FIGURE 11.

(A–C) Estimated SNRs for EAP and LFP signals from hippocampal neurons. To estimate the SNR, the dependence of the main parameters on electrode size was considered: spatial-averaging effect; the effect of being at the right spot; signal-attenuation due to the impedance ratio (Z_el/Z_a); and noise – both thermal noise of electrode and background activity. The background activity level played a pivotal role in determining the optimal electrode size in both, the EAP and LFP band. Colored bands indicate the SNR levels at different levels of background activity (lower bound of the band is for 8 μV_rms, upper bound at 1 μV_rms and the median at 3 μV_rms). For an axonal branch (A), small electrodes (size < 16 × 16 μm) show peak SNRs. But for somatic or dendritic signals (B), a medium-size electrode (size 8 × 8 μm² – 30 × 30 μm²) were observed to be optimal. LFP signals generally feature high SNRs (C), and electrodes down to 16 × 16 μm² size provide good SNR for all LFP signals. (D) The table summarizes the effects of electrode size on EAP and LFP recording for hippocampal neurons.