Electrocortical stimulation (ECS) mapping is routinely used to identify critical language
sites before resective neurosurgery. The precise locations of these sites are highly
variable across patients, occurring in the frontal, temporal, and parietal lobes-it
is this variability that necessitates individual patient mapping. But why these particular
anatomical sites are so privileged in each patient is unknown. We hypothesized that
critical language sites have greater functional connectivity with nearby cortex than
sites without critical functions, since they serve as central nodes within the language
network. Functional connectivity across language, motor, and cleared sites was measured
in 15 patients undergoing electrocortiographic (ECoG) mapping for epilepsy surgery.
Critical language sites had significantly higher connectivity than sites without critical
functions (P = 0.001), and this also held for motor sites (P = 0.022). These data
support the hypothesis that critical language sites are highly connected within the
local cortical network, perhaps explaining why their disruption with ECS leads to
transient disturbances in language function. It is our hope that improved understanding
of the mechanisms of ECS will permit improved surgical planning and perhaps contribute
to the understanding of normal language physiology.