Functional mapping of thalamic nuclei and their integration into cortico-striatal-thalamo-cortical loops via ultra-high resolution imaging-from animal anatomy to in vivo imaging in humans

Abstract

The thalamus, a crucial node in the well-described cortico-striatal-thalamo-cortical circuits, has been the focus of functional and structural imaging studies investigating human emotion, cognition and memory. Invasive work in animals and post-mortem investigations have revealed the rich cytoarchitectonics and functional specificity of the thalamus. Given current restrictions in the spatial resolution of non-invasive imaging modalities, there is, however, a translational gap between functional and structural information on these circuits in humans and animals as well as between histological and cellular evidence and their relationship to psychological functioning. With the advance of higher field strengths for MR approaches, better spatial resolution is now available promising to overcome this conceptual problem. We here review these two levels, which exist for both neuroscientific and clinical investigations, and then focus on current attempts to overcome conceptual boundaries of these observations with the help of ultra-high resolution imaging.

Keywords: functional brain networks; high-resolution imaging; thalamo-cortical circuits; thalamus; ultra high field fMRI.

Figure 1

Thalamic section from anterior (back) to posterior (front). Highlighted are the mediodorsal thalamic nucleus (blue), the centromedian/parafascicular thalamic complex (red), the laterodorsal and parataenial thalamic nucleus (yellow) and the ventral anterior thalamic nucleus (green). Figure adapted from Mai et al. (2004).

Figure 2

(adapted from Eckert et al., 2011): Network segregation based on relative fiber counts. (A) Sagittal plane; (B) cornal plane; (C) transversal plane (D) color bars: indicating the level of T-values for each region shown in (A–C). Regions with preferential connectivity to the MD are shown in blue and those connecting stronger to the CM/Pf complex are shown in red, the strength of the connectivity are visualized in the brightness of the blue and red colors. The PCC and the nucleus accumbens do not show significant preferences and appear in green. Abbreviation MD, mediodorsal thalamic nucleus; CM, centromedian/parafasicualar complex of the thalamus; amy, left amygdala; hipp, left hippocampus; PCC, posterior cingulate cortex; put, right putamen; pall, right pallidum; NAcc, right nucleus accumbens; caudate, right caudate nucleus; dlPFC, right dorsolateral prefrontal cortex; dACC, dorsal anterior cingulate cortex; pgACC, pregenual anterior cingulate cortex; aI/fo, left anterior insula-frontal operculum.