Abstract
To survive, animals must learn to control their movements with millisecond-level precision, and adjust the kinematics if conditions, or task requirements, change. Here, we examine adaptive timing of motor output in mice, using a simple eyelid conditioning task. Mice were trained to blink in response to a light stimulus that was always followed by a corneal air-puff at a constant time interval. Different mice were trained with different intervals of time separating the onset of the light and the air-puff. As in previous work in other animal species, mice learned to control the speed of the blink, such that the time of maximum eyelid closure matched the interval used during training. However, we found that the time of maximum eyelid speed was always in the first 100 ms after movement onset and did not scale with the training interval, indicating that adaptive timing is not accomplished by slowing down (or speeding up) the eyelid movement uniformly throughout the duration of the blink. A new analysis, specifically designed to examine the kinematics of blinks in single trials, revealed that the underlying control signal responsible for the eyelid movement is made up of oscillatory bursts that are time-locked to the light stimulus at the beginning of the blink, becoming desynchronized later on. Furthermore, mice learn to blink at different speeds and time the movement appropriately by adjusting the amplitude, but not the frequency of the bursts in the eyelid oscillation.
Highlights
Previous work in a variety of animal species has demonstrated that the timing of the conditioned eyelid response is adjusted to match the interstimulus interval (ISI): maximum eyelid closure in “test-trials” without an air-puff occurs at the time when the air-puff is normally delivered, regardless of the particular ISI used during training (Boneau, 1958; Mauk and Ruiz, 1992; Domingo et al, 1997; Freeman et al, 2003; Koekkoek et al, 2003)
We begin by characterizing in full detail the kinematic properties of the conditioned eyelid response in mice trained at different ISIs
To allow for unbiased comparisons across different ISI conditions, analysis was performed on test sessions that began after asymptotic performance had been achieved, and by examining conditioned eyelid responses only on conditioned stimulus (CS)-alone trials in which no air-puff is delivered
Summary
The meaning of this expression is perhaps most obvious in motor control, where a delay of just few milliseconds can make the difference between hitting a home-run or striking out (Williams and Underwood, 1986; Gray, 2002). To achieve such remarkable precision, we must learn to estimate temporal contingencies accurately despite living in an ever-changing world, and adjust the timing of our movements . Measuring the latency to maximum eyelid closure, does not provide information about the particular trajectory that the eyelid takes from open to closed
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