Saccadic Eye Movements and Gaze Holding in the Head‐Restrained Pigmented Rat

Abstract

Spontaneous saccadic eye movements were recorded in seven head-restrained pigmented rats by means of a phase detection search coil system, both in the light and in the dark. In an illuminated environment, all the rats made numerous spontaneous saccades with an average amplitude of 13.2 deg (+/- 2.2 SD) and a maximal amplitude of 35 deg. In the dark, mean saccadic amplitude was significantly reduced to 9.2 deg (+/- 2.0 SD). Saccadic peak velocity increased linearly as a function of saccadic size, with no saturation at high amplitude values. In the light, peak velocity increase was 32.7 deg/s/deg (+/- 3.5 SD). This value is higher than that described in many other species including man and is similar to that of the monkey. Also saccadic duration increased linearly as a function of size at a rate of 1 ms/deg, which is closer to that of monkey than to that of other species including man. Both peak velocity and duration were not significantly different in the dark from those measured in the light. In the light, following a saccadic gaze shift, the rats were able to maintain a steady eye position for long periods, also at large orbital eccentricities. In the dark, on the contrary, the eye presented a drift towards the central position in the orbit. Such a drift had an exponential-like time course with a time constant of 1567 ms (+/- 829 SD), a value which is much shorter than that of cat and primates. This indicates that in the absence of a visual input, the rat has a poor gaze holding ability compared to other species.

Functional specialization in rat occipital and temporal visual cortex

“…In particular, the characteristics of eye movements in typical traces turned out to be very similar to previously published findings (Chelazzi et al 1989;Niell and Stryker 2010;Zoccolan et al 2010). For most of the time (75%), eye position was at one particular central position (within 1.25°from the median X and Y position for the whole trace).…”

Synaptic Mechanism for the Sustained Activation of Oculomotor Integrator Circuits in the Rat Prepositus Hypoglossi Nucleus: Contribution of Ca2+-Permeable AMPA Receptors

“…It has been reported that the time constant of a centripetal drift after an eye movement to an eccentric direction (i.e., the time constant for the neural integrator) is Ͼ20 s in the cat (Robinson, 1974), monkey (Cannon and Robinson, 1987), and human (Becker and Klein, 1973). Although the time constant in the rodent (Ϸ2 s) [rat (Chelazzi et al, 1989); mouse (van Alphen et al, 2001)] is shorter than that in the cat and primates, it is longer than the duration of the EPSC responses observed in the present study. Therefore, the local PHN network alone is unlikely to be sufficient to explain the mechanism of gaze holding.…”

Saccade direction encoding in the primate entorhinal cortex during visual exploration

“…It is interesting to consider whether the differences between rodent and primate vision could help to explain the apparent disparity between encoding of head orientation in rodent EC and encoding of eye movements in primate EC. The primate visual system is distinctly different from the visual system of common laboratory rodents, which have a larger field of view, make few saccades, and lack a specialized retinal region like the primate fovea (29)(30)(31)(32). Consequently, sampling by moving the visual field via head movements in rodents might be similar to moving the fovea with the eyes in primates.…”