Theta-frequency resonance in hippocampal CA1 neurons in vitro demonstrated
by sinusoidal current injection.
L. Stan Leung and Hui-Wen Yu.
Departments of Physiology and Clinical Neurological Sciences, The
University of Western Ontario, London, Canada N6A 5A5.
APStracts 4:331N, 1997.
ABSTRACT
Sinusoidal currents of various frequencies were injected into hippocampal CA1
neurons in vitro, and the membrane potential responses were analyzed by cross
power spectral analysis. Sinusoidal currents induced a maximal (resonant)
response at a theta frequency (3 - 10 Hz) in slightly depolarized neurons. As
predicted by linear systems theory, the resonant frequency was about the same
as the natural (spontaneous) oscillation frequency. However, in some cases,
the resonant frequency was higher than the spontaneous oscillation frequency,
or, resonance was found in the absence of spontaneous oscillations. The
sharpness of the resonance (Q), measured by the peak frequency divided by the
half-peak-power bandwidth, increased from a mean of 0.44 at rest to 0.83
during a mean depolarization of 6.5 mV. The phase of the driven oscillations
changed most rapidly near the resonant frequency and it shifted about 90o over
the half-peak bandwidth of 8.4 Hz. Similar results were found using a
sinusoidal function of slowly changing frequency, the ZAP function, as the
input. Sinusoidal currents of peak-to-peak intensity of > 100 pA may evoke
nonlinear responses characterized by second and higher harmonics. The theta-
frequency resonance in hippocampal neurons in vitro suggests that the same
voltage-dependent phenomenon may be important in enhancing a theta-frequency
response when hippocampal neurons are driven by medial septal or other inputs
in vivo.
Received 3 March 1997; accepted in final form 17 November 1997.
APS Manuscript Number J188-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997