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Review
. 2019 Jan 2;39(1):3-14.
doi: 10.1523/JNEUROSCI.0479-18.2018. Epub 2018 Nov 2.

The Cognitive Thalamus as a Gateway to Mental Representations

Mathieu Wolff  1   2 , Seralynne D Vann  3
Affiliations
Review

The Cognitive Thalamus as a Gateway to Mental Representations

Mathieu Wolff et al. J Neurosci. .

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 Viewpoints article, 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 indeed 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. Furthermore, the role of the thalamus for subcortical integration is highlighted as a key mechanism for maintaining and updating representations. Finally, we discuss future areas of research and stress the importance of incorporating new experimental findings into existing knowledge to continue developing thalamic models. The presence of thalamic pathology in a number of neurological conditions reinforces the need to better understand the role of this region in cognition.

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Figures

Figure 1.
Figure 1.
Different degrees of complexity for thalamocortical architecture. Basically defined as the reciprocal projections between prefrontal and thalamic areas (A), the thalamocortical loop includes an additional layer constituted by the reticular thalamic nucleus (TRN, B). This area is one of the main sources of thalamic inhibition. Both thalamocortical and corticothalamic pathways send collaterals to the TRN. In addition, the TRN sends supplemental inhibitory projections to other thalamic nuclei (C), not included in the actual loop, thus opening this loop, which may allow gating of specific thalamocortical inputs (see also Fig. 3).
Figure 2.
Figure 2.
In addition to the reciprocity of projections, divergence (A) and convergence (B) are two prominent features of thalamocortical organization. Whereas the former underscores the possibility that multiple thalamic microcircuits act in parallel to achieve cognitive functions, the latter offers enhanced integrative properties. Regarding convergence, MD innervation of the dmPFC and the OFC originates from essentially separate neuronal populations (light blue), even though some MD cells branch to several prefrontal areas. Sub, Submedius thalamic nucleus.
Figure 3.
Figure 3.
A, Divergence, convergence, and gating are essential functional principles of thalamocortical circuits. Divergent and convergent thalamocortical pathways may promote parallel functioning and integrative processing at the cortical level, respectively. In addition, returning corticothalamic pathways are able to gate relevant thalamocortical inputs through lateral inhibition at the level of the 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), whereas others become more prominent (blue solid arrows).
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