numbered tags. Sites for stimulation mapping are randomly selected to cover all exposed cortex, including areas where essential language areas are likely to be located and those near or overlying the site of resection. Using a computer, the patient is shown images of simple objects. A new image is shown every 2-4 seconds (depending on the patient's verbal ability). Cortical stimulation is applied prior to the presentation of each image and continued until there is a correct response or the next image is presented. Each pre-selected site is stimulated three to four times, though never twice in succession. Sites where stimulation produces consistent speech arrest or anomia are considered essential to language function. Injury to essential language areas will lead to permanent difficulties.
It is important to remember that the topography of essential language varies from individual to individual. Furthermore, patients who are adept in more than one language will have separate essential language areas for each of their different languages. Standard anatomical temporal lobe resections (e.g. measured resections, resections anterior to the central sulcus, resections anterior to Labbe's vein) do not always spare essential language areas. Ojemann et al.  noted that subjects typically have two language areas: one in the posterior inferior frontal gyrus, and one in the posterior temporal lobe. However, individuals displayed a wide variety of language topography and some had three or more sites identified. The basal language area can probably be resected with relative impunity, indicating that, although this site is involved in language function, it is not essential.
As with the other types of mapping described above, language mapping can be performed through the dura or directly on the cortical surface. Furthermore, when the surgeon wishes to stimulate unexposed cortex, this can be accomplished by sliding a strip electrode beneath the edge of the bone flap and then utilizing a device that attaches to the electrode lead wire connection that permits direct bipolar stimulation . When the resection is within 2 cm of the identified language area, it is best to have the patient continue object naming during the part of the resection that is close to the identified language site. The resection can then proceed slowly and be halted if naming errors occur.
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