Purpose: Posterior, "Wenicke's;" language areas have a high degree of betwe
en-subject variability, as shown by electrical-stimulation mapping. We inve
stigated the possibility of an organized structure in the distribution of p
osterior language areas.
Methods: Extraoperative subdural grid stimulation was performed on 67 left
hemisphere-dominant patients before resective epilepsy surgery during count
ing, naming, and reading. Intersubject-averaged language maps were generate
d in which stimulation disrupted only one language function and not the oth
ers, or combinations of language functions.
Results: Language sites, although highly variable between subjects, were no
t organized randomly and appeared to be arranged into several focal, non-co
ntiguous, higher probability "nodes" devoted to different aspects of langua
ge processing. Speech-arrest sites were concentrated in classic Wernicke's
area. Areas where stimulation induced only reading errors were found in the
posterior middle temporal gyrus and the inferior parietal lobule. These re
gions may correspond with an orthographic input lexicon. Areas eliciting on
ly naming errors were found in the posterior inferior temporal gyrus extend
ing into the mid-middle temporal gyrus and may represent a visual-represent
ation input lexicon. Sites where stimulation elicited errors in both naming
and reading were more variable in location than sites devoted to only one
function, extended farther anteriorly along the temporal neocortex, and may
correspond with a semantic lexicon.
Conclusions: The existence of high-probability nodes in posterior language
cortex supports a modality-specific modular architecture and the possibilit
y of a conserved, universal structure.