Figure 1. Different types of eye movement: (a) vestibulo-ocular reflex; (b) optokinetic reflex; (c) saccade and eye fixation; (d) smooth pursuit; (e) vergence; (f) air-puff evoked reflex blink. RH, LH, horizontal position of the right and left eyes; RV, vertical position of the right eye; LP, lid position. HP, FP, TP, head, global visual field and visual target position; AP, air-puff presentation. Calibration in (e) applies also to (a)–(d).

Figure 2. Typical discharge rate of an abducens motor neuron (ABD Mn) during different types of eye movement: (a) diagram illustrating the location of the abducens nucleus in the brainstem and of the innervated lateral rectus muscle; (b) firing rate of abducens motor neurons during saccades in the on and off direction, and during spontaneous eye movements, and vestibulo-ocular and optokinetic reflexes.

Figure 3. Neuronal organization of the premotor system for horizontal eye movements: (a) diagram illustrating the location of the different neuronal groups projecting monosynaptically on abducens nucleus (ABDn); (b) typical discharge rate recorded in neuronal elements of each premotor centre during saccades in the on and off direction and the subsequent eye fixation. EBN, excitatory burst neurons; IBN, inhibitory burst neurons; MVn, medial vestibular neurons; PHn, prepositus hypoglossi neurons; LH, horizontal position of the left eye; i, c, ipsi- and contralateral.

Figure 4. Basic circuit underlying conjugate eye movements in the horizontal plane: (a) diagram illustrating the location of abducens motor neurons (ABD Mns) and internuclear neurons (ABD Ints), and medial rectus motor neurons (MR Mns); (b) expected discharge rate of neuronal elements depicted in (a) during a leftward conjugated saccade followed by a new eye fixation. Note the different firing rates of Mns and Ints. i, c, ipsi- and contralateral.