Combining Electrostimulation With Fiber Tracking to Stratify the Inferior Fronto-Occipital Fasciculus

Abstract

The inferior fronto-occipital fasciculus (IFOF) is one of the longest association fiber tracts of the brain. According to the most recent anatomical studies, it may be formed by several layers, suggesting a role in multiple cognitive functions. However, to date, no attempt has been made to dissociate the functional contribution of the IFOF subpathways. In this study, real-time, cortico-subcortical mapping with direct electrostimulation was performed in 111 patients operated on in wide-awake surgery for a right low-grade glioma. Patients performed two behavioral tasks during stimulation, tapping, respectively, mentalizing and visual semantic cognition—two functions supposed to be partly mediated by the IFOF. Responsive white matter sites were first subjected to a clustering analysis to assess potential topological differences in network organization. Then they were used as seeds to generate streamline tractograms based on the HC1021 diffusion dataset (template-based approach). The tractograms obtained for each function were overlapped and contrasted to determine whether some fiber pathways were more frequently involved in one or the other function. The obtained results not only provided strong evidence for a role of the right IFOF in both functions, but also revealed that the tract is dissociable into two functional strata according to a ventral (semantic) and dorsal (mentalizing) compartmentalization. Besides, they showed a high degree of anatomo-functionnal variability across patients in the functional implication of the IFOF, possibly related to symmetrical/hemispheric differences in network organization. Collectively, these findings support the view that the right IFOF is a functionally multi-layered structure, with nevertheless interindividual variations.

Awake Surgery for Left Posterior Insular Low-Grade Glioma Through the Parietorolandic Operculum: The Need to Preserve the Functional Connectivity. A Case Series

“…Replacement of stimulation point was done by using intrasurgical photos (enabling to accurately identify the location of functional areas marked with sterile numbered tags), written surgical reports, cortical (e.g., gyri, sulci, and vessels) and subcortical (e.g., edges of the resection cavity) landmarks identifiable on both the postsurgical MRI and the intraoperative photographs. This method has been successfully used and validated in the previous series (15)(16)(17).…”

Awake Mapping With Transopercular Approach in Right Insular–Centered Low-Grade Gliomas Improves Neurological Outcomes and Return to Work

“…Indeed, a major risk is to generate long-lasting deficit due to damages of the lenticulostriate arteries. 17,18 In group 2, detection of the right ventral route, mainly underpinned by the inferior fronto-occipital fasciculus which elicits semantic and/or mentalistic disturbances during DES, [38][39][40] permitted to prevent any stroke. This pathway runs within the temporal stem, 41 which represents the lateral wall of the anterior perforating substance.…”

“…Yet, this should be mitigated by the fact that patients in group 1 were recruited over a long period (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009), whereas the slope of the learning curve for brain glioma surgery is short, approximately 2-3 years. 45 Finally, a better understanding of the functional connectivity, even if partly due to DES, 29,[38][39][40] might have participated in an improvement of the functional outcomes in the second period.…”

Neural Connectivity: How to Reinforce the Bidirectional Synapse Between Basic Neuroscience and Routine Neurosurgical Practice?

“…Beyond a transitory dys-synchronization within a discrete critical circuit, ESM can also disrupt between-network inter-communication, resulting in multi-tasking disorders, e.g., the patient is still able to move or to speak separately, but cannot do both simultaneously ( 10 ). Such original anatomo-functional correlations gained from on-line intraoperative cortico-subcortical ESM led researchers to re-visit the functional connectivity mediating neural systems, such as movement execution and control ( 11 ), oral and written language ( 12 , 13 ), semantics ( 14 ), executive control ( 15 ), self-evaluation ( 16 ), or theory of mind ( 17 , 18 ). Interestingly, this ESM permitted a reappraisal of the model of the human connectome ( 19 ), and proposed a new theory relying on a meta-network (network of networks) organization of the brain, i.e., with perpetual changes of intra- and across circuit interactions allowing adapted behavior ( 20 ).…”