Human EEG and the mechanisms of memory: investigating long-term potentiation (LTP) in sensory-evoked potentials

Information-Theoretical Analysis of the Cycle of Creation of Knowledge and Meaning in Brains under Multiple Cognitive Modalities

It is of great interest to develop advanced sensory technologies allowing non-invasive monitoring of neural correlates of cognitive processing in people performing everyday tasks. A lot of progress has been reported in recent years in this research area using scalp EEG arrays, but the high level of noise in the electrode signals poses a lot of challenges. This study presents results of detailed statistical analysis of experimental data on the cycle of creation of knowledge and meaning in human brains under multiple cognitive modalities. We measure brain dynamics using a HydroCel Geodesic Sensor Net, 128-electrode dense-array electroencephalography (EEG). We compute a pragmatic information (PI) index derived from analytic amplitude and phase, by Hilbert transforming the EEG signals of 20 participants in six modalities, which combine various audiovisual stimuli, leading to different mental states, including relaxed and cognitively engaged conditions. We derive several relevant measures to classify different brain states based on the PI indices. We demonstrate significant differences between engaged brain states that require sensory information processing to create meaning and knowledge for intentional action, and relaxed-meditative brain states with less demand on psychophysiological resources. We also point out that different kinds of meanings may lead to different brain dynamics and behavioral responses.

Stability of steady-state visual evoked potential contrast response functions

Repetitive sensory stimulation has been shown to induce neuroplasticity in sensory cortical circuits, at least under certain conditions. We measured the plasticity-inducing effect of repetitive contrast-reversal-sweep steady-state visual-evoked potential (ssVEP) stimuli, hoping to employ the ssVEP's high signal-to-noise electrophysiological readout in the study of human visual cortical neuroplasticity. Steady-state VEP contrast-sweep responses were measured daily for 4 days (four 20-trial blocks per day, 20 participants). No significant neuroplastic changes in response amplitude were observed either across blocks or across days. Furthermore, response amplitudes were stable within-participant, with measured across-block and across-day coefficients of variation (CV = SD/mean) of 15-20 ± 2% and 22-25 ± 2%, respectively. Steady-state VEP response phase was also highly stable, suggesting that temporal processing delays in the visual system vary by at most 2-3 ms across blocks and days. While we fail to replicate visual stimulation-dependent cortical plasticity, we show that contrast-sweep steady-state VEPs provide a stable human neurophysiological measure well suited for repeated-measures longitudinal studies.

Analysis of Meditation vs. Sensory Engaged Brain States Using Shannon Entropy and Pearson's First Skewness Coefficient Extracted from EEG Data

It has been proposed that meditative states show different brain dynamics than other more engaged states. It is known that when people sit with closed eyes instead of open eyes, they have different brain dynamics, which may be associated with a combination of deprived sensory input and more relaxed inner psychophysiological and cognitive states. Here, we study such states based on a previously established experimental methodology, with the aid of an electro-encephalography (EEG) array with 128 electrodes. We derived the Shannon Entropy (H) and Pearson's 1st Skewness Coefficient (PSk) from the power spectrum for the modalities of meditation and video watching, including 20 participants, 11 meditators and 9 non-meditators. The discriminating performance of the indices H and PSk was evaluated using Student's t-test. The results demonstrate a statistically significant difference between the mean H and PSk values during meditation and video watch modes. We show that the H index is useful to discriminate between Meditator and Non-Meditator participants during meditation over both the prefrontal and occipital areas, while the PSk index is useful to discriminate Meditators from Non-Meditators based on the prefrontal areas for both meditation and video modes. Moreover, we observe episodes of anti-correlation between the prefrontal and occipital areas during meditation, while there is no evidence for such anticorrelation periods during video watching. We outline directions of future studies incorporating further statistical indices for the characterization of brain states.

Sensory tetanisation to induce long-term-potentiation-like plasticity: A review and reassessment of the approach

There is great interest in developing non-invasive approaches for studying cortical plasticity in humans. High-frequency presentation of auditory and visual stimuli, or sensory tetanisation, can induce long-term-potentiation-like (LTP-like) changes in cortical activity. However, contrasting effects across studies suggest that sensory tetanisation may be unreliable. We review these contrasting effects, conduct our own study of auditory and visual tetanisation, and perform meta-analyses to determine the average effect of sensory tetanisation across studies. We measured auditory-evoked amplitude changes in a group of younger (18-29 years of age) and older (55-83 years of age) adults following tetanisation to 1 and 4 kHz tone bursts and following a slow-presentation control. We also measured visual-evoked amplitude changes following tetanisation to horizontal and vertical sign gradients. Auditory and visual response amplitudes decreased following tetanisation, consistent with some studies but contrasting with others finding amplitude increases (i.e. LTP-like changes). Older adults exhibited more modest auditory-evoked amplitude decreases, but visual-evoked amplitude decreases like those of younger adults. Changes in response amplitude were not specific to tetanised stimuli. Importantly, slow presentation of auditory tone bursts produced response amplitude changes approximating those observed following tetanisation in younger adults. Meta-analyses of visual and auditory tetanisation studies found that the overall effect of sensory tetanisation was not significant across studies or study sites. The results suggest that sensory tetanisation may not produce reliable changes in cortical responses and more work is needed to determine the validity of sensory tetanisation as a method for inducing human cortical plasticity in vivo.

A randomized, double-blind, placebo-controlled, hybrid parallel-arm study of low-dose naltrexone as an adjunctive anti-inflammatory treatment for major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a leading cause of disability worldwide. The current treatments are ineffective in approximately one-third of patients, resulting in a large economic burden and reduced quality of life for a significant proportion of the global population. There is considerable evidence that increased inflammation may distinguish a sub-type of MDD, and there are no validated diagnostic tools or treatments for neuroinflammation in MDD patients. The current study aims to explore the potential role of low-dose naltrexone (LDN), a drug with purported anti-inflammatory properties in the central nervous system, as an adjunctive treatment in patients with MDD.

METHODS/DESIGN

This double-blind placebo-controlled hybrid parallel arm study enables the exploration of peripheral and central inflammatory markers with LDN as an approach to investigate inflammation as a pathophysiological contributor to MDD. Eligible participants with MDD (n = 48) will be stratified into the high and low inflammatory groups according to the levels of high-sensitivity C-reactive protein (hs-CRP) and then randomized to receive LDN or placebo for an initial 12 weeks, followed by a further 12 weeks during which all participants will receive LDN. The primary outcome measure will be the Montgomery-Åsberg Depression Rating Scale (MADRS) administered at baseline, 2 weeks, 4 weeks, 8 weeks, 12 weeks, 14 weeks, 16 weeks, 20 weeks, and 24 weeks, to assess the effectiveness of the anti-depressant response. The secondary outcomes include the use of MRI techniques including quantitative magnetization transfer (qMT), echo-planar spectroscopic imaging (EPSI), and diffusion-weighted imaging (DWI) to help to elucidate the neurobiological mechanism of LDN, and the inflammatory mechanisms in action in MDD. Electroencephalography, blood samples, cognitive tasks, and additional questionnaires will also be used to determine if there is a specific profile of symptoms in individuals with inflammatory MDD. Healthy participants (n = 24) will be recruited for baseline outcome measures only, to enable comparison with patients with MDD.

DISCUSSION

This trial contributes to the literature on inflammation in MDD, including the understanding of the pathophysiology and efficacy of anti-inflammatory treatments. The investigation of inflammatory mechanisms in MDD is an important first step in the development of biomarkers to classify patient sub-groups, increase the accuracy of diagnosis, and tailor the approach to patients in clinical practice. This study may provide evidence of the benefit of LDN for the groups in whom conventional anti-depressants are ineffective and lead the way for translation into clinical practice.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12622000881730 . Registered on 21 June 2022.

Comparing the effects of crocin at different doses on excitability and long-term potentiation in the CA1 area, as well as the electroencephalogram responses of rats under chronic stress

Stress adversely affects the cellular and electrophysiological mechanisms of memory; however, crocin has beneficial effects on brain functions. Nonetheless, the electrophysiological effects of using this active saffron component at different doses are not yet studied in rats under chronic restraint stress. Therefore, this study compared the impact of crocin at different doses on the excitability and long-term potentiation (LTP) in the CA1 area of rats, as well as their electroencephalogram (EEG) responses, hippocampal and frontal cortical glucose levels under chronic restraint stress (an emotional stress model). Forty rats were allocated into five groups of control, sham, restraint stress (6 h/day/21 days), and two stress groups receiving intraperitoneal injections of crocin (30, 60 mg/kg/day). Besides measuring the slope and amplitude of field excitatory postsynaptic potentials (fEPSPs) in the input-output and LTP curves, the EEG waves and hippocampal and frontal cortical glucose levels were assessed in all groups. Chronic restraint stress significantly decreased the fEPSP slope and amplitude in the input-output curves and after LTP induction. Both doses of crocin (60 and particularly 30 mg/kg) significantly improved fEPSP slope and amplitude in the stressed groups. Also, stress and crocin only at a dose of 30 mg/kg altered the EEG waves. Hippocampal and frontal cortical glucose levels displayed no significant differences in the experimental groups. Crocin at doses of 60 mg/kg/day and particularly 30 mg/kg/day reversed the harmful effects of chronic restraint stress on LTP as a cellular memory-related mechanism. However, only the lower dose of crocin affected the electrical brain activity in EEG.