The tract terminations in the temporal lobe: Their location and associated functions

Abstract

Temporal lobe networks are associated with multiple cognitive domains. Despite an upsurge of interest in connectional neuroanatomy, the terminations of the main fibre tracts in the human brain are yet to be mapped. This information is essential given that neurological, neuroanatomical and computational accounts expect neural functions to be strongly shaped by the pattern of white-matter connections. This paper uses a probabilistic tractography approach to identify the main cortical areas that contribute to the major temporal lobe tracts. In order to associate the tract terminations to known functional domains of the temporal lobe, eight automated meta-analyses were performed using the Neurosynth database. Overlaps between the functional regions highlighted by the meta-analyses and the termination maps were identified in order to investigate the functional importance of the tracts of the temporal lobe. The termination maps are made available in the Supplementary Materials of this article for use by researchers in the field.

Keywords: Brain mapping; Diffusion MRI; Temporal lobe; Tractography; White matter.

Fig. 1

The group-averaged global connectivity profile (green) for the left temporal lobe showing an ROI placed in the main body of the arcuate fasciculus and the resultant termination maps: a) the raw probability map b) the statistical comparison map.

Fig. 2

Statistical termination maps for each temporal tract. The colour scale represents the number of tracts had greater evidence for in the pairwise comparisons, thresholded to show voxels that were significant on at least half (three) of the comparisons. a) anterior commissure; b) arcuate fasciculus; c) cingulum; d) middle longitudinal fasciculus; e) the extreme capsule tract complex; f) the occipital tract complex. The splenium is not presented, as it did not demonstrate any voxels above threshold.

Fig. 3

Results of the Neurosynth meta-analyses for the eight cognitive domains examined. Results display the ‘reverse inference maps’ for all regions across the entire brain, thresholded at .01 FDR corrected.

Fig. 4

Matrices depicting the proportion of tract termination overlapped by the meta-analysis map of each cognitive domain. Epi = episodic memory, Hear = hearing, Sp_per = speech perception, Phon = phonology, Sp_pro = speech production, Sem = semantics, Soc = social, Vis = visual. Note the upper section is the original overlap with all the tract termination, the lower section sub divides the occipital termination into three components (anterior inferior, anterior superior, posterior).

Supplementary Image

Image of ROI placements to extract the tracts of interest. Blue = Emc; Red = Occipital complex; violet = arcuate; yellow = cingulum; cyan = MdLF; green = AC; turquoise = splenium; black-grey = group connectivity profile used to identify tracts of interest.