Trigeminal deafferentation and prehension in the pigeon.

During the grasping and manipulation phases of the pigeon's ingestive pecking behavior, jaw opening movements are scaled to the size of the target (food) object. To assess the contribution of beak mechanoreceptor afferents to the control of scaling we examined the effects of bilateral trigeminal deafferentation upon the kinematics of jaw opening trajectories. Deafferented subjects exhibited both a transient reduction in the accuracy of peck localization and a more persistent deficit in the effectiveness of their ingestive pecking response. However, they continued to exhibit the same classes of jaw movement described for the normal pigeon. The functional relation between target size and gape remained unchanged after deafferentation as did the relationships among kinematic variables controlling jaw opening. However, deafferentation produced small but significant increase in the absolute values of peak gape for both grasping and mandibulation which reflects an increase in peak opening velocity. The results are discussed in relation to the problem of sensory control of rapid targeted movements.