Synchronization of pacemaker cell firing by weak ELF fields: simulation by a circuit model

Area of Science:

• Neuroscience
• Computational Biology
• Biophysics

Background:

• Neural entrainment to external stimuli is a known phenomenon.
• Extremely low frequency (ELF) electric fields can synchronize neural firing.
• Direct neural excitation requires high current densities, but entrainment of pacemaker cells requires less.

Purpose of the Study:

• To model neural spike generation and investigate entrainment by ELF currents.
• To characterize the stimulus-response relationship under varying current conditions.
• To determine the current densities required for subharmonic locking.

Main Methods:

• Developed a neural spike generator circuit model.
• Simulated repetitive action potential generation in a patch of excitable membrane.
• Applied direct current (DC) and alternating current (AC) with superimposed noise.

Main Results:

• DC current variations produced a smooth stimulus-response characteristic.
• Superposed AC current caused subharmonic locking at 30, 20, 15 Hz and higher.
• Subharmonic locking persisted at 30, 20, 15 Hz even with superimposed noise.
• Observed subharmonic locking at root mean square AC current densities of approximately 10(-5) A-m(-2).

Conclusions:

• Neural spike generators exhibit subharmonic locking to ELF currents.
• This locking phenomenon is robust and observable even in the presence of physiological noise.
• The model provides insights into neural entrainment mechanisms at low current densities.