Can primates help us better understand OCD?

Check to make sure the front door is locked, look to see if your cell phone is in your purse, make sure the keys to the car are in your pocket, recheck the front door... We pay little attention to these daily micro-tasks, but some French researchers at the National Institute of Health and Medical Research (INSERM) wanted to understand them better by studying primate brains. What are the brain mechanisms used in these micro-checks?

For the purposes of the study published in the journal Nature Communications, a group of researchers from the Stem Cell and Brain Institute (SBRI) attached electrodes to monkeys in order to record their brain activity. More precisely, Emmanuel Procyk and colleagues examined "the activity of 411 neurons in two areas of the frontal cortex known for their involvement in decision making: the middle cingulate cortex and the lateral prefrontal cortex." But how were the scientists able to create a protocol that would provoke the monkeys to "check” something?

The team set up a system in which the primate had two options: either work on a visual memory task or check a gauge showing how long they had to wait before being allowed to receive a reward (fruit juice). The genius of the protocol lies in the fact that the monkey had to correctly perform the memory task in order to make the gauge go up (but failure caused is to go back down). What did E. Procyk’s team discover?

The monkeys cleverly decided to carry out the memory task in 87.5% of the trials. And in 12.5% of the remaining cases, the monkey decided to wait for the reward to be made available with, as predicated, an increase in the number of checks as the reward grew nearer (just as we might check our watch more toward the end of the work day). When the monkey checked the gauge, the neurons of the middle cingulate cortex were first activated, followed by the lateral prefrontal cortex (500 milliseconds later). Even more surprising, using high-performance statistical tools, the scientists were able to correctly predict when the monkeys were about to check the gauge... up to one second before the monkeys performed the actual movement! In their study, the authors also noted that the neural pathways used for this type of verification are different from those involved in other types of decisions (like for example when the monkeys decided to press a button to answer one of the memory test questions).

A dysfunction in the brain mechanism involved in our daily checks could explain the repetitive checking behavior observed in patients suffering from Obsessive Compulsive Disorder (OCD). Regulating dysfunctions in the cingulate cortex could be the key to treating the condition. While the method is only effective in 30-40% of cases, in the United States, specialists are already trying to treat OCD by destroying certain parts of this brain area (electrocoagulation technique). But Emmanuel Procyk’s team recently launched a project that aims to "precisely identify the areas of the cingulate cortex involved in OCD in humans […] and assess the impact of altering these same areas of the cingulate cortex in macaques," he explains. The results of this study, which bring hope to people suffering from OCD, will be available in 2017-2018.
Source: F.M. Stoll, V. Fontanier, E. Procyk, Specific frontal neural dynamics contribute to decisions to check, Nature Communications, June 2016.

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