[MUSIC, Title: "The Importance of Forgetting in Learning, Life, and Overcoming Stress"] [Barb] We often think our lives would be SO much easier if we could just remember EVERYTHING. But as physician and professor of neurology and psychiatry, Scott Small, who we've mentioned before, relates in his wonderful book: "Forgetting, The Benefits of Not Remembering" you wouldn't really want to have a perfect memory. If you'll remember, our memories are formed when we make connections between neurons. The little bouton at the end of the axon of one neuron reaches out to almost touch the end of a dendritic spine. As we witness events unfolding during a typical day, vast fields of hundreds of millions of new dendritic spines are cropping up related to all that we've seen, heard, and experienced. But think about it. Hundreds of millions of dendritic spines popping up every day, that's a LOT of spines! In fact, it's so many spines that if we didn't have chemicals to cause the less important connections and memories to fall away, there could be a problem. The brain could start filling up with too many spines. With all these spines, as they connect to form memories, a person would recall so many details that it would be hard for them to see the forest for the trees, so to speak. They would be aware of all the lovely intricate details which would simultaneously make it harder for them to see the big picture. And with the deluge of new information pouring in every second, the world could seem overwhelming. Interestingly, as Dr. Small notes, it seems that in people with autism, the control knob for forgetting appears to have been turned down. This leads to behavioral inflexibility, which can reduce the deluge of new information, but cause other problems, as with the child with autism who must have the table set in an identical way every day. [Terry] There are certain neural chemicals that help dendritic spines form and fix in place, and other chemicals that cause those spines to melt away. You want just the right balance of those chemicals. You want to be able to make memories, but also to lose others so as not to overwhelm or interfere with each other. It can be deeply unhealthy to remember every experience, especially bad experiences, resentments, and neurotic fear. It's better for people— and for society as a whole— to be able to both remember and to forget. Francis Crick, the Nobel Prize winning co-discoverer of the structure of DNA, once theorized that the main purpose of sleep could be to unlearn spurious memories, leaving more room for new memories to emerge the next day. This was done by instantiating the spurious memories during sleep and then unlearning them. A spurious memory occurs when two related memories collide with each other. Did you ever wonder why even vivid dreams fade so quickly after you wake up? As the Francis Crick Professor at the Salk Institute, I inherited Francis' brain when he passed away in 2004. Not his real brain, but this model. Francis once told me that it sat in his office for many years until one day he looked at it and realize that it was a lot bigger than his own brain—and mine too. Forgetting is important not only for flexibility but also for creativity. However, forgetting is not the same as eliminating connections. A single memory is stored in a huge number of synapses and many memories share the same synapses. It's the patterns of activity among many neurons that distinguish different memories. So, eliminating a memory means that small adjustments have to be made in a large number of synapses. Some weakened and other strengthened. This is called a "distributed memory system." It's now well-established that memories of experiences you've had during the day are consolidated in the neocortex during sleep. New experiences must be stored in the neocortex without interfering with other memories. This is a more complex process than simply pruning synapses. Why do we sleep so long? Modifying synapses requires biochemical reactions that can take hours. If your home was being renovated, would you prefer to live there with all the workmen and the noise, or to check into a quiet hotel and have sweet dreams? [MUSIC, Title: "The Importance of Forgetting for Students"] [Barb] Students can experience times of extraordinary stress. One of my Russian teachers survived the Holodomor; the forced starvation of Ukraine by Stalin and his henchmen only because her mother found glue for her to eat. In China, tens of millions died during the Sino-Japanese wars, the Civil War, the Great Leap Forward, and the Cultural Revolution. In South Africa, apartheid meant that learning was a pipe dream for those who were virtually enslaved to work in the mines. One of my favorite professors of electrical engineering grew up in Poland during World War II. As a six-year-old, he would dodge Nazi soldiers and wander among the bombed-out buildings, picking up unexploded hand grenades and throwing them against buildings to see what might happen. As he put it, "With what I've seen, I should be a psychopath." Instead, he was one of the best and kindest professors I've ever had. Many students in countries all over the world have long-lived stressful, dangerous lives. One could argue that it has been more common for students throughout history to live lives of utter duress than to attend humdrum daily classes. [Beth] Life is not easy for our 21st-century students either. It is not out of the norm for a tragic life event to occur the night before your student is sitting in your class. On any given day, any of our students may experience community violence, sexual and physical abuse, peer pressure, cyberbullying, divorce, break-ups and abandonment. Or it could just be that they overslept and missed breakfast, had a fight with their bestie, or got a bad grade in their previous class. Despite the few difficult- to-work-with types, educators can be some of the most caring people around. So it's natural for teachers to want to do whatever they can to help ease students' anxieties. Especially when facing pandemics, civil unrest, national disasters, and the many other less-than-optimal conditions that will inevitably unfold. An idea that can allow teachers to more effectively help their students involves something called neurogenesis. Terry? [Terry] Neurogenesis means the creation of new neurons, which until recently were not thought to occur in adult brains. Rusty Gage, my colleague here at the Salk Institute, discovered neurogenesis in the adult hippocampus— exactly where they are needed to help us remember new experiences. New neurons serve a variety of purposes. For example, new neurons can help people overcome depression. Neurogenesis has become a hot area for depression research. Why would new neurons be so important for overcoming depression? Because new neurons learn more easily than old neurons. They find it easier to make new synaptic connections than older neurons. And if you're trying to train a brain to get out of its funk; fresh, young or flexible neurons are just what's needed. Remember, new neurons emerge in your hippocampus no matter how old you are. It's the age of the NEURONS, not the age of the PERSON, that matters. What helps promote neurogenesis? New learning! Exercise also promotes the survival of new neurons. In collaboration with Rusty's lab, my lab showed that exercise can also make it possible for the new neurons to make much stronger links. Ever since then, I run on the beach near my lab whenever I can take a break. And what's also interesting is that the new neurons help not only with new learning, they can also help with forgetting. [Beth] So, what does this practically mean for teachers? It means one of the best things that we can do to help students overcome stress in their lives is to excite and encourage them about new learning. Learning something new actually serves as a sort of trellis. New neurons have some place to park and grow if a student is learning something new. So, as we wrap up our first week of this course, we can contrast two approaches to teaching under stressful societal circumstances. One approach is to halt your teaching of new topics and instead sympathetically encourage students to air and share, retrieving and re-retrieving memories and thoughts of their discomfort during difficult times. The second approach briefly acknowledges the discomfort, but then instead focuses students with upbeat encouragement and makes students curious about the new learning ahead. Given what you now know in this course, which approach would YOU choose? [Beth] I'm Beth Rogowsky. [Barb] I'm Barb Oakley. [Terry] I'm Terry Sejnowski. [All] Learn it, link it, let's do it!
