The Complex Hodological Architecture of the Macaque Dorsal Intraparietal Areas as Emerging from Neural Tracers and DW-MRI Tractography

Abstract

In macaque monkeys, dorsal intraparietal areas are involved in several daily visuo-motor actions. However, their border and sources of cortical afferents remain loosely defined.Combining retrograde histological tracing and MRI diffusion-based tractography we found a complex hodology of the dorsal bank of the IPS, which can be subdivided into a rostral area PEip, projecting to the spinal cord, and a caudal area MIP lacking such projections. Both include a rostral and a caudal sector, emerging from their ipsilateral, gradient-like connectivity profiles. As tractography estimations, we used the cross-sectional volume of the white matter bundles connecting each area with other parietal and frontal regions, after selecting ROIs corresponding to the injection sites of neural tracers. For most connections, we found a significant correlation between the proportions of cells projecting to all sectors of PEip and MIP along the continuum of the dorsal bank of the IPS and tractography. The latter also revealed "false positive" but plausible streamlines awaiting histological validation. Significance StatementCombined histological and DW-MRI tractography revealed that intraparietal areas PEip and MIP share common inputs from other parietal, frontal and, to a lesser extent, cingulate areas, although with different gradient-like connectivity profiles. Both tractography and histology revealed a high number of common paths, although tractography showed false positive connections awaiting histological validation. A correlation was performed between the proportion of labelled cells projecting to PEip and MIP and the diffusion-based connectivity estimation of the regions of interest corresponding to the injection sites of retrograde tracers. The results showed a significant correlation from most connections studied, opening a window for future studies contrasting proportions of cells giving rise to the fiber bundles connecting cortical areas with measures of diffusion tractography connectivity.

Surface‐based morphometry of the corpus callosum in young children of ages 1–5

“…As a child grows, changes are observed throughout the CC. These to-caudal directions (Ozaki & Wahlsten, 1998;Olivares et al, 2001;Caminiti et al, 2021;Innocenti et al, 2022). Furthermore, DTI tractography studies of WM fiber projections from the CC have shown that the fibers from the genu project to the prefrontal lobe, and fibers from the CC body project to the premotor and supplementary motor areas, the primary motor cortex, and primary sensory regions (Fabri & Polonara, 2023).…”

Involvement of the claustrum in the cortico-basal ganglia circuitry: connectional study in the non-human primate

“… Cortical connections described in a Borra et al ( 2022 ), b Luppino et al ( 1993 ), c Matelli et al ( 1998 ), Luppino et al ( 2001 , 2003 ), d Borra et al ( 2010 ), e Gerbella et al ( 2010 ), f Borra et al ( 2019 ), g Borra et al ( 2011 ), h Gerbella et al ( 2013 ), i Borra et al ( 2008 ), j Rozzi et al ( 2006 ), k Caminiti et al ( 2021 ) …”

“…Table 1 summarizes the cases used in the present study. As most of these cases have been already used in previous studies focused on corticocortical or corticostriatal connectivity (see for references Table 1 ), in this section for the sake of clarity and consistency we reuse the description of authorizations, surgical procedures, brain perfusion, histological processing, and immunohistochemical procedures already provided in previous studies (Matelli et al 1998 ; Luppino et al 1993 , 2001 , 2003 ; Rozzi et al 2006 ; Borra et al 2008 , 2010 , 2011 , 2019 , 2022 ; Gerbella et al 2010 ; 2013 ; Caminiti et al 2021 ).…”

The functional characterization of callosal connections

“…How streamlines correspond to axons is unknown and the relationship between the two is not very tight ( Aydogan and Shi, 2018 ). However, the connections traced by DW-MRI and axonal transport methods match in about 60 %–80 % of cases ( Seehaus et al, 2013 ; Girard et al, 2020 ; Caminiti et al, 2021 ), with a good correlation between connectivity weights and the number of labelled cells obtained through tracing experiments ( Caminiti et al, 2021 ; Donahue et al, 2016 ). Estimates in the conduction compartment of axons can be obtained with DW-MRI albeit for diameters above 2–2.5 μm ( Fig.…”