Decision-Making involves a little known Brain Region in the Thalamus

To visualize the neural pathways, two markers (red and green) were applied to two regions of the orbitofrontal cortex. These compounds then migrated, accumulating in the thalamic neurons. Dense labeling with the two tracers is visible in the submedius thalamic nucleus (delimited by a dotted line). Credit: Images generated at the Bordeaux Imaging Centre and obtained by Fabien Alcaraz

When faced with a change to our environment, we have to make appropriate decisions, which usually involves the orbitofrontal cortex. Yet unexpectedly, scientists have discovered that a brain region located in the thalamus also plays a crucial role in using these evolved skills.

Using a labeling technique, the scientists evidenced a specific area, the thalamic submedius nucleus, which is closely linked to the orbitofrontal cortex and whose functional role is unknown.

The team then tested the role of these 3 brain structures (the submedius thalamic nucleus and orbitofrontal cortex) in decision-making and adaptive behavior. To achieve this, they studied 3 groups of rats: the 1st presented lesions to the orbitofrontal cortex, the 2nd had lesions on the submedius nucleus and the third was made up of lesion-free control animals. The objective was to test their ability to establish a link between an auditory cue and obtaining a food reward.

The experiment was in 2 phases. The initial learning phase allowed the animals to learn that 2 different sounds (S1 and S2) each signaled a specific food reward. During the second phase, the procedure remained unchanged for the first cue, but for S2, the scientists distributed food rewards during, and mostly outside, cue test periods. This sound thus lost its predictive value and lesion-free animals started to take no account of the S2 auditory stimulus, only visiting the dispenser when they heard S1. On the other hand, animals with a lesion — of either the orbitofrontal cortex or the submedius thalamic nucleus — proved incapable of making this distinction, and thus of adapting.

This study identified the existence of a circuit between the thalamus and the cortex, which proved crucial to adaptive decision-making. The findings suggest that numerous functional circuits underlying this type of behavior may involve a contribution from the thalamus. The team is now planning to explore these “thalamocortical” circuits, whose understanding could shed light on numerous diseases, such as schizophrenia or addiction.
http://www2.cnrs.fr/en/2627.htm