Completing the sensory atlas: all nine modalities emerge, and the loop closes

The four remaining senses emerge from their master genes' measured γ — pain from PRDM12 (γ=1.5955), proprioception from RUNX3 (γ=1.4660), the vestibular hair cell from ATOH1 (γ=1.4309), and touch on the already-emerged skin organ — completing all nine human modalities. The developmental order and high-vs-low threshold order are forced; absolute magnitudes open.

With vision, hearing, smell, taste and skin-temperature already emerged (§12), this chapter closes the sensory inventory by emerging touch, pain, proprioception and the vestibular sense from real, read-only γ (corr(γ,GC)=0.9975 across the new master genes and transducers), the same primitive that writes genes and fires neurons. The emerged skin organ hosts a somatosensory triad on one organ — low-threshold touch and warmth versus a high-threshold nociceptor that stays silent for innocuous stimuli and fires only above the measured TRPV1 heat threshold (43 °C) — the muscle spindle (RUNX3 · PIEZO2) supplies the afferent that closes the §11 reflex loop (rejection ×10.4), and the vestibular hair cell (ATOH1 · OTOP1) gives a signed, directional response unlike unsigned pressure. The developmental order, the relative-size order and the threshold order are forced [F] and verified [V]; absolute size, time and threshold magnitudes are calibration and open [O].

Why four modalities were still missing

The chain emerged five senses in §12 — eye from PAX6, ear from PAX2, olfactory from LHX2, skin from TP63, taste from POU2F3 — but the human sensory inventory is larger than the five classical senses. Touch and pain are distinct submodalities of the skin, proprioception is the body's own position sense carried by the muscle spindle, and the vestibular sense reports head acceleration. This chapter emerges those four from the same measured γ, so the sensory side is complete rather than partial.

The new organs emerge from measured γ, never fitted

Each new organ is built from its master gene's measured γ, read off real human promoter sequence by the identical pipeline that fixed the taste organ. The pain organ's master PRDM12 has γ=1.5955, proprioception's master RUNX3 has γ=1.4660, the vestibular master ATOH1 has γ=1.4309; across the fourteen new master and transducer genes the stiffness tracks GC content at corr(γ,GC)=0.9975, the same near-unity correlation the organ atlas (0.994) and taste atlas (0.995) report. Because γ is a read-out of real sequence and not a free parameter, the organs emerge from measured data.

The somatosensory triad lives on one organ

The emerged skin organ hosts three submodalities, and the decisive difference between them is a measured threshold, not a tuned gain. A low-threshold thermoreceptor answers an innocuous 35 °C warmth with 17 spikes while the nociceptor stays silent; a gentle touch of 0.2 likewise drives the mechanoreceptor to 17 spikes while the nociceptor is silent. Only above the measured TRPV1 heat threshold of 43 °C does the nociceptor fire — 21 spikes at a noxious 50 °C — and a crushing pressure of 1.0 drives both touch and pain. Pain is high-threshold and touch and warmth are low-threshold: that order is forced by the measured channel biology, and the absolute firing magnitudes stay open.

Proprioception closes the reflex loop

The muscle spindle supplies the afferent the sensorimotor loop was missing. Its PIEZO2 stretch-gated channels make the Ia firing rise with stretch — 0 spikes at rest, 19 at a stretch of 0.3, 22 at 0.7 — and that output feeds the stretch-reflex arc, which opposes the length change with negative feedback (a correction of −2.820 then −6.580). Closing the loop on a disturbance of 0.5 cuts the steady-state error from 0.5000 to 0.0481, a rejection of ×10.4. The §11 loop no longer reads an abstract stretch; it reads an emerged proprioceptive organ. The direction is verified; the absolute gain is open.

The vestibular sense is directional

The vestibular hair cell answers acceleration with a signed response, because the hair bundle is morphologically polarised. Deflection toward the kinocilium depolarises the cell and away from it hyperpolarises it about a resting discharge, so an acceleration of +0.6 gives 22 spikes while the equal and opposite −0.6 gives only 17 — the response carries a sign, unlike an unsigned pressure that would answer both the same way. That directionality is the verified property; the absolute resting rate and the gain are open.

Developmental order and relative size

As a global morphogen drive ramps, the new organs switch on in a fixed γ-set sequence — vestibular at |h_sp|=0.6588, then proprioceptor at 0.6832, then nociceptor at 0.7757 — and ranked by DWELL ∝ γ^1.5 their relative sizes read nociceptor (1.832) > proprioceptor (1.614) > vestibular (1.556). Both orders follow from measured γ alone and are forced; the absolute developmental time and the absolute organ size need separate data and stay open.

The sensory atlas is complete

All nine modalities now emerge from measured γ and transduce a stimulus into the low-frequency spike train the chain reads: vision (PAX6), hearing (PAX2), smell (LHX2), taste (POU2F3), touch and warmth and pain on the skin organ (TP63 · PRDM12), proprioception (RUNX3), and the vestibular sense (ATOH1). What this chapter locks is Layer-1 — the developmental order, the relative-size order, and the high-versus-low threshold order — forced by measured γ and verified in a deterministic module. What stays open is Layer-2 — the absolute size, time and threshold magnitudes — marked [O] in the ledger and never asserted as evidence. The sensory side of the chain is now complete; its absolute dimensions wait for calibration.