We have an unbelievable amount to learn from using optogenetics in humans. Not just about what the brain does, but what it feels like to be a brain when it’s perturbed in precise ways. Most neuroscience tools are behavioral: e.g. poke a circuit and see what the mouse does. Imagine being able to ask the subject directly: What changed in your experience when we activated this region? Does rhythmically pulsing the retrosplenial cortex with a laser make you feel like you are dissociating from the world (Vesuna S et al., https://doi.org/10.1038/s41586-020-2731-9)?