Is the left uncinate fasciculus essential for language? A cerebral stimulation study

Area of Science:

• Neuroscience
• Neurosurgery
• Linguistics

Background:

• The precise function of the uncinate fasciculus (UF) in language processing remains unclear despite anatomical knowledge.
• The ventral stream may involve parallel language networks supported by distinct subcortical tracts, including the inferior occipito-temporal fasciculus (IOF) and UF.

Purpose of the Study:

• To investigate the specific role of the uncinate fasciculus (UF) in language functions.
• To explore the existence of parallel language networks within the ventral stream supported by subcortical tracts.

Main Methods:

• Intraoperative electrostimulation was used in 13 awake patients undergoing surgery for gliomas in the left anterior temporal lobe or orbitofrontal area.
• Anatomofunctional correlations were established by stimulating cortical and subcortical sites and correlating language disturbances with postoperative MRI findings.

Main Results:

• Subcortical stimulation of the IOF induced semantic paraphasias in all patients.
• Stimulation of the arcuate fasciculus generated phonological paraphasias in 6 patients.
• Stimulation at the level of the UF did not elicit any language disturbances, and patients recovered despite partial UF removal.

Conclusions:

• The uncinate fasciculus (UF) may not be systematically essential for language, potentially due to functional compensation by parallel pathways like the IOF.
• The semantic ventral stream likely involves at least two parallel pathways: a direct IOF pathway crucial for semantics and an indirect UF pathway that can be compensated.
• Further research with more sensitive tasks is needed to fully probe all language functions during surgery.