A light switch for selected brain cells! 🤯 This vid is Part 2! Make sure to check out Part 1 if you missed it. The 2026 Nobel Prize in Physiology or Medicine honors Karl Deisseroth, Peter Hegemann and Georg Nagel. Optogenetics made causal experiments much more precise: scientists already tested causation using stimulation, lesions and drugs. Observational research is science too! The spaghetti and switch metaphors simplify a network in which cells can have several roles. “86 billion” is an approximate estimate from sampled adult brains. Crick's calls for selective control and his light proposal came in separate publications, in 1979 and 1999. Here, “channelrhodopsin” means ChR2. It conducts several positive ions, not just sodium. The resulting depolarization can trigger a spike if firing threshold is reached. Blue-for-go/yellow-for-stop describes this particular pairing of ChR2 with halorhodopsin, an archaeal chloride pump demonstrated for neuronal silencing in 2007. Other tools respond to other colous. A genetic “address label” helps target a population, not necessarily a single neuron or every cell of that type. Delivery, expression and illumination determine which cells respond, and specificity needs controls. Gene delivery plus an implanted fibre describes these mouse experiments; other approaches include transgenic animals and experimental implant-free light delivery in mice. This does not establish arbitrary remote control of an unmodified human brain. The dated recording comes from Boyden's own account: August 4, 2004, in Richard Tsien's lab, after Deisseroth delivered the gene. The 2005 paper was by Boyden, Feng Zhang, Ernst Bamberg, Georg Nagel and Karl Deisseroth. Earlier genetic optical-control approaches also existed; this is not a claim that they alone invented every form of optogenetics. Boyden reports that Science rejected the paper before its eventual publication in Nature Neuroscience. Sources: Boyden et al. (2005), DOI: 10.1038/nn1525; Boyden (2011, historical account), DOI: 10.3410/B3-11; Han & Boyden (2007, neuronal silencing), DOI: 10.1371/journal.pone.0000299; Adamantidis et al. (2007, awakening), DOI: 10.1038/nature06310; — TikTok @distilledscience