How sounds may cheat sight? Introduction to a article from Neuron Neuron 73, 814–828, February 23,

Background : Multimodal objects and events activate many sensory cortical areas simultaneously. Cross-modal modulatory effects, assessed by extracellular recordings, are thought to consist of subthreshold responses, because suprathreshold, cross-modal sensory responses are rare in primary areas. The synaptic character of these interareal interactions, and their impact on synaptic and behavioral sensory responses are unclear. 2

Introduction ： Auditory cortex activation directly engages local GABAergic circuits in V1 to induce sound-driven hyperpolarizations in layer 2/3 and layer 6 pyramidal neurons. Thereby, sounds can directly suppress V1 activity and visual driven behavior. 3

A noise burst (50 ms; 72 dB SPL) elicited a positive- going FP(Field Potential) response in V1 of both lightly anaesthetized and awake mice Results 1 ： Sound Hyperpolarizes L2/3Ps of V1 4

The upward FP responses were accompanied by hyperpolarizing membrane potential (Vm) responses in all cells Results 1 ： Sound Hyperpolarizes L2/3Ps of V1 5

The response was barely detectable for 48 dB SPL sound intensity and quickly reached a saturating plateau for sound intensities > 64 dB SPL Results 1 ： Sound Hyperpolarizes L2/3Ps of V1 6

Results 2: Sound-Driven Hyperpolarizations in V1 Require Activation of Auditory Cortex and Are Relayed via Cortico-cortical Connections 7

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Results 3: Local GABAergic synapses of V1 are responsible to the Sound-Driven Hyperpolarizations in V1 Due to the change of inhibitory conductance The membrane resistance decreased 9

Results 3: Local GABAergic synapses of V1 are responsible to the Sound-Driven Hyperpolarizations(SH) in V1 PTX/Cs ( GABAa Receptor Antagonist, which block the chloride channel) abolished the SH 10

Results 3: Local GABAergic synapses of V1 are responsible to the Sound-Driven Hyperpolarizations in V1 11

Result 4: Sound-Driven Activation of an Interlaminar Inhibitory Circuit in V1 12

L5Ps account for the SHs in V1 Thy1::ChR2-EYFP mice, expressionof ChR2 is largely restricted to L5Ps. Result 4: Sound-Driven Activation of an Interlaminar Inhibitory Circuit in V1 13

Acute activation of L5Ps by local perfusion of Muscimol counteracted the SHs in L2/3 Result 4: Sound-Driven Activation of an Interlaminar Inhibitory Circuit in V1 14

15 The muscimol perfusion was restrict in L5/6

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17 Result 5: Heteromodal Hyperpolarizations Are Widespread among Primary Sensory Cortices

18 Result 6: Effects of Sound-Driven Hyperpolarizations on Electrophysiological and Behavioral Visual Responsiveness Acoustic Stimulation Reduced Synaptic Responses to Visual Stimuli

Behavial test diagram 19 Visually driven conditioned motor response (V-CMR) The movement data of an animal is calculated by indirectly measuring its acceleration on the platform. This was done by determining the changes in force exerted on the platform by the animal's movements (expressed in grams).

Acoustic simulation strongly diminished V-CMRs when presented simultaneously to the flash 20

The suppressive effect of sound on V-CMRs was independent of sound intensity 21

The suppressive effect of sound on V-CMRs was abolished by acute, bilateral infusion of V1 with GABA antagonists 22

23 The End