Figure 8.

Global intracellular impedance of cortical neurons recorded in vivo in current-clamp. (A) Scheme of the recording configuration, with a similar representation as in Fig. 2A, but performed in rat somatosensory cortex in vivo (with a contralateral reference electrode), using white-noise current injection. For these experiments, we injected 20 times the same Gaussian white-noise current trace (top, in red), then recorded at 20 kHz and averaged the intracellular potential (top, in blue). We calculated the impedance seen by the neuron. (B) Modulus of the impedance obtained, as a function of frequency. (C) Phase of the impedance. Parameters of the models: (resistive) R_m = 230 MΩ, C_s = 28 pF, and R_e = 29 MΩ; (diffusive) R_m = 100 MΩ, C_m = 21 pF, A = 250 MΩ, B = 24 MΩ, and f_W = 20 Hz. (A, B, and f_W are parameters of the diffusive impedance scaling; respectively, its amplitude, phase, and cutoff frequency.) Representative of N = 18 cells. (D) Distribution of the slopes of Z_eq fitted between 25 and 250 Hz (linear fit, red dashed lines on the figures). (E) Coordinates of the minima of the Fourier phases for each cell. To see this figure in color, go online.