Sound-driven synaptic inhibition in primary visual cortex

Abstract

Multimodal objects and events activate many sensory cortical areas simultaneously. This is possibly reflected in reciprocal modulations of neuronal activity, even at the level of primary cortical areas. However, the synaptic character of these interareal interactions, and their impact on synaptic and behavioral sensory responses are unclear. Here, we found that activation of auditory cortex by a noise burst drove local GABAergic inhibition on supragranular pyramids of the mouse primary visual cortex, via cortico-cortical connections. This inhibition was generated by sound-driven excitation of a limited number of cells in infragranular visual cortical neurons. Consequently, visually driven synaptic and spike responses were reduced upon bimodal stimulation. Also, acoustic stimulation suppressed conditioned behavioral responses to a dim flash, an effect that was prevented by acute blockade of GABAergic transmission in visual cortex. Thus, auditory cortex activation by salient stimuli degrades potentially distracting sensory processing in visual cortex by recruiting local, translaminar, inhibitory circuits.

Figure 1

Sound Causes Upward FP Deflections in V1 that Are Accompanied by Cellular Hyperpolarizations (A) The grand average ± SEM of FP responses recorded in lightly anesthetized (n = 12) and awake, head-restrained (n = 3), and freely moving (n = 6) mice. Dashed lines are stimulus onsets. (B) Left: examples of individual FP recordings (black) aligned with the onset of a noise burst, averaged over 50 presentations (red). Right: change of spectral content over time relative to the baseline (1 s) of the averaged FP response. (C) Same plot as in B for individual trials (left) and intertrial coherence, measured as the phase-locking factor between trials (right). Note the prominent gamma band after the SH. (D) Examples of simultaneous FP and whole cell (WC) recordings of the V_m from a L2/3P in V1. Magnified SHs are depicted in gray. (E) Overlaid FP and V_m responses of a L2/3P in an awake mouse. Upward FP responses reflect hyperpolarizations. (F) Intensity response of SHs. Examples of V_m (top) and FP (bottom) responses for different sound intensities. The response was barely detectable for 48 dB SPL sound intensity and quickly reached a saturating plateau for sound intensities > 64 dB SPL (^∗p < 0.05 for post hoc tests). Error bars in right plot are SEMs. The gray band depicts the detection level (>baseline ± 2 SD). See also Figure S1.

Figure 2

A1 Activation Causes SHs in L2/3Ps of V1 (A) Left: suprathreshold responses were recorded in layer 5 of A1 in juxtasomal configuration (JS) and V_m responses of L2/3Ps were measured in V1 upon A1 photostimulation. Middle: A1 photostimulation caused spiking of A1 L5Ps, as assessed by JS recordings. Right: A1 photostimulation caused hyperpolarizing responses in L2/3Ps of V1 (n = 8; grand average ± SEM). (B) Example of hyperpolarization of a V1 L2/3P evoked by photostimulation of A1 and by sound in a Thy1::ChR2-EYFP mouse (black). Both evoked a comparable pattern of excitatory (Ge, green) and inhibitory (Gi, red) conductance changes. (C) Muscimol in A1 silenced acoustically-evoked FP (gray) and spiking (black; MUA: multiunit activity) responses measured in the layer 5 of A1. (D) Top: representative sound-driven V_m responses in V1 in controls (black), after A1 inactivation (red) and after the functional recovery of A1 (blue). Bottom: corresponding box plots (^∗∗∗p < 0.001 for Tukey post hoc tests). (E) Sketch of an ISI-targeted transection between V1 and A1. The bottom inset shows the coronal level and that the depth of the transection in Nissl-stained sections reached the white matter. Bars, 1 mm. (F) Drawing of a cortical transection across a coronal slice. The transection did not affect VEP and AEP response in V1 and A1, respectively (n = 6; grand averages; black traces: before the transections, red: after the transections). (G) Examples (top) and box plots (bottom) showing that A1-V1 transection abolished SHs in L2/3Ps of V1 (^∗∗∗p < 0.001). Dashed lines are stimulus onsets. See also Figure S2.

Figure 3

Heteromodal Hyperpolarizations Are Widespread among Primary Sensory Cortices Auditory stimulation (red) caused hyperpolarizations in V1 and S1 (n = 19 and n = 6, respectively). Multiwhisker deflections (blue) caused hyperpolarizations in V1 and A1 (n = 6 for both groups). Visual stimulation (green), failed to evoke detectable responses in A1 (n = 14), but depolarized S1 L2/3Ps (n = 13). Grand averages ± SEM are shown. Dashed lines are stimulus onsets. See also Figures S2 and S3.

Figure 4

GABAergic Inhibition Is Responsible for SHs in L2/3Ps of V1 (A) Changes in excitatory (Ge, green) and inhibitory (Gi, red) conductances evoked by sound in a V1 L2/3P. Top: V_m responses under different current injections (from top: 100 pA, 0 pA, −100 pA). Middle: note the decrease of membrane resistance (R) during the SH. Bottom: time courses of the changes of G_e and G_i. (B) Examples and box plots of subthreshold acoustic responses in controls (black) and during intracellular perfusion with 1 mM PTX/Cs (red). This manipulation significantly counteracted SHs (^∗∗p < 0.01). (C) Examples, grand-averages (left) and amplitudes (right plots) of subthreshold responses to sound measured within 150 ms (top plot) and between 150 and 400 ms (bottom plot) poststimulus in the presence of GABA_A (gabazine 1.5 μM, green, n = 8), GABA_B (CGP52432 1 μM, red; n = 15) antagonists or both (blue; n = 6). Gabazine and CGP52432 effectively counteracted SHs in the early (^∗∗∗p < 0.001, for post hoc test) and late (^∗∗p < 0.01, for post hoc test) time windows, respectively. (D and E) Effects of GABA_A and GABA_B antagonists on SH kinetics. Onset latencies (D) and half-widths (E) of SHs under GABA_A (green) or GABA_B (red) antagonists. (D) Gabazine significantly delayed the onset of SHs (^∗∗∗p < 0.001, for post hoc test). (E) Both gabazine and CGP52432 significantly shortened SHs (^∗∗∗p < 0.001, for post hoc test). See also Figure S4.

Figure 5

Layer-Specific Effects of Sound on V1 Pyramids (A) Subthreshold (left) and suprathreshold (right) responses to sound in pyramidal neurons of different layers. Grand averages ± SEM.; bin size: 50 ms. Sound hyperpolarized all L2/3Ps (n = 19) and L6Ps (n = 7). L4Ps were not responsive (n = 5), whereas responses of L5Ps were heterogeneous (from top to bottom: n = 3 depolarizing; n = 5 not responsive; n = 4 hyperpolarizing). Note that the onsets and peaks of depolarizing responses of L5Ps preceded those of SHs in the other layers. (B) Spike recordings from a tetrode in layer 5 of V1 showing the raster plots (top) and the corresponding instantaneous firing rates (bottom) of three units that were excited, inhibited or unresponsive to noise (blue, red, and black, respectively). See also Figure S5.

Figure 6

Activation of Infragranular Layers Mediates SHs in L2/3Ps of V1 (A) Photostimulation (PS) of L5Ps hyperpolarized overlying L2/3Ps in V1 (grand-average ± SEM; n = 5). (B) Diagram showing the mean onset latencies ± SEM of (1) hyperpolarizations of V1 L2/3Ps driven by A1 photostimulation, (2) SHs of L2/3Ps in V1, (3) sound-driven activation of L5Ps in V1 (left) and hyperpolarizations of L2/3Ps in V1 driven by the phostimulation of L5Ps in V1 (right). (C) Top: whole-cell recordings from L2/3Ps after the injection of muscimol in infragranular layers of V1. Bottom: Nissl-counterstained, coronal section through V1 showing that the injected fluorescent muscimol did not leak into supragranular layers. Bar, 400 μm. (D) Muscimol abolished spiking in L5 (gray) without modifying the resting V_m of L2/3Ps (black) and its variance over time (“L5/6” in bottom plots). On the contrary, muscimol diffusion to the entire cortex dramatically affected the resting V_m and its variance (“Cortex” in bottom plots, ^∗∗∗p < 0.001 for post hoc test). (E) Acute inactivation of L5/6 activity by a local puff of muscimol counteracted SHs in overlying L2/3Ps of V1 (red, n = 16) with respect to controls (black, n = 19; ^∗∗∗p < 0.01). Squares in the box plot (right) indicate the experiments with fluorescent muscimol. See also Figure S6.

Figure 7

Acoustic Stimulation Reduced Synaptic Responses to Visual Stimuli (A) Example of averaged sub- and suprathreshold responses (PSTH and raster plot) of a L2/3P in V1 upon stimulation with an optimally oriented moving bar with (left) and without (right) concurrent acoustic stimulation. (B) Acoustic stimulation reduced subthreshold (top left; ^∗∗∗p < 0.001) and suprathreshold (top right and bottom left; ^∗p < 0.05) visual responses. Sound also reduced reliability of visually-driven spiking, as expressed by the increase of the coefficient of variation of single-trial AP counts (bottom right; ^∗p < 0.05).

Figure 8

Behavioral Effects of Acoustic Stimulation on a V1-Dependent Task (A) Protocol to test acoustic influences on visually driven behavior. A flash was paired to a footshock (red), causing the emergence of a V-CMR. Twenty-four hours later, V-CMRs were measured following the pairing of the flash with a noise burst presented at different SOAs. (B) Time course of the motor activity of the mouse expressed as percentage of the maximal response. Muscimol in V1 (dashed line, n = 3) during conditioning prevented the acquisition of the V-CMR as observed in controls (continuous line, n = 8; p < 0.01). Traces represent grand-averages. Vertical dashed line represent flash onset. (C) Acoustic simulation strongly diminished V-CMRs when presented simultaneously to the flash (SOA 0 ms, dashed line), but not later (SOA +100 ms, continuous line; grand averages are shown, n = 8; p < 0.01). (D) Effect of different SOAs on V-CMRs. Sound significantly reduced V-CMRs when simultaneously presented to light (SOAs = 0 ms and −25 ms; ^∗∗p < 0.01 and ^∗p < 0.05, respectively), but not when presented later (SOAs from +25 to +100 ms; p > 0.2). Gray bar is the mean V-CMR ± 2SD. (E) Heteromodal suppression depends on sound intensity. The auditory suppression of V-CMR was present for sound intensities larger than 50 dB SPL and did not depend on sound intensities (p > 0.3). Gray bar is mean ± 2SD. (F) The suppressive effect of sound on V-CMRs was abolished by acute, bilateral infusion of V1 with GABA antagonists (red, 100 μM PTX + 3 μM CGP55845) compared to vehicle-injected controls (black, at SOA 0 ms, ^∗p < 0.01 for post hoc test). Means ± SEM are shown. See also Figure S7.