Seminars are open to all visitors and start Monday at 16:00 sharp. Coffee and tea will be served from 15:45. The seminar series lectures are in a colloquiumzaal at the third floor (entrance level) of the Faculty building of Erasmus MC.
John van Opstal
Dept. Biophysics, Radboud University, NL
How linear population coding underlies nonlinear kinematics
| 2008-02-04 | Room: AE 406 |
Recently, we proposed an ensemble-coding scheme of the midbrain superior colliculus (SC) in which, during a saccade, each spike emitted by each recruited SC neuron contributes a fixed minivector to the gaze-control motor output. The size and direction of this spike vector depend exclusively on a cells location within the SC motor map (Goossens and Van Opstal, 2006). According to this simple scheme, the planned saccade trajectory results from instantaneous linear summation of all spike vectors across the motor map. In our simulations with this model, the brainstem saccade generator was simplified by a linear feedback system, rendering the total model (which has only three free parameters) essentially linear. Interestingly, when this scheme was applied to actually recorded spike trains from 139 saccade-related SC neurons, measured during thousands of eye movements to single visual targets, straight saccades resulted with the correct velocity profiles and nonlinear kinematic relations (main sequence properties and component stretching). Hence, we concluded that the kinematic nonlinearity of saccades resides in the spatial-temporal distribution of SC activity, rather than in the brainstem burst generator. The latter is generally assumed in models of the saccadic system. I will discuss how this behaviour might emerge from this simple scheme. In addition, we will show new experimental evidence in support of the proposed mechanism.