Infra-Low Frequency Neurofeedback

Research Papers

Endogenous Neuromodulation at Infra-Low Frequencies (2023)
by Siegfried Othmer, Ph.D. - Chief Scientist, The EEG Institute
This monograph is an augmented version of Chapter 3 in Restoring the Brain, Second Edition; Hanno Kirk, editor; Taylor and Francis (2020)

This book chapter places Infra-Low Frequency neurofeedback within the context of traditional neurofeedback and traces the history of the emergence of endogenous neuromodulation as a competent, and often preferable, alternative to standard operant conditioning. Endogenous neuromodulation offers unique advantages in training within the infra-low frequency regime, which is seen to play a key role in tonic state regulation. Endogenous neuromodulation led to the discovery of the principle of optimal response frequency (ORF) within the EEG spectral range. The ORF then became the pilot light for the exploration of the infra-low frequency regime. The method is fully described and theoretical models are proposed.

Citation
Othmer, S. (2023). Endogenous Neuromodulation at infra-low frequencies, Chapter 17, Introduction to Quantitative EEG and Neurofeedback, Third Edition, Chartier, DR, Dellinger, MB, Evans, JR, Budzynski, HK, editors, Academic Press, London, pp. 283-299 DOI: https://doi.org/10.1016/B978-0-323-89827-0.00001-2

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Infra-Low Frequency Neurofeedback: A Systematic Mixed Studies Review
by Fabian Bazzana, Sarah Finzi, Giulia Di Finzi, Fabio Veglia
This is a review of the published research literature to date on Infra-Low Frequency Neurofeedback (ILF NF), covering existing formal studies meeting certain criteria. It includes 18 papers covering endogenous neuromodulation as well as studies utilizing reward-based training in the ILF regime. Clinical conditions include depression, PTSD, ADHD, autism, eating disorders, addiction recovery, fibromyalgia, chronic pain, and post-concussion syndrome. Four neurophysiological investigations are also covered.

Some 36 papers were evaluated and eighteen made the cut on the basis of two criteria: ILF NF had to be the sole intervention, and there had to be an objective measure to assess the outcome in addition to symptom tracking.

This paper appeared as part of a Special Topics issue of the Journal Frontiers of Human Neuroscience, in which seventeen additional research studies were published. This yields a total of 53 research studies on the topic of infra-low frequency training to date (2022).

Front. Hum. Neurosci. 16:920659. doi: 10.3389/fnhum.2022.920659

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Toward a Theory of Infra-Low Frequency Neurofeedback
by Siegfried Othmer, Ph.D. - Chief Scientist, The EEG Institute
This monograph is an augmented version of Chapter 3 in Restoring the Brain, Second Edition; Hanno Kirk, editor; Taylor and Francis (2020)

Abstract
In Infra-Low Frequency Neurofeedback one is gifted with a cornucopia of compelling clinical data, along with a paucity of quantifiability and sparseness of theory for their interpretation. The real-time signal is meaningful only to the brain that produces it, and for the real-time response one is dependent on client report. The training process is entirely self referential, i.e. endogenous, operating at the limit of subtlety at which good neuro-regulation must necessarily take place. Nevertheless, clear patterns of responding have been observed. Two primary failure modes have been identified and linked to two principal protocols that are broadly impactful for the clinical population. Precision is available to us in the frequency domain, and that has yielded a basis for understanding how the different brain regions coordinate in the frequency domain. The identified pattern holds over the entire range of frequencies of therapeutic relevance. Infra-Low Frequency Neurofeedback engages with a slow control system that was first identified in animal research. This takes us to the foundations of the developmental hierarchy, and as such facilitates recovery from early childhood trauma at any time in life, as well as enabling the re-direction of developmental trajectories in infancy and early childhood.

Introduction
Infra-low frequency neurofeedback is not readily subjected to formal evaluation by way of group studies in the classic mode. Not only does the procedure have to be individualized to a degree that is likely unprecedented in clinical practice, but the training procedure has to remain adaptive throughout the training process. The multi-dimensional discovery process involved here could only flourish in the clinical realm, and ILF training will likely remain a clinical frontier. Undoubtedly, we are only at the beginning of the exploitation of this new modality.

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Evidentiary Basis for Infra-Low Frequency Neurofeedback
by Siegfried Othmer, Ph.D. - Chief Scientist, The EEG Institute
September 12, 2018

Abstract
Infra-Low Frequency Neurofeedback impinges on brain-based dysfunctions quite comprehensively, but the resulting improvements in self-regulatory competence cannot typically be captured both quantitatively and unambiguously. A measurable functional challenge is called for, and the Continuous Performance Test (CPT) offers such a challenge, one that both tests critical neuro-regulatory functions and has the benefit of broad acceptance within the neuropsychological community. A concise appraisal of results from a large database, one that extends over more than a decade and over thousands of clinical offices, is offered here as supportive testimony to the clinical effectiveness and practical utility of ILF neurofeedback in application to a wide variety of clinical conditions.

Introduction
The conventional terms of discourse in mental health are the diagnostic categories and symptom descriptors relevant to those categories. Prominent in connection with childhood issues are terms such as distractibility, impulsivity, inattention, hyperactivity, perseverative behavior, rage behavior, stimming, oppositionality, etc. With reference to neurofeedback, a new terminology is required that is descriptive of the task at hand. In neurofeedback we are engaged with the means of enhancing the brain's self-regulatory competence, which calls for us to view the brain in the perspective of a regulatory system.

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Infra-Low Frequency Neurofeedback for Optimum Performance
by Siegfried Othmer, Ph.D., and Sue Othmer,
Biofeedback, 44(2), pp. 81-89 (2016)
DOI: 10.5298/1081-5937-44.2.07

ABSTRACT
A method of non-prescriptive neurofeedback is described that is based on the brain interacting with its own tonic slow cortical potential. In the absence of any explicit guidance by the clinician, the training depends entirely on the brain's response to the unfolding signal. When this training is performed under optimal conditions in terms of placement and target frequency, there is a bias toward optimal functioning. The brain utilizes the information for its own benefit. The outcomes of the training are either comparable to or exceed expectations based on conventional EEG band-based neurofeedback. Results are shown for a cognitive skills test for an unselected clinical population.


The Growing Role of Neurofeedback in Integrative Medicine | View PDF
by Siegfried Othmer, Ph.D. and Susan F. Othmer, B.A.
Townsend Letter, November 2015, pp.67-73

ABSTRACT
We are at the threshold of revolutionary change in our approach to mental dysfunctions as they come to be seen primarily in the frame of neural network relations. To date the recovery of brain function has been approached mainly in the frame of neurochemical models, but even this principally involves neurochemistry in the service of neural communication. The medications in common use for mental dysfunctions by and large target the neuromodulator systems that regulate synaptic excitability. But there is another aspect to the problem. Information transport via the action potential mechanism is subject to tight timing constraints, and this represents a major potential failure mechanism for the brain under duress. This is a particular issue following physical or emotional trauma, or when the brain has been diverted from its proper developmental pathway early in life. In these cases there may be little or no evidence of structural injury to the brain. The deficits must lie almost entirely in the functional realm, and therefore should be accessible to a functional remedy. And yet we know that pharmacotherapy is largely ineffective in application to these conditions. The deficits are more easily understood in the bioelectrical domain of timing and frequency. And when remedies emerge based on an appeal to neural network functioning in the frequency domain, the case for a new departure in understanding mental dysfunctions is consolidated. This is where we now find ourselves.
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Endogenous Neuromodulation at Infra-Low Frequencies
by Othmer S, Othmer S, Kaiser D, Putman J

ABSTRACT
Neuromodulation in the bioelectrical domain is an attractive option for the remediation of functionally-based deficits. Most of the interest to date has focused on exogenous methods such as repetitive transcranial magnetic stimulation (rTMS), transient DC Stimulation (tDCS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS). Much less attention has been given to endogenous methods of exploiting latent brain plasticity. These have reached a level of sophistication and maturity that invites attention. Over the last seven years the domain of infra-low frequencies has been exploited productively for the enhancement of neuroregulation. The principal mechanism is putatively the re-normalization of functional connectivity of our resting state networks. The endogeneous techniques are particularly attractive for the pediatric population, where they can be utilized before dysfunctional patterns of brain behavior become consolidated and further elaborated into clinical syndromes.


A Rationale and Model for Infra-Low Frequency Neurofeedback Training
by Othmer S, PhD

ABSTRACT
We are in the midst of a scientific quest to understand the underpinnings of human behavior in the organization of our neural networks. The impact of our improved understanding is being felt both at the conceptual and the clinical level. Commonly, however, clinical developments precede an understanding of mechanisms. Such has been the case of neurofeedback, the roots of which go back some forty years. It is appropriate to assess that therapeutic approach in the light of current models of neuroregulation.

This article focuses on the relatively recent development of feedback on the dynamics of our slow cortical potentials, a therapeutic method that has shown itself to be highly effective in addressing even severe psychopathologies. This development needs to be seen in the context of the prior history of neurofeedback. It also needs to be illuminated by the latest findings on the structural and functional organization of our core regulatory networks.


Clinical Neurofeedback: Training Brain Behavior [2011 - pdf]
by Othmer S. and Othmer S., Legarda S.

ABSTRACT
The current work describes the evolution of the method of infra-low frequency brain training. To illustrate its clinical effectiveness, we report on the comprehensive recovery of a case of adult posttraumatic stress disorder (PTSD), an example of a multi-symptom complex or syndromic disorder reflecting CNS dysregulation. Many adult intractable medical conditions such as irritable bowel, migraine, and PTSD are traceable to precursor conditions that prevailed in childhood, in particular physical abuse and emotional abuse or trauma. Earlier intervention to exploit available neuroplasticity in the remediation of some of the most serious challenges facing us in pediatrics enhances the life prospects of children with respect to their risk for significant health issues later in life.


Clinical Neurofeedback: Case Studies, Proposed Mechanism, and Implications for Pediatric Neurology Practice [2011 - pdf]
by Legarda S., McMahon D., Othmer S. and Othmer S.

ABSTRACT
Trends in alternative medicine use by American health care consumers are rising substantially. Extensive literature exists reporting on the effectiveness of neurofeedback in the treatment of autism, closed head injury, insomnia, migraine, depression, attention deficit hyperactivity disorder, epilepsy, and posttraumatic stress disorder. We speculated that neurofeedback might serve as a therapeutic modality for patients with medically refractory neurological disorders and have begun referring patients to train with clinical neurofeedback practitioners. The modality is not always covered by insurance. Confident their child's medical and neurological needs would continue to be met, the parents of 3 children with epilepsy spectrum disorder decided to have their child train in the modality. The children's individual progress following neurofeedback are each presented here. A proposed mechanism and practice implications are discussed.


Infra-Low Frequency Training [pdf]
by Othmer S Ph.D., Othmer Susan

ABSTRACT
An individually optimized dynamic EEG reinforcement protocol has been recently extended to the domain of very low EEG frequencies, down to 0.01 Hz in center frequency of the reinforcement band. This represents a straight-forward extension to very low frequencies of a fairly generic training strategy that has been in productive use for many years. Improved clinical outcomes have been observed for a variety of hitherto intractable conditions, including the autistic spectrum, attachment disorder, eating disorders, and migraine conditions that have been refractory to prior neurofeedback.


Clinical Decision Making and Protocol Selection in Infra-Low Frequency (ILF) Neurofeedback Using the Othmer Method [April 8, 2011]
by Othmer S Ph.D.

ABSTRACT
Bringing neurofeedback into a mental health practice means acquiring a working model by means of which all the clinical phenomenology can be reframed in a psychophysiological perspective. Clinical decision-making then emerges largely out of that framework. As the training proceeds, clinical observations are interpreted in terms of that framework and lead to fine-tuning of the clinical strategy. There are two feedback loops here. One involves the client and the feedback signal. The other involves the client and the clinician. (Also published in NeuroConnections - Spring 2011)


Post-Traumatic Stress Disorder - The Neurofeedback Remedy [pdf]
by Othmer S Ph.D., Othmer Susan F.
Biofeedback, 37(1), 24-31 (2009), AAPB

ABSTRACT
The application of neurofeedback to post traumatic stress disorder (PTSD) in returning veterans is described herein and is illustrated with two case histories. Initially, frequency-based electroencephalogram training was employed to promote functional recovery, in the manner of the traditional sensorimotor rhythm/beta approach. An optimization procedure was employed in which the reinforcement frequency is tailored to the client on the basis of symptom response, with particular regard for the regulation of arousal. Low frequencies, down to .01 Hz, have been found especially useful in the remediation of posttraumatic stress disorder. This training was complemented with traditional alpha-theta work as pioneered at the Menninger Foundation and by Peniston.


ATP-Dependent Infra-Slow (<0.1 Hz) Oscillations in Thalamic Networks
by Lörincz ML, Geall F, Bao Y, Crunelli V, and Hughes SW

ABSTRACT
An increasing number of EEG and resting state fMRI studies in both humans and animals indicate that spontaneous low frequency fluctuations in cerebral activity at <0.1 Hz (infra-slow oscillations, ISOs) represent a fundamental component of brain functioning, being known to correlate with faster neuronal ensemble oscillations, regulate behavioural performance and influence seizure susceptibility. Although these oscillations have been commonly indicated to involve the thalamus their basic cellular mechanisms remain poorly understood. Here we show that various nuclei in the dorsal thalamus in vitro can express a robust ISO at ~0.005-0.1 Hz that is greatly facilitated by activating metabotropic glutamate receptors (mGluRs) and/or Ach receptors (AchRs).


Is Neurofeedback an Efficacious Treatment for ADHD? A Randomised Controlled Clinical Trial [abs.]
by Gevensleben H, Holl B, Albrecht B, Vogel C, Schlamp D, Kratz O, Studer P, Rothenberger A, Moll GH, Heinrich H

ABSTRACT
For children with attention deficit/hyperactivity disorder (ADHD), a reduction of inattention, impulsivity and hyperactivity by neurofeedback (NF) has been reported in several studies. But so far, unspecific training effects have not been adequately controlled for and/or studies do not provide sufficient statistical power. To overcome these methodological shortcomings we evaluated the clinical efficacy of neurofeedback in children with ADHD in a multisite randomised controlled study using a computerised attention skills training as a control condition.


Neurofeedback for Children with ADHD: A Comparison of SCP with Theta/Beta Protocols [abs.]
by Leins U, Goth G, Hinterberger T, Klinger C, Rumpf N, Strehl U

ABSTRACT
This study fills a niche in the research to date in that it compares two neurofeedback techniques that rely on very different challenges to the brain. The capacity for learned self-regulation was demonstrated once again with both techniques. Significantly, there was no difference between them in terms of cognitive and behavioral outcomes. Measured improvement in IQ was both statistically and clinically significant. Results held up over a six-month follow-up period.


Very Slow EEG Fluctuations Predict the Dynamics of Stimulus Detection and Oscillation Amplitudes in Humans [abs.]
by Monto S, Palva S, Voipio J, Matias Palva

ABSTRACT
Our ability to perceive weak signals is correlated among consecutive trials and fluctuates slowly over time. Although this "streaking effect" has been known for decades, the underlying neural network phenomena have remained largely unidentified. We examined the dynamics of human behavioral performance and its correlation with infraslow (0.01-0.1 Hz) fluctuations in ongoing brain activity. Full-band electroencephalography revealed prominent infraslow fluctuations during the execution of a somatosensory detection task.


Functionally Linked Resting-State Networks Reflect the Underlying Structural Connectivity Architecture of the Human Brain [pdf]
by Martijn P. van den Heuvel, René C.W. Mandl, Rene S. Kahn, and Hilleke E. Hulshoff Pol

ABSTRACT
During rest, multiple cortical brain regions are functionally linked forming resting-state networks. This high level of functional connectivity within resting-state networks suggests the existence of direct neuroanatomical connections between these functionally linked brain regions to facilitate the ongoing interregional neuronal communication. White matter tracts are the structural highways of our brain, enabling information to travel quickly from one brain region to another region.

Articles

The Deep Roots of Infra-Low Frequency Training
by Othmer S, PhD

ABSTRACT
On first acquaintance, infra-low frequency training requires a lot of explanation because it seems to stand apart from conventional neurofeedback. If that were really the case, however, it would likely not have emerged out of this field at all. Infra-low frequency training did not burst full-grown upon the scene like Venus out of a lotus blossom. Its roots are traceable to the standard SMR training developed by Sterman. It is instructive to review this history and to retrace the path of discovery.


Infra-Low Frequencies and Ultradian Rhythms
by Kaiser D, PhD

ABSTRACT
Ultradian rhythms are present in every aspect of biology. Ultradian means many times a day, and we have many habits that we perform regularly across the day. We eat three times a day, brush our teeth once or twice a day, take breaks periodically, and we have newer rhythms in our behavioral repertoire like checking Facebook or our email twice a day or every half-hour. Ultradian rhythms are observed in our daily behavior and in the brain. Our brain is autorhythmic and demonstrates amazing stability over a vast array of rhythms spanning multiple time frames.


Magnetoencephalography Discriminates Modality-Specific Infraslow Signals Less Than 0.1 Hz [abs.]
by Leistner S, Sander T, Wuebbeler G, Link A, Elster C, Curio G, Trahms Lutz, Mackert Bruno-Marcel

ABSTRACT
DC-magnetoencephalography (DC-MEG) technique has been refined and allows to record cortical activity in the infraslow frequency range less than 0.1 Hz noninvasively. Important questions however, remained, especially, how specific these infraslow activations can be recorded and whether different activations, for example, motor versus acoustic, can be separated.


Infra-Slow Rhythmic Oscillations of The Steady Potential of the Cerebral Cortex
by Aladjalova A

ABSTRACT not available


Neurofeedback at Infra-low Frequencies of the EEG
by Othmer S

ABSTRACT
It is time for an update on our collective experience with infra-low frequency neurofeedback training. One impetus is the continuing confusion in the rest of the field about the implications of this kind of training, both theoretically and practically. Some are still skeptical of the whole enterprise. Others are coming to terms with it, but would prefer to regard it as filling certain niches within the panoply of neurofeedback approaches. Such pigeon-holing would nicely leave unperturbed whatever has come before in terms of neurofeedback approaches and understandings. While it is probably true that no single neurofeedback technique will cover all the bases, the infra-low training gives every sign of being broadly applicable to the concerns that surface in neurofeedback offices. It's not just for PTSD and for the autism spectrum. It follows, then, that it must be folded into our thinking generally about neurofeedback and cannot be compartmentalized.


The Ongoing Saga of Infra-low Frequency Training
by Othmer S

ABSTRACT
Our infra-low frequency training is sending ripples through the field of neurofeedback because it appears to represent such a fundamental departure from prevailing models. It is at such a bifurcation point that a professional community is tested in its assumptions, in its procedures, in its processes for finding accommodation, and indeed in its humanity. Unfortunately, the field of neurofeedback already has a history of fragmentation behind it. Therefore history does not augur for a benign accommodation to our new findings. More than likely we will just be in for continuing Balkanization of our field.


Infra-low Frequency Neurofeedback Training
by Othmer S

ABSTRACT
The recent newsletter on Infra-low Frequency Training raised a number of issues within our readership and within the larger neurofeedback community. The principal issues are addressed in the following.

First of all there is the issue of how we detect infra-low frequency activity with an amplifier that "cuts off" at 0.08 Hz. The Cygnet system incorporates a single stage of high-pass filtering into its design. We did so to provide more stable and more graceful operation of the system in its most common applications. Little did we know that down the line our most common applications would extend well into the frequency range that we were cutting off with our filter.


Northeast Regional Biofeedback Society Fall Conference
by Othmer S

ABSTRACT
The program of the Northeast Regional Biofeedback Society Fall Conference, convening on the grounds of the former Women's adjunct college of Rutgers University in New Brunswick, NJ, quite possibly pointed the way to our near-term future, namely the mutual accommodation of the biofeedback and neurofeedback perspectives. The one-day conference was preceded by an all-day seminar on Heart Rate Variability (HRV) training, conducted by Paul Lehrer, Bronya and Evgeny Vaschillo, and Maria Karavidas.


Infra-Low Frequency Neurofeedback
by Othmer S

ABSTRACT
Over the last several years we have increasingly explored the low-frequency domain of the EEG for neurofeedback applications. Surprisingly to us all this has led us to the realm of infra-low frequency training, below the 0.5 Hz cutoff that is commonplace in EEG work. It is tempting to refer to this very low frequency neurofeedback as a breakthrough, but in fact this has simply been the latest iteration of a long progression from one milestone to the next in an evolution of our particular protocol-based approach. So it does not feel like a breakthrough to those who have been involved every step of the way. It only appears like a breakthrough because when considered on its own it seems like a complete negation of the standard assumptions of neurofeedback. Perhaps in consequence of that the method has already attracted the usual gallery of skeptics. The survival of this kind of skepticism at this late date reminds us that the typical understanding people have about neurofeedback is being grossly violated. A reappraisal of the usual assumptions is therefore in order.


Introduction to Infra-low Frequency Training
by Othmer S

ABSTRACT
The first convincing evidence for EEG feedback efficacy in the management of pathophysiology was with regard to generalized seizures. The early work by Sterman, Lubar, as well as the subsequent follow-up by others, therefore remains a crucial point of reference for the various feedback techniques that have built upon the early protocol of SMR reinforcement combined the theta-band and high-beta band inhibition. Remarkably, the essential features of the early approach have been retained in the various evolutionary pathways that have emanated from the early work. This essential similarity has perhaps obscured other aspects of the training approach that have changed substantially over time, the significance of which may not have been fully appreciated except in reflection. In this newsletter we consider some of these changes and their implications generally, as well as for seizure management in particular.

Presentations

2011 COSC Presentation [2011]
by Othmer S.

ABSTRACT
The occasion of Memorial Day 2011 is a good opportunity to reflect on what has been happening in the remediation of PTSD using our latest Infra-Low Frequency (ILF) neurofeedback training. The word breakthrough is over-used, but it does describe the progress that has occurred over the last several years. The most significant event over that time frame was the actual utilization of our methods on a large scale in realistic settings within the military. By now more than 350 service persons have experienced this training at Camp Pendleton, one of six military bases where this work is being conducted. In this fashion, we were able to move from a series of isolated clinical observations in our clinic to a more substantial evaluation in a real-world environment, with independent clinicians guiding the neurofeedback training on the basis of our standard introductory training course, plus the occasional consultation.

Books

Process in Brain Research - Volume 7: Slow Electrical Processes in the Brain
by Aladjalova A

ABSTRACT
Many phenomena in animal nerve tissue are accompanied by electrical processes. These processes are largely due to mechanisms of nervous activity. They provide special opportunities for studying those aspects of nervous activity which generally do not lend themselves to other research techniques.

Related Research

Pentagon's Brain-Powered Videogames Might Treat PTSD [video]
by Drummond K.

ABSTRACT
Soldiers and veterans looking to alleviate the devastating symptoms of post-traumatic stress disorder might soon have a new way to help themselves. Strangely, it involves using their gray matter to control a videogame.


Nonpharmacologic Management of Epilepsy Comorbidities [pdf]
by Stella B Legarda, MD; Susan Ford, BCIA-EEG4; Alexei Kondratyev, PhD; Karen Gale, PhD

ABSTRACT
Neurofeedback is in essence EEG operant conditioning. The individual receiving neurofeedback is given a computerized visual program to watch, the content of which is mostly driven by real-time EEG "behavior" at examiner-selected EEG frequencies. Along these lines, the individual is cued with respect to the presence of excessive excursions in EEG amplitudes that may arise from paroxysmal activity and other physiologic noncephalic factors.


Intro to the Brain [video]
DETAILS
An excerpt of a talk by Jay Gunkelman where he provides an introduction to infra-low frequency activity and a discussion of the potenial glial cell explanation for this activity.


Very Low Frequency EEG Oscillations and the Resting Brain in Young Adults: A Preliminary Study of Localisation, Stability and Association with Symptoms of Inattention [abs.]
by Helps S., James C., Debener S., Karl A., Sonuga-Barke E.J.S.

ABSTRACT
Spontaneous very low frequency oscillations (VLFO: <0.2 Hz) in functional magnetic-resonance imaging are proposed to identify a default-mode network of resting brain activity. Activity in this network has been related to lapses of attention during goal-directed tasks and may provide a basis for ADHD. This study assessed the relation between scalp-recorded EEG VLFO at rest and ADHD.


Very Slow EEG Fluctuations Predict the Dynamics of Stimulus Detection and Oscillation Amplitudes in Humans [abs.]
by Monto S, Palva S, Voipio J, Palva JM.

ABSTRACT
Our ability to perceive weak signals is correlated among consecutive trials and fluctuates slowly over time. Although this "streaking effect" has been known for decades, the underlying neural network phenomena have remained largely unidentified. We examined the dynamics of human behavioral performance and its correlation with infraslow (0.01-0.1 Hz) fluctuations in ongoing brain activity.


Evaluation of Commercially Available Electrodes and Gels for Recording of Slow EEG Potentials [pdf]
by Tallgrena P., Vanhatalo S., Kailaa K., Voipioa J.

ABSTRACT
Recent work has shown that a vast amount of information can be lost when recording EEG-signals using conventional AC-coupled (alternating current coupled; i.e. high-pass filtered) recording methods (Vanhatalo et al., 2004a). For instance, infraslow (also called ultraslow, super-slow, or multisecond) oscillations within the frequency range of 0.02-0.2 Hz are seen during nonREMsleep and they show a distinctive relationship with higher frequency EEG events (Vanhatalo et al., 2004b). Furthermore, long-lasting DC shifts are observed during awakening or falling asleep, or during changes of sleep stage (Marshall et al., 1994, 1998).