The subcortical system beneath the visible tree: four neuromodulatory currents rising from the brainstem — will, knowledge, courage, and silence — each a strand, a circuit, and, when it inverts, a disorder. Tap any river.
Tap any river to see its virtue, its neuromodulator strand and brainstem source, the two regions it connects, its circuit and lateralization, and the inversion — the disorder that strand produces when it floods or fails.
The four rivers rise from their brainstem nuclei (shown at the base) and ascend through the medial forebrain bundle to govern the cortex. Each is a distinct neuron type — the hidden, subcortical layer beneath the visible cortico-cortical paths.