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Synaptic integration in
rat frontal cortex shaped by network
activity.
Leger JF, Stern EA, Aertsen A, Heck
D.
University of Tennessee Health Science Center, Dept. of
Anatomy and Neurobiology, 855 Monroe Ave., Room 405, Memphis, TN 38163.
dheck@utmem.edu).
Neocortical neurons in vivo are embedded in
networks with intensive ongoing activity. How this network activity
affects the neurons' integrative properties and what function this may
imply at the network level remain largely unknown. Most of our knowledge
regarding synaptic communication and integration is based on recordings
in vitro, where network activity is strongly diminished or even absent.
Here, we present results from two complementary series of experiments
based on intracellular in vivo recordings in anesthetized rat frontal
cortex. Specifically, we measured 1) the relationship between the
excursions of a neuron's membrane potential and the spiking activity in
the surrounding network and 2) how the summation of several inputs to a
single neuron changes with the different levels of its membrane
potential excursions and the associated states of network activity. The
combination of these measurements enables us to assess how the level of
network activity influences synaptic integration. We present direct
evidence that integration of synaptic inputs in frontal cortex is
linear, independent of the level of network activity. However, during
periods of high network activity, the neurons' response to synaptic
input is markedly reduced in both amplitude and duration. This results
in a drastic shortening of its window for temporal integration,
requiring more precise coordination of presynaptic spike discharges to
reliably drive the neuron to spike under conditions of high network
activity. We conclude that ongoing activity, as present in the active
brain, emphasizes the need for neuronal cooperation at the network
level, and cannot be ignored in the exploration of cortical
function.
PMID: 15306631 [PubMed - in process]
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