Figure 4. SIn_ACh Neurons Facilitate Weak and Suppress Strong Auditory Responses.

(A) Schematic of the experimental strategy. AAV-FLEX-ChR2-GFP was injected into SIn of ChAT-Cre mice. Multielectrode extracellular recordings were made from ACtx while photostimulating ChR2-expressing SIn_ACh axons and playing sounds. (B) Raster plots for an isolated single unit in response to tone playback (2 kHz, blue or 4 kHz, orange) alone (bottom half), or with photostimulation of SIn_ACh axons (top half). The blue shaded box indicates the light stimulation period. (C) Peristimulus time histograms of response strength (RS) to tone stimulation alone (solid blue/orange traces), or tone + light stimulation (dashed blue/orange traces). (D) Tuning curve for the example unit without (solid trace) or with (dashed trace) stimulation of SIn_ACh axons. (E) Tone RS without light plotted against tone RS with light, for a single experiment. All significantly driven tone responses for each unit are included as individual data points. On average, tone responses are facilitated with light (p = 0.0058). The lighter blue shading indicates the functional prediction bounds for the linear regression. (F) Population tuning curve without (black) and with (blue) light stimulation (data are from 5 mice). (G) Population tone RS plotted against population tone + light RS for each group of responses (± 0, 1, 2, 3 octaves from peak response). The blue line is the linear fit. Values are mean ± SEM.