Memory of Learning Facilitates Saccadic Adaptation in the Monkey

Abstract

A motor learning mechanism called saccadic adaptation ensures accuracy of saccades throughout life despite growth, aging, and some pathologies of the oculomotor plant or nervous system. The present study investigates effects of preceding adaptation on the speed of subsequent adaptation during single experiments. Adaptive changes in gain (movement size divided by target eccentricity) were induced by intrasaccadic step (ISS) of the target. After the gain was altered (control block), we reversed the direction of ISS to bring the gain back to approximately 1.0 (recovery). We then reversed ISS direction again to induce another adaptation (test block). Analyses revealed that the gain changed at a higher rate in the early part of test adaptation than in the corresponding part of control. After approximately 100-300 saccades in the test block, adaptation slowed down. The gain value at which adaptation slowed was correlated with the gain achieved in the control. We further examined effects of a 30 min intervention inserted between recovery and test blocks. When zero-visual-error trials ( approximately 700 saccades) were repeated during this period, the rate of test adaptation was similar to that of control. In contrast, when the animal was deprived of visual inputs during this period, test adaptation was still influenced by preceding learning. We conclude that a memory of previous learning remains during recovery to facilitate subsequent adaptation and that such a memory does not disappear merely with time but is erased actively by repeated zero-error movements. Our results, which cannot be explained by a single mechanism, suggest that the saccadic system is equipped with more than one plasticity process.

Error Correction, Sensory Prediction, and Adaptation in Motor Control

“…Spontaneous recovery of memory refers to the natural reemergence of a learned response after that response has been extinguished through extinction training. This phenomenon has been observed in a wide range of paradigms (Rescorla, 2004;Kojima et al, 2004;Stollhoff et al, 2005). Our recent work proposed a mechanism that explains spontaneous recovery as an interaction between the decay of two adaptive processes (Fig.…”

Intermittent Practice Facilitates Stable Motor Memories

“…But such interruptions, in and of themselves, may not be sufficient to stabilize motor memories. Research into saccadic adaptation by primates with either a block of catch trials or an equivalent period of rest without visual inputs suggests that actual practice under null conditions is required to cause active unlearning and relearning of the novel condition (Kojima et al, 2004).…”

Complex Spike Activity of Purkinje Cells in the Oculomotor Vermis during Behavioral Adaptation of Monkey Saccades

“…After many repetitions of this deception, saccade amplitude gradually changes to bring the eye more nearly to the displaced target location. If saccades to target steps of one amplitude and direction experience an intrasaccadic target adapt jump, ϳ500 -1000 erroneous trials are required for nearly complete adaptation in the monkey (Straube et al, 1997;Kojima et al, 2004). Because the number of trials required for nearly complete adaptation is directly proportional to the number of adapted target directions, it was impractical to adapt target steps in eight different directions.…”