Essentials: How Your Brain Functions & Interprets the World | Dr. David Berson

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance.
I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now for my discussion with Dr. David Berson. For more than 20 years, you've been my go-to source for all things, nervous system, how it works, how it's structured. So today, I want to ask you some questions about that. I think people would gain a lot of insight into this machine that makes them think and feel and see, etc. If you would, could you tell us how we see? You know, a photon of light enters the eye, what happens?

**David Berson** (0:47)
Right.

**Andrew Huberman** (0:48)
I mean, how is it that I look outside, I see a truck drive by, or I look on the wall, I see a photo of my dog? How does that work?

**David Berson** (0:56)
Right. So this is an old question, obviously. And clearly, in the end, the reason you have a visual experience is that your brain has got some pattern of activity that it associates with the input from the periphery. But you can have a visual experience with no input from the periphery as well. When you're dreaming, you're seeing things that aren't coming through your eyes.

**Andrew Huberman** (1:17)
Are those memories?

**David Berson** (1:19)
I would say, in a sense, they may reflect your visual experience. They're not necessarily specific visual memories, but of course, they can be. But the point is that the experience of seeing is actually a brain phenomenon. But of course, under normal circumstances, we see the world because we're looking at it and we're using our eyes to look at it. And fundamentally, when we're looking at the exterior world, it's what the retina is telling the brain that matters. So there are cells called ganglion cells. These are neurons that are the key cells for communicating between eye and brain. The eye is like the camera. It's detecting the initial image, doing some initial processing. And then that signal gets sent back to the brain proper. And of course, it's there at the level of the cortex that we have this conscious visual experience. There are many other places in the brain that get visual input as well doing other things with that kind of information.

**Andrew Huberman** (2:12)
So I get a lot of questions about color vision. If you would, could you explain how is it that we can perceive reds and greens and blues and things of that sort?

**David Berson** (2:23)
Right. So the first thing to understand about light is that it's just a form of electromagnetic radiation. It's vibrating. It's oscillating.

**Andrew Huberman** (2:33)
But when you say it's vibrating, it's oscillating, you mean that photons are actually moving?

**David Berson** (2:38)
Well, in a sense, photons are, they're certainly moving through space. We think about photons as particles. And that's one way of thinking about light, but we can also think of it as a wave like a radio wave. Either way is acceptable. And the radio waves have frequencies, like the frequencies on your radio dial. And certain frequencies in the electromagnetic spectrum can be detected by neurons in the retina. Those are the things we see. But there's still different wavelengths within the light that can be seen by the eye. And those different wavelengths are unpacked, in a sense, or decoded by the nervous system to lead to our experience of color.
Essentially, different wavelengths give us the sensation of different colors through the auspices of different neurons that are tuned to different wavelengths of light.

**Andrew Huberman** (3:27)
So when a photon, so when a little bit of light hits my eye, goes in, the photoreceptors convert that into electrical signal.

**David Berson** (3:36)
Right.

**Andrew Huberman** (3:37)
How is it that a given photon of light gives me the perception, eventually leads to the perception of red versus green versus blue?

**David Berson** (3:45)
Right. So if you imagine that in the first layer of the retina, where this transformation occurs from electromagnetic radiation into neural signals, that you have different kinds of sensitive cells that are expressing, they're making different molecules within themselves for this express purpose of absorbing photons, which is the first step in the process of seeing.
Now, it turns out that altogether there are about five proteins like this that we need to think about in the typical retina. But for seeing color really, it's three of them. So there are three different proteins. Each absorbs light with a different, you know, preferred frequency. And then the nervous system keeps track of those signals, compares and contrasts them to extract some understanding of the wavelength composition of light. So you can see just by looking at a landscape, oh, it must be late in the day because things are looking golden. That's all, you know, a function of our absorbing the light that's coming from the world and interpreting that with our brain because of the different composition of the light that's reaching our eyes.