Interictal sleep recordings during presurgical evaluation: Bidirectional perspectives on sleep related network functioning.

Sleep recordings are an integral part of presurgical evaluation in drug-resistant focal epilepsy. Physiological network functioning is substantially different between wakefulness and sleep and thus may add further complexity to the task of determining the epileptogenic zone (EZ). A thorough understanding of changes in epileptic networks in relation to sleep is therefore essential in order to fully appreciate the added value of sleep recordings. Furthermore, shared expertise in epilepsy and sleep is beneficial for both domains, as intracerebral EEG during presurgical evaluation offers a unique window into physiological networks and their interaction during sleep. This review intends to delineate the way in which sleep modifies interictal epileptic discharges (IEDs), and to summarize which sleep state is the most appropriate for aiding in discerning the EZ. Two approaches will be reviewed. First, classical scalp electroencephalography (EEG) recordings help to localize the EZ, especially during rapid-eye-movement (REM) sleep. REM sleep tends to narrow the field size of IEDs, and thus helps to target the core of the EZ. Second, automated analysis of intracerebral recordings can make use of both IEDs and sleep-related oscillations in combination. Notably, high frequency oscillations and directed connectivity measures can be assessed in a single sleep cycle and are valuable tools to probe epileptogenicity. In this approach, which exploits increased network interactions during sleep, non-REM-sleep is the most suitable sleep stage to extract multiple features of local and distributed neuronal activity in order to predict the EZ. The added value of intracerebral recordings is perfectly bidirectional. From a sleep perspective, invasive EEG recordings are a unique opportunity to unravel local sleep-related network function of superficial and deeply situated brain structures. Intracerebral EEG has thus allowed the dissection of sleep features and oscillations and their anatomical sources. A multicenter effort led by the Montreal Neurological Institute resulted in a detailed open-access atlas on normative EEG activity during sleep (https://mni-open-ieegatlas.research.mcgill.ca/). It contributed to our understanding that the human brain does not sleep uniformly but that specifically deep structures have distinct signatures that are discernable from the rest of the brain. Also, this research direction allowed us to gain insights into our understanding of the important neurocognitive functions of sleep. Finally, this review provides a clinical outlook on the benefit of genuine sleep recordings, i.e. recordings with additional sleep sensors, concomitant to presurgical evaluation, in order to fully discern common sleep disorders as a frequent comorbidity of epilepsy. In conclusion, shared expertise in sleep and epilepsy is of mutual added value for improving the management of patients with epilepsy.

Visual Information Routes in the Posterior Dorsal and Ventral Face Network Studied with Intracranial Neurophysiology and White Matter Tract Endpoints.

Occipitotemporal regions within the face network process perceptual and socioemotional information, but the dynamics and information flow between different nodes of this network are still debated. Here, we analyzed intracerebral EEG from 11 epileptic patients viewing a stimulus sequence beginning with a neutral face with direct gaze. The gaze could avert or remain direct, while the emotion changed to fearful or happy. N200 field potential peak latencies indicated that face processing begins in inferior occipital cortex and proceeds anteroventrally to fusiform and inferior temporal cortices, in parallel. The superior temporal sulcus responded preferentially to gaze changes with augmented field potential amplitudes for averted versus direct gaze, and large effect sizes relative to other network regions. An overlap analysis of posterior white matter tractography endpoints (from 1066 healthy brains) relative to active intracerebral electrodes in the 11 patients showed likely involvement of both dorsal and ventral posterior white matter pathways. Overall, our data provide new insight into the timing of face and social cue processing in the occipitotemporal brain and anchor the superior temporal cortex in dynamic gaze processing.

Surgical treatment of hypothalamic hamartomas.

Hypothalamic hamartomas are aberrant masses, composed of abnormally distributed neurons and glia. Along endocrine and cognitive symptoms, they may cause epileptic seizures, including the specific gelastic and dacrystic seizures. Surgery is the treatment of drug-resistant hamartoma epilepsy, with associated positive results on endocrine, psychiatric, and cognitive symptoms. Recently, alternatives to open microsurgical treatment have been proposed. We review these techniques and compare their efficacy and safety. Open resection or disconnection of the hamartoma, either through pterional, transcallosal, or transventricular approach, leads to good epileptological control, but its high complication rate, up to 30%, limits its indications. The purely cisternal peduncular forms remain the only indication of open, pterional approach, while other strategies have been developed to overcome the neurological, endocrine, behavioral, or cognitive complications. Laser and radiofrequency thermocoagulation-based disconnection through robot-guided stereo-endoscopy has been proposed as an alternative to open microsurgical resection and stereotactic destruction. The goal is to allow safe and complete disconnection of a possibly complex attachment zone, through a single intraparenchymal trajectory which allows multiple laser or radiofrequency probe trajectory inside the ventricle. The efficacy was high, with 78% of favorable outcome, and the overall complication rate was 8%. It was especially effective in patients with isolated gelastic seizures and pure intraventricular hamartomas. Stereotactic radiosurgery has proved as efficacious and safer than open microsurgery, with around 60% of seizure control and a very low complication rate. Multiple stereotactic thermocoagulation showed very interesting results with 71% of seizure freedom and 2% of permanent complications. Stereotactic laser interstitial thermotherapy (LiTT) seems as effective as open microsurgery (from 76 to 81% of seizure freedom) but causes up to 20% of permanent complications. This technique has however been highly improved by targeting only the epileptogenic onset zone in the hamartoma, as shown on preoperative functional MRI, leading to an improvement of epilepsy control by 45% (92% of seizure freedom) with no postoperative morbidity. All these results suggest that the impact of the surgical procedure does not depend on purely technical matters (laser vs radiofrequency thermocoagulation or stereotactic vs robot-guided stereo-endoscopy) but relies on the understanding of the epileptic network, including inside the hamartoma, the aim being to plan an effective disconnection or lesion of the epileptogenic part while sparing the adjacent functional structures.

[Not Available]. / Obstructive sleep apnea in drug-resistant epilepsy: A significant comorbidity warranting diagnosis and treatment.

INTRODUCTION: Drug-resistant epilepsy is a debilitating condition that warrants new therapeutic options. The last two decades have seen a growing interest in the relationship between epilepsy and obstructive sleep apnea syndrome (OSAS), which could ultimately yield non-pharmaceutical treatment strategies. Based on a Medline search of the literature, this review develops lines of evidence for a clinically significant role of OSAS in refractory epilepsy. STATE OF THE ART: OSAS is a primary sleep disorder that could presumably lower the seizure threshold via mechanisms such as sleep fragmentation, oxygen desaturation and chronic sleep deprivation. In comparison to the general population, patients with epilepsy probably have a higher prevalence of OSAS (9-33 % overall; 13-16 % with moderate to severe OSAS). Several common risk factors for OSAS have proven to be significant in patients with epilepsy, notably advanced age, male gender and obesity. Moreover, certain specific conditions, such as refractory seizures, antiepileptic polytherapy and vagus nerve stimulation, appear to render these patients particularly vulnerable to OSAS. Prospective data regarding the efficacy of continuous positive airway pressure (CPAP) therapy for seizure control is scarce. However, there is compelling retrospective evidence that severe OSAS can exacerbate the seizure burden and that CPAP may yield a pronounced reduction in seizure frequency, excessive daytime somnolence and, potentially, cognitive complaints. PERSPECTIVES: In the light of the severity of drug-resistant epilepsy and its impact on quality of life, our current knowledge justifies systematic questionnaire screening for OSAS and a low threshold for referral to sleep laboratory exploration. In the long run, a large prospective trial is needed to confirm the therapeutic interest of CPAP treatment for mild to moderate OSAS in patients with epilepsy. CONCLUSION: OSAS is a significant comorbidity of drug-resistant epilepsy that has the potential to yield new treatment options for better seizure control.

Congenital prosopagnosia: multistage anatomical and functional deficits in face processing circuitry.

Face recognition is a primary social skill which depends on a distributed neural network. A pronounced face recognition deficit in the absence of any lesion is seen in congenital prosopagnosia. This study investigating 24 congenital prosopagnosic subjects and 25 control subjects aims at elucidating its neural basis with fMRI and voxel-based morphometry. We found a comprehensive behavioral pattern, an impairment in visual recognition for faces and buildings that spared long-term memory for faces with negative valence. Anatomical analysis revealed diminished gray matter density in the bilateral lingual gyrus, the right middle temporal gyrus, and the dorsolateral prefrontal cortex. In most of these areas, gray matter density correlated with memory success. Decreased functional activation was found in the left fusiform gyrus, a crucial area for face processing, and in the dorsolateral prefrontal cortex, whereas activation of the medial prefrontal cortex was enhanced. Hence, our data lend strength to the hypothesis that congenital prosopagnosia is explained by network dysfunction and suggest that anatomic curtailing of visual processing in the lingual gyrus plays a substantial role. The dysfunctional circuitry further encompasses the fusiform gyrus and the dorsolateral prefrontal cortex, which may contribute to their difficulties in long-term memory for complex visual information. Despite their deficits in face identity recognition, processing of emotion related information is preserved and possibly mediated by the medial prefrontal cortex. Congenital prosopagnosia may, therefore, be a blueprint of differential curtailing in networks of visual cognition.

The readily releasable pool of vesicles in chromaffin cells is replenished in a temperature-dependent manner and transiently overfills at 37 degrees C.

Maturation of exocytic vesicles to the release-ready state is regulated by several factors, including intracellular calcium concentration ([Ca(2+)](int)) and the state of protein phosphorylation. Here we investigated the effects of temperature on the recovery from depletion of the readily releasable pool (RRP) of vesicles in adrenal chromaffin cells. Exocytosis and [Ca(2+)](int) were monitored by combined membrane capacitance and fura-2 measurements. At higher temperatures, a faster pool refilling and a larger RRP size were observed. The time constants of the recovery from depletion ranged from 3.6 to 1.1 sec (22 and 37 degrees C, respectively) yielding a Q(10) of 2.3. The changes of the Ca(2+) signal between the different temperatures could not account for the differences in recovery kinetics. At 32 and 37 degrees C, we observed a transient overfilling of the RRP after pool depletion, which stands in clear contrast to the sustained secretory depression seen at lower temperatures. The overshoot in RRP size was very prominent in cells with lower basal [Ca(2+)](int), hence with a large difference between prestimulus and poststimulus [Ca(2+)](int). In cells with higher basal [Ca(2+)](int), the pool was larger under steady-state conditions but showed less overfilling on stimulation. We conclude that vesicle maturation is markedly accelerated at physiological temperature, thus allowing for a rapid adaptation of the pool size to the relatively short-lived Ca(2+) transient.