Figure 12.

Schematic summary diagram showing the neural circuit for triggering and suppressing vertical saccades via INC IBNs and OPNs. Red neurons (u-EBN, u-IBN, SR and IO, u-SC) indicate neurons in the upward saccade system with upward ipsitorsional on-direction (thick red arrows) [Takahashi et al. (2007), their Fig. 14A]. Blue neurons (d-EBN, d-IBN, IR and SO, d-SC) indicate neurons in the downward saccade system with downward ipsitorsional on-direction (thick blue arrows) [Takahashi et al. (2007), their Fig. 14B]. The proposed SC–INC IBN–OPN pathway is highlighted with heavier red lines. Open neurons, excitatory neurons; filled neurons, inhibitory neurons. Red filled lines indicate upward saccade driving pathways, and blue dashed lines indicate downward saccade driving pathways that are suppressed by INC IBNs in the contralateral upward saccade system during upward saccades (Takahashi and Shinoda, 2018). Note that for pure vertical upward saccades, TRNs in the upward ipsitorsional saccade areas in the rostromedial SCs are simultaneously activated due to excitatory SC commissural connections in order to cancel torsional components. IR, inferior rectus; SR, superior rectus; IO, inferior oblique; SO, superior oblique; PPRF, paramedian pontine reticular formation; OPN, omnipause neuron; Abd nucl, abducens nucleus; PMRF, paramedian medullary reticular formation.