layered structure
- Three phylogenetic categories of cerebral cortex exist: archicortex, paleocortex, and neocortex
- Archicortex has 3-4 layers
- Paleocortex has 3 layers
- Neocortex has 6 layers, and is involved in complex functions like perception, learning, and intelligence
- Wilder Penfield's "Montreal procedure" involved stimulating and destroying neurons in the neocortex to treat epilepsy
- This procedure helped to identify primary sensory and motor areas
- Most of the human brain's surface is covered by association cortices, whose functions are known as cognition
- Cognition involves attending to external and internal stimuli, understanding their significance and responding appropriately
- Lower mammals have smooth cerebral cortex, which is simpler, while higher mammals and humans have more folds with well-defined temporal and larger frontal lobes
- Gyri are bumps, and sulci are valleys in the brain
- Fissures are very deep sulci, and function to increase the surface area of the brain and decrease axonal distance
- Brodmann's Areas are numbered areas in the brain, based on the cytoarchitectural organization of neurons
- Brodmann's Areas were identified using Nissl stain, but with little initial knowledge of their functional significance
- Prefrontal cortex is the highest level of cortical hierarchy involved in planning, decision-making, social skills, conscience, working memory and more.
- Prefrontal cortex, especially the dorsolateral and ventromedial areas including the orbitofrontal PFC, are involved in motivated decisions, emotions and autonomic responses, conscience and social skills.
- Prefrontal cortex develops slowly, reaching functional maturity around 15-19 years old
- Neurons in the prefrontal cortex (PFC) demonstrate persistent, or stable activity during delay periods, indicating a potential role in working memory
- Domain specificity theory refers to the idea that different regions of the PFC contribute to different types of working memories
- Different PFC regions play different roles in working memory.
- Persistent activity in the PFC is likely caused by neural connectivity and neuronal biophysics
- The organization of the neocortex shows several recurrent excitatory loop patterns and also shows "up" and "down" states, which are related to sleep and memory
PFC and Working Memory
- Different regions of the PFC contribute to different types of working memory
- Evidence indicates that dorsal PFC is involved in spatial working memory while the ventral PFC is involved in object working memory
- Neural circuits in the PFC can sustain stimulus-selective activity without external input
- Recurrent excitatory loops and local inhibition are possible neural mechanisms for sustained activity and involve rapid turning on and off (around 100ms).
Neocortical Principal cells
- Principal cells (pyramidal cells, Stellate cells, approximately 80% of the neurons): Release glutamate.
- Pyramidal cells are the main output neurons in the cortex; they are large and conical with apical and basal dendrites.
- Granule cells are small and round, and found primarily in layer 4, which receives input from thalamus
- The primary function is to receive input from the thalamus and to make connections onto other neurons in the cortex.
Neocortical GABAergic Cells
- These are local neurons (approximately 20%) that release GABA, an inhibitory neurotransmitter
- There are many different subtypes (bitufted, double bouquet, small basket, large basket, chandelier, and neurogliaform)
Neocortical Canonical Organization
- The circuitry of cortical regions has common features:
- Primary source of input
- Primary output target
- Columnar (radial connections) and horizontal connections
- Thalamus is a major source of input to layer 4
- Cortico-cortical (primarily Layer 2/3) and cortico-cortical (via white matter) connections are primary connections among pyramidal cells
- Layer 5 and 6 pyramidal cells mostly form outputs from the cortex to other cortical areas, the thalamus, other cortical regions, and subcortical structures
Neocortical Afferents (Inputs)
- Thalamus provides input to layer 4, which is considered the main input to the neocortex
- Cortico-cortical projections are the major internal projections in the neocortex, originating from layers 2/3 and often targeting layer 2/3
Neocortical Efferents (Outputs)
- The majority of axons remain within the cortex (90-99%)
- Cortico-cortical projections send output signals to other cortical areas
- Layer 5/6 pyramidal cells target the thalamus, sub-cortical structures, and superior colliculus
Cortical Microcircuit
- Recurrence and feedforward excitation are crucial for persistent activity, involving a balance of excitation and inhibition
Information Processing in Neocortex
- Grandmother cell versus distributed coding theory: which is correct?
- Updated models of sensory information processing show thalamus -> layer 4 -> layer 2/3-> layers 5/6
- Deep cortical layer respond to thalamic inputs
Functional Cortical Columns
- The primary visual cortex consists of hypercolumns for analyzing regions of the visual field (e.g., ocular dominance, orientation columns, and blobs)
- Functional columns can also be found in regions other than primary sensory and motor cortices
Persistent Activity
- Persistent activity is likely correlated with specific circuit configurations that support persistent memory
- There is evidence of multiple recurrent excitatory loops participating in persistent activity
- The model of local circuit recurrent excitation can be useful to understand persistent activity in the cortex by demonstrating feedback loops, recurrent excitation loops, and inhibitory mechanisms that are responsible for the functionality of networks
Vertical Organization - Cell Columns
- "Barrel" cortex has distinctly organized regions of cells in primary sensory cortex, reflecting input from whiskers
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Description
Test your knowledge on the synaptic organization of the neocortex, including its layered structure and phylogenetic categories. Explore the key functions and significance of this complex brain region, and learn about the implications of Wilder Penfield's Montreal procedure in treating epilepsy. Understand how the neocortex contributes to cognition and sensory processing.
