Anticipation-induced delta phase reset improves human olfactory perception.

Anticipating an odor improves detection and perception, yet the underlying neural mechanisms of olfactory anticipation are not well understood. In this study, we used human intracranial electroencephalography (iEEG) to show that anticipation resets the phase of delta oscillations in piriform cortex prior to odor arrival. Anticipatory phase reset correlates with ensuing odor-evoked theta power and improvements in perceptual accuracy. These effects were consistently present in each individual subject and were not driven by potential confounds of pre-inhale motor preparation or power changes. Together, these findings suggest that states of anticipation enhance olfactory perception through phase resetting of delta oscillations in piriform cortex.

Common functional connectivity alterations in focal epilepsies identified by machine learning.

OBJECTIVE: This study was undertaken to identify shared functional network characteristics among focal epilepsies of different etiologies, to distinguish epilepsy patients from controls, and to lateralize seizure focus using functional connectivity (FC) measures derived from resting state functional magnetic resonance imaging (MRI). METHODS: Data were taken from 103 adult and 65 pediatric focal epilepsy patients (with or without lesion on MRI) and 109 controls across four epilepsy centers. We used three whole-brain FC measures: parcelwise connectivity matrix, mean FC, and degree of FC. We trained support vector machine models with fivefold cross-validation (1) to distinguish patients from controls and (2) to lateralize the hemisphere of seizure onset in patients. We reported the regions and connections with the highest importance from each model as the common FC differences between the compared groups. RESULTS: FC measures related to the default mode and limbic networks had higher importance relative to other networks for distinguishing epilepsy patients from controls. In lateralization models, regions related to somatosensory, visual, default mode, and basal ganglia showed higher importance. The epilepsy versus control classification model trained using a 400-parcel connectivity matrix achieved a median testing accuracy of 75.6% (median area under the curve [AUC] = .83) in repeated independent testing. Lateralization accuracy using the 400-parcel connectivity matrix reached a median accuracy of 64.0% (median AUC = .69). SIGNIFICANCE: Machine learning models revealed common FC alterations in a heterogeneous group of patients with focal epilepsies. The distribution of the most altered regions supports the hypothesis that shared functional alteration exists beyond the seizure onset zone and its epileptic network. We showed that FC measures can distinguish patients from controls, and further lateralize focal epilepsies. Future studies are needed to confirm these findings by using larger numbers of epilepsy patients.

Low-frequency stimulation of a fiber tract in bilateral temporal lobe epilepsy.

OBJECTIVE: Pharmacoresistant bilateral mesial temporal lobe epilepsy often implies poor resective surgical candidacy. Low-frequency stimulation of a fiber tract connected to bilateral hippocampi, the fornicodorsocommissural tract, has been shown to be safe and efficacious in reducing seizures in a previous short-term study. Here, we report a single-blinded, within-subject control, long-term deep-brain stimulation trial of low-frequency stimulation of the fornicodorsocommissural tract in bilateral mesial temporal lobe epilepsy. Outcomes of interest included safety with respect to verbal memory scores and reduction of seizure frequency. METHODS: Our enrollment goal was 16 adult subjects to be randomized to 2-Hz or 5-Hz low-frequency stimulation of the fornicodorsocommissural tract starting at 2 mA. The study design consisted of four two-month blocks of stimulation with a 50%-duty cycle, alternating with two-month blocks of no stimulation. RESULTS: We terminated the study after enrollment of five subjects due to slow accrual. Fornicodorsocommissural tract stimulation elicited bilateral hippocampal evoked responses in all subjects. Three subjects underwent implantation of pulse generators and long-term low-frequency stimulation with mean monthly seizures of 3.14 ±â€¯2.67 (median 3.0 [IQR 1-4.0]) during stimulation-off blocks, compared with 0.96 ±â€¯1.23 (median 1.0 [IQR 0-1.0]) during stimulation-on blocks (p = 0.0005) during the blinded phase. Generalized Estimating Equations showed that low-frequency stimulation reduced monthly seizure-frequency by 0.71 per mA (p < 0.001). Verbal memory scores were stable with no psychiatric complications or other adverse events. SIGNIFICANCE: The results demonstrate feasibility of stimulating both hippocampi using a single deep-brain stimulation electrode in the fornicodorsocommissural tract, efficacy of low-frequency stimulation in reducing seizures, and safety as regards verbal memory.

Continuous Electroencephalogram Evaluation of Paroxysmal Events in Critically Ill Patients: Diagnostic Yield and Impact on Clinical Decision Making.

BACKGROUND: Continuous electroencephalogram (cEEG) monitoring has been widely used in the intensive care unit (ICU) for the evaluation of patients in the ICU with altered consciousness to detect nonconvulsive seizures. We investigated the yield of cEEG when used to evaluate paroxysmal events in patients in the ICU and assessed the predictors of a diagnostic findings. The clinical impact of cEEG was also evaluated in this study. METHODS: We identified patients in the ICU who underwent cEEG monitoring (> 6 h) to evaluate paroxysmal events between January 1, 2018, and December 31, 2019. We extracted patient demographics, medical history, neurological examination, brain imaging results, and the description of the paroxysmal events that necessitated the monitoring. We dichotomized the cEEG studies into those that captured habitual nonepileptic events or revealed epileptiform discharges (ictal or interictal), i.e., those considered to be of positive diagnostic yield (Y +), and those studies that did not show those findings (negative diagnostic yield, Y -). We also assessed the clinical impact of cEEG by documenting changes in administered antiseizure medication (ASM) before and after the cEEG. RESULTS: We identified 159 recordings that were obtained for the indication of paroxysmal events, of which abnormal movements constituted the majority (n = 123). For the remaining events (n = 36), descriptions included gaze deviations, speech changes, and sensory changes. Twenty-nine percent (46 of 159) of the recordings were Y + , including the presence of ictal or interictal epileptiform discharges (n = 33), and captured habitual nonepileptic events (n = 13). A history of epilepsy was the only predictor of the study outcome. Detection of abnormal findings occurred within 6 h of the recording in most patients (30 of 46, 65%). Overall, cEEG studies led to 49 (31%) changes in ASM administration. The changes included dosage increases or initiation of ASM in patients with epileptiform discharges (n = 28) and reduction or elimination of ASM in patients with either habitual nonepileptic events (n = 5) or Y - cEEG studies (n = 16). CONCLUSIONS: Continuous electroencephalogram monitoring is valuable in evaluating paroxysmal events, with a diagnostic yield of 29% in critically ill patients. A history of epilepsy predicts diagnostic studies. Both Y + and Y - cEEG studies may directly impact clinical decisions by leading to ASMs changes.

Seizure recurrence after prolonged seizure control: Patterns and risk factors.

OBJECTIVE: To identify the patterns and possible predictors of seizure recurrence after durable seizure freedom during maintenance of anti-seizure medication (ASM) treatment. METHODS: We conducted a retrospective longitudinal study that identified all adult individuals with epilepsy (IWE) at the George Washington University outpatient epilepsy clinic between 1/1/2014 and 12/31/2016 who had been seizure free for at least 2 years. We followed up the patients until 5/30/2020 for seizure recurrence. The data were analyzed using survival analysis, univariate analysis, and multivariate regression with Cox proportional hazard model. Outcomes were dichotomized into seizure relapse and seizure freedom. The total number of relapses and triggers of the initial relapse for individual patient were also analyzed. RESULTS: This single-center cohort consisted of 220 IWE (age 21-80) of whom 99 patients had been seizure free for 2-3 years and 121 patients had been seizure free for more than 3 years. In this cohort, 48 patients (22%) experienced at least one seizure relapse during the span of the study. Of the relapsing patients, 25 (52%) had a single seizure relapse, and 8 (15%) had frequent seizure relapses (n ≥ 5) and developed pharmacoresistance. Half of the initial seizure relapses occurred without a trigger. Among those with at least one year of follow-up after relapsing (n = 33), 29 (86%) regained seizure freedom for at least 1 year. Among 26 patients with at least 2 years of follow-up, only 14 (55%) regained at least 2 years of seizure freedom. Previous longer duration of seizure freedom and ASM monotherapy predicted less chances of seizure relapse and fewer seizure numbers after relapse. No difference in prognosis was noted among relapsing patients between those with or without triggers. SIGNIFICANCE: Patients with well-controlled epilepsy may have seizure relapses with or without identifiable triggers. Most patients regained at least 1-year seizure freedom after the initial relapse, whereas about half patients reachieved 2-year seizure remission. About 15% of the relapsing patients may subsequently develop pharmacoresistance. Prognostic factors of seizure recurrences include duration of initial seizure remission and the number of ASMs used during remission. The presence of identifiable triggers for the initial seizure relapse does not predict future outcome.

The effects of ammonia stimulation on kainate-induced status epilepticus and anterior piriform cortex electrophysiology.

OBJECTIVE: Strong olfactory stimulation (OS) with such substances as toluene or ammonia has been reported to suppress seizures. We aimed to investigate the role of ammonia stimulation on acute kainic acid (KA)-induced seizures. We also investigated any possible effects of ammonia stimulation on the electrophysiology of the anterior piriform cortex (APC). METHODS: Adult male Sprague-Dawley rats were implanted with bilateral hippocampal electrodes and an electrode in the left APC. Animals were exposed to either distilled water (control) or ammonia stimulation for 20 s every 5 min during KA induction of status epilepticus (SE). The electroencephalogram (EEG) was analyzed for seizure frequency, duration, severity, and total KA doses given prior to reaching SE. Seizure-free EEG epochs that coincided with OS were chosen and analyzed via wavelet analysis for any spectral changes. RESULTS: We found no significant differences in seizure frequency, duration, severity, or administered KA doses before SE between the groups. In the experimental group, a wavelet analysis of variance (WANOVA) revealed a significant stimulation-induced increase of power in the delta and alpha bands prior to the first KA injection and higher power in the delta and theta bands after KA injection. CONCLUSIONS: Whereas the spectral analysis of the APC revealed specific OS-induced changes, our findings suggest that OS with ammonia does not result in altering the threshold of attaining KA-induced SE. This does not rule out a potential role for OS in reducing recurrent seizures in the KA or other epilepsy models.

Using 3D-Printed Mesh-Like Brain Cortex with Deep Structures for Planning Intracranial EEG Electrode Placement.

Surgical evaluation of medically refractory epilepsy frequently necessitates implantation of multiple intracranial electrodes for the identification of the seizure focus. Knowledge of the individual brain's surface anatomy and deep structures is crucial for planning the electrode implantation. We present a novel method of 3D printing a brain that allows for the simulation of placement of all types of intracranial electrodes. We used a DICOM dataset of a T1-weighted 3D-FSPGR brain MRI from one subject. The segmentation tools of Materialise Mimics 21.0 were used to remove the osseous anatomy from brain parenchyma. Materialise 3-matic 13.0 was then utilized in order to transform the cortex of the segmented brain parenchyma into a mesh-like surface. Using 3-matic tools, the model was modified to incorporate deep brain structures and create an opening in the medial aspect. The final model was then 3D printed as a cerebral hemisphere with nylon material using selective laser sintering technology. The final model was light and durable and reflected accurate details of the surface anatomy and some deep structures. Additionally, standard surgical depth electrodes could be passed through the model to reach deep structures without damaging the model. This novel 3D-printed brain model provides a unique combination of visualizing both the surface anatomy and deep structures through the mesh-like surface while allowing repeated needle insertions. This relatively low-cost technique can be implemented for interdisciplinary preprocedural planning in patients requiring intracranial EEG monitoring and for any intervention that requires needle insertion into a solid organ with unique anatomy and internal targets.

Acute and spontaneous seizure onset zones in the intraperitoneal kainic acid model.

OBJECTIVE: Hippocampal monitoring is often used in the intraperitoneal kainic acid (KA) seizure model for detection and quantification of early ictal activity. Here, we investigated extra-hippocampal seizure onset zones (SOZs) in this model. METHODS: Eight male Sprague Dawley rats implanted with depth electrodes were continuously recorded during intraperitoneal KA injections until status epilepticus (SE) was induced. Another group of four rats was monitored chronically up to two weeks after emergence of spontaneous recurrent seizures. All rats had hippocampal electrodes. Other sampled brain regions included, among others, the claustrum, piriform cortex, and orbital cortex. Seizures recorded with video-EEG were visually analyzed. RESULTS: In the 58 seizures recorded during KA injections, the SOZ was extrahippocampal in 7 (12%), diffuse in 29 (50%), and hippocampal in 22 (38%). Of the 14 spontaneous seizures recorded, none were solely extrahippocampal, 10 (71%) were diffuse, and 4 (29%) were of hippocampal onset. All extra-hippocampal seizures propagated to the hippocampus within 4 to 50s (mean=14, n=7). No distinctive semiological manifestations correlated with the SOZs. SIGNIFICANCE: We conclude that seizures can have multifocal SOZs in the KA model. This finding is important to consider when using this model, among other purposes, to screen for new therapies, study pharmacoresistance, or investigate comorbidities of epilepsy.

Yawning induced by focal electrical stimulation in the human brain.

The primary function of yawning is not fully understood. We report a case in which electrical stimulation of the putamen in the human brain consistently elicited yawning. A 46-year-old woman with intractable epilepsy had invasive depth electrode monitoring and cortical stimulation mapping as part of her presurgical epilepsy evaluation. The first two contacts of a depth electrode that was intended to sample the left insula were in contact with the putamen. Stimulation of these contacts at 6mA and 8mA consistently elicited yawning on two separate days. Engagement in arithmetic and motor tasks during stimulation did not result in yawning. When considering the role of the putamen in motor control and its extensive connectivity to cortical and brainstem regions, our findings suggest that it plays a key role in the execution of motor movements necessitated by yawning. Furthermore, given the role of the anterior insula in attention and focused tasks, activation of this area while engaged in arithmetic and motor tasks could inhibit the putaminal processing necessary for yawning. Many have hypothesized the function of yawning; however, it remains debatable whether yawning serves a primarily physiological or communicative function or perhaps both.

Effects of low-frequency electrical stimulation of the anterior piriform cortex on kainate-induced seizures in rats.

OBJECTIVE: Recent evidence in animals and humans suggests that low-frequency stimulation (LFS) has significant antiepileptic properties. The anterior piriform cortex (APC) is a highly susceptible seizure-trigger zone and may be critical for the initiation and propagation of seizures originating from cortical and limbic foci. We used the kainic acid (KA) seizure model in rats to assess the therapeutic effect of LFS of the APC on seizures. METHODS: Adult male Sprague-Dawley rats were implanted with electrodes in the left APC and recording electrodes bilaterally in the hippocampal CA3 regions. Rats were monitored continuously with video-EEG after the emergence of spontaneous recurrent seizures that followed induction of status epilepticus by intraperitoneal KA. After two weeks of baseline recordings to determine seizure frequency, LFS of the APC was applied 60-min On 15-min Off, for two weeks with 1Hz biphasic square waves, 0.2ms pulse width, at 200µA. Another 2-week period of video-EEG monitoring was done after the cessation of LFS to study the carry-over effect. Changes in seizure frequency, severity, and duration between baseline, during LFS, and post-LFS were analyzed using the Poisson regression model. RESULTS: Overall seizure frequency decreased during the post-LFS period to 5% of that at baseline (p=0.003). Severe seizures (stages 4 and 5 on the Racine scale) decreased to 0% of the baseline during the post-LFS period. CONCLUSIONS: Two weeks of LFS of the APC reduced spontaneous seizure frequency and severity in the KA model with the effect outlasting the stimulation. Our findings suggest that the APC can be an important therapeutic target for stimulation in epilepsy.

Prevalence and Risk Factors for Early Seizure in Patients with Traumatic Brain Injury: Analysis from National Trauma Data Bank.

BACKGROUND: Traumatic brain injury (TBI) is a well-known risk factor for seizures. We aimed to identify the frequency and risk factors for seizure occurrence during hospitalization for TBI. METHODS: We used ICD-9-CM codes to identify patients 18 years of age or older from the National Trauma Data Bank who were admitted with TBI. We also used ICD-9-CM codes to identify the subset who had seizures during hospitalization. Patient demographics, comorbidities, Glasgow Coma Scale (GCS) score, Injury Severity Score Abbreviated Injury Scale (ISSAIS), in-hospital complications, and discharge disposition were compared in the seizure group (SG) and no-seizure group (NSG). RESULTS: A total of 1559 patients had in-hospital seizures, comprising 0.4% of all patients admitted with TBI. The mean age of SG was 3 years older than NSG [51 vs. 48; p < 0.0001]. African-American ethnicity (20 vs. 12%, p < 0.0001) and moderate TBI (8 vs. 4%, p < 0.0001) were more common in SG. History of alcohol dependence was more common in the SG (25 vs. 11%, p < 0.0001). Fall was the most common mechanism of injury in SG (56 vs. 36% in NSG; p < 0.0001). Subdural hematoma was more common in SG (31 vs. 21%, p < 0.0001). SG had higher rates of pneumonia, ARDS, acute kidney injury, and increased ICP. The average length of hospital stay was significantly higher in SG (10 vs. 6 days, p < 0.0001), and these patients had higher rate of discharge to nursing facility (32 vs. 25%, p < 0.0001). CONCLUSION: In-hospital seizures occur in 0.4% of all TBI patients. Although infrequent, seizure occurrence is associated with higher rates of hospital complications such as pneumonia and ARDS and is an independent predictor of longer hospital stay and worse hospital outcome.

Multiple hippocampal transections for intractable hippocampal epilepsy: Seizure outcome.

PURPOSE: The purpose of this study was to evaluate the seizure outcomes after transverse multiple hippocampal transections (MHTs) in 13 patients with intractable TLE. METHODS: Thirteen patients with normal memory scores, including 8 with nonlesional hippocampi on MRI, had temporal lobe epilepsy (TLE) necessitating depth electrode implantation. After confirming hippocampal seizure onset, they underwent MHT. Intraoperative monitoring was done with 5-6 hippocampal electrodes spaced at approximately 1-cm intervals and spike counting for 5-8min before each cut. The number of transections ranged between 4 and 7. Neuropsychological assessment was completed preoperatively and postoperatively for all patients and will be reported separately. RESULTS: Duration of epilepsy ranged between 5 and 55years. There were no complications. Intraoperatively, MHT resulted in marked spike reduction (p=0.003, paired t-test). Ten patients (77%) are seizure-free (average follow-up was 33months, range 20-65months) without medication changes. One of the 3 patients with persistent seizures had an MRI revealing incomplete transections, another had an additional neocortical seizure focus (as suggested by pure aphasic seizures), and the third had only 2 seizures in 4years, one of which occurred during antiseizure medication withdrawal. Verbal and visual memory outcomes will be reported separately. Right and left hippocampal volumes were not different preoperatively (n=12, p=0.64, Wilcoxon signed-rank test), but the transected hippocampal volume decreased postoperatively (p=0.0173). CONCLUSIONS: Multiple hippocampal transections provide an effective intervention and a safe alternative to temporal lobectomy in patients with hippocampal epilepsy.

Proceedings of the Seventh International Workshop on Advances in Electrocorticography.

The Seventh International Workshop on Advances in Electrocorticography (ECoG) convened in Washington, DC, on November 13-14, 2014. Electrocorticography-based research continues to proliferate widely across basic science and clinical disciplines. The 2014 workshop highlighted advances in neurolinguistics, brain-computer interface, functional mapping, and seizure termination facilitated by advances in the recording and analysis of the ECoG signal. The following proceedings document summarizes the content of this successful multidisciplinary gathering.

Low-frequency electrical stimulation of a fiber tract in temporal lobe epilepsy.

OBJECTIVE: Surgical resection of the temporal lobe is an effective treatment for medically intractable temporal lobe epilepsy, but can cause memory impairment. Deep brain stimulation in epilepsy has targeted gray matter structures using high frequencies, but achieved limited success. We tested the hypothesis that low-frequency stimulation of the fornix reduces interictal epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy, without affecting memory. METHODS: We implanted depth electrodes in 11 patients for surgical evaluation of intractable epilepsy. Low-frequency stimulation of the fornix occurred in 4-hour sessions in the video-electroencephalography unit. Mental status assessment was performed at baseline and during stimulation. We studied the effect of stimulation on hippocampal spikes and seizures. RESULTS: There were no complications, and the patients were unaware of the stimulation. Fornix stimulation elicited evoked responses in the hippocampus and the posterior cingulate gyrus. Hourly Mini-Mental Status Examination (MMSE) scores showed an increase during stimulation when compared to prestimulation MMSE, largely due to improvement in recall, possibly representing a practice effect. Hippocampal spikes were significantly reduced during and outlasting each stimulation session. Seizure odds (n = 7) were reduced by 92% in the 2 days that followed stimulation. INTERPRETATION: Low-frequency stimulation of the fornix activates the hippocampus and other areas of the declarative memory circuit. The results of this preliminary study suggest that low-frequency stimulation is tolerable and reduces epileptiform discharges and seizures in patients with intractable mesial temporal lobe epilepsy. A controlled clinical trial may be warranted.

Role of ictal baseline shifts and ictal high-frequency oscillations in stereo-electroencephalography analysis of mesial temporal lobe seizures.

OBJECTIVE: To assess the role of ictal baseline shifts (IBS) and ictal high-frequency oscillations (iHFOs) in intracranial electroencephalography (EEG) presurgical evaluation by analysis of the spatial and temporal relationship of IBS, iHFOs with ictal conventional stereo-electroencephalography (icEEG) in mesial temporal lobe seizures (MTLS). METHODS: We studied 15 adult patients with medically refractory MTLS who underwent monitoring with depth electrodes. Seventy-five ictal EEG recordings at 1,000 Hz sampling rate were studied. Visual comparison of icEEG, IBS, and iHFOs were performed using Nihon-Kohden Neurofax systems (acquisition range 0.016-300 Hz). Each recorded ictal EEG was analyzed with settings appropriate for displaying icEEG, IBS, and iHFOs. RESULTS: IBS and iHFOs were observed in all patients and in 91% and 81% of intracranial seizures, respectively. IBS occurred before (22%), at (57%), or after (21%) icEEG onset. In contrast, iHFOs occurred at (30%) or after (70%) icEEG onset. The onset of iHFOs was 11.5 s later than IBS onset (p < 0.0001). All of the earliest onset of IBS and 70% of the onset of iHFOs overlapped with the ictal onset zone (IOZ). Compared with iHFOs, interictal HFOs (itHFOs) were less correlated with IOZ. In contrast to icEEG, IBS and iHFOs had smaller spatial distributions in 70% and 100% of the seizures, respectively. An IBS dipole was observed in 66% of the seizures. Eighty-seven percent of the dipoles had a negative pole at the anterior/medial part of amygdala/hippocampus complex (A-H complex) and a positive pole at the posterior/lateral part of the A-H complex. SIGNIFICANCE: The results suggest that evaluation of IBS and iHFOs, in addition to routine icEEG, helps in more accurately defining the IOZ. This study also shows that the onset and the spatial distribution of icEEG, IBS, and iHFOs do not overlap, suggesting that they reflect different cellular or network dynamics.

Electrical stimulation of a small brain area reversibly disrupts consciousness.

The neural mechanisms that underlie consciousness are not fully understood. We describe a region in the human brain where electrical stimulation reproducibly disrupted consciousness. A 54-year-old woman with intractable epilepsy underwent depth electrode implantation and electrical stimulation mapping. The electrode whose stimulation disrupted consciousness was between the left claustrum and anterior-dorsal insula. Stimulation of electrodes within 5mm did not affect consciousness. We studied the interdependencies among depth recording signals as a function of time by nonlinear regression analysis (h(2) coefficient) during stimulations that altered consciousness and stimulations of the same electrode at lower current intensities that were asymptomatic. Stimulation of the claustral electrode reproducibly resulted in a complete arrest of volitional behavior, unresponsiveness, and amnesia without negative motor symptoms or mere aphasia. The disruption of consciousness did not outlast the stimulation and occurred without any epileptiform discharges. We found a significant increase in correlation for interactions affecting medial parietal and posterior frontal channels during stimulations that disrupted consciousness compared with those that did not. Our findings suggest that the left claustrum/anterior insula is an important part of a network that subserves consciousness and that disruption of consciousness is related to increased EEG signal synchrony within frontal-parietal networks.

Lacosamide-induced rash.

Cutaneous eruptions and hypersensitivity represent frequently reported side effects of anti-seizure medications. However, these side-effects have rarely been previously reported for lacosamide, a newer-generation anti-seizure medication with a novel mechanism of action. Here, we report a case of diffuse skin eruption in a patient with history of epilepsy soon after initiation of lacosamide. The rash resolved after discontinuation of lacosamide and use of antihistamines and steroids. We also review the information on drug hypersensitivity syndrome.

Evaluation of Paroxysmal Events in Critically Ill Patients: Relationship of Primary Diagnosis to Long-Term Electroencephalogram Yield.

Continuous EEG (cEEG) is indicated for the workup of paroxysmal events. We aimed to assess whether primary admission diagnoses predict the yield of cEEG when ordered for evaluating paroxysmal events. We identified patients in the ICU who underwent at least 6 hours of cEEG monitoring to evaluate paroxysmal events. Primary admission diagnoses were categorized into neurological or non-neurological conditions. cEEG results were dichotomized into presence or absence of epileptiform discharges. We identified 159 recordings that were obtained for the evaluation of paroxysmal events. Most patients (n = 100, 63%) were admitted with primary admission diagnoses of neurological disorders, such as ischemic stroke, or intracranial hemorrhage. We found that patients with primary neurological conditions were more likely to have brain surgeries, abnormal brain imaging, and focal neurological deficits on examination compared to those with primary non-neurological conditions. However, there was no significant difference in the prevalence of epileptiform discharges in cEEG among patients with primary diagnoses of neurological or non-neurological disorders. These results suggest that cEEG is often necessary to evaluate paroxysmal events, even among patients without primary neurological disorders.

Connectivity between perisylvian and bilateral basal temporal cortices.

Language processing requires the orchestrated action of different neuronal populations, and some studies suggest that the role of the basal temporal (BT) cortex in language processing is bilaterally distributed. Our aim was to demonstrate connectivity between perisylvian cortex and both BT areas. We recorded corticocortical evoked potentials (CCEPs) in 8 patients with subdural electrodes implanted for surgical evaluation of intractable epilepsy. Four patients had subdural grids over dominant perisylvian and BT areas, and 4 had electrode strips over both BT areas and left posterior superior temporal gyrus (LPSTG). After electrocortical mapping, patients with grids had 1-Hz stimulation of language areas. Patients with strips did not undergo mapping but had 1-Hz stimulation of the LPSTG. Posterior language area stimulation elicited CCEPs in ipsilateral BT cortex in 3/4 patients with left hemispheric grids. CCEPs were recorded in bilateral BT cortices in 3/4 patients with strips upon stimulation of the LPSTG, and in the LPSTG in the fourth patient upon stimulation of either BT area. This is the first in vivo demonstration of connectivity between LPSTG and both BT cortices. The role of BT cortex in language processing may be bilaterally distributed and related to linking visual information with phonological representations stored in the LPSTG.