Infraslow closed-loop brain training for anxiety and depression (ISAD): a protocol for a randomized, double-blind, sham-controlled pilot trial in adult females with internalizing disorders.

BACKGROUND: The core intrinsic connectivity networks (core-ICNs), encompassing the default-mode network (DMN), salience network (SN) and central executive network (CEN), have been shown to be dysfunctional in individuals with internalizing disorders (IDs, e.g. major depressive disorder, MDD; generalized anxiety disorder, GAD; social anxiety disorder, SOC). As such, source-localized, closed-loop brain training of electrophysiological signals, also known as standardized low-resolution electromagnetic tomography (sLORETA) neurofeedback (NFB), targeting key cortical nodes within these networks has the potential to reduce symptoms associated with IDs and restore normal core ICN function. We intend to conduct a randomized, double-blind (participant and assessor), sham-controlled, parallel-group (3-arm) trial of sLORETA infraslow (<0.1 Hz) fluctuation neurofeedback (sLORETA ISF-NFB) 3 times per week over 4 weeks in participants (n=60) with IDs. Our primary objectives will be to examine patient-reported outcomes (PROs) and neurophysiological measures to (1) compare the potential effects of sham ISF-NFB to either genuine 1-region ISF-NFB or genuine 2-region ISF-NFB, and (2) assess for potential associations between changes in PRO scores and modifications of electroencephalographic (EEG) activity/connectivity within/between the trained regions of interest (ROIs). As part of an exploratory analysis, we will investigate the effects of additional training sessions and the potential for the potentiation of the effects over time. METHODS: We will randomly assign participants who meet the criteria for MDD, GAD, and/or SOC per the MINI (Mini International Neuropsychiatric Interview for DSM-5) to one of three groups: (1) 12 sessions of posterior cingulate cortex (PCC) ISF-NFB up-training (n=15), (2) 12 sessions of concurrent PCC ISF up-training and dorsal anterior cingulate cortex (dACC) ISF-NFB down-training (n=15), or (3) 6 sessions of yoked-sham training followed by 6 sessions genuine ISF-NFB (n=30). Transdiagnostic PROs (Hospital Anxiety and Depression Scale, HADS; Inventory of Depression and Anxiety Symptoms - Second Version, IDAS-II; Multidimensional Emotional Disorder Inventory, MEDI; Intolerance of Uncertainty Scale - Short Form, IUS-12; Repetitive Thinking Questionnaire, RTQ-10) as well as resting-state neurophysiological measures (full-band EEG and ECG) will be collected from all subjects during two baseline sessions (approximately 1 week apart) then at post 6 sessions, post 12 sessions, and follow-up (1 month later). We will employ Bayesian methods in R and advanced source-localisation software (i.e. exact low-resolution brain electromagnetic tomography; eLORETA) in our analysis. DISCUSSION: This protocol will outline the rationale and research methodology for a clinical pilot trial of sLORETA ISF-NFB targeting key nodes within the core-ICNs in a female ID population with the primary aims being to assess its potential efficacy via transdiagnostic PROs and relevant neurophysiological measures. TRIAL REGISTRATION: Our study was prospectively registered with the Australia New Zealand Clinical Trials Registry (ANZCTR; Trial ID: ACTRN12619001428156). Registered on October 15, 2019.

Prefrontal and hippocampal theta rhythm show anxiolytic-like changes during periaqueductal-elicited "panic" in rats.

Anxiety and panic are both elicited by threat and co-occur clinically. But, at the neural level, anxiety appears to inhibit the generation of panic; and vice versa. Anxiety and panic are thought to engage more anterior (a) and mid-posterior (m) parts of the periaqueductal gray (PAG), respectively. Anxiety also engages the hippocampus and medial prefrontal cortex. Here, we tested if mPAG but not aPAG stimulation would suppress prefrontal and hippocampal theta rhythm as do anxiolytic drugs. Twelve male rats with implanted electrodes were stimulated alternately (30 s interval) in the left PAG or right reticular formation (reticularis pontis oralis [RPO]-as a positive control) with recording in the left prelimbic cortex and left and right hippocampus. PAG stimulation was set to produce freezing and RPO to produce 7-8 Hz theta rhythm before tests lasting 10 min on each of 5 days. mPAG stimulation decreased, and aPAG increased, theta power at all sites during elicited freezing. mPAG, but not aPAG, stimulation decreased prefrontal theta frequency. Stimulation did not substantially change circuit dynamics (pairwise phase consistency and partial directed coherence). Together with previous reports, our data suggest that panic- and anxiety-control systems are mutually inhibitory, and neural separation of anxiety and panic extends down to the aPAG and mPAG, respectively. Our findings are consistent with recent proposals that fear and anxiety are controlled by parallel neural hierarchies extending from PAG to the prefrontal cortex.

Dynamic interaction between hippocampus, orbitofrontal cortex, and subthalamic nucleus during goal conflict in the stop signal task in rats.

Action stopping depends on at least two (fast, slow) frontal circuits depending on the urgency of execution of the 'go' response. Human EEG suggests a third (even slower, limbic) circuit that activates frontal areas at frequencies typical of 'hippocampal theta'. Here we test in male rats whether stop-go conflict engages the hippocampus and so may send theta-modulated information via the frontal cortex to the subthalamic nucleus. We recorded from multi-electrode arrays in the hippocampus, orbitofrontal cortex, and subthalamus in 5 male Long Evans rats performing a stop signal task and, as in previous human experiments, assessed stop-signal specific power for effects of goal conflict. Conflict increased 11-12 Hz theta power modestly in all three structures but with the largest increase in power being at 5 Hz in the frontal cortex but not the hippocampus. There was increased conflict-related coherence in all circuits in the range 5-8 Hz and particularly at 5-6 Hz. Increased coherence coupled with an increase in conflict-induced low frequency power in the frontal cortex may reflect communication with the hippocampus. The data are consistent with a third limbic circuit that can generate stopping when go responses are particularly slow (as, e.g., in a go/no go task). [199 words; 200 max].

Sharp Tuning of Head Direction and Angular Head Velocity Cells in the Somatosensory Cortex.

Head direction (HD) cells form a fundamental component in the brain's spatial navigation system and are intricately linked to spatial memory and cognition. Although HD cells have been shown to act as an internal neuronal compass in various cortical and subcortical regions, the neural substrate of HD cells is incompletely understood. It is reported that HD cells in the somatosensory cortex comprise regular-spiking (RS, putative excitatory) and fast-spiking (FS, putative inhibitory) neurons. Surprisingly, somatosensory FS HD cells fire in bursts and display much sharper head-directionality than RS HD cells. These FS HD cells are nonconjunctive, rarely theta rhythmic, sparsely connected and enriched in layer 5. Moreover, sharply tuned FS HD cells, in contrast with RS HD cells, maintain stable tuning in darkness; FS HD cells' coexistence with RS HD cells and angular head velocity (AHV) cells in a layer-specific fashion through the somatosensory cortex presents a previously unreported configuration of spatial representation in the neocortex. Together, these findings challenge the notion that FS interneurons are weakly tuned to sensory stimuli, and offer a local circuit organization relevant to the generation and transmission of HD signaling in the brain.

Speed modulation of hippocampal theta frequency and amplitude predicts water maze learning.

Theta oscillations in the hippocampus have many behavioral correlates, with the magnitude and vigor of ongoing movement being the most salient. Many consider correlates of locomotion with hippocampal theta to be a confound in delineating theta contributions to cognitive processes. Theory and empirical experiments suggest theta-movement relationships are important if spatial navigation is to support higher cognitive processes. In the current study, we tested if variations in speed modulation of hippocampal theta can predict spatial learning rates in the water maze. Using multi-step regression, we find that the magnitude and robustness of hippocampal theta frequency versus speed scaling can predict water maze learning rates. Using a generalized linear model, we also demonstrate that speed and water maze learning are the best predictors of hippocampal theta frequency and amplitude. Our findings suggest movement-speed correlations with hippocampal theta frequency may be actively used in spatial learning.

Mixed Effects of Low-dose Ethanol on Cortical and Hippocampal Theta Oscillations.

Ethanol is one of the most widely used drugs - with many psychoactive effects, including anxiolysis. The deleterious effects on brain function and general health of chronic and high-level ethanol use are well-studied. However, the neurophysiology of acute low dose ethanol has not been systematically investigated. Here, we examined the effects of low dose (0.25 and 0.5 g/kg) ethanol on midline (prefrontal, cingulate and retrosplenial) neocortical and hippocampal theta oscillations in freely moving rats. We also tested low dose ethanol on reticular-elicited and running-elicited hippocampal theta frequency and assessed the linear relationship of theta frequency to stimulation intensity and running speed, respectively. Low dose ethanol had mixed effects on neocortical theta oscillations. It most reliably reduced theta frequency, produced a weak inverted-U effect on theta power, and had no detectable effect on cortico-hippocampal theta coherence. Ethanol dose-dependently decreased the y-intercept of the speed-theta frequency function without affecting the slope, but decreased the slope of the stimulation intensity-theta frequency function without affecting the y-intercept; thus decreasing theta frequency in both cases. We conclude low dose ethanol has weak but detectable effects on neocortical and hippocampal theta oscillations. These effects may underlie positive cognitive and behavioural outcomes reported in the literature using low dose ethanol. The double dissociation of slope and y-intercept specific changes relating to different methods of hippocampal theta elicitation presents the potential to probe multiple mechanisms contributing to anxiolytic effects on theta and so hippocampal function.

A Critical Assessment of Directed Connectivity Estimates with Artificially Imposed Causality in the Supramammillary-Septo-Hippocampal Circuit.

Algorithms for estimating directed connectivity have become indispensable to further understand the neurodynamics between functionally coupled brain areas. The evaluation of directed connectivity on the propagation of brain activity has largely been based on simulated data or toy models, where various hidden properties of neurophysiological data may not be fully recapitulated. In this study, directionality was unequivocally manipulated in the freely moving rat in a unique dataset, where normal oscillatory interactions between the supramammillary nucleus (SuM) and hippocampus (HPC) were attenuated by temporary medial septal (MS) inactivation, and replaced by electrical stimulation of the fornix to evaluate the performance of several directed connectivity assessment methods. The directed transfer function, partial directed coherence, directed coherence, pair-wise Geweke-Granger causality, phase slope index, and phase transfer entropy, all found SuM to HPC theta propagation when the MS is inactivated, and HPC activity was driven by peaks of simultaneously recorded SuM theta. As expected from theoretical expectations and simulated data, signal features including coupling strength, signal-to-noise ratio, and stationarity all weakly affected directed connectivity measures. We conclude that all the examined directed connectivity estimates correctly identify artificially imposed uni-directionality of brain oscillations in freely moving animals. Non-auto-regressive modeling based methods appear to be the most robust, and are least affected by inherent features in data such as signal-to-noise ratio and stationarity.

Bi-Directional Theta Modulation between the Septo-Hippocampal System and the Mammillary Area in Free-Moving Rats.

Hippocampal (HPC) theta oscillations have long been linked to various functions of the brain. Many cortical and subcortical areas that also exhibit theta oscillations have been linked to functional circuits with the hippocampus on the basis of coupled activities at theta frequencies. We examine, in freely moving rats, the characteristics of diencephalic theta local field potentials (LFPs) recorded in the supramammillary/mammillary (SuM/MM) areas that are bi-directionally connected to the HPC through the septal complex. Using partial directed coherence (PDC), we find support for previous suggestions that SuM modulates HPC theta at higher frequencies. We find weak separation of SuM and MM by dominant theta frequency recorded locally. Contrary to oscillatory cell activities under anesthesia where SuM is insensitive, but MM is sensitive to medial septal (MS) inactivation, theta LFPs persisted and became indistinguishable after MS-inactivation. However, MS-inactivation attenuated SuM/MM theta power, while increasing the frequency of SuM/MM theta. MS-inactivation also reduced root mean squared power in both HPC and SuM/MM equally, but reduced theta power differentially in the time domain. We provide converging evidence that SuM is preferentially involved in coding HPC theta at higher frequencies, and that the MS-HPC circuit normally imposes a frequency-limiting modulation over the SuM/MM area as suggested by cell-based recordings in anesthetized animals. In addition, we provide evidence that the postulated SuM-MS-HPC-MM circuit is under complex bi-directional control, rather than SuM and MM having roles as unidirectional relays in the network.

Behavioral significance of hippocampal θ oscillations: looking elsewhere to find the right answers.

The function of hippocampal theta oscillations has been subjected to constant speculation. Dynamic coupling of theta field potentials and spiking activity between the hippocampus and extra-hippocampal structures emphasizes the importance of theta-frequency oscillations in global spike-timing precision in the brain. Recent advances in understanding theta coupling between distant brain structures are discussed and explored in this article.

Functional MRI response and correlated electrophysiological changes during posterior hypothalamic nucleus deep brain stimulation.

Identification of active networks involved in behavior is central to understanding brain function as an emergent property. Functional magnetic resonance imaging (fMRI) allows the identification of areas with increased or decreased activity, but the cellular correlates to changes in fMRI response is still controversial. Deep brain stimulation of the posterior hypothalamic nucleus (PH) is known to facilitate locomotor behaviors and rescue locomotion in rodent models of parkinsonian akinesia by an unknown mechanism. Here, we performed 9.4 T fMRI during deep brain stimulation of PH in the anesthetized rat as a model system to explore the network substrates for its behavioral consequences. In addition, multi-unit and field potential recordings were made to examine the physiological correlates to changes in fMRI response. The most robust and reliable MR signal increases were observed in the somatosensory and motor cortices, with minor limbic and sparse thalamic activation. Electrophysiological experiments demonstrated that increased fMRI response in the neocortex corresponds to general increases in spiking activity, decreased slow oscillations and increased delta band activity. Forelimb movements evoked by intracortical microstimulation had reduced thresholds and larger representational (motor map) areas during and following PH stimulation. These findings identify the sensorimotor cortices as major contributors for behavioral effects of PH stimulation, and that coincident increase in spiking, synaptic activity and MR signal reflect functional facilitation of neocortical output.

Minimal driving of hippocampal theta by the supramammillary nucleus during water maze learning.

Previous studies have shown only modest effects of supramammillary nucleus (SuM) dysfunction on theta frequency and learning in the water maze (WM), with larger effects in other tasks. However, theta recorded from SuM, and used to trigger the production of theta-like oscillations in the hippocampus, produced reversal of the deficit in WM learning produced by theta blocking. We explored this apparent inconsistency by analyzing the relationship between SuM and hippocampal theta in the control group of this theta-blocking experiment using coherence, phase analysis, and the directed transfer function. We found little evidence of an influence of SuM on the hippocampus in the bulk of WM learning-with some possibility of SuM becoming involved briefly later in learning. A learning-related increase in coherence was observed in conjunction with gradual phase reorganization of hippocampal theta in relation to SuM theta. This change in phase dynamics between the two structures was also correlated with a relative increase of the estimated direction of theta propagation from the SuM to the hippocampus. These results are consistent with the previous weak effects of SuM lesions and suggest that the use of SuM as a source to trigger hippocampal theta and recover function is likely to be due to coherence between SuM and some other structure that normally controls hippocampal theta during WM learning.

Coupling of mesoscopic brain oscillations: recent advances in analytical and theoretical perspectives.

Oscillatory brain activities have been traditionally studied in the context of how oscillations at a single frequency recorded from a single area could reveal functional insights. Recent advances in methodology used in signal analysis have revealed that cross-frequency coupling, within or between functional related areas, is more informative in determining the possible roles played by brain oscillations. In this review, we begin by describing the cellular basis of oscillatory field potentials and its theorized as well as demonstrated role in brain function. The recent development of mathematical tools that allow the investigation of cross-frequency and cross-area oscillation coupling will be presented and discussed in the context of recent advances in oscillation research based on animal data. Particularly, some pitfalls and caveats of methods currently available are discussed. Data generated from the application of examined techniques are integrated back into the theoretical framework regarding the functional role of brain oscillations. We suggest that the coupling of oscillatory activities at different frequencies between brain regions is crucial for understanding the brain from a functional ensemble perspective. Effort should be directed to elucidate how cross-frequency and area coupling are modulated and controlled. To achieve this, only the correct application of analytical tools may shed light on the intricacies of information representation, generation, binding, encoding, storage and retrieval in the brain.

Coupling of theta oscillations between anterior and posterior midline cortex and with the hippocampus in freely behaving rats.

Theta oscillations in the hippocampus support cognitive processing. Theta-range rhythmicity has also been reported in frontal and posterior cortical areas--where it tends to show consistent phase-relations with hippocampal rhythmicity. Theta-range rhythmicity may, then, be important for cortico-cortical and/or cortico-hippocampal interactions. Here, we surveyed the rat frontal and posterior midline cortices for theta-related oscillations and examined their relationships with hippocampal activity in freely moving rats. Variation in electroencephalography across 4 general classes of spontaneous behavior demonstrated different profiles of theta-like activities through the rat midline cortices. Analysis of cortico-cortical and cortico-hippocampal coherences showed distinct, behavior-dependent, couplings of theta and delta oscillations. Increased theta coherence between structures was most obvious during nonautomatic behaviors and least during immobility or grooming. Extensive coupling of theta oscillations throughout the rat midline cortices and hippocampus occurred during rearing, and exploratory behavior. Such increases in coherence could reflect binding of cortico-hippocampal pathways into temporary functional units by behavioral demands. Extensive coupling of frontal delta, which lacked coherence with posterior areas (including the hippocampus), suggests that different frequencies of rhythmicity may act to bind groups of structures into different functional circuits on different occasions.

High frequency stimulation of the posterior hypothalamic nucleus restores movement and reinstates hippocampal-striatal theta coherence following haloperidol-induced catalepsy.

Deep brain stimulation (DBS) of the subthalamic nucleus has been used extensively in the treatment of Parkinson's disease. However, the efficacy of such treatments on bradykinesia/akinesia remains low. DBS of the posterior hypothalamic nucleus (PH) elicits spontaneous, non-stereotypical motor behaviours. We tested the hypothesis that PH stimulation could restore movement in animals made cataleptic by the D(2) receptor antagonist haloperidol. We further hypothesized that hippocampal-striatal neural synchrony may be important in the organization of motor behaviours. Animals chronically implanted with hippocampal and striatal recording electrodes and PH stimulating electrode were tested in open field, catalepsy and active avoidance paradigms. The degree of hippocampal-striatal theta (5-10 Hz) field coherence was assessed during baseline avoidance testing and following the administration of haloperidol. Haloperidol abolished movement in open field and active avoidance tasks and increased the latency to respond in the catalepsy test. Stimulation of the PH under haloperidol reversed catalepsy. Hippocampal-striatal theta coherence was high throughout the active avoidance task in control experiments but was greatly reduced under haloperidol. PH stimulation was able to reinstate the hippocampal-striatal theta coherence while restoring task-related behaviours. These results support the hypothesis that DBS of the PH could restore motor behaviours in rats made cataleptic with haloperidol, thus providing strong support for the PH as a promising candidate for DBS in the treatment of Parkinson's disease. Furthermore, the results support the view that hippocampal-striatal theta coherence may be important for the planning and execution of goal-oriented behaviors.