The thalamus: Structure, function, and neurotherapeutics

Abstract

The complexity and expansive nature of thalamic research has led to numerous interventions for varied disease states. At the same time, this complexity along with siloed areas of study can hinder a comprehensive understanding. The goal of this paper is to give the reader a broader and more detailed perspective on the thalamus. In order to accomplish this goal, the paper begins with a summary of the function, electrophysiology, and anatomy of the normal thalamus. With this foundation, thalamic involvement in neurological diseases is discussed with a focus on epilepsy. Therapeutic interventions in the thalamus for epilepsy as well as movement disorders, psychiatric conditions and disorders of consciousness are described. Lastly limitations in the field and future models of data sharing and cooperation are explored.

Keywords: Coma; Drug-resistant epilepsy; Neuromodulation; Thalamus; Tourette's syndrome; Tremor.

Fig. 1

The anatomy of the thalamus. Right and left thalami shown. The left thalamus is shown with the reticular nucleus removed. The anterior division (blue), medial division (purple), lateral division dorsal tier (greens), lateral division ventral tier (reds/oranges), and intralaminar nuclei (yellow/blue) are shown. The reticular nucleus (gray) covers the lateral surface of the right thalamus. This diagram adheres most closely to the Morel atlas with the exception that the ventral intermediate nucleus is considered part of the ventral lateral nucleus in the Morel atlas. Diagram courtesy of artist Vera Liu.

Fig. 2

Thalamic segmentations using high field imaging and automatic segmentations. Example of single-slice segmentation of the thalamus and three subnuclei of interest, the anterior, centromedian, and medial pulvinar overlaid on a T1-MPRAGE of a single subject (TR ​= ​6000 ​ms, TE ​= ​3.62 ​ms, FOV ​= ​240 ​mm ​× ​320 ​mm, resolution ​= ​0.7 ​mm isotropic) acquired using a 7 ​tesla Siemens MRI scanner. FreeSurfer 7.2 (Fischl et al., 2001; Fischl et al., 2004) with motion correction, intensity normalization, skull stripping and neck removal, automatic segmentation, and parcellation processing steps was used with the T1 image to segment the thalamus and subsequent subnuclei.

Fig. 3

Connectivity of thalamic nuclei in a single subject using diffuse-weighted MRI. Example of 3D rendering of tracts emanating from the anterior, centromedian, and medial pulvinar nucleus in an individual subject. Each subnuclei, segmented with the methods used in Fig. 1 is displayed along with the tracts which were generated from a high-angular-resolved diffusion-weighted imaging MRI (dMRI) sequence (b ​= ​1500 ​s/mm², TR ​= ​7200 ​ms, TE ​= ​67.6 ​ms, FOV ​= ​210 ​× ​210 ​mm, resolution ​= ​1.05 ​mm isotropic, 64 directions, and 5 b0 acquisitions) acquired at 7T. The dMRI series in both anterior-to-posterior and posterior-to-anterior directions were collated into a single volume which was denoised and corrected for eddy current distortions, motion, and B1 inhomogeneity. MRtrix was used to generate tractography seeding from each individual subnuclei to whole brain using SIFT2 and tcksample with 1000 seeds per voxel.

Fig. 4

Thalamic recordings from SEEG to RNS. A woman with DRE and bilateral independent seizure onsets on scalp EEG with semiology of unresponsiveness and occasional falling. SEEG had broad bilateral coverage including CM leads whose trajectory included the posterior insular and the parietal operculum [A]. [B] Seizures had broad bilateral independent onsets with CM involvement within 100 ​msec (right onset shown, only subset of SEEG shown). Patient underwent bilateral CM RNS [C] and seizures were well detected (left sided onset shown). Patient has not had a fall since RNS but continues to have very brief focal impaired awareness seizures.