Left Spatial Neglect Evoked by Electrostimulation of the Right Inferior Fronto-occipital Fasciculus

Left spatial neglect is a debilitating condition that may occur after lesion of many cortical territories in the right hemisphere. At the subcortical level, the second and third branches of the right superior longitudinal fasciculus has emerged as strong candidates in conveying information exchanges within the attention networks as their damage has been repeatedly associated to spatial neglect in neuromodulation and neuropsychological studies. Yet, a few cases of spatial neglect have also been observed after damage to the right inferior fronto-occipital fasciculus (IFOF), suggesting an involvement of this associative connectivity in spatial attention. Here we report three rare cases of patients having undergone a wide-awake craniotomy with direct electrostimulation for right temporal glioma. An intraoperative monitoring of spatial cognition was performed using a standard line bisection task. Responsive cortical sites were observed in the supramarginal gyrus and the posterior part of both the middle and superior temporal gyri. Critically, in all patients, significant rightward deviations were observed by the stimulation of the white matter deep in the temporal lobe, along the roof of the inferior horn of the lateral ventricle-a well-known anatomical landmark to identify the IFOF. Disconnection analyses confirmed the high probability of IFOF disconnection during neglect-related stimulations. Taken together, our findings provide support for a role of the right IFOF in spatial cognition. We discuss these results in the light of the newly discovered fronto-parietal connections of the IFOF and suggest that some subcomponents of this tract might be involved in between-system integration within the attention network.