The role of inferior parietal cortex and fornix in route following and topograhic orientation in cynomolgus monkeys

Abstract

The effects of inferior parietal cortex lesions (Area 7a/PG) and bilateral transection of the fornix were compared within a single species (cynomolgus monkeys) and using a single paradigm of route running in a traditional (fixed entry and exit) whole-body maze. Experiment 1 showed that Area 7a/PG but not fornix lesions impaired post-operative retention of route running. Experiment 2 assessed the contribution of visual cues and proprioceptive/kinaesthetic guidance to route running and showed that in nonlesioned monkeys route running was influenced to varying degrees by proprioceptive guidance, visual extra-maze room cues and visual maze stimuli. Post-operative assessment of maze performance, including error patterns, retraining and misreaching (Experiment 1), suggested that monkeys in the Parietal Group were not topographically disoriented and did not have a spatial long-term memory deficit, but it was their difficulty responding to local spatial cues which initially impaired route running. Investigation of cue use (Experiment 2) also showed the sensitivity of the Parietal Group to local spatial cues; they were significantly impaired on entry through a new start position when the relationship between maze stimuli and extra-maze cues was changed. The Fornix Group showed no retrograde long-term memory deficit for route-running (Experiment 1). However, in Experiment 2, where a new goal position was learnt, the Fornix Group did show an anterograde memory deficit.