Abstracts

Rationale: The receptive aphasia sites are defined as the left temporal lobe neocortical sites at which 50-Hz electrical stimulation elicits transient receptive aphasia, and often referred to as the Wernicke areas in the presurgical epilepsy evaluation. Localization of the receptive aphasia sites is vital to minimize the risk of postoperative receptive aphasia. Some investigators have recently inferred that the connectivity from the stimulation-defined eloquent areas may also be essential to reduce the risk of functional deficits following cortical resection. Here, we determined the spatial extent of effective connectivity from the receptive aphasia sites by measurement of cortico-cortical evoked potentials (CCEPs). Methods: We studied six patients with pharmacoresistant focal epilepsy who underwent surgical resection following extraoperative electrocorticography (ECoG) recording and revealed the receptive aphasia sites in our routine 50-Hz electrical stimulation mapping (ESM). We measured CCEPs for localization of the remote sites effectively connected to eloquent areas as part of our standard clinical management. Trains of biphasic single-pulse electrical stimulation was delivered to adjacent electrode pairs. At all ECoG electrode sites, we measured the voltages of CCEPs elicited by single-pulse stimulation of the receptive aphasia sites. We subsequently delineated the dynamics of CCEP voltage changes, at the whole brain level, on the three-dimensional averaged brain surface image. Results: The ESM localized the receptive aphasia sites within the left superior- and middle-temporal gyri. Single-pulse stimulation of the receptive aphasia sites elicited an initial negative CCEP (referred to as N1) within the superior-temporal, precentral, post-central, inferior-frontal, middle-frontal, and superior-frontal gyri at 10-30 ms. Many of the temporal lobe neocortical sites inferior to the superior-temporal sulcus showed an initial CCEP with positive polarity during the same period. The second negative CCEP (referred to as N2) involved the superior-temporal, middle-temporal, inferior-temporal, precentral, inferior-frontal, middle-frontal, and superior-frontal gyri at 50-150 ms. Conclusions: The receptive aphasia sites are effectively connected to widespread supra-sylvian regions. The difference in the spatial profiles between N1 and N2 suggests the need for an additional study to determine which of the CCEP components is more useful to localize the entire language-related network. Funding: NIH grant NS064033 (to E. Asano).