A Monkey’s Ability to Ignore Distractions When Focused

Nerve cells in an ape’s brain, especially in a specific area called the dorsolateral prefrontal cortex, are known to have the ability to filter distractions from a set target. They help to concentrate better on the target. However, the extent of this capacity of the primate brain is not known. This study showed that that nerves and neurons in this area of the experimental monkeys became more efficient at filtering out distractions if the distance between the target and the animal was increased.

Studies and experiments have shown that the brain of humans and apes have special neurons or nerve cells in a specific area called the “dorsolateral prefrontal cortex.” These cells play a role in memory formation, preparing for an action, selecting an objective, planning toward achieving the goal and deciding on the route to achieving that goal. Studies on apes have shown that these neurons respond when presented with a task. Although some studies have been conducted on monkeys to explore their neurons and their filtering function, the extent of their capacity in primates has not yet been fully studied. This study attempted to explore this hypothesis in two macaque monkeys.

* For the experiment, two male adult monkeys were trained.
* The monkeys were shown some color dots on a projected screen, from a distance of around 22 inches.
* For the training session that lasted around three to five months, the monkeys were taught to release a switch or button when a target dot changed its direction while moving. They were shown other distracter dots of different colors in the background and were rewarded if they could focus on the target dot, ignoring the distractions.
* The distracter and target dots were shown from different relative distances for the actual experiment and the brain activity was mapped accordingly.

Results/Key findings
* The results from the study showed that as the relative distance of the distracter dots increased, the animals were able to focus on the target better.
* When mapping the brain, it was noted that nerve cells of the dorsolateral prefrontal cortex were more active as the distracters moved away, thereby showing an improvement in their filtering capacity.
* The results suggest that the filtering capacity in primates depends on the ability of the prefrontal cortex neurons to suppress the distracters. It is also dependent on the ability to focus on the target dots.

Next steps/Shortcomings
The authors agree that one important aspect remains to be seen. This includes the definition of the roles of two different parts of the brain in filtering targets in a three dimensional space, which may be based on features or based on object recognition. While the prefrontal cortex is one such area of the brain, there may be other areas like the “frontal eye fields.” This definition of roles needs further studies, say the authors.

This study finds that the macaque monkeys are able to differentiate between a target and distracter visual stimuli on the basis of distance. As the relative distance of the distracter stimuli increased, the focus on the target improved. Brain mapping also showed that the nerves in the dorsolateral prefrontal cortex of these monkeys improved with this distance. The authors speculate that this improvement in nerve function could be due to suppression of the distracter by the brain. The results also showed that this suppression causes certain behavioral modulation in the animal. The authors suggest further studies to explore if these manipulations of stimuli could lead to behavioral changes in the animals as well.

For More Information:
Strength of Response Suppression to Distracter Stimuli Determines Attentional-Filtering Performance in Primate Prefrontal Neurons
Publication Journal: Neuron, April 2011
By Therese Lennert; Julio Martinez-Trujillo; McGill University, Montreal, Canada

*FYI Living Lab Reports Are Summaries of the Original Research.

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