Figure 2.
Cortical Requirement for Sound Discrimination Depends on Discrimination Complexity
(A) Sketch of the optogenetic inactivation strategy through a cranial window covering the primary and secondary auditory cortex. For calibration, silicon probes were inserted beneath the window.
(B) Sound response post-stimulus time histogram (PSTH) of a sample PV-negative cell with and without light-driven PV neuron activation.
(C) Mean population response to sounds with and without optogenetic activation of parvalbumin neurons (15 ± 1.4 Hz versus 4.7 ± 0.9 Hz; n = 125 single units; p = 6.2 × 10−18; Wilcoxon rank-sum test) and distribution of sound response reduction during light-ON trials for putative PV-negative neurons.
(D) S+ versus S− discrimination performance for linear SVM classifiers trained on a sample of normal population responses (5 repetitions; one classifier for each 50-ms time bin) and tested on either normal population responses or on population responses recorded during optogenetic inactivation (5 independent repetitions on the same 50-ms time bin; n = 125 single units from 4 mice).
(E) Discrimination performance without (black) and with (blue) optogenetic inactivation of AC during PTvsPT (left; 91% ± 2.4% versus 82% ± 2%; n = 6 mice; p = 0.025; Wilcoxon rank-sum test) and FMvsPT (right; 83% ± 1.7% versus 52% ± 3.5%; n = 7 mice; p = 0.002; Wilcoxon rank-sum test) tasks in mice expressing ChR2 in PV interneurons. The same measurements are shown for control mice without ChR2 expression (dark blue).
(F) Discrimination performance without (black) and with (blue) optogenetic inactivation of inferior colliculus during PTvsPT (left; 85% ± 2.3% versus 54% ± 1.9%; n = 6 mice; p = 0.004; Wilcoxon rank-sum test) and FMvsPT (right; 75% ± 2.7% versus 52% ± 5.6%; n = 5 mice; p = 0.016; Wilcoxon rank-sum test) tasks.
(G) Left: example histological section showing the extent of bilateral AC lesions. Right: mean discrimination performance during PTvsPT before and after AC lesion (97% ± 1.1% versus 87% ± 2.9%; n = 4 mice; p = 0.043; Wilcoxon rank-sum test) or sham surgery (93% ± 1.4% versus 91% ± 4.5%; n = 4 mice; p = 0.8; Wilcoxon rank-sum test) is shown. Bar plots show the mean and SEM throughout the figure.