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Salient features of synaptic organisation in the cerebral cortex
1Medical Research Council, Anatomical Neuropharmacology Unit, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3TH, UK. peter.somogyi@pharmacology.oxford.ac.uk
Brain Research. Brain Research Reviews
|July 4, 1998
Summary
The cerebral cortex features a basic circuit comprising excitatory and inhibitory neurons, with specific rules governing their connections across areas and layers. This organization suggests information processing relies on precise timing and neuronal firing rates.
Area of Science:
- Neuroscience
- Cellular Biology
- Synaptic Plasticity
Background:
- The cerebral cortex's complex neuronal and synaptic organization necessitates defining a basic cortical circuit for analysis.
- Quantitative studies over two decades have revealed general rules of synaptic connectivity and molecular organization in cortical neurons.
Purpose of the Study:
- To examine the precise location of postsynaptic GABA and glutamate receptors at cortical synapses.
- To define organizational principles of the basic cortical circuit, including neuronal populations, connectivity patterns, and receptor localization.
Main Methods:
- Review of quantitative studies on synaptic connectivity and molecular dissection of identified cortical neurons.
- Analysis of postsynaptic receptor localization (GABA and glutamate) at cortical synapses.
- Examination of organizational principles including neuronal types, connection patterns, and receptor/synapse distribution.
Main Results:
- The synapse definition is expanded to include membrane areas beyond the postsynaptic density due to receptor distribution.
- The cortex comprises principal excitatory neurons and local circuit inhibitory GABAergic neurons with differential connections.
- Specific organizational principles include co-aligned synapses on neuronal surfaces and unique GABAergic axo-axonic cells influencing axon initial segments.
Conclusions:
- Cortical connectivity exhibits remarkable selectivity and adaptability, with a basic circuit repeated and scaled across layers and areas.
- The hippocampus and isocortex share organizational rules, with layered structures in the isocortex allowing for superimposed basic circuits.
- Information coding in the cortex likely involves precise timing, influenced by neuronal geometry, receptor placement, and action potential discharge rates.