Lateral, but not medial, frontal lesions impair fixed ratio performance in rats

Preoperatively, male hooded rats were reduced to 85% of their free-feeding weight, and trained to receive food reinforcement on a fixed ratio 32 schedule in standard operant chambers. When response rates stabilized, the rats were randomly assigned to one of the following surgical treatments: lateral frontal ablation, medial frontal ablation, or sham operate control (N=6/group). On the day following surgery, and continuing for a total of 15 postoperative days, the rats were retested on FR32. Lateral frontal lesions produced a dramatic reduction in response rate, while medial frontal lesions produced only a mild and transient effect. The sham operative procedure did not influence performance. These results suggest a dissociation of motor and associative functions in the frontal cortex of the rat and support anatomical evidence demonstrating this division.