Dr. David Berson — Professor of Medical Science, Neurobiology and Ophthalmology at Brown University whose lab discovered the melanopsin-expressing retinal cells that set circadian rhythms. He is Andrew Huberman's longtime neuroscience mentor.
The gist
Andrew Huberman interviews his mentor Dr. David Berson for a layer-by-layer tour of the nervous system. They start at the eye, explaining color vision, the three cone types, and the surprising light-sensing ganglion cells (melanopsin) that set the circadian clock and influence melatonin, mood, and even depression. The conversation then climbs through the vestibular system and motion sickness, the cerebellum, the midbrain and reflexes, the basal ganglia's go/no-go control, and finally the cortex, visual maps, and plasticity. Berson closes with his current passion, connectomics, and advice for learning neuroscience.
Big reveals
- Berson explains we have 'a bit of fly eye in our eye' — the melanopsin ganglion cells use a chemical cascade resembling a fly photoreceptor, not a human rod or cone.
- Getting up at night and turning on a bright light slams melatonin 'to the floor' — any bright light, not just blue, suppresses it.
- Wearing blue blockers during the middle of the day makes no sense, since that's exactly when you want bright light into your eyes.
- A little-known retinal side pathway to the frontal cortex can make animals depressed when activated at the wrong time of day.
- Motion sickness is explained as 'visual vestibular conflict' — your brain punishes you with nausea when senses disagree.
- Berson tells Huberman it doesn't matter whether you blow out or suck in to unpop your ears, winning Huberman a $100 bet with Harvey Karten.
- A woman blind from birth lost her ability to read braille after a stroke in her 'unused' visual cortex, which had been repurposed for touch.
Things worth remembering
- Dreaming proves seeing is a brain phenomenon — you see vivid things with no input coming through your eyes.
- Most mammals, including dogs and cats, have only two cone types, so a dog sees the world like a particular kind of colorblind human.
- In a cave with no sunlight, the human body clock keeps time to within a handful of minutes of 24 hours but slowly drifts out of phase.
- Childhood myopia is strongly linked to time spent outdoors — more outdoor time means less nearsightedness.
- Pigeons bob their heads while walking to hold the visual image of the world stable on their retina, the same goal as your eye's stabilization reflex.
- Rattlesnakes 'image' heat through facial pit organs and combine it with vision in the same midbrain center (the tectum).
- Flies taste things with their feet, having taste receptors in lots of unusual places.
- Non-mammalian vertebrates like frogs and lizards have no real visual cortex; their main visual center is the midbrain optic tectum.
- A connectome maps neural tissue at nanometer scale — a million times smaller than a millimeter — to reconstruct the brain's complete wiring diagram.