Functional connectivity in the human language system: a cortico-cortical evoked potential study

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neurology

Background:

• Understanding higher cortical functions necessitates detailed knowledge of neuronal connectivity.
• Existing methods for tracking in vivo neuronal connectivity in humans are limited.
• The human language system relies on complex inter-areal connections.

Purpose of the Study:

• To investigate in vivo inter-areal connections within the human language system.
• To introduce and validate a novel method: cortico-cortical evoked potentials (CCEPs).
• To explore the network properties of language areas, including Broca's and Wernicke's areas.

Main Methods:

• Utilized invasive electrocorticography (ECoG) monitoring in eight epilepsy patients.
• Applied single-pulse electrical stimulation to anterior language, posterior language, or face motor areas.
• Recorded and averaged CCEPs time-locked to stimuli to map functional connectivity.

Main Results:

• Stimulation of the anterior language area elicited CCEPs in the lateral temporo-parietal region.
• Bidirectional CCEPs were observed between anterior (Broca's) and posterior (Wernicke's) language areas.
• CCEPs indicated a broader neuronal network than previously defined language regions.

Conclusions:

• Perisylvian and extrasylvian language areas function as a network with feed-forward and feed-back projections.
• Demonstrated bidirectional connectivity between Broca's and Wernicke's areas, likely via the arcuate fasciculus.
• The novel CCEPs method effectively maps in vivo human brain connectivity for language functions.