Fig 6.

Isoflurane raises thresholds for facilitation of burst probability by paired stimulation. (A) Individual trials of MUA bursts elicited by TC, L1 and paired stimuli in control conditions and at two concentrations of isoflurane (same conventions as in Fig. 3C apply). (B) Plots of P(Bu) vs recording site for TC, L1 and P bursts in control and isoflurane for the same experiment (full range of parameters shown; TC and L1 stimulation intensities were identical). Data corresponding to the example shown in A are indicated by arrows. Note that in this experiment stimulation intensities in the isoflurane conditions were increased substantially compared with control (control: 35, 45, 55, 65 µA; 0.14 mM isoflurane: 35, 45, 55, 75, 95 µA; 0.29 mM isoflurane: 55, 75, 95, 120 µA; 0.58 mM isoflurane: 55, 75, 95, 120 µA), and that bursts were most reliably elicited by paired stimuli, except at the highest isoflurane concentration. (C) Plot of P(Bu) vs P(Bu)_P,exp of all experiments in the data set. Each point represents P(Bu) averaged across recording sites for a specific pair of stimulation strengths and isoflurane condition (cf. Fig. 3E). For better visibility, data were binned according to isoflurane concentration. Note facilitation of paired responses in control and at low-to-intermediate isoflurane concentrations (points in upper-left quadrant) and absence of facilitation at concentrations >0.5 mM (lower-left quadrant). (D) Zoom-in on lower-left corner of C, illustrating accumulation of points around P(Bu) close to zero at high [isoflurane]. (E) AUROC values and 95% confidence intervals [comparison of P(Bu) vs P(Bu)_P,exp for each concentration bin]. TC, thalamo-cortical; L1, layer 1; P, paired; MUA, multi-unit activity; P(Bu), probability of network burst; P(Bu)_P,exp, expected P(Bu) of paired stimuli; AUROC, area under the receiver-operating curve.