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.

Los efectos de la omisión de refuerzo han sido tradicionalmente interpretados en términos de facilitación comportamental después de la omisión del refuerzo inducida por la frustración, o de supresión comportamental después de la liberación del refuerzo inducida por el estado posconsumo. Los estudios revisados indican que la amígdala está involucrada en la modulación de estos efectos. Sin embargo, el hecho de que las lesiones generales o selectivas de la amígdala puedan eliminar, reducir, e incluso mejorar los efectos de la omisión, hace que sea difícil entender cuál es la naturaleza exacta de su participación en dicho fenómeno. La amígdala está relacionada con una serie de funciones, cada una de las cuales depende de sus conexiones con otros sistemas cerebrales. Por lo tanto, es necesario considerar la participación de una red neuronal más compleja en la modulación de los efectos de la omisión de refuerzo. Las conexiones de los distintos núcleos de la amígdala con las estructuras corticales y subcorticales pueden estar implicadas en esta modulación, ya que también están vinculadas a procesos relacionados con la recompensa y la expectativa.

The reinforcement omission effects have been traditionally interpreted in terms of: behavioral facilitation after reinforcement omission induced by primary frustration or behavioral suppression after reinforcement delivery induced by postconsummatory states. The studies reviewed here indicate that amygdala is involved in modulation of these effects. However, the fact that amygdala lesions, extensive or selective, can eliminate, reduce and enhance the omission effects makes it difficult to understand how it is the exact nature of their involvement. The amygdala is related to several functions that depend on its connections with other brain systems. Thus, it is necessary to consider the involvement of a more complex neural network in the modulation of the reinforcement omission effects. The connection of amygdala subareas to cortical and subcortical structures may be involved in this modulation since they also are linked to processes related to reward and expectancy.

Os efeitos de omissão do reforço têm sido tradicionalmente interpretados em termos de: facilitação comportamental após a omissão do reforço induzida por frustração ou supressão comportamental após a liberação do reforço induzida pelo estado pós-consumatório. Os estudos revisados indicam que a amígdala está envolvida na modulação destes efeitos. Porém, o fato de que lesões da amígdala, amplas ou seletivas, podem eliminar, reduzir ao até mesmo potencializar os efeitos de omissão torna mais difícil compreender qual é a natureza exata do seu envolvimento. A amígdala está relacionada a uma série de funções e cada uma delas depende de suas conexões com outros sistemas cerebrais. Assim, pode haver necessidade de se considerar o envolvimento de uma rede neural mais complexa na modulação dos efeitos de omissão do reforço. A conexão de subáreas da amígdala com estruturas corticais e subcorticais pode estar envolvida nesta modulação, uma vez que também estão ligadas a processos relacionados a recompensas e expectativa.

The reinforcement omission effect (ROE) has been attributed to both motivational and attentional consequences of surprising reinforcement omission. Recent evidence suggests that the basolateral complex of the amygdala is involved in motivational components related to reinforcement value, whereas the central nucleus of the amygdala is involved in the processing of the attentional consequences of surprise. This study was designed to verify whether the mechanisms involved in the ROE depend on the integrity of either the basolateral amygdala complex or central nucleus of the amygdala. The ROE was evaluated in rats with lesions of either the central nucleus or basolateral complex of the amygdala and trained on a fixed-interval schedule procedure (Experiment 1) and fixed-interval with limited hold signaled schedule procedure (Experiment 2). The results of Experiment 1 showed that sham-operated rats and rats with lesions of either the central nucleus or basolateral area displayed the ROE. In contrast, in Experiment 2, subjects with lesions of the central nucleus or basolateral complex of the amygdala exhibited a smaller ROE compared with sham-operated subjects. Thus, the effects of selective lesions of amygdala subregions on the ROE in rats depended on the training procedure. Furthermore, the absence of differences between the lesioned groups in either experiment did not allow the dissociation of attentional or motivational components of the ROE with functions of specific areas of the amygdala. Thus, results did not show a functional double-dissociation between the central nucleus and basolateral area in the ROE.