Our everyday actions depend on the context in which we behave. Image, for instance, to be sitting at the restaurant with a dear friend. It would be appropriate to grab a piece of food from his/her plate. On the contrary, it would be very unbecoming to taste the food of a stranger who is sitting at the table next to ours. This ability to switch between rules is critical for healthy and reasonable decision making and, in more general term, for executive controls. Several studies have shown that neurons in prefrontal cortex (PF) may serve this function (Tsujimoto et al., 2011). In particular, Rudebeck P.H. and Murray E.A., (2008) showed that monkeys with lesions in orbital prefrontal cortex (PFo) were not able to switch between rules, suggesting that the PFo is a critical site for adaptive and flexible behavior. How, then, the switch between behavioral rules, according to environmental circumstances, is linked to the activity of PFo neurons? This is the question we would answer to.
In the experimental task we would analyze, two monkeys were trained to choose between two spatial targets, one on the left and one on the right of a central spot that appeared on a screen. In each execution of the task, called trial, the choice was made according to a strategy rule. This strategy rule could be 'stay' or 'shift'. The stay rule instructed the monkey to choose the same spatial target chosen in the preceding trial, while the shift rule instructed the monkey to choose the alternative target. It is worth noting that in each trial the strategy rule could be the same as the previous trial (no switch) or it can be different (switch).
Tsujimoto S, Genovesio A, Wise SP. 2009. Comparison of strategy signals in the dorsolateral and orbital prefrontal cortex. J. Neurosci. 31(12):4583-4592;
Rudebeck Peter H. and Murray Elisabeth A. 2008. Amygdala and orbitofrontal cortex lesions differentially influence choices during object reversal learning. J. Neurosci. 28(33): 8338-8343.
This project aims to investigate the encoding of the rule switching in a visually cued strategy task by studying the single neuron activity recorded in the orbital prefrontal cortex (PFo) of two macaques. The experimental task provides an optimal framework to study the rule switching neural modulation since consecutive rules are instructed to the monkey in order to select the spatial target. These rules could be the same or not between two consecutive trials. The monkeys could recognize the maintenance or the switch in the strategy rules even this is not relevant to get the reward. In this case, we would be able to investigate the encoding of rule switching at more abstract level and then not related to any reward expectation.
The current available study on the role of PFo in the encoding of the rule switching is a lesion study that put on evidence the inability of the monkey to reverse a well known rule after a lesion in the PFo (Rudebeck P.H. and Murray E.A., 2008). Another neurophysiological study (Sleezer et al.,2017) supported the idea that the PFo could be involved in the encoding of rule switching, albeit this experimental task did not disentangle the rule switching from the reward expectation. The important advantage of our project is that the task allows to investigate the role of PFo in the rule switching without any linkage to the correct response in order to get the reward. This would represent a very innovative study and it would shed light on the role of PFo in reconfiguration of rules at abstract level.
The innovative feature will not be only from the neurophysiology point of view, but also from the methodology used to perform the data analysis. New analysis techniques, indeed, taken from the physics field will be re adapted and applied to the analysis of the PFo dataset, in parallel to the standard analysis techniques widely used in the neuroscience research field.
Rudebeck Peter H. and Murray Elisabeth A. 2008. Amygdala and orbitofrontal cortex lesions differentially influence choices during object reversal learning. J. Neurosci. 28(33): 8338-8343.
Sleezer Brianna J., loConte Giuliana A., Castagno Meghan D., Hayden Benjamin Y. 2017. Neuronal responses support a role for orbitofrontal cortex in cognitive set reconfiguration. European Journal of Neuroscience.45:940-951.doi:10.1111/ejn.13532.