Saccadic gain adaptation is predicted by the statistics of natural fluctuations in oculomotor function

Mark V Albert,Peter Thier,Konrad Kording,Nicolas Catz

doi:10.3389/fncom.2012.00096

Abstract

Due to multiple factors such as fatigue, muscle strengthening, and neural plasticity, the responsiveness of the motor apparatus to neural commands changes over time. To enable precise movements the nervous system must adapt to compensate for these changes. Recent models of motor adaptation derive from assumptions about the way the motor apparatus changes. Characterizing these changes is difficult because motor adaptation happens at the same time, masking most of the effects of ongoing changes. Here, we analyze eye movements of monkeys with lesions to the posterior cerebellar vermis that impair adaptation. Their fluctuations better reveal the underlying changes of the motor system over time. When these measured, unadapted changes are used to derive optimal motor adaptation rules the prediction precision significantly improves. Among three models that similarly fit single-day adaptation results, the model that also matches the temporal correlations of the non-adapting saccades most accurately predicts multiple day adaptation. Saccadic gain adaptation is well matched to the natural statistics of fluctuations of the oculomotor plant.

Highlights

Our movement system changes due to a large number of factors including fatigue, disease, attention, nutrition, exercise, growth, and depletion of neurotransmitters
With lesions of the posterior cerebellar vermis the ability of these monkeys to adapt their saccade gains based on errors is severely impaired, at least in the timescales of the experiment (Figure 1B)
Here we have shown that a simple model can capture the spectrum of fluctuations of the oculomotor system of monkeys with lesions in the posterior cerebellar vermis that impair saccadic gain adaptation

Summary

Introduction

Our movement system changes due to a large number of factors including fatigue, disease, attention, nutrition, exercise, growth, and depletion of neurotransmitters. Recent models of motor adaptation have been derived based on the idea that movement adaptation serves to undo such changes to maintain stable responses to movement commands (Korenberg and Ghahramani, 2002; Kording et al, 2007; Burge et al, 2008; van Beers, 2009; Wei and Koerding, 2009; Shadmehr et al, 2010) These models assume how the movement system might fluctuate over time and derive the optimal solution to the adaptation problem. Energy is more plentiful, movement commands are modulated to perform the same reach movement Under normal circumstances, this ongoing adaptation largely masks the effects of underlying changes to the motor system (Shelhamer and Joiner, 2003). It has never been quantitatively tested if adaptation is matched to ongoing fluctuations in the responsiveness of the motor plant

Methods

Results

Conclusion