Intra-operative multi-site stimulation: Expanding methodology for cortical brain mapping of language functions

Abstract

Direct cortical stimulation (DCS) is considered the gold-standard for functional cortical mapping during awake surgery for brain tumor resection. DCS is performed by stimulating one local cortical area at a time. We present a feasibility study using an intra-operative technique aimed at improving our ability to map brain functions which rely on activity in distributed cortical regions. Following standard DCS, Multi-Site Stimulation (MSS) was performed in 15 patients by applying simultaneous cortical stimulations at multiple locations. Language functioning was chosen as a case-cognitive domain due to its relatively well-known cortical organization. MSS, performed at sites that did not produce disruption when applied in a single stimulation point, revealed additional language dysfunction in 73% of the patients. Functional regions identified by this technique were presumed to be significant to language circuitry and were spared during surgery. No new neurological deficits were observed in any of the patients following surgery. Though the neuro-electrical effects of MSS need further investigation, this feasibility study may provide a first step towards sophistication of intra-operative cortical mapping.

Fig 1. Examples of single and multi-site effects.

One case example of a multi-site temporal effect (a,d—patient 10), one case example of a cross-lobal multi-site effect (fronto-temporal; b,e—patient 8) and one case example of a multi-site frontal effect (c,f—patient 6). (a-c) intra-operative photography, (d-f) stimulation location on scheme (effects were aligned using both angio and navigation system photographs). (a) Patient 10: single site DCS found a single word deafness effect (1). A cortical strip was placed on the superior temporal gyrus, and a two-site stimulation retrieval disturbance effect was found (A-B). An Ojemann stimulator was simultaneously applied on location 5, causing a three site semantic paraphasia effect. (b) Patient 8: single site DCS found a speech arrest effect (4), a word deafness effect (2) and two motor effects (1,3). A cortical strip was placed crossing the sylvian fissure, and a two-site stimulation syntax disturbance effect was found using a frontal site and a temporal site.). An Ojemann stimulator was simultaneously applied on location C, causing a three site verb-generation effect. (c) Patient 6: single site DCS found a speech arrest effect (5), five semantic effects (1,2,3,7,8) and a word deafness effect (6). A cortical strip was placed upon the inferior and middle frontal gyri and a two-site stimulation phonological effect was found. Dashed lines represent 2-site and 3-site MSS affects.

Fig 2. Schematic localization and classification of functional effects.

The locations of stimulation sites (both single and multi) causing functional effects is plotted on a scheme of the left hemisphere for 7 of the 11 patients with multi-site effects (for the remaining four patients: 1,4,11 and 12, intra-operative imaging was not sufficient to map stimulation locations). Single sites (SSS) are marked with unfilled shapes, multi-site (MSS) are marked with filled shapes. Language disturbances are classified to phonological (square), semantic (triangle), syntactic (diamond) and auditory hallucinations (pentagon).