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Optimal control of saccades by spatial-temporal activity patterns in the monkey superior colliculus
H H L M Goossens1, A J van Opstal
1Radboud University Nijmegen Medical Centre, Donders Institute for Brain, Cognition, and Behaviour, Department of Cognitive Neuroscience, Section Biophysics, Nijmegen, The Netherlands. J.Goossens@donders.ru.nl
Plos Computational Biology
|May 23, 2012
Summary
Computational neurobiology research reveals how the superior colliculus (SC) optimizes eye movements (saccades). This study shows SC neuron activity patterns explain saccade kinematics, challenging previous models.
Area of Science:
- Computational neurobiology
- Systems neuroscience
- Motor control
Background:
- Understanding how neural populations generate accurate goal-directed actions like saccades is a major challenge.
- Saccades exhibit nonlinear kinematics (duration increases with amplitude, peak velocity saturates) potentially optimizing speed-accuracy tradeoff amidst signal-dependent noise.
- The superior colliculus (SC), a sensorimotor hub with a saccade vector map, is hypothesized to implement this optimization.
Purpose of the Study:
- To investigate the role of the SC's spatial-temporal dynamics in generating saccade kinematics.
- To challenge the prevailing model attributing nonlinear saccade kinematics to downstream brainstem mechanisms.
- To present neurophysiological evidence supporting the SC as the locus of saccade kinematic control.
Main Methods:
- Analysis of neurophysiological data from saccade-related neurons in the SC.
- Examination of burst properties (firing rate, duration, skewness) along the SC's rostral-caudal (amplitude-coding) dimension.
- Investigation of neuronal burst synchronization and its relation to saccade vectors and anatomical location.
Main Results:
- A systematic organization of burst properties was found along the SC's motor map: peak firing rates decrease, while burst durations and skewness increase for larger saccades.
- These spatial gradients in SC activity correlate with the amplitude-dependent increases in saccade duration and skewness.
- Neuronal burst profiles were synchronized across the population, indicating timing is determined by the planned saccade vector, not cell location.
- SC neurons exhibit signal-dependent noise, consistent with optimal motor control principles.
Conclusions:
- The spatial-temporal dynamics of SC activity, not downstream saturation, likely underlie nonlinear saccade kinematics.
- The SC's motor map is precisely tuned to implement an optimal motor-control principle for saccades.
- This organization fully accounts for saccade trajectory straightness and kinematic nonlinearity, supporting the SC's central role in motor control.
