Electrical properties of layer IV FS neurons in the Somatosensory Cortex.

*P**PVrest, resting membrane potential; Rin, input resistance; τm, membrane time constant. Data are mean ± SEM. Numbers in parantheses are N.Selected values shown in bold are significantly different from the same parameter measured in control cells.*Value is significantly (P**Value is significantly (PResting membrane potential (Vrest) was recorded within the first two minutes after break in. Input resistance (Rin) was calculated from the voltage response measured at the end of hyperpolarizing current steps (600 ms). Membrane time constant (τ) was obtained by fitting a single exponential to the relaxation of membrane potential (Vm) to a −300 pA current injection. Ih current was calculated by the formula Vm2−Vm1, where Vm2 was measured at the end of a −300 pA current step and Vm1 was measured at the maximal hyperpolarization. Depolarizing currents were injected to elicit action potentials (AP) and the AP firing patterns were used to characterize accommodation ratio, APl duration at half-width, AP amplitude and rise time. Single AP properties were measured from the first AP elicited by a minimally supra-threshold current step which elicited a continuous train of APs. AP firing threshold was determined by differentiating the voltage trace (dV/dt) evoked by the current step in current-clamp mode. The voltage and time at which the first AP discharged were taken as the value at which dV/dt≥10. In all recordings, this value exceeded baseline values (an average of the preceding 10–100 ms) by≥20-fold. AP half-width was defined as the period between the half-amplitude point in the rising and decaying phase of the AP. The ratio of the 1st AP/2nd AP was calculated using the peak amplitudes as one measure of accommodation. The ratio of the interval between the first APs and the average interval of the last three APs during a train was calculated as a second measure of AP accommodation. The after hyperpolarization (AHP) amplitude was calculated as the difference from AP threshold to the maximum trough of hyperpolarization.Electrical properties of layer IV FS neurons in the Somatosensory Cortex.