Electrical Stimulation Modulates High γ Activity and Human Memory Performance.

Direct electrical stimulation of the brain has emerged as a powerful treatment for multiple neurological diseases, and as a potential technique to enhance human cognition. Despite its application in a range of brain disorders, it remains unclear how stimulation of discrete brain areas affects memory performance and the underlying electrophysiological activities. Here, we investigated the effect of direct electrical stimulation in four brain regions known to support declarative memory: hippocampus (HP), parahippocampal region (PH) neocortex, prefrontal cortex (PF), and lateral temporal cortex (TC). Intracranial EEG recordings with stimulation were collected from 22 patients during performance of verbal memory tasks. We found that high γ (62-118 Hz) activity induced by word presentation was modulated by electrical stimulation. This modulatory effect was greatest for trials with poor memory encoding. The high γ modulation correlated with the behavioral effect of stimulation in a given brain region: it was negative, i.e., the induced high γ activity was decreased, in the regions where stimulation decreased memory performance, and positive in the lateral TC where memory enhancement was observed. Our results suggest that the effect of electrical stimulation on high γ activity induced by word presentation may be a useful biomarker for mapping memory networks and guiding therapeutic brain stimulation

The effects of direct brain stimulation in humans depend on frequency, amplitude, and white-matter proximity

BACKGROUND: Researchers have used direct electrical brain stimulation to treat a range of neurological and psychiatric disorders. However, for brain stimulation to be maximally effective, clinicians and researchers should optimize stimulation parameters according to desired outcomes. OBJECTIVE: The goal of our large-scale study was to comprehensively evaluate the effects of stimulation at different parameters and locations on neuronal activity across the human brain. METHODS: To examine how different kinds of stimulation affect human brain activity, we compared the changes in neuronal activity that resulted from stimulation at a range of frequencies, amplitudes, and locations with direct human brain recordings. We recorded human brain activity directly with electrodes that were implanted in widespread regions across 106 neurosurgical epilepsy patients while systematically stimulating across a range of parameters and locations. RESULTS: Overall, stimulation most often had an inhibitory effect on neuronal activity, consistent with earlier work. When stimulation excited neuronal activity, it most often occurred from high-frequency stimulation. These effects were modulated by the location of the stimulating electrode, with stimulation sites near white matter more likely to cause excitation and sites near gray matter more likely to inhibit neuronal activity. CONCLUSION: By characterizing how different stimulation parameters produced specific neuronal activity patterns on a large scale, our results provide an electrophysiological framework that clinicians and researchers may consider when designing stimulation protocols to cause precisely targeted changes in human brain activity

A Methodology for Systematic Volumetric Analysis of Perioperative Cranial Imaging in Neurosurgical Patients

Background Although objective assessment of perioperative imaging provides a rigorous evaluation method of neurosurgical techniques in epilepsy, its use remains far from mainstream. Open surgery remains the gold standard for treatment of mesial temporal lobe epilepsy (MTLE); however, stereotactic laser ablation is a promising minimally invasive alternative. Nevertheless, the variables that may affect seizure outcome in stereotactic laser amygdalohippocampectomy (SLAH) remain unclear. While an objective endpoint such as ablated mesial temporal volumes may be significant, a standard methodology for calculating such volumes has yet to be proposed. Objectives To formulate and test a methodology, which can aid in critical evaluation of laser trajectories, and ablation cavities in seizure patients. Methods We performed a retrospective study involving 16 patients undergoing SLAH our institution’s approved IRB protocol. Preoperative MRIs were processed and segmented. Postoperative MRIs were co-registered to preoperative MRIs. Laser trajectories and ablation cavities were segmented from this co-registered image. Segmented trajectories, and cavities were superimposed upon the initial MRI. The percentage of each structure affected was calculated, using a voxel by voxel comparison. Results We were successfully able to determine ablation volumes and critically evaluate laser placement. Conclusion This semi-automated methodology showcases a systematic workflow that objectively evaluates perioperative imaging in neurosurgical patients. Pages: 16-2