TY - JOUR T1 - Dual Encoding of Muscle Tension and Eye Position by Abducens Motoneurons JF - The Journal of Neuroscience JO - J. Neurosci. SP - 2271 LP - 2279 DO - 10.1523/JNEUROSCI.5416-10.2011 VL - 31 IS - 6 AU - María A. Davis-López de Carrizosa AU - Camilo J. Morado-Díaz AU - Joel M. Miller AU - Rosa R. de la Cruz AU - Ángel M. Pastor Y1 - 2011/02/09 UR - http://www.jneurosci.org/content/31/6/2271.abstract N2 - Extraocular muscle tension associated with spontaneous eye movements has a pulse-slide-step profile similar to that of motoneuron firing rate. Existing models only relate motoneuron firing to eye position, velocity and acceleration. We measured and quantitatively compared lateral rectus muscle force and eye position with the firing of abducens motoneurons in the cat to determine fundamental encoding correlations. During fixations (step), muscle force increased exponentially with eccentric eye position, consistent with a model of estimate ensemble motor innervation based on neuronal sensitivities and recruitment order. Moreover, firing rate in all motoneurons tested was better related to eye position than to muscle tension during fixations. In contrast, during the postsaccadic slide phase, the time constant of firing rate decay was closely related to that of muscle force decay, suggesting that all motoneurons encode muscle tension as well. Discharge characteristics of abducens motoneurons formed overlapping clusters of phasic and tonic motoneurons, thus, tonic units recruited earlier and had a larger slide signal. We conclude that the slide signal is a discharge characteristic of the motoneuron that controls muscle tension during the postsaccadic phase and that motoneurons are specialized for both tension and position-related properties. The organization of signal content in the pool of abducens motoneurons from the very phasic to the very tonic units is possibly a result of the differential trophic background received from distinct types of muscle fibers. ER -