December 13, 2021 • 1hr 49min

Dr. David Berson: Understanding Your Brain's Logic & Function

Huberman Lab

In this episode, Dr. Andrew Huberman interviews Dr. David Berson, Professor of Medical Science, Neurobiology and Ophthalmology at Brown University. Dr. Berson's lab discovered the intrinsically photosensitive retinal ganglion cells that set circadian rhythms. He is an expert on the visual system and neural circuits more broadly. The discussion covers how various sensory systems and brain regions work together to create our perceptions and behaviors, from basic reflexes to higher cognitive functions.

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Key Takeaways

The visual system converts light into electrical signals in the retina, which are then processed by various brain regions to create our visual experience
There are specialized neurons in the eye called intrinsically photosensitive retinal ganglion cells that regulate circadian rhythms, mood, and other non-visual functions
The vestibular system in the inner ear detects head movement and orientation, working with the visual system to maintain balance and stable vision
The cerebellum integrates sensory information and fine-tunes movements and motor learning
The basal ganglia are involved in initiating and suppressing behaviors ("go" and "no-go" signals)
The cerebral cortex is involved in higher-level processing, including visual perception, planning, and decision making
Neuroplasticity allows the brain to repurpose regions, like visual cortex being used for tactile processing in blind individuals
Connectomics aims to map the detailed wiring of neural circuits to better understand brain function

Introduction

In this episode, Dr. Andrew Huberman interviews Dr. David Berson, Professor of Medical Science, Neurobiology and Ophthalmology at Brown University. Dr. Berson's lab discovered the intrinsically photosensitive retinal ganglion cells that set circadian rhythms. He is an expert on the visual system and neural circuits more broadly. The discussion covers how various sensory systems and brain regions work together to create our perceptions and behaviors, from basic reflexes to higher cognitive functions.

Topics Discussed

The Visual System and Color Vision (8:02)

Dr. Berson explains how the visual system works, starting with photons of light entering the eye:

Photoreceptors in the retina convert light into electrical signals
Retinal ganglion cells send this information to the brain
The brain processes these signals to create our visual experience
Color vision relies on three types of cone photoreceptors sensitive to different wavelengths of light
The brain compares signals from these cones to determine 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." - Dr. David Berson

Intrinsically Photosensitive Retinal Ganglion Cells (16:56)

Dr. Berson discusses the specialized retinal neurons his lab discovered:

These cells contain melanopsin, a light-sensitive pigment
Unlike other retinal neurons, they are directly light-sensitive
They send brightness information to brain regions controlling circadian rhythms and other functions
The signal processing in these cells is more similar to invertebrate photoreceptors than mammalian ones

"This pathway that we're talking about from the retina and from these peculiar cells that are encoding light intensity are sending signals directly into a center that's surrounded by all of these centers that control autonomic nervous system and your hormonal systems." - Dr. David Berson

Circadian Rhythms and Melatonin (25:45)

The discussion covers how light regulates our internal biological clocks:

The suprachiasmatic nucleus (SCN) in the hypothalamus is the master circadian pacemaker
Light information from intrinsically photosensitive retinal ganglion cells helps synchronize the SCN to the external day/night cycle
The SCN coordinates rhythms throughout the body via neural and hormonal signals
Bright light exposure at night can suppress melatonin production, disrupting sleep
Blue light is particularly effective, but any bright light can have this effect

The Vestibular System and Balance (41:03)

Dr. Berson explains how we sense our orientation and movement:

The vestibular system in the inner ear detects head rotation and linear acceleration
It works with the visual system to maintain balance and stable vision
Reflexes like the vestibulo-ocular reflex help stabilize gaze during head movements
Motion sickness can result from conflicts between visual and vestibular information

"The brain works really hard to mostly stabilize the image of the world on your retina. Of course, you're moving through the world, so you can't stabilize everything. But the more you can stabilize, most of the time, the better you can see." - Dr. David Berson

The Cerebellum and Motor Coordination (53:53)

The cerebellum's role in coordinating movement and learning is discussed:

It integrates sensory information and fine-tunes movements
It's involved in motor learning and improving precision of movements
Damage to the cerebellum can result in ataxia - impaired coordination and balance
The cerebellum helps compensate for sensory deficits through learning

The Midbrain and Reflexive Behaviors (1:02:35)

Dr. Berson describes the role of the midbrain in processing sensory information and generating reflexive behaviors:

The superior colliculus integrates visual, auditory, and somatosensory information
It's involved in orienting responses and reflexive eye movements
The midbrain processes information about the location of stimuli in space
It can trigger rapid, reflexive responses to potential threats or important stimuli

Basal Ganglia and Behavioral Control (1:16:35)

The discussion covers the basal ganglia's role in initiating and suppressing behaviors:

The basal ganglia are involved in "go" and "no-go" decisions
They work closely with the cortex in decision-making and action selection
The ability to suppress reflexive behaviors involves cortical control over basal ganglia circuits
Practicing "no-go" responses may help improve behavioral control

"If you have the ability to withhold behavior or to execute it, how do you decide which to do? Well, the cortex is gonna have to do that thinking for you. You have to be looking at all the contingencies of your situation to decide, is this a crazy move, or is this a really smart investment right now?" - Dr. David Berson

The Cerebral Cortex and Higher Cognitive Functions (1:24:40)

Dr. Berson explains the role of the cerebral cortex in visual processing and other higher functions:

The visual cortex contains multiple maps of visual space
Different cortical areas specialize in processing different aspects of visual information
The cortex is involved in recognizing objects, faces, and scenes
It integrates information from multiple senses and memory to guide behavior
The frontal cortex is particularly important for planning and decision-making

Neuroplasticity and Brain Adaptation (1:33:33)

The discussion covers how the brain can adapt and repurpose regions:

In blind individuals, the visual cortex can be repurposed for tactile processing
This allows them to use this brain region for tasks like reading Braille
Damage to this repurposed visual cortex can impair Braille reading ability
This demonstrates the brain's remarkable ability to adapt to sensory loss

"What appears to have been the case, and this has been confirmed in other ways by imaging experiments in humans, is that in people who are blind from very early in birth, the visual cortex gets repurposed as a center for processing tactile information." - Dr. David Berson

Connectomics and Mapping Neural Circuits (1:36:27)

Dr. Berson explains the emerging field of connectomics:

Connectomics aims to map the detailed wiring of neural circuits
It uses high-resolution electron microscopy to image brain tissue
This allows researchers to trace the connections between individual neurons
Understanding the precise wiring can help generate hypotheses about circuit function
It complements functional studies to provide a more complete understanding of the brain

"If you don't know the cell types and the connections, how do you really understand how that the machine works?" - Dr. David Berson

Learning About Neuroscience (1:45:20)

Dr. Berson offers advice for those interested in learning more about neuroscience:

Explore online resources like Wikipedia for introductory information
Read popular science books on neuroscience topics
Participate in citizen science projects like EyeWire to contribute to research
Follow your interests - there are neuroscience fields related to many topics
Consider formal education in neuroscience if deeply interested

Conclusion

This wide-ranging discussion with Dr. David Berson provides a comprehensive overview of how different brain systems work together to create our perceptions and guide our behaviors. From the basic mechanisms of vision to the complex integration of information in the cortex, the episode highlights the intricate and fascinating ways our brains process information from the world around us. Dr. Berson's expertise and clear explanations make complex neuroscience concepts accessible, offering listeners a deeper understanding of their own neural processes and the current state of neuroscience research.