Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (UMR5287)

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Adaptive decision-making and the directionality of information flows within thalamocortical circuits

by Wolff - published on , updated on

Adaptive decision-making and the directionality of information flows within thalamocortical circuits

Access the full paper here: https://doi.org/10.7554/eLife.32517
Thalamocortical and corticothalamic pathways differentially contribute to goal-directed behaviors in the rat. Fabien Alcaraz, Virginie Fresno, Alain R Marchand, Eric J Kremer, Etienne Coutureau & Mathieu Wolff.

INSB communication: http://www.cnrs.fr/insb/recherche/parutions/articles2018/m-wolff.html

Reaching specific goals within volatile environments requires complex cognitive abilities thought to be supported by highly evolved brain regions such as the prefrontal cortex. Within the neural circuits involved, the mediodorsal thalamus appears of special interest due to the extensive reciprocal projections connecting these two areas.
In this study, the DECAD team examined the respective contribution of thalamocortical and corticothalamic pathways connecting the medial prefrontal cortex and the mediodorsal thalamus. To do so, a dual-viral chemogenetic strategy was developed to reversibly inhibit projection-defined thalamic and cortical neurons (see figures below). This enabled to test selectively the functional contribution of each of these pathways with respect to the two main goal attributes: current goal value and current action-outcome contingency.
Interestingly, these manipulations produced dissociable behavioral alterations. While inhibiting the thalamocortical pathway impaired both the ability to guide choice based on current goal value and, to a much larger extent, current action-outcome contingency, inhibiting the corticothalamic pathway only impeded choice based on current goal value. Thus the ability to perform adaptive actions is differentially supported by thalamocortical and corticothalamic pathways.
These results confirm the crucial role of thalamocortical circuits in adaptive cognition. Moreover, they indicate that the direction of information flows within these circuits is one of their fundamental features, which has possible functional relevance for virtually any neural circuit with reciprocal connections. This may also be important to better apprehend mental dysfunctions conceptualized as connectivity disorders such as Schizophrenia.

Figure caption. Left, dual-viral strategy to target either PFC-projecting MD cells (top) or MD-projecting PFC cells (bottom). Resulting DREADD expression (revealed by mCherry) at the level of the MD (top) or the PFC (bottom). After initial instrumental training during which rats learned that performing two distinct actions enabled to gain two specific food rewards, specific choice tests were conducted to assess either current action-outcome contingency or current goal value. Inhibiting the MD-to-PFC was particularly detrimental for the former ability (top, CNO) while inhibiting the PFC-to-MD route only impaired the latter (bottom, CNO).


eLife Digest:

Planning and decision-making rely upon a region of the brain called the prefrontal cortex. But the prefrontal cortex does not act in isolation. Instead, it works together with a number of other brain regions. These include the thalamus, an area long thought to pass information on to the cortex for further processing. But signals also travel in the opposite direction, from the cortex back to the thalamus. Does the cortex-to-thalamus pathway carry the same information as the thalamus-to-cortex pathway?
To find out, Alcaraz et al. blocked each pathway in rats performing a decision-making task. The rats had learned that pressing a lever led to one type of reward, whereas moving a rod led to another. Alcaraz et al. reduced the desirability of one of the rewards by giving the rats free access to it for an hour. Afterwards, the rats opted mainly for the action associated with the reward that had remained desirable. However, blocking either the thalamus-to-cortex or cortex-to-thalamus pathway prevented this preference from emerging. This suggests that an information flow in both directions is necessary to update knowledge about the value of a reward.
In a second experiment, Alcaraz et al. removed the link between one of the actions and its reward. The reward instead appeared at random, irrespective of the rat’s own behavior. Control rats responded by focusing their efforts on the action that still delivered a reliable reward, and by performing the other action less often. Blocking the thalamus-to-cortex pathway prevented this response, but blocking the cortex-to-thalamus pathway did not. This suggests that only the former pathway is necessary to re-evaluate the relationship between an action and an outcome.
Two key aspects of goal-directed behavior – recognizing the value of a reward and the link between an action and an outcome – thus depend differently on the thalamus-to-cortex and cortex-to-thalamus pathways. This same principle may also be at work in other neural circuits with bidirectional connections. Understanding such principles may lead to better strategies for treating disorders of brain connectivity, such as schizophrenia.