Response variation in instrumental extinction in rats with fornix transections.

The present experiment examined spatial and response variation interpretations of the large difference in magnitude between operant and instrumental extinction deficits seen in hipocampally damaged animals. Latency measures and detailed behaviors of rats with fornix transections were compared to those of control rats during acquisition and extinction in an enriched spatial runway. Control rats, in comparison to rats with fornix transections, exhibited larger increases in start box, runway, and goal box latencies, but no spatial gradients were found. Control rats also exhibited less goal persistence and more response variation following the transition to extinction. The results suggest no fundamental difference between operant and instrumental deficits following hippocampal damage, but an interaction between strategies employed and traditional response measures.