Mapping the temporal pole with a specialized electrode array: technique and preliminary results

Abstract

Temporopolar cortex plays a crucial role in the pathogenesis of temporal lobe epilepsy and subserves important cognitive functions. Because of its shape and position in the middle cranial fossa, complete electrode coverage of the temporal pole (TP) is difficult to achieve using existing devices. We designed a novel TP electrode array that conforms to the surface of temporopolar cortex and achieves dense electrode coverage of this important brain region. A multi-pronged electrode array was designed that can be placed over the surface of the TP using a straightforward insertion technique. Twelve patients with medically intractable epilepsy were implanted with the TP electrode array for purposes of seizure localization. Select patients underwent cognitive mapping by electrocorticographic (ECoG) recording from the TP during a naming task. Use of the array resulted in excellent TP electrode coverage in all patients. High quality ECoG data were consistently obtained for purposes of delineating seizure activity and functional mapping. During a naming task, significant increases in ECoG power were observed within localized subregions of the TP. One patient developed a transient neurological deficit thought to be related to the mass effect of multiple intracranial recording arrays, including the TP array. This deficit resolved following removal of all electrodes. The TP electrode array overcomes limitations of existing devices and enables clinicians and researchers to obtain optimal multi-site recordings from this important brain region.

Figure 1

30-contact TP grid before and after cutting columns (left and right panel, respectively).

Figure 2

Intraoperative photograph depicting placement of a TP electrode grid (indicated with arrows).

Figure 3

X-ray/CT imaging of four subjects (left to right) implanted with the TP grid.

Figure 4

CT – MRI fusion images from a single patient (S05) showing location of implanted electrode contacts. Different electrode arrays are shown in different colors (TP grid and anteromedial strip contacts are shown in red and blue, respectively).

Figure 5

ECoG trace demonstrating spread of ictal activity from the posterior hippocampus to the TP. PHD, posterior hippocampal depth; TP, temporal pole; PST, posterior subtemporal. TP contacts are shown in white; other subdural contacts are shown in grey.

Figure 6

Spectrotemporal analysis of cortical activity recorded from the TP during the naming task. Data from three subjects (S01, S10, S09) are shown. Exemplary response to images of famous people recorded from contact #22 in subject S01 (marked by an asterisk) is shown in detail in the bottom left panel.