Chapter 16 Open-loop and closed-loop optokinetic nystagmus in Squirrel monkeys (Saimiri sciureus) and in man

The Optokinetic Uncover Test

“…32 In rabbits and in monkeys, these pathways project down to the inferior olive and contralateral flocculus and then on to the vestibular nuclei to modulate visuovestibular responses to full-field optokinetic rotation during turning movements (Figure 2). [33][34][35] In primates, development of binocular corticopretectal pathways to the NOT and the DTN of the accessory optic system, which provide ipsilateral pursuit re- sponses (temporalward for the viewing eye), are necessary to cancel this optokinetic asymmetry within the first year of life (Figure 3). [11][12][13][14][15][16][17][18]36 These corticopretectal projections to the NOT-DTN come predominantly from the middle temporal area and the medial superior temporal area, as well as from V1 and V2, 16 while those to accessory optic nuclei (lateral terminal nucleus and medial terminal nucleus) come exclusively from the middle temporal area and the medial superior temporal area.…”

Neostigmine-induced alterations in fast phase of optokinetic responses in myasthenic ocular palsies

“…That is why closed-loop OKN does not clearly demonstrate the alterations in neuromuscular transmission of myasthenia. On the other hand, in open-loop condition, the optokinetic response is dissociated from the stimulus and the intrinsic characteristics of this tracking system are revealed [10,12,15,16,28,29] s Comparison with other regular OKN investigation…”

Open-Loop and Closed-Loop Optokinetic Nystagmus (OKN) in Myasthenia Gravis and Nonmyasthenic Subjects

“…The OKN system is normally controlled by the deep negative feedback that can reduce the slip of retinal image to keep the moving patterns steady on the retina (6,14,28,46,47). For a negative feedback system, if its open-loop gain (or the intrinsic gain) is K, the closedloop gain (G) could be theoretically calculated by the equation G ϭ K/(1 ϩ K).…”

“…Eye movements elicited by a moving pattern in a large visual field are called optokinetic nystagmus (OKN), which serves to stabilize the retinal image of a moving scene. Due to involuntary response to motion stimulus, OKN can be regarded as an objective method for exploring the information processing in visual neural pathways (6,11,14,15,40). The performance of the optokinetic movements can be expressed by the OKN gain, which is a ratio of slow phase velocity of OKN to stimulus velocity (14,28,29).…”

“…Therefore, for effectively detecting the changes of OKN system, it is necessary to eliminate the negative feedback loop (open loop). The open-loop condition of OKN system can be achieved by immobilizing one eye or by keeping the retinal image slip constant with optic or electronic method (6,8,13,14,16,22,26,28,42,44,46,47). In comparison with the closed-loop OKN, the gain of open-loop OKN is much larger than 1 at low velocity of stimulus and is more sensitive to disorders in the OKN neural pathway (6,8,14,16,20,28,46,47).…”