Suppression of EEG gamma activity — an informative measure of spreading depression waves in the neocortex of the conscious rabbit

Neurometabolic and electrophysiological changes during cortical spreading depolarization: multimodal approach based on a lactate-glucose dual microbiosensor arrays

Spreading depolarization (SD) is a slow propagating wave of strong depolarization of neural cells, implicated in several neuropathological conditions. The breakdown of brain homeostasis promotes significant hemodynamic and metabolic alterations, which impacts on neuronal function. In this work we aimed to develop an innovative multimodal approach, encompassing metabolic, electric and hemodynamic measurements, tailored but not limited to study SD. This was based on a novel dual-biosensor based on microelectrode arrays designed to simultaneously monitor lactate and glucose fluctuations and ongoing neuronal activity with high spatial and temporal resolution. In vitro evaluation of dual lactate-glucose microbiosensor revealed an extended linear range, high sensitivity and selectivity, fast response time and low oxygen-, temperature- and pH- dependencies. In anesthetized rats, we measured with the same array a significant drop in glucose concentration matched to a rise in lactate and concurrently with pronounced changes in the spectral profile of LFP-related currents during episodes of mechanically-evoked SD. This occurred along with the stereotypical hemodynamic response of the SD wave. Overall, this multimodal approach successfully demonstrates the capability to monitor metabolic alterations and ongoing electrical activity, thus contributing to a better understanding of the metabolic changes occurring in the brain following SD.

Gamma, fast, and ultrafast waves of the brain: their relationships with epilepsy and behavior

Gamma waves, defined as rhythms from 25 to 100 Hz, are reviewed along with fast (100-400 Hz) and ultrafast (400-800 Hz) activity. Investigations on animals, especially those involving interneurons from the hippocampus, are reviewed. Gamma waves and fast rhythms likely play a role in neural communication, reflecting information from the external world to the brain. These rhythms become evident when the GABA-A system shifts from excitation to inhibition; are seen mainly in the hippocampus, the dentate gyrus, and CA(1)-CA(3) system; and are likely involved in long-term memory and cognitive task performance. These waves are also involved in spreading depression, but especially with epileptiform activity, progressively increasing in frequency from the pre-ictal to the ictal state. After status epilepticus, their presence predicts the development of spontaneous seizures. Gamma waves and fast activity have been studied in all sensory modalities, especially visual systems, providing a mechanism for awareness and processing of visual objects. In humans, gamma waves develop in the young, peak at 4-5 years of age, and are observed especially during alertness and after sensory stimulation. These fast rhythms are seen in the majority of seizures, especially in infantile spasms and during ictal activity in extratemporal and regional onsets, and, if low in amplitude, seem to be a good prognostic sign after seizure surgery. They have been studied in all sensory systems and are associated with selective attention, transient binding of cognitive features, and conscious perception of the external world.