[Abstract Title]. - Society for Neuroscience

Topic: D.06.d. Saccades and Pursuit
Title: Smooth pursuit adaptation (SPA) exhibits features useful to compensate changes in the
properties of the smooth pursuit eye movement system due to usage
Authors: *S. DASH 1 , P. THIER 2 ;
1 Cognitive Neurol., Hertie Inst. for clinical brain res., Tuebingen, Germany; 2 Cognitive Neurol.,
Hertie Inst. for Clin. Brain Research., Tuebingen, Germany
Abstract: During the first 100-150ms of smooth pursuit eye movements (SP) made in an attempt
to compensate a ramp-like movement of a visual target, the eyes basically move open-loop due
to the inherent delays of the visual system. Smooth-pursuit adaptation (SPA) refers to the fact
that the pursuit gain in this early response phase can be adjusted based on experience. For
instance, if the target moves initially at a constant velocity for around 100-200ms and then steps
to a higher velocity, subjects learn to upregulate the pursuit gain evoked by the initial target
velocity (gain increase SPA) in order to reduce the retinal error resulting from the velocity step.
Correspondingly, a step to a lower target velocity leads to a decrease in gain (gain decrease
SPA). Unadapted SP shows a characteristic initial acceleration profile with distinct peak
acceleration and duration. Gain increase SPA is a consequence of expanding the duration of this
profile while keeping peak acceleration constant. Conversely, gain decrease SPA exhibits
reduced peak acceleration but unaltered duration (Takagi et al. J Neurophysiol. 83: 2047ff).
In the present study we asked two monkeys to carry out stereotyped SP guided by ramp-like
target movements (15 or 20°/s, fixation duration 500-800ms, ramp duration 600ms, and no intertrial
interval). After 200-300 trials we observed a clear drop in initial peak acceleration which
was compensated by an increase in the duration of the acceleration profile, thereby keeping
initial pursuit gain constant. This drop in peak acceleration is similar to the one found in gaindecrease
SPA and must reflect changes of the oculomotor periphery or other parts of SP system
due to usage (“fatigue”). The compensatory increase in the duration of the acceleration profile
during pursuit onset is reminiscent of the one leading to gain-increase SPA. This striking
congruence in the kinematic changes during fatigue compensation and SPA suggests a common
functional basis of the two: specifically, gain-decrease SPA seems to be at least in part a passive
process building on the acceleration loss due to fatigue. On the other hand, both gain-increase
SPA and fatigue compensation exploit the ability of the system to expand the duration of the
initial acceleration response. The ability to adjust acceleration duration depends on the integrity
of the oculomotor vermis (OV). This is suggested by the consequences of surgically lesioning
the OV in one of the two monkeys we have studied.
Disclosures: S. Dash , None; P. Thier, None.
Poster
264. Eye Movements: Smooth Pursuit