Precise optical probing of perceptual detection

Summary Establishing causal links between patterns of neuronal activity and perception is crucial for understanding brain function. Electrical and optogenetic stimulation experiments demonstrated that animals can detect activation of a few neurons. However, these methodologies offer very limited control of ensemble activity and yielded highly divergent thresholds. Here, we use holographic two-photon (2P) optogenetic stimulation to probe the detection of evoked neuronal activity at cellular and single action potential resolution, with millisecond precision. We find that mice can detect single action potentials evoked synchronously across <20 olfactory bulb neurons, while ruling out detection of indirect effects using a novel optical sham-photostimulation technique. Our results demonstrate that mice are acutely attuned to sparse, synchronous ensemble activity signals, introducing order-of-magnitude revisions to earlier estimates of perceptual thresholds.