The dendrite - to - soma input / output function of continuous time - varying signals in hippocampal CA 1 pyramidal neurons

We examined how hippocamal CA1 neurons process complex time-varying inputs that dendrites are likely to receive in vivo. We propose a functional model of the dendrite-to-soma input/output relationship that combines temporal integration and static-gain control mechanisms. Using simultaneous dual whole-cell recordings, we injected fifty seconds of subthreshold and suprathreshold zero-mean white-noise current into the primary dendritic trunk along the proximal two-thirds of stratum radiatum and measured the membrane potential at the soma. Applying a nonlinear system-identification analysis we found that a cascade of a linear filter followed by an adapting static-gain term fully accounted for the non-spiking input/output relationship between the dendrite and soma. The estimated filters contained a prominent bandpass region in the 1 to 10 Hz frequency range that remained constant as a function of stimulus variance. The gain of the dendrite-to-soma input/output relationship, in contrast, varied as a function of stimulus variance. When the contribution of the voltage-dependent current I h was eliminated, the estimated filters lost their bandpass properties and the gain regulation was substantially altered. Our findings suggest that the dendrite-to-soma input/output relationship for proximal apical inputs to CA1 pyramidal neurons is well described as a bandpass filter in the theta frequency range followed by a gain-control nonlinearity that dynamically adapts to the statistics of the input signal.