Yukta Kulkarni ’22

The human brain’s prefrontal cortex plays an important role in cognitive behavior. It contains several sections including the lateral prefrontal cortex (LPFC), which is associated with working memory, reasoning, and planning; and the orbitofrontal cortex (OFC), which directs reversal and reinforcement learning, reward evaluation, and alternative option evaluation.  These structures are also present in animals and have similar functions. To learn more about the LPFC and OFC, La Camera et al. conducted a study to observe monkeys with bilateral LPFC and OFC lesions using two methods: delayed match to sample (DMS) tasks for concept formation and rule-based tasks for no concept formation.

Under the supervision of the Animal Care and Use Committee by NIMH, the research team collected a total of nine rhesus monkeys to examine; three of which were controls, three with LPFC lesions, and 3 with OFC lesions. The incisions were limited to the frontal pole, rostrally, and the principal sulcus, caudally, ensuring that anything related to the eye was untouched. To begin the experiment, the monkeys performed a preliminary behavioral test in which they had to let go of a bar whenever they saw a green light. Once they scored sufficiently high (>70%), the monkeys moved on to the next task, delayed match to sample (iDMS). They were shown two images that either matched (resulting in a reward) or didn’t match (resulting in no reward), and it was their job to predict whether they would receive a prize. The monkeys with OFC lesions took significantly longer to understand and perform the task compared to the control monkeys and monkeys with LPFC lesions. The researchers then switched the rule-outcome association, so that if the images match, they did not receive an award, and if the images didn’t match, they received an award. It was difficult for the OFC lesion monkeys and LPFC monkeys to comprehend the reversal, taking them at least 10 sessions to get it correct. These results indicated that the orbitofrontal cortex is important for the concept-based rule, while the lateral prefrontal cortex is important for modifications of the rules.

These conclusions can assist medical diagnoses. In cases where a patient has trouble linking two ideas, a problem in their OFC may be a plausible cause. Furthermore, if a patient can’t alter a previously given rule, they may have damage in their LPFC. With the improvement of anatomical knowledge, better healthcare and informed diagnoses are possible. 

Works Cited:

1. G. La Camera, et al., Contributions of lateral and orbital frontal regions to abstract rule acquisition and reversal in monkeys. Frontiers in Neuroscience 12, 165 (2018). Doi: https://doi.org/10.3389/fnins.2018.00165 
2. Image retrieved from: https://www.pxfuel.com/en/search?q=rhesus+monkeys