Neuronal integration of synaptic input in the fluctuation-driven regime

Area of Science:

• Neuroscience
• Computational Neuroscience
• Computational Biology

Background:

• Visual cortical neurons experience significant synaptic bombardment during sensory stimulation.
• This bombardment increases input conductance, leading to action potentials primarily driven by membrane potential fluctuations.
• Understanding neuronal responses in this high-conductance state is crucial for deciphering neural coding.

Purpose of the Study:

• To investigate the response properties of model neurons under high-conductance conditions.
• To analyze the impact of simultaneous excitation and inhibition on neuronal firing rates.
• To elucidate the role of synaptically induced conductance changes in modulating neuronal activity.

Main Methods:

• Development of a model neuron incorporating synaptic inputs as transient membrane conductance changes.
• Simulation of simultaneous increases in excitatory and inhibitory inputs.
• Analysis of firing rate dynamics in response to varying input rates and conductance levels.

Main Results:

• Neuronal firing rate initially increases with rising input rates but then decreases at higher rates when excitation and inhibition are comodulated.
• Synaptically induced conductance increase has a dual effect: it shunts fluctuations (decreasing firing) and reduces the membrane time constant (increasing firing).
• These findings are model-independent and applicable to neurons in various cortical areas.

Conclusions:

• Comodulation of excitation and inhibition is not a simple mechanism for controlling neuronal firing rates in high-conductance states.
• The interplay between shunting inhibition and reduced membrane time constant due to conductance changes dictates the complex firing rate response.
• This study provides insights into how cortical neurons process sensory information under dynamic synaptic input conditions.