Déjà-rêvé: Prior dreams induced by direct electrical brain stimulation

Complex memories induced by intracranial electrical brain stimulation are related to complex networks

The precise and fleeting moment of rich recollection triggered by an environmental cue is difficult to reproduce in the lab. However, epilepsy patients can experience sudden reminiscences after intracranial electrical brain stimulation (EBS). In these cases, the transient brain state related to the activation of the engram and its conscious perception can be recorded using intracerebral EEG (iEEG). We collected various EBS-induced reminiscences for iEEG analysis, classifying them as follows: no or weak details (familiarity); moderate details and context (semantic and personal semantic memories); high details and context (episodic). Nine brain areas were selected within the temporal lobes (including the hippocampus and temporal neocortex, ipsi- and contralateral) and the insula, defining a network (each area as a node). Functional connectivity was measured by estimating pair-wise non-linear correlations between signals recorded from these brain regions during different memory events. Seventeen reminiscences in six patients (2 episodic, 10 personal semantic, 2 semantic memories, 5 familiar objects, 1 déjà-rêvé) were compared to 18 control experiential phenomena (unrelated to reminiscence), 18 negative EBS (which failed to elicit memories or other phenomena) in the same locations, and pre-EBS baseline activity. The global functional connectivity in the network was higher following EBS-induced reminiscences than during baseline activity, control phenomena, or negative EBS. The degree of connectivity increased with the complexity of memories; it was higher for detailed and contextualized memories like episodic memories. More significant links compared to baseline (edges with higher non-linear correlation relative to baseline) were observed for episodic memories than for less contextualized memories. These increases in connectivity occurred in all frequency bands, except the delta band. Our results support understanding declarative memory retrieval as having a multiplexed organization. They also show that richer memories activated by intracranial EBS are related to more complex connectivity patterns across medial and neocortical temporal lobe structures.

Relationship Between Epilepsy and Dreaming: Current Knowledge, Hypotheses, and Perspectives

The interactions between epilepsy and sleep are numerous and the impact of epilepsy on cognition is well documented. Epilepsy is therefore likely to influence dreaming as one sleep-related cognitive activity. The frequency of dream recall is indeed decreased in patients with epilepsy, especially in those with primary generalized seizures. The content of dreams is also disturbed in epilepsy patients, being more negative and with more familiar settings. While several confounding factors (anti-seizure medications, depression and anxiety disorders, cognitive impairment) may partly account for these changes, some observations suggest an effect of seizures themselves on dreams. Indeed, the incorporation of seizure symptoms in dream content has been described, concomitant or not with a focal epileptic discharge during sleep, suggesting that epilepsy might directly or indirectly interfere with dreaming. These observations, together with current knowledge on dream neurophysiology and the links between epilepsy and sleep, suggest that epilepsy may impact not only wake- but also sleep-related cognition.

A prospective controlled study on the impact of anterior temporal lobectomy on dream content

OBJECTIVE

Changes of dream ability and content in patients with brain lesions have been addressed in only about 100 case reports. All of these reports lack data regarding prelesional baseline dream content. Therefore, it was the objective of this study to prospectively assess dream content before and after anterior temporal lobectomy.

METHODS

Using the Hall and Van de Castle system, 30 dreams before and 21 dreams after anterior temporal lobectomy for drug-resistant epilepsy were analyzed. Fifty-five dreams before and 60 dreams after stereoelectroencephalography served as controls.

RESULTS

After anterior temporal lobectomy, patients had significantly less physical aggression in their dreams than preoperatively (p < 0.01, Cohen's h statistic). Dream content of patients undergoing stereoelectroencephalography showed no significant changes.

CONCLUSIONS

Within the default dream network, the temporal lobe may account for aggressive dream content. Impact of general anesthesia on dream content, as a possible confounder, was ruled out.

Intracerebral electrical stimulations of the temporal lobe: A stereoelectroencephalography study

The functional anatomy of the anteromesial portion of the temporal lobe and its involvement in epilepsy can be explored by means of intracerebral electrical stimulations. Here, we aimed to expand the knowledge of its physiological and pathophysiological symptoms by conducting the first large-sample systematic analysis of 1529 electrical stimulations of this anatomical region. We retrospectively analysed all clinical manifestations induced by intracerebral electrical stimulations in 173 patients with drug-resistant focal epilepsy with at least one electrode implanted in this area. We found that high-frequency stimulations were more likely to evoke electroclinical manifestations (p < .0001) and also provoked 'false positive' seizures. Multimodal symptoms were associated with EEG electrical modification (after discharge) (p < .0001). Visual symptoms were not associated with after discharge (p = .0002) and were mainly evoked by stimulation of the hippocampus (p = .009) and of the parahippocampal gyrus (p = .0212). 'False positive seizures' can be evoked by stimulation of the hippocampus, parahippocampal gyrus and amygdala, likely due to their intrinsic low epileptogenic threshold. Visual symptoms evoked in the hippocampus and parahippocampal gyrus, without EEG changes, are physiological symptoms and suggest involvement of these areas in the visual ventral stream. Our findings provide meaningful guidance in the interpretation of intracranial EEG studies of the temporal lobe.

Direct Targeting of the Anterior Nucleus of the Thalamus via 3 T Quantitative Susceptibility Mapping

Objective: Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is a potentially effective, minimally invasive, and reversible method for treating epilepsy. The goal of this study was to explore whether 3 T quantitative susceptibility mapping (QSM) could delineate the ANT from surrounding structures, which is important for the direct targeting of DBS surgery.

Methods: We obtained 3 T QSM, T1-weighted (T1w), and T2-weighted (T2w) images from 11 patients with Parkinson’s disease or dystonia who received subthalamic nucleus (STN) or globus pallidus interna (GPi) DBS surgery in our center. The ANT and its surrounding white matter structures on QSM were compared with available atlases. The contrast-to-noise ratios (CNRs) of ANT relative to the external medullary lamina (eml) were compared across the three imaging modalities. Additionally, the morphology and location of the ANT were depicted in the anterior commissure (AC)-posterior commissure (PC)-based system.

Results: ANT can be clearly distinguished from the surrounding white matter laminas and appeared hyperintense on QSM. The CNRs of the ANT-eml on QSM, T1w, and T2w images were 10.20 ± 4.23, 1.71 ± 1.03, and 1.35 ± 0.70, respectively. One-way analysis of variance (ANOVA) indicated significant differences in CNRs among QSM, T1w, and T2w imaging modalities [F(2) = 85.28, p < 0.0001]. In addition, both the morphology and location of the ANT were highly variable between patients in the AC–PC-based system.

Conclusion: The potential utility of QSM for the visualization of ANTs in clinical imaging is promising and may be suitable for targeting the ANT for DBS to treat epilepsy.

Direct visualization of deep brain stimulation targets in patients with Parkinson's disease via 3-T quantitative susceptibility mapping

BACKGROUND

The direct visualization of brain nuclei on magnetic resonance (MR) images is important for target localization during deep brain stimulation (DBS) in patients with Parkinson's disease (PD). We demonstrated the superiority of 3-T high-resolution submillimeter voxel size quantitative susceptibility mapping (QSM) for delineating the subthalamic nucleus (STN) and the globus pallidus internus (GPi).

METHODS

Preoperative 3-T QSM and T2 weighted (T2w) images were obtained from ten patients with PD. Qualitative visualization scores were analyzed by two neurosurgeons on both images using a 4-point and 5-point scale, respectively. Images were also compared with regard to contrast-to-noise ratios (CNRs) and edge detection power for the STN and GPi. The Wilcoxon rank-sum test and the signed-rank test were used to compare measurements between the two images.

RESULTS

Visualization scores for the STN and GPi, the mean CNR of the STN relative to the zona incerta (ZI) and the substantia nigra, and the mean CNR of the GPi relative to the internal capsule (IC) and the globus pallidum externum, were significantly higher on QSM images than on T2w images (P < 0.01). The edge detection powers of the STN-ZI and GPi-IC on QSM were significantly larger (by 2.6- and 3.8-fold, respectively) than those on T2w images (P < 0.01). QSM detected asymmetry of the STN in two patients.

CONCLUSIONS

QSM images provided improved delineation ability for the STN and GPi when compared to T2w images. Our findings are important for patients with PD who undergo DBS surgery, particularly those with asymmetric bilateral nuclei.

Precise targeting of the globus pallidus internus with quantitative susceptibility mapping for deep brain stimulation surgery

OBJECTIVE

The goal of this study was to demonstrate the use of quantitative susceptibility mapping (QSM)-based images to precisely localize the globus pallidus internus (GPi) for deep brain stimulation (DBS) planning and to enhance postsurgical visualization of the DBS lead positions.

METHODS

Presurgical T1-weighted (T1w), T2-weighted (T2w), and QSM images as well as postsurgical CT images were obtained in 29 patients with Parkinson's disease. To enhance the contrast within the GP, a hybrid contrast was created by linearly combining T1w and QSM images. Contrast-to-noise ratios (CNRs) of the GPi on T1w, T2w, QSM, and hybrid images were compared. The CNR differences were tested using the 1-way ANOVA method. The visualization of the DBS lead position was demonstrated by merging the postsurgical CT with presurgical MR images.

RESULTS

The hybrid images yield the best CNRs for GPi depiction and the visualization of the postsurgical DBS lead position was significantly improved.

CONCLUSIONS

QSM-based images allow for confident localization of borders of the GPi that is superior to T1w and T2w images. High-contrast hybrid images can be used for precisely directed DBS targeting, e.g., GPi DBS for the treatment of advanced Parkinson's disease.

Experiential seizures related to the hippocampal-parahippocampal spatial representation system

Ictal visual hallucinations may have occipital as well as temporal lobe origin. We report a patient with clustering of focal aware seizures with visual hallucinations. Ictal EEG findings and seizure semiology with alternating contralateral elementary visual phenomena and non-lateralizing experiential hallucinations (visual scenes, memory flashbacks, spatial distortion) corresponded to a lesion in the posterior part of the right parahippocampal gyrus. This area is part of the hippocampal-parahippocampal system for mapping allocentric space. Within this system, the parahippocampal cortex encodes information about visual environmental scenes in concert with functionally defined neurons relevant for episodic memory and spatial cognitive processes (place, grid, border and head direction cells, as well as neurons tracking the passage of time). These functions are tightly linked to visual exploration. We suggest that the hippocampal-parahippocampal spatial navigation system is a crucial part of the networks responsible for the semiology of experiential seizures with complex visual hallucinations and elements of recall.

Acute Effects and the Dreamy State Evoked by Deep Brain Electrical Stimulation of the Amygdala: Associations of the Amygdala in Human Dreaming, Consciousness, Emotions, and Creativity

Accurate localization of complex human experiences such as emotions, dreaming, creativity, and consciousness to specific cerebral structures or neural networks has remained elusive despite technological advances. We report the use of acute deep brain stimulation (DBS) to evoke behavioral and emotional effects by applying electrical stimulation (ES) at various voltage strengths to the basolateral and central subnuclei of the amygdala in addition to the head of hippocampus (HC) for two subjects with medically refractory post-traumatic stress disorder (PTSD). Our results suggest that the amygdala could be a node in a neural network responsible for the generation of complex vivid mental imagery and integrated sensory experiences similar to John Hughlings Jackson's "dreamy state" and "double consciousness," which have been classically associated with temporal lobe epilepsy during uncinate seizures. That we were able to elicit similar vivid, dynamic, complex, bizarre, and original mental imagery with ES in non-epileptic subjects suggests that Jackson's seizure related "dreamy state" and "double consciousness" may arise from heightened innate brain mechanisms with the amygdala acting as a node in the neural network responsible for physiologic dreaming and creative functions. Furthermore, our subjects experienced different emotions with different stimulation strengths at various electrode contacts. Our results suggest that higher voltage stimulation of the amygdala and HC at 4-5 V leads to predominantly negative responses and 2-4 V stimulation showed inversely coupled positive and negative responses of the amygdala in either hemisphere which may imply hemispheric dominance of emotional valences without relation to handedness. Due to the unique and complex responses dependent on location and strength of stimulation, we advise that all patients receiving DBS of the amygdala undergo acute stimulation mapping in a monitored setting before selecting therapeutic parameters for chronic stimulation.