Evidence for frequency-dependent extracellular impedance from the transfer function between extracellular and...

Area of Science:

• Neuroscience
• Computational Neuroscience
• Biophysics

Background:

• The relationship between intracellular membrane potential (V(m)) and local field potential (V(LFP)) is crucial for understanding neural activity.
• The properties of the extracellular medium can influence V(LFP) recordings.

Purpose of the Study:

• To analyze the transfer function F(T) = V(m)/V(LFP) in the cerebral cortex.
• To determine the frequency dependence of the extracellular medium's impedance.

Main Methods:

• Theoretical analysis of the transfer function in the subthreshold regime.
• Experimental recordings of V(m) and V(LFP) in rat barrel cortex in vivo during desynchronized states.
• Application of a mean-field approximation to estimate extracellular medium impedance.

Main Results:

• The frequency dependence of both the extracellular medium and membrane potential affects F(T).
• Experimental F(T) data matched theoretical models only when assuming a frequency-dependent extracellular medium impedance (1/√ω, Warburg impedance) between 3 and 500 Hz.
• A method was developed to estimate extracellular medium impedance without current injection.

Conclusions:

• The extracellular medium exhibits non-resistive properties, evidenced by frequency-dependent impedance.
• These findings have significant implications for accurate modeling of local field potentials.
• The study provides indirect evidence for the complex electrical properties of the brain's extracellular environment.