Macromolecular tissue volume mapping of lateral geniculate nucleus subdivisions in living human brains

Abstract

The human lateral geniculate nucleus (LGN) is composed mainly of the magnocellular and parvocellular subdivisions. The non-invasive identification of these subdivisions is, however, difficult due to the small size of the LGN. Here we propose a method to identify these subdivisions by combining two structural MR measures: high-resolution proton-density weighted images and macromolecular tissue volume maps. We collected MRI data from 15 healthy subjects and found that the spatial organization of these subdivisions identified by our method was consistent with post-mortem histological data. Furthermore, the stimulus selectivity in these regions measured by functional MRI was consistent with physiological studies. These results suggest that macromolecular tissue volume mapping is a promising approach to evaluating the tissue properties of LGN subdivisions in living humans. This method potentially will enable neuroscientific and clinical hypotheses about the human LGN to be tested.

Evaluating Quantitative and Functional MRI As Potential Techniques to Identify the Subdivisions in the Human Lateral Geniculate Nucleus

“…By fitting a two-component model to the qT1 data, we selected the smaller proportion component as M and the larger proportion component as P. The P component showed shorter T1 relaxation time (i.e., qT1) than the M component, indicating more myelination in the P region. This is consistent with Müller-Axt et al’s (2021) results (also see preprint Oishi et al, 2020) and with higher cell density and more myelination in the P compared to the M divisions (Hassler, 1966; Pistorio et al, 2006). Previous studies used a fixed proportion as the criterion to segregate the M and P sections (Denison et al, 2014; Oishi et al, 2020), based on the histology findings that, on average, 20% of the LGN is M (Andrews et al, 1997; Selemon & Begović, 2007), but this approach, even if correct, would not allow the independent measurement of the M division properties.…”

“…To segregate the M and P regions based on the qT1 maps, we followed a data-driven approach to replicate Müller-Axt et al ( 2021 2021) results (also see preprint Oishi et al, 2020) and with higher cell density and more myelination in the P compared to the M divisions (Hassler, 1966;Pistorio et al, 2006). Previous studies used a fixed proportion as the criterion to segregate the M and P sections (Denison et al, 2014;Oishi et al, 2020), based on the histology findings that, on average, 20% of the LGN is M Selemon & Begovic , 2007), but this approach, even if correct, would not allow the independent measurement of the M division properties. Individuals show great variation in the proportions of the subdivisions Müller-Axt et al, 2021), and indeed our participants had M divisions ranging from 12-19% of the LGN volume.…”