Decrease In Low-frequency Power Research Articles

Decoupling of cortical activity from behavioral state following administration of the classic psychedelic DOI

Administration or consumption of classic psychedelics (CPs) leads to profound changes in experience which are often described as highly novel and meaningful. They have shown substantial promise in treating depressive symptoms and may be therapeutic in other situations. Although research suggests that the therapeutic response is correlated with the intensity of the experience, the neural circuit basis for the alterations in experience caused by CPs requires further study. The medial prefrontal cortex (mPFC), where CPs have been shown to induce rapid, 5-HT2A receptor-dependent structural and neurophysiological changes, is believed to be a key site of action. To investigate the acute neural circuit changes induced by CPs, we recorded single neurons and local field potentials in the mPFC of freely behaving male mice after administration of the 5-HT2A/2C receptor-selective CP, 2,5-Dimethoxy-4-iodoamphetamine (DOI). We segregated recordings into active and rest periods in order to examine cortical activity during desynchronized (active) and synchronized (rest) states. We found that DOI induced a robust decrease in low frequency power when animals were at rest, attenuating the usual synchronization that occurs during less active behavioral states. DOI also increased broadband gamma power and suppressed activity in fast-spiking neurons in both active and rest periods. Together, these results suggest that the CP DOI induces persistent desynchronization in mPFC, including during rest when mPFC typically exhibits more synchronized activity. This shift in cortical dynamics may in part underlie the longer-lasting effects of CPs on plasticity, and may be critical to their therapeutic properties.

Effect of dynamic binaural beats on sleep quality: a proof-of-concept study with questionnaire and biosignals.

Binaural beat (BB) has been investigated as a potential modality to enhance sleep quality. In this study, we introduce a new form of BB, referred to as dynamic BB (DBB), which incorporates dynamically changing carrier frequency differences between the left and right ears. Specifically, the carrier frequency of the right ear varied between 100 and 103 Hz over a period, while the left ear remained fixed at 100 Hz, yielding a frequency difference range of 0 to 3 Hz. The objective of this study was to examine the effect of DBB on sleep quality. Ten healthy participants were included in a cross-over design, where they experienced both DBB and a SHAM (absence of sound) condition across two consecutive nights, with polysomnography evaluation. DBB was administrated during pre-sleep initiation, sleep onset, and transition from rapid eye movement (REM) to non-REM stage. DBB significantly reduced sleep latency compared to the SHAM condition. Electrocardiogram analysis revealed that exposure to DBB led to diminished heart rate variability during the pre-sleep initiation and sleep onset periods, accompanied by a decrease in low-frequency power of heart rate during the sleep onset period. DBB might be effective in improving sleep quality, suggesting its possible application in insomnia treatments.

Replay of Stimulus-specific Temporal Patterns during Associative Memory Formation.

Forming a memory often entails the association of recent experience with present events. This recent experience is usually an information-rich and dynamic representation of the world around us. We here show that associating a static cue with a previously shown dynamic stimulus yields a detectable, dynamic representation of this stimulus. We further implicate this representation in the decrease of low-frequency power (∼4-30 Hz) in the ongoing EEG, which is a well-known correlate of successful memory formation. The reappearance of content-specific patterns in desynchronizing brain oscillations was observed in two sensory domains, that is, in a visual condition and in an auditory condition. Together with previous results, these data suggest a mechanism that generalizes across domains and processes, in which the decrease in oscillatory power allows for the dynamic representation of information in ongoing brain oscillations.

Similar patterns of neural activity predict memory function during encoding and retrieval

Neural networks that span the medial temporal lobe (MTL), prefrontal cortex, and posterior cortical regions are essential to episodic memory function in humans. Encoding and retrieval are supported by the engagement of both distinct neural pathways across the cortex and common structures within the medial temporal lobes. However, the degree to which memory performance can be determined by neural processing that is common to encoding and retrieval remains to be determined. To identify neural signatures of successful memory function, we administered a delayed free-recall task to 187 neurosurgical patients implanted with subdural or intraparenchymal depth electrodes. We developed multivariate classifiers to identify patterns of spectral power across the brain that independently predicted successful episodic encoding and retrieval. During encoding and retrieval, patterns of increased high frequency activity in prefrontal, MTL, and inferior parietal cortices, accompanied by widespread decreases in low frequency power across the brain predicted successful memory function. Using a cross-decoding approach, we demonstrate the ability to predict memory function across distinct phases of the free-recall task. Furthermore, we demonstrate that classifiers that combine information from both encoding and retrieval states can outperform task-independent models. These findings suggest that the engagement of a core memory network during either encoding or retrieval shapes the ability to remember the past, despite distinct neural interactions that facilitate encoding and retrieval.

Intracranial Recordings of Occipital Cortex Responses to Illusory Visual Events.

Ambiguous visual stimuli elicit different perceptual interpretations over time, creating the illusion that a constant stimulus is changing. We investigate whether such spontaneous changes in visual perception involve occipital brain regions specialized for processing visual information, despite the absence of concomitant changes in stimulation. Spontaneous perceptual changes observed while viewing a binocular rivalry stimulus or an ambiguous structure-from-motion stimulus were compared with stimulus-induced perceptual changes that occurred in response to an actual stimulus change. Intracranial recordings from human occipital cortex revealed that spontaneous and stimulus-induced perceptual changes were both associated with an early transient increase in high-frequency power that was more spatially confined than a later transient decrease in low-frequency power. We suggest that the observed high-frequency and low-frequency modulations relate to initiation and maintenance of a percept, respectively. Our results are compatible with the idea that spontaneous changes in perception originate from competitive interactions within visual neural networks. Ambiguous visual stimuli elicit different perceptual interpretations over time, creating the illusion that a constant stimulus is changing. The literature on the neural correlates of conscious visual perception remains inconclusive regarding the extent to which such spontaneous changes in perception involve sensory brain regions. In an attempt to bridge the gap between existing animal and human studies, we recorded from intracranial electrodes placed on the human occipital lobe. We compared two different kinds of ambiguous stimuli, binocular rivalry and the phenomenon of ambiguous structure-from-motion, enabling generalization of our findings across different stimuli. Our results indicate that spontaneous and stimulus-induced changes in perception (i.e., "illusory" and "real" changes in the stimulus, respectively) may involve sensory regions to a similar extent.

Distinction in EEG slow oscillations between chronic mild traumatic brain injury and PTSD

Spectral information from resting state EEG is altered in acute mild traumatic brain injury (mTBI) and in disorders of consciousness, but there is disagreement about whether mTBI can elicit long term changes in the spectral profile. Even when identified, any long-term changes attributed to TBI can be confounded by psychiatric comorbidities such as PTSD, particularly for combat-related mTBI where postdeployment distress is commonplace. To address this question, we measured spectral power during the resting state in a large sample of service members and Veterans varying in mTBI history and active PTSD diagnosis but matched for having had combat blast exposure. We found that PTSD was associated with decreases in low frequency power, especially in the right temporoparietal region, while conversely, blast-related mTBI was associated with increases in low frequency power, especially in prefrontal and right temporal areas. Results support the idea that long-term neurophysiological effects of mTBI share some features with states of reduced arousal and cognitive dysfunction, suggesting a role for EEG in tracking the trajectory of recovery and persisting vulnerabilities to injury. Additionally, results suggest that EEG power reflects distinct pathophysiologies for current PTSD and chronic mTBI.

Baroreflex mechanisms in Irritable Bowel Syndrome: Part I. Traditional indices

ObjectiveThis study was conducted to present evidence of differences in autonomic regulation of cardiovascular activity and its role in the severity of specific (disease-related) and non-specific (negative affect and chronic pain-related) symptoms in individuals with Irritable Bowel Syndrome (IBS). MethodsSeventy-eight female patients with IBS and 27 healthy women age 18–62years were assessed for IBS symptoms, negative affect, and baroreceptor sensitivity (BRS), blood pressure (BP), heart rate, and heart rate variability (HRV) at rest. Direct and indirect regression effects were examined with application of the bootstrap procedure to validate findings. ResultsIBS was reliably related to lower resting BRS, higher BP, and higher negative affect compared to healthy controls. Longer disease duration (chronicity) was related to BRS decrease coupled with systolic BP increase (95% CIs=−0.14 to −0.01). Three autonomic mechanisms associated with BRS decrease were found to further regulate severity of IBS symptoms. Lower BRS was related to higher IBS severity in general if the effect was transferred through the decrease of low frequency power of HRV (e.g., 95% CIs=−0.039 to −0.001 for abdominal pain severity). However, lower BRS was related to lower IBS severity in general if the effect was transferred through diastolic BP increase (95% CIs=0.01–0.11 for abdominal pain severity). Lower BRS was related to higher abdominal pain severity coupled with high negative affect if the effect was transferred through the decrease of higher frequency power of HRV (95% CIs=−0.026 to −0.003). ConclusionsThese findings indicate that different cardiovascular mechanisms are associated with IBS development and the increase and decrease of severity of IBS symptoms. Their assessment suggests ways to personalize treatment of IBS.

Changes in heart-rate variability of survivors of nasopharyngeal cancer during Tai Chi Qigong practice.

[Purpose] To explore the changes in heart-rate variability (HRV) of survivors of nasopharyngeal cancer (NPC) before, during, and after a Tai Chi (TC) Qigong exercise. [Subjects and Methods] Eleven survivors of NPC participated voluntarily in the study. The heart rate of each participant was measured continuously for 1 minute before the TC Qigong intervention, during the 5-minute TC Qigong intervention, and for 1 minute after the intervention, using a Polar heart-rate monitor. Spectral HRV was expressed in terms of normalised low frequency (LF) power, normalised high frequency (HF) power, and the low frequency/high frequency (LF/HF) power ratio. [Results] Both the LF-power and the HF-power components had significant time effects. However, the time effect of the LF/HF power ratio was not significant. Post hoc contrast analysis revealed a significant decrease in LF power and a concomitant increase in HF power during the 4th minute and 5th minute of the TC Qigong exercise. [Conclusion] Five minutes of TC Qigong exercise was found to improve HRV by increasing HF power and decreasing LF power, but these effects were transient. TC Qigong might be an appropriate exercise for improving the ANS function and psychological and cardiac health of survivors of NPC.

Changes in Autonomic Control of Heart Associated with Classical Appetitive Conditioning in Rats

The aim of this study was to examine the changes in autonomic control of the heart associated with classical appetitive conditioning in rats. We trained rats to learn that a movement into a test chamber was followed by delivery of reward (contextual conditioning) and performed power spectral analysis of heart rate variability from electrocardiograms recorded using the telemetry system. We investigated the sympathovagal balance of autonomic regulation of the heart in response to not only the conditioned stimulus (the movement into the test chamber), but also the unconditioned stimulus (reward), and compared the results of these two kinds of emotional states; it might be considered that "the reward-expecting state" is evoked by the conditioned stimulus and "the reward-receiving state" is evoked by the unconditioned stimulus in rats. The reward-expecting state resulted in a significant increase in both low frequency (LF) power and high frequency (HF) power with no change in heart rate (HR) and LF/HF ratio, indicating that both sympathetic and parasympathetic activity increased with no change in sympathovagal balance. The reward-receiving state resulted in a significant increase in HR and a significant decrease in LF power, HF power, and LF/HF ratio, indicating that both sympathetic and parasympathetic activity decreased with predominance in the parasympathetic activity. These results suggest that the method performed in our present study might be useful for distinguishing between two different emotional states evoked by classical appetitive conditioning in rats.

Relationship between electroencephalogram slow-wave magnitude and heart rate variability during sleep in rats

To explore whether depth of sleep is related to changes in autonomic control in rats, continuous power-spectral analysis of electroencephalogram (EEG) and heart rate variability (HRV) was performed in unanesthetized rats during normal daytime sleep. Quiet sleep (QS) was associated with an increase in high-frequency power of HRV (0.6–2.4 Hz, HF) but a decrease in low-frequency power (0.06–0.6 Hz) to HF ratio (LF/HF) compared with awakening. During QS, LF/HF was significantly and negatively correlated with delta power of EEG (0.5–4.0 Hz), whereas mean R-R interval and HF were not. As in humans, cardiac sympathetic regulation in rats is negatively related to the depth of sleep during QS, although vagal regulation is not. Our methodology offers a parallel way of studying the interaction between cerebral cortical and autonomic functions in rats.

Relationship between electroencephalogram slow-wave magnitude and heart rate variability during sleep in humans

To explore whether depth of sleep is related to changes in autonomic control, continuous power-spectral analysis of the electroencephalogram (EEG) and heart rate variability (HRV) was performed in ten normal subjects during nocturnal sleep. Quiet sleep (QS) was associated with an increase in high-frequency power (HF) of HRV (0.15–0.4 Hz) but a decrease in low-frequency power (LF) (0.04–0.15 Hz) to HF ratio (LF/HF) compared with awakening. During QS, LF/HF was significantly and negatively correlated with delta power of EEG (0.5–4.0 Hz), whereas mean R–R interval and HF were not. We conclude that during QS, cardiac sympathetic regulation is negatively related to the depth of sleep, although vagal regulation is not. Our methodology offers a quantitative analysis to study the interaction between cerebral cortical and autonomic functions.

Neurally mediated cardiac syncope: autonomic modulation after normal saline infusion

OBJECTIVESThis study assessed the heart variability response to orthostatic stress during tilt table testing before and after normal saline administration.BACKGROUNDThe efficacy of sodium chloride and mineralocortoid in the treatment of neurally mediated cardiac syncope is attributed to intravascular volume expansion; however, their modulation of autonomic nervous system activity has not been evaluated.METHODSHeart rate variability analysis was performed on 12 adolescents with a history of syncope or presyncope (mean age 15.2 ± 0.7 years) during tilt table testing. Subjects were upright 80° for 30 min or until syncope. After normal saline administration, the patient was returned upright for 30 min. Heart rate variability analysis data were analyzed by an autoregression model (Burg method).RESULTSAll subjects reproducibly developed syncope during control tilt table testing; median time to syncope was 9.4 ± 2.1 min. After normal saline infusion, none of the subjects developed syncope after 30 min upright. In the control tilt, there was an initial increase followed by a progressive decrease in low frequency power until syncope. Repeat tilt after normal saline administration demonstrates that low frequency power increased but the magnitude of initial change was blunted when compared with control. In addition, low frequency power increased during normal saline tilt sequence compared with the control tilt, during which it decreased.CONCLUSIONSNormal saline blunted low frequency power stimulation and prevented paradoxical low frequency power (sympathetic) withdrawal. Increasing intravascular volume with normal saline alters autonomic responses that may trigger neurally mediated syncope reflexes.