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Efficacy of Thalamocortical and Intracortical Synaptic Connections:Quanta, Innervation, and Reliability

Authors
Journal
Neuron
0896-6273
Publisher
Elsevier
Publication Date
Volume
23
Issue
2
Identifiers
DOI: 10.1016/s0896-6273(00)80788-6

Abstract

Abstract Thalamocortical (TC) synapses carry information into the neocortex, but they are far outnumbered by excitatory intracortical (IC) synapses. We measured the synaptic properties that determine the efficacy of TC and IC axons converging onto spiny neurons of layer 4 in the mouse somatosensory cortex. Quantal events from TC and IC synapses were indistinguishable. However, TC axons had, on average, about 3 times more release sites than IC axons, and the mean release probability at TC synapses was about 1.5 times higher than that at IC synapses. Differences of innervation ratio and release probability make the average TC connection several times more effective than the average IC connection, and may allow small numbers of TC axons to dominate the activity of cortical layer 4 cells during sensory inflow.

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