Does the left inferior longitudinal fasciculus play a role in language? A brain stimulation study

Abstract

Although advances in diffusion tensor imaging have enabled us to better study the anatomy of the inferior longitudinal fasciculus (ILF), its function remains poorly understood. Recently, it was suggested that the subcortical network subserving the language semantics could be constituted, in parallel with the inferior occipitofrontal fasciculus, by the left ILF, joining the posterior occipitotemporal regions to the temporal pole, then relayed by the uncinate fasciculus connecting the anterior temporal pole to the frontobasal areas. Nevertheless, this hypothesis was solely based on neurofunctional imaging, allowing a cortical mapping but with no anatomofunctional information regarding the white matter. Here, we report a series of 12 patients operated on under local anaesthesia for a cerebral low-grade glioma located within the left temporal lobe. Before and during resection, we used the method of intraoperative direct electrostimulation, enabling us to perform accurate and reliable anatomofunctional correlations both at cortical and subcortical levels. In order to map the ILF. Using postoperative MRI, we correlated these functional findings with the anatomical locations of the sites where language disturbances were elicited by stimulations, both at cortical and subcortical levels. Our goal was to study the potential existence of parallel and distributed language networks crossing the left dominant temporal lobe, subserved by distinct subcortical pathways--namely the inferior occipitofrontal fasciculus and the ILF. Intraoperative stimulation of the anterior and middle temporal cortex elicited anomia in four patients. At the subcortical level, semantic paraphasia were induced in seven patients during stimulation of the inferior occipitofrontal fasciculus, and phonological paraphasia was generated in seven patients by stimulating the arcuate fasciculus. Interestingly, subcortical stimulation never elicited any language disturbances when performed at the level of the ILF. In addition, following a transient postoperative language deficit, all patients recovered, despite the resection of at least one part of the ILF, as confirmed by control MRI. On the basis of these results, we suggest that the "semantic ventral stream" could be constituted by at least two parallel pathways within the left dominant temporal lobe: (i) a direct pathway, the inferior occipitofrontal fasciculus, that connects the posterior temporal areas and the orbitofrontal region, crucial for language semantic processing, since it elicits semantic paraphasia when stimulated; (ii) and also possibly an indirect pathway subserved by the ILF, not indispensable for language, since it can be compensated both during stimulation and after resection.

Distinct loci of lexical and semantic access deficits in aphasia: Evidence from voxel-based lesion-symptom mapping and diffusion tensor imaging

“…The correlation between the structural integrity of the IFOF connecting the LIFG with the posterior temporal cortex and the relatedness effect in naming is consistent with evidence elsewhere demonstrating that the regions the IFOF connects are involved in blocked-cyclic naming (Pisoni et al, 2012;Schnur et al, 2009) and that this pathway is critical in picture naming in general (Duffau, Gatignol, Mandonnet, Capelle, & Taillandier, 2008;Duffau, Gatignol, Moritz-Gasser, & Mandonnet, 2009;Mandonnet, Nouet, Gatignol, Capelle, & Duffau, 2007). However, that IFOF integrity correlated with individual relatedness effects and not…”

White matter measures correlate with essential tremor severity—A pilot diffusion tensor imaging study

“…At this point, we might only speculate about relationships between tremor symptoms and WM clusters located in UF, ILF, and IFOF. All these bundles are involved in memory retrieval, reward processing, emotional regulation, impulsive responding, semantic language processing, attention, and reversal learning (Mandonnet, Nouet, Gatignol, Capelle, & Duffau, 2007; Martino & De Lucas, 2014; Olson, Von Der Heide, Alm, & Vyas, 2015), although orbitofrontal WM, part of both UF and ILF, was associated with the FTM score (Klein et al., 2011) and showed affected in previous ET study (Shin et al., 2008). Also, atrophy in frontal and temporal gray matter regions, which are interconnected by UF, was found related to the FTM scale (Bagepally et al., 2012) and an improvement of WM integrity within the ILF and IFOF was consistently reported among longitudinal DTI studies evaluating effects of physical training (Huang, Lu, Song, & Wang, 2015; Scholz et al., 2009), implying their involvement in motor functions.…”

Epistasis between the DAT 3′ UTR VNTR and the COMT Val158Met SNP on cortical function in healthy subjects and patients with schizophrenia

“…In patients, both the Val-158-9-repeat combination and the Met-158-10-repeat combination were associated with higher activation, whereas in healthy subjects, there was a trend in the opposite direction. Although its reports of association with verbal fluency and differential activation in schizophrenia have not been as frequent as those in the adjacent inferior frontal gyrus (46,47,50,51,53,63,64), the right orbitofrontal cortex has shown abnormal volume in schizophrenic patients (71)(72)(73)(74)(75) and significant activation during verbal fluency in females (50); it has also been linked to semantic processing (76,77). An interaction between diagnostic group and genetic variations that influence dopamine transmission in the orbitofrontal cortex is also consistent with the presence of dopaminergic inputs to the prefrontal cortex, and with the putative disruption of dopaminergic inputs to prefrontal cortex in schizophrenia (36)(37)(38)(39)(40).…”