The spike generation zone of the ampullary electroreceptor

1998

Bioelectromagnetics

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Entrainment of output action potentials from repetitively firing pacemaker cells, brought about by regularly spaced excitatory or inhibitory postsynaptic inputs, is a well‐known phenomenon. Synchronization of neural firing patterns by extremely low frequency (ELF) external electric fields has also been observed. Whereas current densities of ≈10 A‐m−2 are required for direct excitation of otherwise quiescent neural tissue, much lower peak current densities (≈10−2 A‐m2) have been reported to entrain spontaneously firing molluscan pacemaker cells. We have developed a neural spike generator circuit model that simulates repetitive spike generation by a space clamped patch (area ≈ 10−7 m2) of excitable membrane subjected to depolarizing current. Picoampere (pA) range variation of DC depolarizing current causes a corresponding smooth variation of neural spike frequency, producing a physiologically realistic stimulus‐response (S‐R) characteristic. When lower pA range 60 Hz AC current is superposed upon the DC depolarizing current, smooth variation of the S‐R characteristic is distorted by subharmonic locking of the spike generator at 30, 20, 15, 12, 10 Hz, and higher order subharmonic frequencies. Although the additional superposition of a physiologically realistic level of “white” current noise, covering the bandwidth 4–200 Hz, suffices to obscure higher order subharmonic locking, locking at 30, 20, and 15 Hz is still clearly evident in the presence of noise. Subharmonic locking is observed at a root mean square AC simulated tissue current density of ≈10−5 A‐m−2. Bioelectromagnetics 19:92–97, 1998. © 1998 Wiley‐Liss, Inc.

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

1998

Bioelectromagnetics

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The spike generation zone of the ampullary electroreceptor

1995

Biol. Cybern.

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Neural spike generator entrainment by regularly spaced synaptic input

1997

Biological Cybernetics

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It has been known for 30 years that the output of a repetitively firing neuron or pacemaker can be synchronized (locked) to regularly spaced inhibitory or excitatory postsynaptic input potentials. Conditions for stable locking have been determined mathematically, demonstrated in computer simulation, and locking has been observed in vivo. We have developed a neural spike generator circuit model which exhibits stable locking to externally derived simulated inhibitory or excitatory postsynaptic inputs. Conditions for stable 1 : 1 lock, in which pacemaker output frequency matches that of the periodic input, are derived. These take the form of expressions for stable delay and convergence factor which incorporate known or measurable parameters of the circuit model. The expressions have been evaluated and shown to compare satisfactorily with experimental observations of locking by our circuit model.