Leech neurons are attached to metal-free field-effect transistors in electrolyte. The voltage in a neuron is controlled through a pipette fused to its membrane. Gaussian transients and ac voltages are applied. The response of the source-drain current is measured. Two types of neuron-transistor couplings are observed. (A) Efficient coupling above 100 Hz with a phase shift of 90°. (B) Efficient coupling from 0.1–1000 Hz without a phase shift. The responses are described by a circuit made of capacitance and resistance of the membrane, by the gate capacitance and by the resistance of the junction.

• Received 26 July 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.4079