Abstracts

Rationale: Temporal lobe epilepsy (TLE) is a common type of drug-resistant epilepsy (DRE). Patients with DRE TLE may undergo surgery to control seizures, and intracranial mapping with stereoelectroencephalography (sEEG) is increasingly used for presurgical workup to guide subsequent resective surgery and reduce postsurgical neurocognitive problems. Mapping includes measuring changes in gamma oscillations during cognitive tasks, and electrocortical stimulation to identify neural pathways involved in functions of interest. While intracranial mapping has become an established gold-standard technique for motor and language functions, further research is required to better understand its utility with regard to memory. We present outcome data on a DRE left TLE patient who underwent intracranial language and memory mapping followed by resective surgery.

Methods: A right-handed, late adolescent male underwent a presurgical workup for drug-resistant dominant (left) TLE that was suspected to be secondary to sports-related concussions. Presurgical neuropsychological findings indicated average intellectual ability and age-appropriate expressive and receptive naming and verbal learning and memory skills. Findings were not strongly lateralizing or localizing. Functional MRI (fMRI) indicated left lateralized language. Patient underwent sEEG to identify the epileptogenic zone and functional brain areas. Electrocortical stimulation mapping (ESM) results implicated the left temporal pole and hippocampus in expressive naming ability. Increased gamma oscillations were seen in the left pars triangularis during expressive language tasks and in the left hippocampus during a verbal learning task. Following workup, the patient underwent an uncomplicated 3.5 cm left temporal polectomy with multiple hippocampal transections, after which he did not exhibit frank language, memory, or motor deficits. He has remained seizure free since surgery but reported word-finding difficulties at a follow-up appointment.

Results: We conducted a brief, highly focused follow-up neuropsychological evaluation approximately six months after surgery to examine the patient’s language and verbal learning and memory skills. Analyses indicated a significant decline in expressive naming skills (RCI = -4.454), and a mild to moderate decline in verbal learning (1SD) and immediate ( >1.5SDs) and delayed verbal memory recall ( > 1SD). No significant change was seen in receptive naming skill (RCI = -1.328).

Conclusions: These findings are consistent with the patient’s resection of brain regions that showed 1) increased gamma activation during intracranial mapping of language and verbal learning and memory, and 2) disruption of these skills when those same brain regions were stimulated during ESM. Results support prior research identifying ESM as a gold-standard technique for presurgical language mapping and add to growing research supporting examination of changes in gamma activity for language mapping. In addition, results provide preliminary support for the utility of ESM and gamma activity mapping of memory prior to resection of the epileptogenic zone in epilepsy patients.

Funding: Please list any funding that was received in support of this abstract.: No funding was received in support of this abstract.