Published: November 15, 2023Animal studies have established that the mediodorsal nucleus (MD) of the thalamus is heavily and reciprocally connected with all areas of the prefrontal cortex (PFC). In humans, however, these connections are difficult to investigate. High-resolution imaging protocols capable of reliably tracing the axonal tracts linking the human MD with each of the PFC areas may thus be key to advance our understanding of the variation, development, and plastic changes of these important circuits, in health and disease. Here, we tested in adult female and male humans the reliability of a new reconstruction protocol based on in vivo diffusion MRI to trace, measure, and characterize the fiber tracts interconnecting the MD with 39 human PFC areas per hemisphere. Our protocol comprised the following three components: (1) defining regions of interest; (2) preprocessing diffusion data; and, (3) modeling white matter tracts and tractometry. This analysis revealed largely separate PFC territories of reciprocal MD–PFC tracts bearing striking resemblance with the topographic layout observed in macaque connection-tracing studies. We then examined whether our protocol could reliably reconstruct each of these MD–PFC tracts and their profiles across test and retest sessions. Results revealed that this protocol was able to trace and measure, in both left and right hemispheres, the trajectories of these 39 area-specific axon bundles with good-to-excellent test-retest reproducibility. This protocol, which has been made publicly available, may be relevant for cognitive neuroscience and clinical studies of normal and abnormal PFC function, development, and plasticity.L.M. was supported by Horizon 2020 the European Union’s research and innovation program under Marie
Skłodowska-Curie Grant 713673 and from “la Caixa” Foundation (Grants 11660016 and 100010434 under
Agreement HR18-00178-DYSTHAL). G.L-U. was supported by the Spanish Ministry of Science and Innovation
(Grants IJC2020-042887-I and PID2021-123577NA-I00) and the Basque Government (Grant PIBA-2022-1-
0014). F.C. was supported by the Spanish Ministry of Science and Innovation (Grants MICINN-AEI PCI2019-
111900-2 and PID2020-115780GB-I00). P.M.P-A. was supported by the Spanish Ministry of Science and
Innovation (Grant PID2021-123574NB-I00), the Basque Government (Grant PIBA-2021-1-0003), and the Red
guipuzcoana de Ciencia, Tecnología e Innovación of the Diputación Foral de Gipuzkoa (Grant FA/OF 422/2022),
and “la Caixa” Foundation (Grant 100010434 under Agreement HR18-00178-DYSTHAL). The Basque Center on
Cognition, Brain and Language (BCBL) acknowledges funding from the Basque Government through the BERC
2022-2025 program and by the Spanish State Research Agency through BCBL Severo Ochoa Excellence
Accreditation CEX2020-001010-S
