Intraoperative dorsal language network mapping by using single‐pulse electrical stimulation

Abstract

Abstract:The preservation of language function during brain surgery still poses a challenge. No intraoperative methods have been established to monitor the language network reliably. We aimed to establish intraoperative language network monitoring by means of cortico-cortical evoked potentials (CCEPs). Subjects were six patients with tumors located close to the arcuate fasciculus (AF) in the language-dominant left hemisphere. Under general anesthesia, the anterior perisylvian language area (AL) was first defined by the CCEP connectivity patterns between the ventrolateral frontal and temporoparietal area, and also by presurgical neuroimaging findings. We then monitored the integrity of the language network by stimulating AL and by recording CCEPs from the posterior perisylvian language area (PL) consecutively during both general anesthesia and awake condition. High-frequency electrical stimulation (ES) performed during awake craniotomy confirmed language function at AL in all six patients. Despite an amplitude decline (32%) in two patients, CCEP monitoring successfully prevented persistent language impairment. After tumor removal, single-pulse ES was applied to the white matter tract beneath the floor of the removal cavity in five patients, in order to trace its connections into the language cortices. In three patients in whom high-frequency ES of the white matter produced naming impairment, this "eloquent" subcortical site directly connected AL and PL, judging from the latencies and distributions of cortico-and subcortico-cortical evoked potentials. In conclusion, this study provided the direct evidence that AL, PL, and AF constitute the dorsal language network. Intraoperative CCEP monitoring is clinically useful for evaluating the integrity of the language network.

A measure of cortico-cortical potentials evoked by 10Hz direct electrical stimulation of the brain and by means of a differential recording mode of electrocorticographic signals

“…Despite, some technical differences with these studies, we observed a similar waveform. The measured latencies of the first negative peak were around 20 ms in accordance with those measured in Matsumoto's group both for CCEPs and ACEPs [4,5]. In contrast, Mandonnet et al [6] measured shorter latencies for ACEPs (~ 10 ms).…”

“…In addition, the presence of axono-cortical evoked potentials (ACEPs) has been highlighted during the propagation of 1 Hz DES between white matter pathways and connected cortical sites [5,6]. Despite, some technical differences with these studies, we observed a similar waveform.…”

“…In previous studies [5], CCEPs recordings were performed for 1 Hz biphasic stimulation applied with in a bipolar fashion to two adjacent subdural electrodes. In addition, the presence of axono-cortical evoked potentials (ACEPs) has been highlighted during the propagation of 1 Hz DES between white matter pathways and connected cortical sites [5,6].…”

“…Usually, it is considered that about 0.5 ms are necessary for the signal to cross one synapse and the conduction velocity in non-myelinated fibers is about [0.4, 2] m/s [7]. Mandonnet et al [6] suggest that the latencies observed for the negative peak are twice that measured by Yamao et al [5] and maybe due to a DES applied about 2 times further on the axon. This interpretation is correct if it is assumed that slow myelinated axons may propagate the evoked potentials (min conduction velocity ~ 10 m/s) and cannot stand for a propagation along fast myelinated axons (max conduction velocity ~ 100 m/s).…”

“…This approach has been used for presurgical planning of drug-resistant epileptic patients by using ECoG and a grid implanted at the surface of the grey matter. Matsumoto et al [4,5] sought to measure in vivo connectivity with DES (rather than study its propagation) but observed that the low-frequency cortical application of DES (1 Hz, constant current, and alternating rectangular wave pulses of 0.3 ms) induces 'cortico-cortical' evoked potentials (CCEPs) around 10 -50 ms after stimulation.…”