The Neurobiology of Speech, Language, Critical Periods, and Brain Plasticity with Dr. Eddie Chang

This episode features Dr. Eddie Chang, Chair of Neurosurgery at UCSF, a leading expert in movement disorders, speech disorders, and bioengineering. Dr. Chang's groundbreaking work includes developing communication methods for individuals with locked-in syndrome using AI and computers. The discussion delves into the fundamental mechanisms of how the brain processes and generates speech and language, exploring both normal function and how these systems can be repaired or augmented. The conversation also touches upon the broader implications of brain research for understanding human cognition and emotion.

A significant portion of the episode focuses on critical periods, specific developmental windows during which the brain is highly receptive to learning, particularly languages. Dr. Chang recounts his early research with Mike Merzenich, demonstrating how raising rodent pups in continuous white noise delayed the maturation of their auditory cortex and extended the critical period for plasticity. This finding raises important questions about the impact of environmental sounds, such as white noise generators used for infants, on early brain development and the potential for long-term effects on auditory processing and speech acquisition.

The podcast also provides a fascinating look into Dr. Chang's clinical practice, specifically awake brain surgery for patients with brain tumors or epilepsy. During these procedures, patients remain conscious and interact with the surgical team while parts of their brain are stimulated or removed. This brain mapping technique allows surgeons to precisely identify and protect critical areas for speech, language, and motor function, offering direct insights into the brain's functional architecture and the localized nature of complex cognitive processes. Examples include inducing 'speech arrest' or temporary memory loss for objects.

Furthermore, Dr. Chang discusses how electrical stimulation of specific brain regions can evoke distinct emotional responses, such as anxiety from the amygdala or a calming effect from the orbitofrontal cortex, and disgust from the insula. He shares a compelling case of a patient whose chronic anxiety was ultimately diagnosed as a form of epilepsy, highlighting the intricate link between brain electrical activity and psychiatric symptoms. The episode underscores the brain's role as a complex computational organ, responsible for everything from generating words and understanding language to processing emotions and shaping our overall experience of the world.

"Dr. Chang's clinical group focuses on the treatment of movement disorders including epilepsy."

"His laboratory is credited with discovering ways to allow people who have fully locked-in syndrome, that is, who cannot speak or move, to communicate through computers and AI devices..."

"In neuroscience, we call this a critical period or a sensitive period. And we have this for our eyes, but we also have it for our ears."

"if you basically mask environmental sounds from these rat pups, the critical period, this sensitive period where it's open to plasticity, it's open to change, it's open to reorganization, that window can stay open much, much longer."

"It's not just about the genetic programming that specifies some of this sensitive period, but it's also a little bit about the nature of the sounds that we hear that help keep that window for the critical period open and closed."

"The only difference between the conversation that I might have with my patient who's undergoing awake brain surgery is that I can't see their face and they can't see my face."

"A person says, 'I wanted to say it, but I couldn't get the words out.' And even though I've seen this thousands of times now, it's still exciting every time that I see it because, it's exciting because you're seeing the brain, it's a physical organ..."

"The orbitofrontal cortex is a part of the brain that's above the eyes... But one of the things that we observed is when you stimulate in there, people tended to have a reduction in their stress..."

"It turns out that it wasn't really an anxiety disorder. It was actually that she had underlying seizures, an epilepsy activating a part of her brain that evokes, you know, anxious feelings."

"The only way that we could actually prove this was actually putting electrodes into her brain and proving that these attacks that she was having were localized to a part called the amygdala..."