Superior longitudinal fasciculus
Fasciculus longitudinalis superior
tract
The largest association fibre system of the cerebral hemispheres, running anterior-posterior along the dorsal aspect of the lateral fissure. The superior longitudinal fasciculus (SLF) connects frontal, parietal, occipital, and temporal cortex through a dense bundle of fibres above the level of the lateral fissure.
Modern diffusion-MRI tractography divides the SLF into three or four parallel sub-pathways. SLF-I (dorsal, fronto-parietal) connects superior parietal cortex with supplementary and pre-supplementary motor areas, supporting spatial working memory and motor planning. SLF-II (middle, fronto-parietal) connects inferior parietal lobule with dorsolateral and middle frontal cortex, supporting visuospatial attention. SLF-III (ventral, fronto-parietal) connects supramarginal gyrus with ventrolateral frontal cortex, supporting articulatory working memory and the dorsal phonological language stream. A fourth, sometimes considered distinct, sub-pathway is the arcuate fasciculus (see separate entry).
The SLF is asymmetrically lateralised, with the right SLF (particularly SLF-II) being larger than the left in most subjects. This asymmetry is the structural substrate for the right-hemisphere dominance of visuospatial attention; lesions to the right SLF produce more severe and lasting hemispatial neglect than left-SLF lesions.
dorsal-attention language
The superior longitudinal fasciculus has no 3D representation in the rendered atlas yet. Like the arcuate and uncinate, sourcing streamline data and rendering tube geometry is on the v1.1 roadmap.
The SLF is the structural backbone of the dorsal frontoparietal attention network. Thiebaut de Schotten and colleagues’ 2011 paper in Nature Neuroscience demonstrated that the right SLF-II is consistently larger than its left counterpart in right-handed individuals, and that this asymmetry predicts attention-task performance: subjects with larger right SLF-II show stronger right-hemispheric bias on visual-attention tasks and faster reorienting to left-hemifield targets.
The three (or four) SLF sub-pathways are distinguished by their cortical terminations rather than by anatomically discrete gross bundles, and dissection-based atlases of the early twentieth century did not resolve them. The Makris and Pandya group’s 2005 quantitative DT-MRI study established the modern sub-pathway nomenclature, which has been broadly adopted in subsequent tractography work.
Right-hemisphere hemispatial neglect after stroke is one of the strongest clinical demonstrations of asymmetric SLF function. The severity and persistence of neglect correlates with the extent of SLF damage on tractography much more closely than with cortical lesion volume alone, supporting a view of attention as fundamentally a network rather than a cortical property.