Clarifying the anatomical organization and cortical projections of multiple major white matter tracts associating the human temporal and parietal lobes

HIROMASA TAKEMURA; BRENT MCPHERSON; DANIEL BULLOCK; LINDSAY KITCHELL; FRANCO PESTILLI; CESAR F. CAIAFA; BRAD CARRON

San Diego

Conferencia; Society for Neuroscience 2018 (SfN 2018); 2018

Society for Neuroscience

Traditionally, norms of neuroscientific attention have caused researchers to primarily study larger white matter tracts that are aligned to the rostral-caudal axis. These tracts include the superior longitudinal fasciculus, the arcuate fasciculus, the inferior fronto-occipital fasciculus, and the inferior longitudinal fasciculus. More recently, modern in-vivo imaging studies have begun elucidating several tracts in the posterior of the human brain that are instead aligned perpendicular to the rostral-caudal axis. These tracts transfer information directly between the dorsal and ventral aspects of the posterior human cortex. Here we examine several of these tracts, namely, the temporal-parietal connection, the posterior arcuate, and the two components of the middle longitudinal fasciculus.In this work, we compare the anatomical features, volumes, and connectivity patterns of the rostro-caudal aligned and rostro-caudal perpendicular tracts using diffusion-weighted magnetic resonance data from the Human Connectome Project (1.25 mm, b=2000 mm^2/s), modern tractography methods (ensemble tractography), and statistical validation techniques (LiFE). Furthermore, we developed an automated segmentation method to identify these four tracts along with the more studied rostro-caudal tracts. Our results indicate a significant degree of interconnectivity between the ventral and dorsal streams of the human brain. We find that the rostro-caudal perpendicular tracts can be reliably segmented across subjects. Their statistical evidence, volume, and fiber length are generally smaller than those of the more well established rostro-caudal aligned tracts. We also report that the collective architecture of these four vertical tracts instantiate a dual set of parallel white matter structures, conducting information directly between the parietal and temporal lobes. These tracts constitute an important but understudied set of connections in the human brain, which are fundamental in linking cortical areas involved in face recognition, object and word perception, and controlling or planning eye and limb movements. As such, this pattern of connectivity suggests that theories of visual perception and action may need to expand their accounts to incorporate models of cortical function with direct information flow between the posterior dorsal and ventral cortex.