The effects of the ablation of a unilateral utricular (otolithic) input and a neck proprioceptive input in an avoidance rail-running situation

A rail-running task for squirrel monkeys (Saimiri sciureus) that consisted of a two-way shuttle avoidance situation and a longitudinally rotating rail was used to investigate the behavioral effects of unilateral utricular nerve section and unilateral upper cervical sensory root section on body balance Baseline rail-running performance was established through training. Five treatment groups were employed using a total of 23 Ss a left utricular nerve section group (UtNC), a stapedectomy group (STAPED) as a control for UtNC, a cervical 1 spinal sensory root section group (C1 DRC), a cervical 1 and 2 spinal sensory root section group (C1 & C2 DRC), and a sham control spinal sensory root section group (SHAM DRC). After surgery, rail-running performance was measured daily until it reached baseline level. This time period was designated the equilibrium 'compensation' period. Treatment groups were compared according to postoperative rail-running performance change, duration (in days) of the compensation period and the direction of ataxia caused by the partial ablations UtNC performance decrement and compensation duration (10. 5 days) was most severe, followed by C1 & C2 DRC (compensation duration, 6. 9 days) The Cl DRC, SHAM DRC, and STAPED groups showed no change m performance. Results were discussed in relation to the relative importance of the utricle and the origin of the neck proprioceptive cues. It was concluded that the utricle is of definite functional importance for body balance but its unilateral loss can be completely compensated for. The importance of neck proprioceptive mechanisms for balance are independent of labyrinthine blood circulation control but are related to sensory input from the upper cervical level.