Fig. 5.

Discharge probability of pyramidal cells is controlled by strong synaptic inhibition during ripples. (A) Synaptic input of participating (n = 9; red circles) and nonparticipating (n = 9; black circles) cells at the peak of SPW-Rs. Both reversal potential and conductance change (i.e., amount of synaptic input) are not different between groups. Note that, in most neurons, the reversal potential during SPW-Rs is close to the reversal potential of the GABA_A receptor. (B) Event cross-correlation between the peak of the SPW-R and action potentials from pyramidal cells recorded with KAc-filled (n = 13; red) or KCl-filled (n = 14; blue) electrodes (on the left). Although all pyramidal cells have their highest firing probability around the peak of SPW-Rs, the discharge probability for cells with a depolarized GABAergic reversal potential is massively increased. (Inset Left) Both peaks were normalized to one. Note that discharge of pyramidal cells recorded with KCl-filled electrodes peaks earlier. (Inset Right) Original trace of a pyramidal cell recorded with a KCl-filled electrode (Inset Right Upper) and corresponding field potential (Inset Right Lower). The cell fired on 98.3% of SPW-R and emitted 2.7 spikes per SPW-R, underlining the critical role of perisomatic inhibition for signal to noise ratio. (C) Raster plot of action potentials from a cell recorded with a KAc-filled electrode. Picrotoxin (200 μM) was added to the pipette solution. Note the recruitment of the nonparticipating cell ∼10 min after impalement. Right shows a typical coupled action potential from the cell. (D) Ripple-associated firing increases after impalement.