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The microcircuit concept applied to cortical evolution: from three-layer to six-layer cortex.

Shepherd GM - Front Neuroanat (2011)

Bottom Line: Here we use the microcircuit concept to focus first on the principles of microcircuit organization of three-layer cortex in the olfactory cortex, hippocampus, and turtle general cortex, and compare it with six-layer neocortex.From this perspective it is possible to identify basic circuit elements for recurrent excitation and lateral inhibition that are common across all the cortical regions.These principles of microcircuit function provide a new approach to understanding the expanded functional capabilities elaborated by the evolution of the neocortex.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Yale University School of Medicine New Haven, CT, USA.

ABSTRACT
Understanding the principles of organization of the cerebral cortex requires insight into its evolutionary history. This has traditionally been the province of anatomists, but evidence regarding the microcircuit organization of different cortical areas is providing new approaches to this problem. Here we use the microcircuit concept to focus first on the principles of microcircuit organization of three-layer cortex in the olfactory cortex, hippocampus, and turtle general cortex, and compare it with six-layer neocortex. From this perspective it is possible to identify basic circuit elements for recurrent excitation and lateral inhibition that are common across all the cortical regions. Special properties of the apical dendrites of pyramidal cells are reviewed that reflect the specific adaptations that characterize the functional operations in the different regions. These principles of microcircuit function provide a new approach to understanding the expanded functional capabilities elaborated by the evolution of the neocortex.

No MeSH data available.


Hypothesized relations between canonical microcircuits for three-layer simple cortex and six-layer neocortex. (A) Simplified representation of the three main types of three-layer microcircuits: olfactory (piriform) cortex, hippocampus; general (dorsal) reptilian cortex. Abbreviations: FI, feedforward inhibition; LI, lateral inhibition; RE, recurrent excitation. For the hippocampus, primary afferents represent the perforant pathway; RE represent the Schaffer collaterals, and LI represent local inhibitory feedback. Pyramidal cells and inhibitory interneurons as in Figure 3. Cortical layers shown on right. (B) Canonical microcircuit for neocortex. Abbreviations: same as A; C-C, cortico-cortical fibers; ST, stellate cell cortical layers shown on right. Arrows indicate direction of flow of activity. Open profiles: excitatory synaptic action; filled profiles: inhibitory synaptic action. From Shepherd (1994).
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Figure 7: Hypothesized relations between canonical microcircuits for three-layer simple cortex and six-layer neocortex. (A) Simplified representation of the three main types of three-layer microcircuits: olfactory (piriform) cortex, hippocampus; general (dorsal) reptilian cortex. Abbreviations: FI, feedforward inhibition; LI, lateral inhibition; RE, recurrent excitation. For the hippocampus, primary afferents represent the perforant pathway; RE represent the Schaffer collaterals, and LI represent local inhibitory feedback. Pyramidal cells and inhibitory interneurons as in Figure 3. Cortical layers shown on right. (B) Canonical microcircuit for neocortex. Abbreviations: same as A; C-C, cortico-cortical fibers; ST, stellate cell cortical layers shown on right. Arrows indicate direction of flow of activity. Open profiles: excitatory synaptic action; filled profiles: inhibitory synaptic action. From Shepherd (1994).

Mentions: The hypothesis is illustrated in the diagrams of Figure 7. The basic circuit common to three-layer cortices is shown in A. The common elements of primary afferents, intrinsic circuits for feedforward inhibition (FI) and lateral inhibition (LI), and RE, are indicated by the labels.


The microcircuit concept applied to cortical evolution: from three-layer to six-layer cortex.

Shepherd GM - Front Neuroanat (2011)

Hypothesized relations between canonical microcircuits for three-layer simple cortex and six-layer neocortex. (A) Simplified representation of the three main types of three-layer microcircuits: olfactory (piriform) cortex, hippocampus; general (dorsal) reptilian cortex. Abbreviations: FI, feedforward inhibition; LI, lateral inhibition; RE, recurrent excitation. For the hippocampus, primary afferents represent the perforant pathway; RE represent the Schaffer collaterals, and LI represent local inhibitory feedback. Pyramidal cells and inhibitory interneurons as in Figure 3. Cortical layers shown on right. (B) Canonical microcircuit for neocortex. Abbreviations: same as A; C-C, cortico-cortical fibers; ST, stellate cell cortical layers shown on right. Arrows indicate direction of flow of activity. Open profiles: excitatory synaptic action; filled profiles: inhibitory synaptic action. From Shepherd (1994).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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Figure 7: Hypothesized relations between canonical microcircuits for three-layer simple cortex and six-layer neocortex. (A) Simplified representation of the three main types of three-layer microcircuits: olfactory (piriform) cortex, hippocampus; general (dorsal) reptilian cortex. Abbreviations: FI, feedforward inhibition; LI, lateral inhibition; RE, recurrent excitation. For the hippocampus, primary afferents represent the perforant pathway; RE represent the Schaffer collaterals, and LI represent local inhibitory feedback. Pyramidal cells and inhibitory interneurons as in Figure 3. Cortical layers shown on right. (B) Canonical microcircuit for neocortex. Abbreviations: same as A; C-C, cortico-cortical fibers; ST, stellate cell cortical layers shown on right. Arrows indicate direction of flow of activity. Open profiles: excitatory synaptic action; filled profiles: inhibitory synaptic action. From Shepherd (1994).
Mentions: The hypothesis is illustrated in the diagrams of Figure 7. The basic circuit common to three-layer cortices is shown in A. The common elements of primary afferents, intrinsic circuits for feedforward inhibition (FI) and lateral inhibition (LI), and RE, are indicated by the labels.

Bottom Line: Here we use the microcircuit concept to focus first on the principles of microcircuit organization of three-layer cortex in the olfactory cortex, hippocampus, and turtle general cortex, and compare it with six-layer neocortex.From this perspective it is possible to identify basic circuit elements for recurrent excitation and lateral inhibition that are common across all the cortical regions.These principles of microcircuit function provide a new approach to understanding the expanded functional capabilities elaborated by the evolution of the neocortex.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Yale University School of Medicine New Haven, CT, USA.

ABSTRACT
Understanding the principles of organization of the cerebral cortex requires insight into its evolutionary history. This has traditionally been the province of anatomists, but evidence regarding the microcircuit organization of different cortical areas is providing new approaches to this problem. Here we use the microcircuit concept to focus first on the principles of microcircuit organization of three-layer cortex in the olfactory cortex, hippocampus, and turtle general cortex, and compare it with six-layer neocortex. From this perspective it is possible to identify basic circuit elements for recurrent excitation and lateral inhibition that are common across all the cortical regions. Special properties of the apical dendrites of pyramidal cells are reviewed that reflect the specific adaptations that characterize the functional operations in the different regions. These principles of microcircuit function provide a new approach to understanding the expanded functional capabilities elaborated by the evolution of the neocortex.

No MeSH data available.