The thalamus plays a central role in relaying sensory information to the cerebral cortex, yet the specific functions of individual thalamic relay nuclei (TRN) remain incompletely understood, particularly in humans. While its broader role in sensory processing is well established, detailed functional differentiation among nuclei is often overlooked or inferred from animal or clinical studies. This systematic review aimed to clarify which thalamic nuclei are involved in the relay of afferent sensory input and to what extent their functions can be specified.

A qualitative review was conducted according to PRISMA 2020 guidelines. Studies were identified through comprehensive searches in PubMed and PsycInfo, focusing on MRI-based research involving healthy adult humans and reporting on thalamic nuclei involved in sensory processing.

Forty-two studies met inclusion criteria, spanning visual (n=23), auditory (n=11), somatosensory (n=13), and gustatory (n=3) modalities. Consistently reported relay nuclei included the LGN and pulvinar (visual), MGN (auditory), VPM and VMb (gustatory), and VPL, VPM, and VPI (somatosensory). Additionally, nuclei such as the MD, VL, and CeM were implicated in multisensory integration, though findings for smaller or multimodal nuclei remained limited.

The results highlight a well-supported set of core relay nuclei but also reveal significant gaps in understanding the functional specificity of less-studied regions. Future research should leverage high-resolution imaging technologies and adopt more targeted approaches to improve anatomical and functional mapping of the human thalamus. These advances are essential for refining clinical interventions and developing a more nuanced understanding of thalamic sensory processing.