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Theta frequency oscillations in the 6- to 10-Hz range dominate the rodent hippocampal local field potential during translational movement, suggesting that theta encodes self-motion. Increases in theta power have also been identified in the human hippocampus during both real and virtual movement but appear as transient bursts in distinct high- and low-frequency bands, and it is not yet clear how these bursts relate to the sustained oscillation observed in rodents. Here, we examine depth electrode recordings from the temporal lobe of 13 presurgical epilepsy patients performing a selfpaced spatial memory task in a virtual environment. In contrast to previous studies, we focus on movement-onset periods that incorporate both initial acceleration and an immediately preceding stationary interval associated with prominent theta oscillations in the rodent hippocampal formation. We demonstrate that movementonset periods are associated with a significant increase in both low (2-5 Hz)- and high (6-9 Hz)-frequency theta power in the human hippocampus. Similar increases in low- and high-frequency theta power are seen across lateral temporal lobe recording sites and persist throughout the remainder of movement in both regions. In addition, we show that movement-related theta power is greater both before and during longer paths, directly implicating human hippocampal theta in the encoding of translational movement. These findings strengthen the connection between studies of theta-band activity in rodents and humans and offer additional insight into the neural mechanisms of spatial navigation. [ABSTRACT FROM AUTHOR]

Introduction Epilepsy surgery is an effective treatment for refractory focal epilepsy. Risks of surgery need to be considered when advising individuals of treatment options. We describe the frequency and nature of physical adverse events associated with epilepsy surgery in a single center. Material and methods We reviewed the prospectively maintained records of adults who underwent epilepsy surgery at our center between 1990 and 2014 to identify peri/postsurgical adverse events. These were categorized into neurological deficits and those related to surgery (e.g. wound infections). Neurological deficits were categorized as expected or unexpected and into transient (≤3 months) or persistent (>3 months), Results There were 911 procedures with no peri-operative deaths. Persistent neurological adverse events were seen following 157 (17.2%) procedures. The most common persistent expected complication was quadrantanopia after temporal lobe resections (72/764, 9.4%). Unexpected persistent neurological complications occurred in 20 procedures (2.2%) and included: quadrantanopia (6, 0.7%); hemianopia (2, 0.2%); hemi/mono-paresis/sensory loss (9, 1%); dysphasia (10, 1%); frontalis muscle weakness (2, 0.2%); and oculomotor weakness (1, 0.1%). 106 surgery related adverse events occurred in 83 procedures, with severe infections requiring bone-flap removal in 24 (2.6%) procedures and intracranial infections in 8 (0.9%). The risk of post-resective severe infection increased by 4 fold (OR 4.32, 95% CI 2.1–8.9, p < 0.001) with use of subdural EEG monitoring prior to resection. In consequence, in August 2011 we introduced antibiotic coverage in all individuals undergoing intracranial monitoring. Also, after August 2011 there was greater use of Stereo-EEG (SEEG) than subdural (OR 9.0 CI 0.36–224.2, p = 0.18 ns). One complicated by severe infection. Other surgical complications included haematoma (0.3%), hydrocephalus (0.3%) and CSF leak (1.2%). None had permanent complications. Conclusions Adverse event rates are similar to other series. Epilepsy surgery carries well defined surgical and neurological risks. The risks of somatic adverse events, in addition to neuropsychiatric and neuropsychological complications need to be made clear to individuals considering this treatment option. [ABSTRACT FROM AUTHOR]

Anteromesial temporal lobe resection is the most common surgical technique used to treat drug-resistant mesial temporal lobe epilepsy, particularly when secondary to hippocampal sclerosis. Structural and functional imaging data suggest the importance of sparing the posterior hippocampus for minimising language and memory deficits. Recent work has challenged the view that maximal posterior hippocampal resection improves seizure outcome. This study was designed to assess whether resection of posterior hippocampal atrophy was associated with improved seizure outcome. Retrospective analysis of a prospective database of all anteromesial temporal lobe resections performed in individuals with hippocampal sclerosis at our epilepsy surgery centre, 2013–2021. Pre- and post-operative MRI were reviewed by 2 neurosurgical fellows to assess whether the atrophic segment, displayed by automated hippocampal morphometry, was resected, and ILAE seizure outcomes were collected at 1 year and last clinical follow-up. Data analysis used univariate and binary logistic regression. Sixty consecutive eligible patients were identified of whom 70% were seizure free (ILAE Class 1 & 2) at one year. There was no statistically significant difference in seizure freedom outcomes in patients who had complete resection of atrophic posterior hippocampus or not (Fisher's Exact test statistic 0.69, not significant at p <.05) both at one year, and at last clinical follow-up. In the multivariate analysis only a history of status epilepticus (OR=0.2, 95%CI:0.042–0.955, p =.04) at one year, and pre-operative psychiatric disorder (OR=0.145, 95%CI:0.036–0.588, p =.007) at last clinical follow-up, were associated with a reduced chance of seizure freedom. Our data suggest that seizure freedom is not associated with whether or not posterior hippocampal atrophy is resected. This challenges the traditional surgical dogma of maximal posterior hippocampal resection in anteromesial temporal lobe resections and is a step further optimising this surgical procedure to maximise seizure freedom and minimise associated language and memory deficits. • Temporal lobe resection is the commonest form of epilepsy surgery. • Surgical dogma is that we have to maximally resect the hippocampus to stop seizures. • We show that taking out the back of the hippocampus isn't needed when it is scarred. • This may help prevent damage to language and memory after surgery. [ABSTRACT FROM AUTHOR]

Anterior temporal lobe resection can control seizures in up to 80% of patients with temporal lobe epilepsy. Memory decrements are the main neurocognitive complication. Preoperative functional reorganization has been described in memory networks, but less is known of postoperative reorganization. We investigated reorganization of memory-encoding networks preoperatively and 3 and 12 months after surgery. We studied 36 patients with unilateral medial temporal lobe epilepsy (19 right) before and 3 and 12 months after anterior temporal lobe resection. Fifteen healthy control subjects were studied at three equivalent time points. All subjects had neuropsychological testing at each of the three time points. A functional magnetic resonance imaging memory-encoding paradigm of words and faces was performed with subsequent out-of-scanner recognition assessments. Changes in activations across the time points in each patient group were compared to changes in the control group in a single flexible factorial analysis. Postoperative change in memory across the time points was correlated with postoperative activations to investigate the efficiency of reorganized networks. Left temporal lobe epilepsy patients showed increased right anterior hippocampal and frontal activation at both 3 and 12 months after surgery relative to preoperatively, for word and face encoding, with a concomitant reduction in left frontal activation 12 months postoperatively. Right anterior hippocampal activation 12 months postoperatively correlated significantly with improved verbal learning in patients with left temporal lobe epilepsy from preoperatively to 12 months postoperatively. Preoperatively, there was significant left posterior hippocampal activation that was sustained 3 months postoperatively at word encoding, and increased at face encoding. For both word and face encoding this was significantly reduced from 3 to 12 months postoperatively. Patients with right temporal lobe epilepsy showed increased left anterior hippocampal activation on word encoding from 3 to 12 months postoperatively compared to preoperatively. On face encoding, left anterior hippocampal activations were present preoperatively and 12 months postoperatively. Left anterior hippocampal and orbitofrontal cortex activations correlated with improvements in both design and verbal learning 12 months postoperatively. On face encoding, there were significantly increased left posterior hippocampal activations that reduced significantly from 3 to 12 months postoperatively. Postoperative changes occur in the memory-encoding network in both left and right temporal lobe epilepsy patients across both verbal and visual domains. Three months after surgery, compensatory posterior hippocampal reorganization that occurs is transient and inefficient. Engagement of the contralateral hippocampus 12 months after surgery represented efficient reorganization in both patient groups, suggesting that the contralateral hippocampus contributes to memory outcome 12 months after surgery. [ABSTRACT FROM AUTHOR]

Resective surgery for selected individuals with frontal lobe epilepsy can be effective, although multimodal outcomes are less established than in temporal lobe epilepsy. We describe long-term seizure remission and relapse patterns, psychiatric comorbidity, and socioeconomic outcomes following frontal lobe epilepsy surgery. We reviewed individual data on frontal lobe epilepsy procedures at our center between 1990 and 2020. This included the presurgical evaluation, operative details and annual postoperative seizure and psychiatric outcomes, prospectively recorded in an epilepsy surgery database. Outcome predictors were subjected to multivariable analysis, and rates of seizure freedom were analyzed using Kaplan-Meier methods. We used longitudinal assessment of the Index of Multiple Deprivation to assess change in socioeconomic status over time. A total of 122 individuals with a median follow-up of seven years were included. Of these, 33 (27 %) had complete seizure freedom following surgery, with a further 13 (11 %) having only auras. Focal MRI abnormality, histopathology (focal cortical dysplasia, cavernoma or dysembryoplastic neuronal epithelial tumor) and fewer anti-seizure medications at the time of surgery were predictive of a favorable outcome; 67 % of those seizure-free for the first 12 months after surgery never experienced a seizure relapse. Thirty-one of 50 who had preoperative psychiatric pathology noticed improved psychiatric symptomatology by two years postoperatively. New psychiatric comorbidity was diagnosed in 15 (13 %). Persistent motor complications occurred in 5 % and dysphasia in 2 %. No significant change in socioeconomic deciles of deprivation was observed after surgery. Favorable long-term seizure, psychiatric and socioeconomic outcomes can be seen following frontal lobe epilepsy surgery. This is a safe and effective treatment that should be offered to suitable individuals early. • Approximately a third who haveFLE surgery will experience long lasting seizure freedom, with another tenth only having auras. • Age < 30 years, taking less than four ASMs, focal MRI abnormality and underlying pathology are predictors of favorable outcome. • Postoperative rates of psychiatric comorbidity are lower after surgery and often resolve in those seizure-free. • No significant change in socioeconomic deciles of deprivation was seen after surgery. [ABSTRACT FROM AUTHOR]

Echo Planar Imaging (EPI) is routinely used in diffusion and functional MR imaging due to its rapid acquisition time. However, the long readout period makes it prone to susceptibility artefacts which results in geometric and intensity distortions of the acquired image. The use of these distorted images for neuronavigation hampers the effectiveness of image-guided surgery systems as critical white matter tracts and functionally eloquent brain areas cannot be accurately localised. In this paper, we present a novel method for correction of distortions arising from susceptibility artefacts in EPI images. The proposed method combines fieldmap and image registration based correction techniques in a unified framework. A phase unwrapping algorithm is presented that can efficiently compute the B 0 magnetic field inhomogeneity map as well as the uncertainty associated with the estimated solution through the use of dynamic graph cuts. This information is fed to a subsequent image registration step to further refine the results in areas with high uncertainty. This work has been integrated into the surgical workflow at the National Hospital for Neurology and Neurosurgery and its effectiveness in correcting for geometric distortions due to susceptibility artefacts is demonstrated on EPI images acquired with an interventional MRI scanner during neurosurgery. [ABSTRACT FROM AUTHOR]

Highlights: [•] Developed pipeline for multimodal image integration to guide epilepsy surgery. [•] Reported the key principles of the pipeline and its detailed description. [•] Demonstrated feasibility of the developed pipeline for multimodal image integration. [•] Illustrated potential benefits of intraoperative use of the pipeline. [ABSTRACT FROM AUTHOR]

Abstract: In epilepsy patients who have electrodes implanted in their brains as part of their pre-surgical assessment, simultaneous intracranial EEG and fMRI (icEEG-fMRI) may provide important localising information and improve understanding of the underlying neuropathology. However, patient safety during icEEG-fMRI has not been addressed. Here the potential health hazards associated with icEEG-fMRI were evaluated theoretically and the main risks identified as: mechanical forces on electrodes from transient magnetic effects, tissue heating due to interaction with the pulsed RF fields and tissue stimulation due to interactions with the switched magnetic gradient fields. These potential hazards were examined experimentally in vitro on a Siemens 3 T Trio, 1.5 T Avanto and a GE 3 T Signa Excite scanner using a Brain Products MR compatible EEG system. No electrode flexion was observed. Temperature measurements demonstrated that heating well above guideline limits can occur. However heating could be kept within safe limits (<1.0 °C) by using a head transmit RF coil, ensuring EEG cable placement to exit the RF coil along its central z-axis, using specific EEG cable lengths and limiting MRI sequence specific absorption rates (SARs). We found that the risk of tissue damage due to RF-induced heating is low provided implant and scanner specific SAR limits are observed with a safety margin used to account for uncertainties (e.g. in scanner-reported SAR). The observed scanner gradient switching induced current (0.08 mA) and charge density (0.2 μC/cm2) were well within safety limits (0.5 mA and 30 μC/cm2, respectively). Site-specific testing and a conservative approach to safety are required to avoid the risk of adverse events. [Copyright &y& Elsevier]