Figure 1. Intra-operative direct electrical stimulation-based mapping.

In panel A, the surgeon is stimulating the subcortical white matter of the middle temporal gyrus using a standard handheld bipolar stimulator while the patient (panel B) is performing a classical naming task. Panel C shows the final cortical (tags 0,1,2,A,B,C) and subcortical (42,43) positive mapping sites. For the naming task, the patient is asked to name the object presented on a computer screen (D) while the neurosurgeon stimulates sites at the cortical and subcortical white matter. In this case, the correct response is “This is a horse.” If the patient makes an error during stimulation at a particular site, the type of error is noted, such as anomia (patient says “This is a ......” but cannot come up with “horse”), semantic paraphasias (e.g. patient incorrectly says “This is a cow.” instead of “This is a horse.”), phonemic paraphasias (e.g. patient incorrectly says “This is a hearse.” instead of “This is a horse.”), speech arrest (no verbal output), or verbal perseveration (patient correctly says “This is a horse” but when a different object is shown after a delay, the patient incorrectly states “This is a horse.” again). In the example depicted in this figure, stimulation of the white matter region corresponding to site 42 (Panel C) caused an anomia. The MNI coordinates (x,y,z) corresponding to site 42 is derived by normalizing this patient’s brain to MNI space and manually plotting this subcortical point onto the normalized brain. For the group mapping and matching analyses, this point is combined with normalized coordinates of all other anomia sites from the entire cohort of subjects.