Physiological paradigm for assessing reward prediction and extinction using cortical direct current potential responses in rats.

Anticipating positive outcomes is a core cognitive function in the process of reward prediction. However, no neurophysiological method objectively assesses reward prediction in basic medical research. In the present study, we established a physiological paradigm using cortical direct current (DC) potential responses in rats to assess reward prediction. This paradigm consisted of five daily 1-h sessions with two tones, wherein the rewarded tone was followed by electrical stimulation of the medial forebrain bundle (MFB) scheduled at 1000 ms later, whereas the unrewarded tone was not. On day 1, both tones induced a negative DC shift immediately after auditory responses, persisting up to MFB stimulation. This negative shift progressively increased and peaked on day 4. Starting from day 3, the negative shift from 600 to 1000 ms was significantly larger following the rewarded tone than that following the unrewarded tone. This negative DC shift was particularly prominent in the frontal cortex, suggesting its crucial role in discriminative reward prediction. During the extinction sessions, the shift diminished significantly on extinction day 1. These findings suggest that cortical DC potential is related to reward prediction and could be a valuable tool for evaluating animal models of depression, providing a testing system for anhedonia.

Concurrent recordings of slow DC-potentials and epileptiform discharges: Novel EEG amplifier and signal processing techniques.

Ionic currents within the brain generate voltage oscillations. These bioelectrical activities include ultra-low frequency electroencephalograms (DC-EEG, frequency less than 0.1 Hz) and conventional clinical electroencephalograms (AC-EEG, 0.5-70 Hz). Although AC-EEG is commonly used for diagnosing epilepsy, recent studies indicate that DC-EEG is an essential frequency component of EEG and can provide valuable information for analyzing epileptiform discharges. During conventional EEG recordings, DC-EEG is censored by applying high-pass filtering to i) obliterate slow-wave artifacts, ii) eliminate the bioelectrodes' half-cell potential asymmetrical changes in ultralow-low frequency, and iii) prevent instrument saturation. Spreading depression (SD), which is the most prolonged fluctuation in DC-EEG, may be associated with epileptiform discharges. However, recording of SD signals from the scalp's surface can be challenging due to the filtering effect and non-neuronal slow shift potentials. In this study, we describe a novel technique to extend the frequency bandwidth of surface EEG to record SD signals. The method includes novel instrumentation, appropriate bioelectrodes, and efficient signal-processing techniques. To evaluate the accuracy of our approach, we performed a simultaneous surface recording of DC- and AC-EEG from epileptic patients during long-term video EEG monitoring, which provide a promising tool for diagnosis of epilepsy. DATA AVAILABILITY STATEMENT: The data presented in this study are available on request.

Neural Sources of Vagus Nerve Stimulation-Induced Slow Cortical Potentials.

OBJECTIVES: This study investigated neuronal sources of slow cortical potentials (SCPs) evoked during vagus nerve stimulation (VNS) in patients with epilepsy who underwent routine electroencephalography (EEG) after implantation of the device. MATERIALS AND METHODS: We analyzed routine clinical EEG from 24 patients. There were 5 to 26 trains of VNS during EEG. To extract SCPs from the EEG, a high-frequency filter of 0.2 Hz was applied. These EEG epochs were averaged and used for source analyses. The averaged waveforms for each patient and their grand average were subjected to multidipole analysis. Patients with at least 50% seizure frequency reduction were considered responders. Findings from EEG analysis dipole were compared with VNS responses. RESULTS: VNS-induced focal SCPs whose dipoles were estimated to be located in several cortical areas including the medial prefrontal cortex, postcentral gyrus, and insula, with a significantly higher frequency in patients with a good VNS response than in those with a poor response. CONCLUSIONS: This study suggested that some VNS-induced SCPs originating from the so-called vagus afferent network are related to the suppression of epileptic seizures.

[Studies of the dc-potential of the brain level distribution in elderly women with high anxiety.]

The article presents the results of studies of the direct current (DC) potential of the brain level distribution in elderly women with high anxiety. Analysis of the DC-potential of the brain level distribution was held by mapping obtained by measuring the monopolar values of the DC-potential of the brain and calculating deviations in each of the leads from the average records which were registrated in all areas of the head. The results of the study indicate an increase in the background level of the DC-potential in most parts of the brain and the peculiarity of its distribution in elderly women with a high level of anxiety. A tendency to deformation of interhemispheric asymmetry with a predominance of energy costs in the central region of the right hemisphere and a smoothing of interhemispheric asymmetry in the temporal and parietal regions have been revealed. The obtained data allow to assume the influence of high anxiety on the change in energy metabolism of the brain in the ederly.

Prolonged dry apnoea: effects on brain activity and physiological functions in breath-hold divers and non-divers.

PURPOSE: The aim of the study was to investigate the effects of voluntary breath-holding on brain activity and physiological functions. We hypothesised that prolonged apnoea would trigger cerebral hypoxia, resulting in a decrease of brain performance; and the apnoea's effects would be more pronounced in breath-hold divers. METHODS: Trained breath-hold divers and non-divers performed maximal dry breath-holdings. Lung volume, alveolar partial pressures of O2 and CO2, attention and anxiety levels were estimated. Heart rate, blood pressure, arterial blood oxygenation, brain tissue oxygenation, EEG, and DC potential were monitored continuously during breath-holding. RESULTS: There were a few significant changes in electrical brain activity caused by prolonged apnoea. Brain tissue oxygenation index and DC potential were relatively stable up to the end of the apnoea in breath-hold divers and non-divers. We also did not observe any decrease of attention level or speed of processing immediately after breath-holding. Interestingly, trained breath-hold divers had some peculiarities in EEG activity at resting state (before any breath-holding): non-spindled, sharpened alpha rhythm; slowed-down alpha with the frequency nearer to the theta band; and untypical spatial pattern of alpha activity. CONCLUSION: Our findings contradicted the primary hypothesis. Apnoea up to 5 min does not lead to notable cerebral hypoxia or a decrease of brain performance in either breath-hold divers or non-divers. It seems to be the result of the compensatory mechanisms similar to the diving response aimed at centralising blood circulation and reducing peripheral O2 uptake. Adaptive changes during apnoea are much more prominent in trained breath-hold divers.

Identification of the extent of cortical spreading depression propagation by Npas4 mRNA expression.

Cortical spreading depression (CSD) is a phenomenon associated with a propagating large shift in direct current (DC) potential followed by suppression of electrophysiological activity. For temporal analysis of CSD propagation, electrophysiological recording is the most reliable tool. However, it is difficult to completely identify the spatial area of the brain influenced by CSD, because recording sites are technically limited. Histological post hoc identification of activated neurons by labeling the induction of an immediate early gene (IEG) could determine areas of CSD propagation. We found that cortical application of potassium chloride induced expression of Npas4 IEG mRNA in the ipsilateral dorsal cortex. Interestingly, induction of Npas4 was never observed in the ipsilateral hippocampus and there was a clear boundary to the area of Npas4 expression. To determine whether the boundary of the area of Npas4 mRNA expression was the limit of CSD propagation, we recorded local field potentials from multiple sites that crossed the boundary of Npas4 expression. We found that the area of Npas4 mRNA expression coincided with the area of DC-potential shift propagation. We propose that induction of Npas4 identifies the area influenced by CSD propagation.

[The DC-potential of the brain in older women with postural instability].

The article presents the results of studies of the DC-potential of the brain level distribution in elderly women with postural instability. Analysis of the DC-potential of the brain level distribution was held by mapping obtained by measuring the monopolar values of the DC-potential of the brain and calculating deviations in each of the leads from the average records which were registered in all areas of the head. It is established that elderly women with postural instability DC-potential of the brain level distribution are characterized by increasing in background values and rigid structure of the interaction between brain regions. The disturbance of the principle of the dome-shaped DC-potential of the brain level distribution due to the alignment of values for brain regions was revealed. Factor model with postural instability reflects the control strengthening over the potential falls from the frontal areas of the brain.