Figure 3.

RTN photostimulation produces quantal breathing in urethane–anesthetized hypocapnic rats. A, When ventilation was adjusted to maintained etCO₂ close to the apneic threshold trains of laser light (7 × 5 ms pulses at 20 Hz; train frequency, 35 min⁻¹) entrained PND in a 3:1 (A1), or 2:1 ratio (A2). B, Quantal entrainment in a different anesthetized rat with etCO₂ maintained below apneic threshold. Laser trains (7 × 5 ms pulse at 20 Hz; train frequency, 50 min⁻¹) delivered during phrenic apnea first produced quantal entrainment in a 2:1 ratio (B1), eventually achieving 1:1 entrainment (B2).