Dynamic Spike Threshold Reveals a Mechanism for Synaptic Coincidence Detection in Cortical Neurons in vivo

Cortical neurons are sensitive to the timing of their synaptic inputs. They can synchronize their firing on a millisecond time scale and follow rapid stimulus fluctuations with high temporal precision. These findings suggest that cortical neurons have an enhanced sensitivity to synchronous synaptic...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2000-07, Vol.97 (14), p.8110-8115
Main Authors: Azouz, Rony, Gray, Charles M.
Format: Article
Language:English
Subjects:
Action potentials
Animals
Biological Sciences
Cats
Cell Membrane - physiology
Cerebral Cortex - cytology
Cerebral Cortex - physiology
Depolarization
Electric potential
Evoked Potentials, Visual - physiology
Female
Male
Membrane potential
Membranes
Modeling
Neurology
Neurons
Neurons - physiology
Neuroscience
Sensory Thresholds - physiology
Sodium channels
Standard deviation
Synaptic Transmission - physiology
Time Factors
Visual stimulation
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Summary:Cortical neurons are sensitive to the timing of their synaptic inputs. They can synchronize their firing on a millisecond time scale and follow rapid stimulus fluctuations with high temporal precision. These findings suggest that cortical neurons have an enhanced sensitivity to synchronous synaptic inputs that lead to rapid rates of depolarization. The voltage-gated currents underlying action potential generation may provide one mechanism to amplify rapid depolarizations. We have tested this hypothesis by analyzing the relations between membrane potential fluctuations and spike threshold in cat visual cortical neurons recorded intracellularly in vivo. We find that visual stimuli evoke broad variations in spike threshold that are caused in large part by an inverse relation between spike threshold and the rate of membrane depolarization preceding a spike. We also find that spike threshold is inversely related to the rate of rise of the action potential upstroke, suggesting that increases in spike threshold result from a decrease in the availability of Na+channels. By using a simple neuronal model, we show that voltage-gated Na+and K+conductances endow cortical neurons with an enhanced sensitivity to rapid depolarizations that arise from synchronous excitatory synaptic inputs. Thus, the basic mechanism responsible for action potential generation also enhances the sensitivity of cortical neurons to coincident synaptic inputs.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.130200797