An SCC (strongly connected component) is a set of nodes
wired into a feedback loop — each reachable from the others. "Highlight whole-body
SCC" shows the largest homeostatic feedback core
(cardiovascular / renal / RAAS / fluid–electrolyte).
Determinate (↑/↓): the intervention forces the node one way
for every reaction strength — a sound prediction (never wrong vs real HPO data).
? (ambiguous): the node sits in a feedback loop where opposing arms fight, so the
steady-state sign is magnitude-dependent — PhysioMap abstains rather than guess.
PhysioMap predicts the steady-state (comparative-statics)
sign, not naive path propagation. See worked disease traces →
Modulation (⊗, dashed purple): a multiplicative gain —
one variable scales the strength of another edge instead of pushing the target
directly (e.g. thyroid hormone amplifies how strongly sympathetic tone drives heart rate).
It is the sign of an interaction (a mixed 2nd derivative), not a magnitude; it leaves
ordinary sign predictions unchanged but answers "does X change the sensitivity of one
variable to another?". A modulation is really a link from a node to an edge (three
endpoints), drawn here as a single arrow to the modulated edge's target; click a ⊗ edge to
highlight the actual edge it modulates.