Dr. Michael Kilgard on Huberman Lab: How to Rewire Brains

Classic work from Kilgard and Merzenich showed that pairing a specific sound with direct stimulation of nucleus basalis (releasing acetylcholine) in adult animals could radically expand cortical representation of that sound—changes previously believed possible only in development. Later work demonstrated that stimulating other neuromodulator hubs (locus coeruleus for norepinephrine, dopamine and serotonin systems) at the right moments similarly drives large-scale plasticity. The crucial factor is not just the presence of these chemicals, but the timing of their release relative to neural firing.

Both speakers distinguish between merely being exposed to stimuli and actively engaging with them. Learning requires focused attention plus “friction”—self-generated effort or challenge (for example, the discomfort of practicing an instrument, learning a language in-country, or physically struggling to move after stroke). Kilgard adds that mental rehearsal and reflection before and after experiences further consolidate changes, and that sleep is when much of the synaptic reorganization is executed. Passive listening (e.g., foreign language on TV to infants) or endless scrolling delivers little durable plasticity because it lacks agency, contingency, and depth.

Kilgard contrasts natural environments—full of coherent visual, auditory, vestibular, tactile, and social cues—with highly simplified or manipulated digital environments (video games, endless short-form videos, phones). He worries that digital experiences often lack the “statistics of the natural world” and coherent multisensory integration, risking poorly calibrated brain predictions and reward expectations. He favors activities like outdoor play, unstructured exploration, travel, and fishing (long stretches of anticipation with occasional reward) because they provide rich, temporally extended information that trains patience, attention, and real-world skill.

The same plasticity mechanisms that help us learn can lock in pathological patterns when inputs are extreme, persistent, or paired with intense emotion. Hearing loss leads the auditory cortex to overrepresent remaining frequencies, sometimes creating self-sustaining tinnitus loops. Repeated pain or rumination can amplify chronic pain circuits. Traumatic events combined with avoidance and hypervigilance can engrain PTSD. In all these cases, the brain’s adaptive “use it or lose it” rules, plus neuromodulator surges, strengthen circuits that are no longer helpful.

Kilgard’s group uses tiny implanted VNS devices to trigger brief bursts of activity in vagal afferents that signal heart–lung status. These signals, delivered for about half a second, cause coordinated release of acetylcholine, norepinephrine, and serotonin without conscious awareness or dopamine-driven reward. By timing these bursts precisely with successful movements in physical therapy, or with specific sensory inputs, they capture the synaptic “eligibility trace” and selectively strengthen the exact circuits being trained, allowing fewer repetitions to produce larger, more durable gains.