Dr. David Berson
- The Huberman Lab podcast is a place to discuss science and science-based tools for everyday life. On the show, host Andrew Huberman interviews Dr. David Berson, professor of medical science, neurobiology, and ophthalmology at Brown University.
- Dr. Berson's laboratory is credited with discovering the cells in the eye that set your circadian rhythms. His lab has also made other important discoveries about how we convert our perceptions of the outside world into motor action.
- Andrew and Dr. Berson have been discussing neuroscience for nearly two decades, and on this podcast, Dr. Berson takes the listener from the periphery of the nervous system all the way into the nervous system layer by layer.
- By the end of the podcast, listeners will have a greater understanding of how their nervous system works than many expert biologists and neuroscientists.
How We See
- Dr. David Berson has been a source of knowledge on the nervous system for over 20 years. In this discussion, questions are asked on how we see when a photon of light enters the eye.
- The visual experience is actually a brain phenomenon, where the retina sends a signal to the brain. These signals are sent to the cortex, which is where we have our conscious visual experience.
- To understand the process further, there are cells called ganglion cells, which are neurons that communicate between the eye and brain. Additionally, other places in the brain get visual input to do other things with it.
- Light is a form of electromagnetic radiation which consists of photons which move through space.
- The frequency of the electromagnetic radiation can be detected by neurons in the retina, which are tuned to different wavelengths of light.
- When a photon of light hits someone's eye, it is converted into an electrical signal. This signal is then decoded by the nervous system to lead to the perception of different colors.
- The biological mechanisms of color perception are highly similar from person to person. However, individual experiences of color may vary.
- Humans have three types of cones that allow them to see colors and other wavelengths of light.
- Most mammals, however, including dogs and cats, have only two types of cones, which limits the range of colors they can see.
- Colorblind people have difficulty seeing some colors, as the world is built primarily for those with more common vision.
- Although humans would hate to give up the ability to see color, it is often more important to have clarity in vision than to be able to see certain colors.
How You Orient In Time
- The co-discovery of Intrinsically Photosensitive Retinal Ganglion Cells (IPRGCs) is a breakthrough in understanding the communication of certain types of information from the eye to the brain.
- These cells absorb light of a particular wavelength and convert it to a neural signal that can be understood by the brain.
- These cells are found in the innermost layer of the retina and are similar to the photoreceptors found in fly eyes.
- They send a "brightness signal" to the brain, which helps to adjust the circadian clock and can also help to correct jet lag. Blind patients may have difficulty with their circadian clock without the rising and setting of the sun, as it is an important synchronization signal.
Body Rhythms, Pineal function, Light & Melatonin, Blueblockers
- The circadian clock is found in millions of cells throughout the body, and is coordinated by a small collection of nerve cells in the brain called the suprachiasmatic nucleus.
- It uses both neural and humeral pathways to communicate with other parts of the body, such as the autonomic nervous system and the hormonal system. Light input from the retina is sent to the suprachiasmatic nucleus, which then communicates with the pineal gland to release melatonin.
- Light of any brightness can have an effect on melatonin levels, and so it is important to avoid bright light exposure in the middle of the night.
- The amount of light one is exposed to during the day can affect their mood, and proper exposure to light can help with seasonal affective disorder. Light exposure is not necessarily good or bad, but rather it is important to consider the kind of light and when it is being used.
Spending Times Outdoors Improves Eyesight
- Myopia is strongly related to the amount of time that children spend outdoors. The more time spent outdoors, the less near-sightedness they have.
- The cause of this relationship is unclear, but may be related to the amount of light and the process of accommodation, which focuses on near or far things.
- There is growing interest in devices that count photons during the day and night to help regulate melatonin and ensure that children are receiving the correct amount of light.
Sensation, Mood, & Self-Image
- Diego Fernandez and Samara's lab recently found that there is a pathway from the retina to the peri Haband ULA, a region in the brain that acts as a linker between peripheral sensory input and the cortex.
- This pathway allows for the integration of sensory input, like visual input and tactile input, into the cortex and the front of the brain, which is involved in higher level functions such as planning and self perception.
- The lab also found that when this pathway is activated at the wrong time of day, animals can become depressed, and when it is silenced, lighting cycles that would normally make them depressed no longer have an effect.
- The pathway is also involved in regulating melatonin and the circadian clock, mood, and hunger, showing that photosensitive cells play an important role in many different functions.
Sense of Balance
- The vestibular system is the sense of balance located in the inner ear and is served by the same nerve that serves the hearing system.
- The vestibular system is composed of three sensors that detect head movement and communicate this information to the brain. Interoception is when you focus on your internal state as opposed to something outside you.
- The vestibular system works by detecting the motion of fluid passing by the hairs in the ear and communicating this through the nerve.
- The visual system and balance system are connected in that the brain senses movement and compensates for it by stabilizing the image on the retina. This is why people are encouraged to look at the horizon when feeling seasick and why image stabilization technology is utilized in cameras.
Why Pigeons Bob Their Heads, Motion Sickness
- The inner ear is an important part of the nervous system involved in coordinating movements. It is responsible for combining visual input with balance input in the cerebellum.
- This is important for keeping the image of the world stable on the retina and preventing motion sickness. People who have cerebellar damage may experience difficulties with coordination and precision in their movements.
- In addition, the cerebellum is used for motor learning and error correction, allowing it to compensate for any damage to the vestibular system.
- To prevent motion sickness, people should look out the front of the windshield and act as if they are driving the car or boat. This can help the brain align the visual input with the vestibular system.
- Harvey Carton, a world-class neuroanatomist, gave a lecture about plugging one's nose and blowing out versus plugging one's nose and sucking in, depending on if one is taking off or landing on a aeroplane.
- This is important for relieving pressure on the eardrums. It does not matter if one blows out or sucks in, as long as the passageway is opened up.
- Harvey discussed the inner ear and the cerebellum, but concluded that the nose blowing/sucking technique was the most important.
- It is important to note that the pressure differential between the cabin and the planet's surface is what matters most in this technique.
Midbrain & Blindsight
- The midbrain is an area beneath the cortex and is rarely discussed. It controls a lot of unconscious stuff, reflexes, et cetera, and is responsible for the phenomenon of blindsight.
- It is the linker from the spinal cord in the periphery up to the cortex. It is a reflex center that can reorient the animal's gaze or body, or attention to particular regions of space.
- It is important because it is able to cross-correlate across sensory systems, giving the brain more sources of information to make decisions.
Why Tilted Motion Feels Good
- The vestibular system is responsible for the sensation of pleasure in moving through space and getting tilted relative to the gravitational pull of the earth. It is thought that this may be due to the involvement of the dopaminergic system in the central nervous system.
- It is also suggested that feeling in control of one's own movement and having finesse may be part of the reward system. Our understanding of this phenomenon is still speculative, however. It is clear that there is a reward system associated with moving through the world with a sense of freedom and control.
Reflexes vs. Deliberate Actions
- The midbrain is responsible for combining signals and reflexive action in order to stay alive and survive in the world.
- High levels of the nervous system are designed to override automatic movements, such as deliberately choosing to put a hot cup down rather than dropping it.
- However, reflexes are also necessary to respond quickly in situations where there is not enough time to think.
- Sports athletes can mess up a play if they overthink it, relying instead on the reps they have done to build knowledge. All of these levels of the nervous system are working in tandem in real time.
Basal Ganglia & the “2 Marshmallow Test”
- The basal ganglia is an area of the brain located deep in the forebrain involved in the control of motor learning and skill execution.
- It is deeply intertwined with the cortex and can be thought of as an instructor or conductor, providing the cortex with information and helping to execute plans.
- It is involved in go-no-go type behaviors, such as deciding to go for a run in the morning or resisting the temptation of a marshmallow.
- Its activity is heavily influenced by genetics and experience, meaning that what is easy or hard for one person may differ from another.
- However, it is possible to practice and become better at using the basal ganglia to better control go-type and no-go type behavior.
- Finally, it is not just one part of the brain, but a complex network of structures all working in parallel, influencing each other.
Suppressing Reflexes: Cortex
- The cortex is responsible for our higher consciousness, self-image, planning, and action. It is also the 'projection screen' that contains a map of the visual world.
- The cortex is made up of dozens of maps, each responsible for different functions such as brightness, motion, and color.
- It is also responsible for making associations between objects and their significance.
A woman who was blind from birth, but her visual cortex was rewired to process tactile information, such as reading braille. This is a form of plasticity, where the brain is able to rewire itself to use real estate for something useful. This story is tragic, but also very informative, as it can go the other way too, with people gaining functional improvements in other modalities in the absence of vision.
What is a Connectome?
- Connectomes are a comprehensive description of the structure of nervous tissue, usually at a very fine scale, such as individual synapses between individual neurons.
- This is made possible through the use of electron microscopy, which allows scientists to take images of tissue and analyze them to create a wiring diagram of the tissue.
- Connectomics is the equivalent of genomics in that it is the idea of getting the whole picture, rather than just looking at a few elements. Connectomes can be used to ask questions about the function of the brain and how information flows through it.
- It is also possible to use connectomes to hypothesize about how certain circuits work, and then use physiological data to test the hypothesis. Connectomics is just beginning to be explored, but it has the potential to revolutionize the field of neuroscience.
How to Learn (More About the Brain)
- People interested in learning more about neuroscience have many resources available to them, such as podcasts, the EyeWire project, and even Wikipedia.
- For more formal learning, there are also popular books on basic neuroscience, such as Richard Maslin's book on vision and the nervous system.
- Additionally, there are many specialized fields of neuroscience that cater to different interests and strengths. It is an exciting time to explore neuroscience and its many possibilities.
Book Suggestion, my Berson Appreciation
- Today we discussed the wonderful resources people can access to learn about the nervous system. We shared the link to Dick's book, "We Know It When We See It".
- David is an incredible wealth of knowledge on the topic, and we discussed the different ways the nervous system works and is organized.
- We are thankful for David taking the time to talk to us, and for his years of teaching. He is someone people can turn to when they want to understand the beauty of the nervous system. We are grateful for the conversation, and for David's willingness to help.
- InsideTracker interview
- Dr. Berson’s website
- Eyewire (contribute to neuroscience research from home/computer)
- Best neuroscience textbook
- We Know It When We See It: What the Neurobiology of Vision Tells Us About How We Think (book)