The immediate and short-term effects of bilateral intrahippocampal depth electrodes on verbal memory

Presurgical video-EEG monitoring with foramen ovale and epidural peg electrodes: a 25-year perspective

Background

Epilepsy surgery cases are becoming more complex and increasingly require invasive video-EEG monitoring (VEM) with intracranial subdural or intracerebral electrodes, exposing patients to substantial risks. We assessed the utility and safety of using foramen ovale (FO) and epidural peg electrodes (FOP) as a next step diagnostic approach following scalp VEM.

Methods

We analyzed clinical, electrophysiological, and imaging characteristics of 180 consecutive patients that underwent FOP VEM between 1996 and 2021. Multivariate logistic regression was used to assess predictors of clinical and electrophysiological outcomes.

Results

FOP VEM allowed for immediate resection recommendation in 36 patients (20.0%) and excluded this option in 85 (47.2%). Fifty-nine (32.8%) patients required additional invasive EEG investigations; however, only eight with bilateral recordings. FOP VEM identified the ictal onset in 137 patients, compared to 96 during prior scalp VEM, p = .004. Predictors for determination of ictal onset were temporal lobe epilepsy (OR 2.9, p = .03) and lesional imaging (OR 3.1, p = .01). Predictors for surgery recommendation were temporal lobe epilepsy (OR 6.8, p < .001), FO seizure onset (OR 6.1, p = .002), and unilateral interictal epileptic activity (OR 3.8, p = .02). One-year postsurgical seizure freedom (53.3% of patients) was predicted by FO ictal onset (OR 5.8, p = .01). Two patients experienced intracerebral bleeding without persisting neurologic sequelae.

Conclusion

FOP VEM adds clinically significant electrophysiological information leading to treatment decisions in two-thirds of cases with a good benefit–risk profile. Predictors identified for electrophysiological and clinical outcome can assist in optimally selecting patients for this safe diagnostic approach.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-022-11208-6.

Cognitive and Emotional Mapping With SEEG

Mapping of cortical functions is critical for the best clinical care of patients undergoing epilepsy and tumor surgery, but also to better understand human brain function and connectivity. The purpose of this review is to explore existing and potential means of mapping higher cortical functions, including stimulation mapping, passive mapping, and connectivity analyses. We examine the history of mapping, differences between subdural and stereoelectroencephalographic approaches, and some risks and safety aspects, before examining different types of functional mapping. Much of this review explores the prospects for new mapping approaches to better understand other components of language, memory, spatial skills, executive, and socio-emotional functions. We also touch on brain-machine interfaces, philosophical aspects of aligning tasks to brain circuits, and the study of consciousness. We end by discussing multi-modal testing and virtual reality approaches to mapping higher cortical functions.

The cognitive costs, contraindications and complications of epilepsy surgery in adults

PURPOSE OF REVIEW

Access to epilepsy surgery is rapidly growing throughout the world. While it is an established and effective treatment for seizures, epilepsy surgery has the potential to exacerbate cognitive comorbidities of the condition.

RECENT FINDINGS

Not all surgical patients experience a postoperative decline in cognitive function. Postoperative cognitive function depends upon the functional integrity of the tissue to be removed and the functional reserve of the structures that remain in situ. While developments in surgical technique can reduce the cognitive morbidity of epilepsy surgery, the same procedure may result in different cognitive outcomes for different candidates, depending on their preoperative characteristics and postoperative trajectories. Multivariate models can be used to identify those most at risk of cognitive decline. There remains a significant lack of research into clinical interventions aimed at reducing the impact of surgically induced cognitive deficits on the lives of the patients who experience them.

SUMMARY

Accurate identification of the cognitive risks associated with surgery, based on an individual's personal risk profile rather than the generic risks associated with the procedure, is now recognized as a mandatory part of the preoperative evaluation and is one of the pillars of informed consent for the procedure.

Pre- and postoperative verbal memory and executive functioning in frontal versus temporal lobe epilepsy

There is accumulating evidence for considerable overlap in preoperatively affected cognitive functions in patients with temporal lobe epilepsy (TLE) and frontal lobe epilepsy (FLE). The current study investigated whether it is possible to differentiate between patients with FLE and TLE prior to surgery, based on measures of verbal memory and executive functioning. Furthermore, the postoperative cognitive development was compared. Pre- and postoperative data from 109 patients with FLE and 194 patients with TLE were retrospectively analyzed. Preoperatively, there were no differences in verbal memory, and postoperatively, no distinctive cognitive change was found between patients with FLE and TLE. However, patients with FLE performed worse on a cognitive switching task. Notably, irrespective of localization, patients with a presumed epileptogenic area in the language-dominant hemisphere performed worse than patients with seizures that originated in the nonlanguage-dominant hemisphere on measures of verbal memory, both pre- and postoperatively. In sum, the results suggest that verbal memory scores may be less valuable for differentiation between TLE and FLE, while measures of executive functioning may help identify patients with FLE. Additionally, rather than the localization, epilepsy lateralization critically impacts the evaluation of verbal memory functioning in both TLE and FLE. The results are discussed in light of the current frameworks of functional disturbances in epileptic networks.

Cognitive safety of intracranial electrodes for epilepsy

Two recent articles in Epilepsia have raised concerns about adverse cognitive effects associated with intracranial electrode implantation. However, both studies have important limitations, and their results contrast with studies that report no adverse cognitive effects of intracranial electrodes for diagnosis or neurostimulation in epilepsy. Furthermore, no data are provided on the relative safety of depth electrodes implanted along the longitudinal axis of the hippocampus vs other electrode locations or types of electrodes. Instituting changes in the use of depth electrodes based solely on these 2 studies is not clinically indicated. Further research is needed.