Components of the neural signal underlying congenital nystagmus

Abstract

Congenital nystagmus is an involuntary bilateral horizontal oscillation of the eyes that develops soon after birth. In this study, the time constants of each of the components of the neural signal underlying congenital nystagmus were obtained by time series analysis and interpreted by comparison with those of the normal oculomotor system. In the neighbourhood of the fixation position, the system generating the neural signal is approximately linear with 3 degrees of freedom. The shortest time constant was in the range of 7-9 ms and corresponds to a normal saccadic burst signal. The other stable time constant was in the range of 22-70 ms and corresponds to the slide signal. The final time constant characterises the unidentified neural mechanism underlying the unstable drift component of the oscillation cycle and ranges between 31 and 32 ms across waveforms. The characterisation of this unstable time constant poses a challenge for the modelling of both the normal and abnormal oculomotor control system. We tentatively identify the unstable component with the eye position signal supplied to the superior colliculus in the normal eye movement system and explore some of the implications of this hypothesis.

Quick Phases of Infantile Nystagmus Show the Saccadic Inhibition Effect

“…2,10,13 The underlying cause of IN has variously been attributed to abnormalities in neural mechanisms responsible for gaze holding, 1,8,14 malfunction of smooth pursuit feedback, 8,[15][16][17] malfunction of the optokinetic response, [18][19][20][21] and malfunction of saccadic termination. [22][23][24][25] More recently, Harris and Berry 6,11,26 proposed that IN results from an intact oculomotor system, but one which has settled on an abnormal viewing strategy. This abnormal strategy may have originally been an adaptive oculomotor response to improve low spatialfrequency information during early development; however, the strategy becomes maladaptive following full development of visual acuity.…”

Slow–fast control of eye movements: an instance of Zeeman’s model for an action

“…Given a state-space reconstruction of the behaviour of the system, geometric analysis of the trajectories associated with individual saccades can then be used to identify equilibria and to approximate the local behaviour around each equilibrium with a set of first-order linear differential equations derived from the eigenvalues and eigenvectors of the linearised vector field. This approach has previously been shown to be applicable to eye movement recordings (Abadi et al 1997;Akman et al 2006;Theodorou and Clement 2007;Akman et al 2012).…”