The Cognitive Thalamus as a Gateway to Mental Representations
Mathieu Wolff and Seralynne D. Vann
Journal of Neuroscience 2 January 2019, 39 (1) 3-14; DOI: https://doi.org/10.1523/JNEUROSCI.0479-18.2018
Thalamic research has evolved at a fast pace over the last few years. Many researchers now better acknowledge the functional contribution of subcortical structures in learning and memory and higher order cognition. However, integrating the many new data with existing thalamic models remain quite challenging. Finding ways to tackle this issue was a central topic in the last Cognitive Thalamus meeting held in Strasbourg last summer.
Mathieu Wolff (DECAD team) and Seralynne Vann (Cardiff University) have been interested in providing a system-level understanding of the role of subcortical structures for years. After a joined contribution in the last NeuroFrance meeting held in Bordeaux, they entered the process of writing a perspective on thalamic research and its relevance for cognition. The result is now published as a Viewpoint at Journal of Neuroscience.
Extended abstract
Historically, the thalamus has been viewed as little more than a relay, simply transferring information to key players of the cast, the cortex and hippocampus, without providing any unique functional contribution. In recent years, evidence from multiple laboratories researching different thalamic nuclei has contradicted this idea of the thalamus as a passive structure. Dated models of thalamic functions are being pushed aside, revealing a greater and far more complex contribution of the thalamus for cognition. In this Viewpoint, we show how recent data support novel views of thalamic functions that emphasize integrative roles in cognition, ranging from learning and memory to flexible adaption. We propose that these apparently separate cognitive functions may, in fact, be supported by a more general role in shaping mental representations. Several features of thalamocortical circuits are consistent with this suggested role and we highlight how divergent and convergent thalamocortical and corticothalamic pathways may complement each other to support these functions.
A. Divergence, convergence and gating are essential functional principles of thalamocortical circuits. Divergent and convergent thalamocortical pathways may respectively promote parallel functioning and integrative processing at the cortical level. In addition, returning corticothalamic pathways are able to gate relevant thalamocortical inputs through lateral inhibition via the reticular thalamus (TRN). This architecture may contribute to the maintenance (B) or updating (C) of cortical representations. In the latter case, some mental constructs may no longer be relevant (outlined in gray dashed line), while others become more prominent (blue solid arrows).
Furthermore, the role of the thalamus for subcortical integration is highlighted as a key mechanism for maintaining and updating representations. Thus, all these functional features of thalamocortical circuits (reciprocity of connections, convergence, divergence, integration) are proposed to act synergistically to achieve cognitively relevant mental events. The presence of thalamic pathology in a number of neurological conditions reinforces the need to better understand the role of this region in cognition. Thalamus research has entered a new era and virtually any brain region has a thalamic story to tell. We believe in the potential of uniting efforts in promoting a cognitive view of the thalamus, from sensory salience to adaptive cognition.