Lesions of the orbitofrontal cortex do not affect the reinforcement omission effect in rats.

Abstract

The reinforcement omission effect (ROE), reflected by response rates that are higher after reinforcement omission than after reinforcement delivery, has been attributed to both motivational and attentional consequences of the surprising reinforcement omission. These processes depend on the operation of separate amygdala areas and their connections with other brain systems. The interaction between the amygdala and orbitofrontal cortex has been suggested to be important in the modulation of motivational processes. The present study sought to verify whether the mechanisms involved in the ROE depend on the integrity of the orbitofrontal cortex. Prior to acquisition training, rats received bilateral excitotoxic lesions of the orbitofrontal cortex or sham lesions. Following postoperative recovery, the rats were trained on a fixed-interval 12 s limited-hold 6 s signaled schedule of reinforcement. After the acquisition of stable performance, the training was changed from a 100% to 50% schedule of reinforcement. The results showed that rats in both groups exhibited the ROE, with no differences in performance between groups following nonreinforcement. These data do not support the hypothesis that the orbitofrontal cortex is included in the neural substrates related to ROE modulation. The results also showed no difference in response rates between groups in the periods that preceded and followed nonreinforcement. These findings confirm previous studies that showed that the ROE is not related to the facilitation of behavior induced by nonreinforcement. Keywords: reinforcement omission effect, orbitofrontal cortex, operant behavior, rats.

Reinforcement omission effects in rats with bilateral lesions in the substantia nigra pars compacta and ventral tegmental area

“…On the other hand, there was a transient behavioral inhibition indicated by the suppression of response rates after reinforcement. These same behavioral patterns were observed in other studies (7,9–11).…”

“…KA was infused with a 5 µL Hamilton syringe over a 2-min period according to the following coordinates: SNc (n=27): –4.3 mm posterior to bregma and 2.2 mm from the midline, with infusions to a depth of 7.4 mm from the skull surface (0.25 µL per site) (19). The Sham-SNc (n=16) groups received the same surgical treatment, with the exception that no solution was infused (7,8,10,11,20,21). After surgery, all rats received a single subcutaneous injection of 0.1 mL per 100 g body mass (2.15 mg/mL) of Flunixin Meglumine (Banamine®, 50 mg/mL, Intervet, Brazil) for pain relief and were allowed to recover from the surgery for 5–7 days before behavioral testing.…”

“…Recent studies have investigated whether the ROEs can be modulated by different brain structures linked to the amygdala such as the nucleus accumbens (NAC), medial prefrontal cortex (mPC), and orbitofrontal cortex (OFC). For example, lesions of the NAC and mPC, but not of the OFC, interfered with ROEs in rats submitted to the FI LH signaled schedule (9–11).…”