Dr. Dawn opens with a passionate plea about E-bike safety after observing riders ignoring stop signs and wearing inadequate helmets in Santa Cruz. She explains the physics of collisions, noting that force equals mass times acceleration, and a car hitting an E-bike rider at 20 mph delivers impact equivalent to falling from a two-story building. She emphasizes that 97% of bike fatalities in New York involved helmetless riders, and brain injuries result from the brain striking the skull twice during impact - once on the impact side and again on the opposite side during deceleration. She urges drivers to honk at helmetless riders and calls for stricter helmet law enforcement.

An emailer asks about hydroxyapatite in toothpaste. Dr. Dawn traces its origins to NASA research in the 1960s by Dr. Bernard Rubin studying crystal growth for preventing bone and tooth mineral loss in astronauts. Japanese company Sangi acquired the patent and created the first hydroxyapatite toothpaste by 1980, receiving official anti-cavity recognition in 1993. Studies show it matches fluoride's cavity prevention effectiveness by filling microscopic cracks where bacteria take root. It also relieves temperature sensitivity by sealing micro-fractures in enamel that expose the dentin layer, making it especially helpful for people who clench their jaws.

Researchers from UC Berkeley and the Allen Institute used electrodes and lasers to study how mouse brains process optical illusions like the Kanizsa triangle. They discovered specialized IC encoder neurons in the visual cortex that fill in missing information, creating complete shapes from partial cues. When these pattern-completing circuits activate inappropriately, they may trigger hallucinations in conditions like schizophrenia. Dr. Dawn explains that illusions occur when the brain perceives something different from actual visual input, while hallucinations create perceptions with no external stimulus. She discusses frontotemporal dementia where visual hallucinations result from protein deposits in the occipital cortex, and notes that a 2021 British Journal of Psychiatry study found hallucination rates varying from 7% in young people to 3% in those over 70.

An emailer describes unbearable chronic lumbar pain with degenerative disc disease shown on MRI. Dr. Dawn emphasizes that MRI findings don't necessarily correlate with pain levels, citing shopping mall studies showing equal degenerative changes in people with and without back pain. She stresses checking for sciatica symptoms including leg pain below the knee, sensory differences between sides, calf size asymmetry, and ability to walk on tiptoes and heels. Without these red flags, the degenerative disease likely isn't causing the pain. She warns against unnecessary surgery citing frequent "failed back" syndrome when surgery for a disk image doesn't "fix" the pain. She recommends water jogging with a ski vest, McKenzie exercises, abdominal strengthening, ergonomics, removing wallets from back pockets, and alternating heat and ice therapy. She discusses mindfulness meditation and cognitive behavioral therapy for pain management.

A caller references Daniel Levitin's book "Your Brain on Music," discussing research using functional MRIs showing distinct brain activation patterns in musicians versus non-musicians due to integrated auditory, visual, and kinesthetic training. Dr. Dawn describes how infant brains develop from three to six layers with increasingly complex synaptic connections resembling circuit boards. She highlights a blindfold study where college students' visual cortices began responding to sound within two weeks as the auditory cortex expanded. She shares her husband's remarkable recovery demonstrating adult brain plasticity through intensive rehabilitation. Learning new musical instruments helps dementia patients by activating multiple brain regions simultaneously and improving standard cognitive test performance.

A caller describes an eight-day chest cold with thick white phlegm. Dr. Dawn recommends guaifenesin as a mucus-thinning expectorant to prevent bacterial growth in respiratory secretions that serve as "bacteria chow." She emphasizes the importance of current flu, COVID, and RSV vaccinations. Secondary bacterial infections develop when bacteria colonize viral-induced mucus in the lungs and invade tissues. She advises aggressive hydration and chicken soup, which research shows helps clear mucus.

Another caller provides additional information about Daniel Levitin as a musicologist, neurologist, and musician who runs the Music Perception, Cognition and Expertise laboratory at McGill University.