Q-Pro

Human Brain Institute

Russia-Switzerland-USA

1.  Personal and clinical data –Questionnaire[1].

2.  Description of the procedure of EEG recording and analysis.

EEG was recorded by means of the Mitsar (Mitsar, Ltd.) amplifier[3] from 19 electrodes (Fp1, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, O2 sites in the International 10-20 system) with 250 Hz sampling rate in 0.3 – 70 Hz frequency range in the following conditions:  1) eyes opened (EO) – at least 3 minutes, 2) eyes closed (EC) – at least 3 minutes, and 3) a modification of GO/NOO task (20 minutes).

The task consisted of 400 trials presenting to a subject every 3 seconds.  In the task we selected four categories of stimuli: 1) 20 different images of animals –referred to later as A, 2) 20 different images of plants - P, 3) 20 different images of humans presented together with an artificial sound - HS[4].  Trials consisted of presentation of a par of stimuli with interstimulus interval of 1.1 sec.  Four categories of trials were selected: A-A, A-P, P-P, and P-HS.  The trials were grouped into four sessions with one hundred trials each.  In each session a unique set of five A stimuli, five P and five HS stimuli was selected.  Each session consisted of a pseudo-random presentation of 100 pairs of stimuli with equal probability for each category and each stimulus. 

The data were stored on the hard disk in the linked ears reference montage and processed offline by means of WinEEG software.  The software is based on the 30 years experience obtained in the laboratory at the Institute of the Human Brain of Russian Academy of Sciences (director Prof. Dr. Juri Kropotov).

Absolute and relative magnitude spectra and coherences in all conditions computed and compared with the corresponding parameters from the Human Brain Institute (HBI) normative database.  The normative database includes data of 1000 healthy people of 7-89 years old age.  EEG was recorded in Chur, Switzerland (under supervision of Dr. Andreas Mueller) in the Institute of the Human Brain, St. Petersburg, Russia (under supervision of Prof., Dr. Juri Kropotov).

Patient’s event related potentials are subjected to spatial filtration.  The spatial filters are computed on the basis of Independent Component Analysis preformed with the whole set of ERPs in healthy individuals.  The extracted components are further compared with the mean values averaged over the corresponding age group.  Each component corresponds to a specific psychological operation.

3.  Automated spike detection.

The method automated spike detection is based on temporal parameters of spikes as well on spatial location of the corresponding spike dipole[5]. The amplitude-temporal parameters have defined on the basis of comparison spike detection by the program and by experienced experts on the data base of more than 300 EEG recordings in epileptic patients.  There are three characteristics that define a spike or a sharp wave in EEG.  They are paroxysmal in character, with a high degree of sharpness and a short duration.  These parameters are presented in Fig[6].

The relative residual energy for dipole approximation of the detected spike is chosen less than 0.2.

For this client the automatic spike detection was performed on EEG in the common average montage for both eyes open and eyes closed conditions.  In total 266 spikes were detected and averaged.  The waveform, topography and dipole approximation of the averaged spikes are presented below.

Note that spiky alpha activity is generated in the left occipital area.

4.  Eyes Open – background EEG rhythms and activities (page1)

Two fragments of EEG recorded in Eyes Opened (EO) condition in a reference-free montage - “weighted average according to Lemos” are presented below.  This montage will be further referred to as the data base montage.

Scale: 50 mcV/cm, speed – 30mm/sec, time constant – 0.3 sec, low frequency filter – 30 Hz. Vertical and horizontal eye movement artifact correction was done by means of Independent Component Analysis (ICA) (see Appendix 2)

4.  Eyes Open – background EEG rhythms and activities (page 2)

Spectra (EEG power vs. EEG frequency) in Eyes Open condition

for all 19 electrodes in the database montage are presented below.  The spectra are computed as follows[7]:  1) The interval in EO condition is divided into equal parts (epochs).  The length of an epoch is 4 s. Overlapping of the epochs is set to 50% so that the first 50% of each epoch overlaps the final 50% of the next epoch.  2)  To suppress energy infiltration through boundaries of epochs maxima, each epoch is filtered by the Hanning time window.  3) The power spectra(periodogram) are computed by means of "fast Fourier transformation" (FFT) algorithm. 4) Finally the averaged (over time of recording) spectra are calculated for each EEG channel separately.EEG rhythms are expressed in form of spectra peaks.  In this client the following rhythms can be separated (topographies and frequencies are depicted at the bottom).

4.  Eyes Open – background EEG rhythms and activities (page 3)

Comparison EEG spectra in eyes open condition with the normative database.

The comparison was made for absolute and relative magnitudes on EEG spectrums.

Relative amplitude was computed as a ratio of the EEG amplitude in the corresponding frequency to the EEG amplitude averaged over 3-30 Hz[8] range.

The bins with statistically significant (t-test) differences are marked by bars at the bottom of each curve.  The smallest ones correspond to p<0.05 (z-score >2), the largest ones - to p<0.001 (z-score>2.6), the medium ones – to p<0.01 (z-score>3).  Topographies of significant deviations from normality are presented at the bottom.

Note: excess of the left temporal-occipital alpha activity both for absolute and relative values.

Absolute magnitude.

Relative magnitude.

4.  Eyes Open – background EEG rhythms and activities (page 4)

The map of theta/beta ratio (Theta=4-8 Hz.  Beta – 13-21 Hz) is presented below (at the left). 

For comparison, at the right the corresponding map for a group of healthy subjects is presented.

Theta beta ratio is called “inattention index” because it negatively correlates with age and positively correlates with errors in continuous performance tasks (such as TOVA – Test for variances of attention or IVA ).  In ADHD patients this index is elevated in comparison to norms[9].

Note NO significant increase of this index at Cz in this patient in comparison to norms.

4.  Eyes Open – background EEG rhythms and activities (page 5)

Asymmetry maps of power spectra in eyes open conditions for 1 Hz bands.

Note that an asymmetry higher than 50% may be a sign of abnormality[10].

4.  Eyes Open – background EEG rhythms and activities (page 6)

Diagrams of excessive (in red) or reduced (in blue) coherence in sagital (top) and coronal (bottom) planes.

Note reduction of coherence in alpha band in frontal areas in coronal planes and between central-parietal areas in sagital planes.

5.  Eyes Closed – background EEG rhythms and activities (page1)

Two fragments of EEG recorded in Eyes Closed (EC) condition

in the data base montage.

Scale: 50 mcV/sm, speed – 30mm/sec, time constant – 0.3 sec, low frequency filter – 30 Hz. Vertical and horizontal eye movement artifact correction was done by means of Independent Component Analysis (ICA) (see Appendix 2)

5.  Eyes Closed – background EEG rhythms and activities (page 2)

Spectra (EEG power vs. EEG frequency) in Eyes Closed condition for all 19 electrodes in the database montage are presented below.  EEG rhythms are expressed in forms of peaks on spectra. 

In this client the following rhythms can be separated (topographies and frequencies are depicted at the bottom).

5.  Eyes Closed – background EEG rhythms and activities (page 3)

Difference spectra Eyes closed – Eyes open.

The results of subtraction spectrograms in Eyes Open condition from those in Eyes Closed condition are presented below.

Note that opening eyes produces an increase of alpha activity at 9.3 Hz at the occipital areas.  This rhythm dominates on the spectra[11] and is named the dominant alpha rhythm.

5.  Eyes Closed – background EEG rhythms and activities (page 4)

Comparison EEG spectra in eyes closed condition with the normative database.

The comparison was made for absolute and relative amplitudes on EEG spectrums.

Relative amplitude was computed as a ratio of the EEG amplitude in the corresponding frequency

Absolute magnitude.

Relative magnitude.

5.  Eyes Closed – background EEG rhythms and activities (page 5)

Asymmetry maps of power spectra in eyes closed conditions for 1 Hz bands.

Note that an asymmetry higher than 50% may be a sign of abnormality[12].

6. GO/NOGO task –EEG rhythms and activities (page 1)

Spectra (EEG power vs. EEG frequency) in GO/NOGO task condition for all 19 electrodes in the database montage are presented below.  EEG rhythms are expressed in forms of peaks on spectra.  In this client the following rhythms can be identified:

6. GO/NOGO task –EEG rhythms and activities (page 2)

Comparison EEG spectra in GO/NOGO task condition with the normative database.

The comparison was made for absolute and relative magnitudes on EEG spectrums.

Absolute magnitude.

Relative magnitude.

(page 1).

Behavioral data (omission and commission errors, reaction times and variances) are presented below.

Note: too many omission errors.

      (page 2).

ERPs in the GONOGO task computed for GO, NOGO stimuli and ERP differences (NOGO-GO).  GO stimuli – green, NOGO stimuli (animal-plant) – red, NOGO-GO – blue.  Bars under ERPs represent levels of statistical significance of deviation from the pre-stimulus interval (small bar – p<0.05, medium – p<0.01, big – p<0.001).

Note: below the head maps show the ERPs topographies taken at the maximums of each ERPs and ERPs differences.

7. Behavioral data and cognitive Event Related Potentials (ERPs) in GO/NOGO task

      (page 3).

ICA analysis of ERPs in GO/NOGO task – comparison with the normative data base.

Table of Normal Components.

The client’s components (green) in comparison to the normative components (red) and difference components (Client – Norm) are presented below.

Note strong deviations in sensory visual information processing component. 

8.  Event Related De/Synchronization - ERD/ERS (pages 1 and 2).

The results of wavelet analysis for GO/NOGO task are presented below.

The wavelet analysis provides the Power-Time-Frequency representations of EEG responses to GO and NOGO trials separately. 

X-axis – time (Zero corresponds to the first stimulus onset).  Y-axis – EEG frequency (from 4 to 40 Hz).  Color reflects increase (red) or decrease (blue) of EEG power in the corresponding frequency band.

The main components in this client are:

For GO+NOGO stimuli:

 9.  Conclusion:

I.  Spontaneous EEG abnormality.

Spectrograms of spontaneous EEG in all conditions (Eyes Open, Eyes Closed, GO/NOGO task) persistently show an abnormality manifested in:

1)      increase of occipital alpha.

2)      Spiky morphology in the occipital areas.

II.  ERPs abnormalities.

ERPs in GONOGO task show strong deviations from normality in sensory-related (not executive) components indicating the hyper-sensitivity of the ventral visual pathway.

III.  Event-related desynchronization (ERD) abnormalities.

ERD in GO/NOGO task show strong alpha desynchronization at the occipital areas.

IV.  Brain dysfunction associated with EEG abnormality.

These QEEG abnormalities are associated with the occipital lobe dysregulation.

This dysregulation is manifested in idling of the occipital area and delay of the sensory component in this area.  This pattern is seen in a dyslexic group.

10.  Recommendations for therapy.

a) Neurofeedback protocol.

Recommendations are made on the basis of the bulldozer principle of neurofeedback and on the client’s complaints.

In the case of memory problems the protocol might be as follows:

Inhibiting (training DOWN) alpha activity at the left occipital (O1).  The map of deviations from normality at 9 Hz in EEG power in Eyes Open condition in this client is presented below.

As you can see from the map electrodes position may be: O1, Pz bipolar.  A spectrogram and an EEG fragment in EO condition in this client in bipolar montage (O1, Pz) are presented below.

On the basis of spectrogram the neurofeedback suppression band for this client is chosen as:

Alpha =8.5-10 Hz.

Appendix 1.  Methodological principles for QEEG/ERP assessment.

Principle 1.

EEG oscillations and event related potentials reflect different qualities of brain electrophysiology. 

They are obtained by different computational algorithms:  EEG oscillations are assessed by means of Fourier and wavelet transformations.  ERPs are assessed by averaging techniques and independent component analysis.

Principle 2.

Different oscillating patterns of the background EEG (such as theta, alpha and beta rhythms) reflect distinct processes of modulation of information processing in neuronal networks.

In the healthy brain, alpha rhythms are generated in cortico-thalamic reciprocally connected networks and reflect idling states of sensory systems.  Beta rhythms are generated by the interplay between excitatory and inhibitory neurons in local cortical networks and serve as a reset following cortical activation.  Frontal midline theta rhythm is generated in septo-hyppocampal circuits and is associated with encoding of episodic memory.  Any type of impairment in the corresponding mechanisms can lead to excess or lack of a particular rhythm when compared with a normative data.

Normal rhythms of the human brain.

Principle 3.

ERPs components are associated with different psychological operations.

For decomposing ERPs or ERPs difference waves into separate components we use independent component analysis on a set of ERPs or ERPs difference waves computed for a large (about 1000) group of healthy subjects.  The extracted components are associated with distinct psychological operations on the basis of correlation with behavior and other imaging (such as PET, fMRI) techniques.

An example of grand averaged ERPs computed for a group of healthy adult (older than 20 years) subjects (N=796) is presented below.  ERPs were computed in a two stimulus task (see description above) for two conditions: GO (depicted as green) and NOGO (depicted as red).

ICA decomposition was performed as described in (Makage et al., 1999) after re-referencing to common average reference.  In Fig. we present the results of ICA analysis of the whole set of ERPs computed for a group of healthy adult subjects for GO and NOGO conditions.  Six independent components were separated.  Each of the component has a unique 2D topography (left), a unique s-LORETA generators (right), and unique temporal pattern (middle, right).  In the middle, left – vertically stalking (from younger age -20 years old – to older age up to 89 years old) thin-color-coded horizontal bars representing a component at a single subject.  Note the latency (but not topography) of some of the components increases with age.

It should be stressed that different psychological tasks may be associated with different components and, consequently, with different psychological operations.  The main of them are listed in the table below.

 Main ERPs components:

Principle 3.

Brain is decomposed into basic systems: sensory systems, affective system, executive system and memory systems. 

Each of the system is characterized by specific rhythms and by ERPs specific components.  Distinct systems are controlled by distinct neuro-modulators of the brainstem, and consequently, can be treated by pharmacological interventions in these systems, such as increasing (or decreasing) the level of neuromodulator by giving to patients pre-coursors of mediators, blocking the post-synaptic receptor, blocking the reuptake mechanism, or and changing the cellular mechanisms of transmission.  Association between psychiatric/neurological diseases and brain systems are presented in Table below.

Principle 4.

Any of the brain systems obeys to the inverted U law.  The law claims that responses of the system are largest if the activity of the system stays within the normal range and are abnormally smaller if the activity turns out to be below or higher than the normal range of activation.

Fig.   The inverted U law.

(Top) Schematic representation of the dependence of the overall activity of a hypothetical neuronal network on the input that drives this system.  (Bottom) Schematic representation of the dependence of the response of the system on its input.  The response is defined as a change in the activity of the system as reaction to a small and elementary increase of the input.

Note that increase of the input (for example, due to a stressful situation) at two points of the system (depicted by black dots with arrows) will lead to enhancing or deteriorating performance depending on the initial state.

The overall activity of the system can be assessed by spectral analysis of the spontaneous EEG while system responses are associated with the corresponding ERPs components.  For example, abnormally high amplitude of beta activity generated in the medial prefrontal cortex indicates over-activation of this part of the executive system while abnormally small P3 monitoring component indicates a reduced response of this system in situations that need monitoring of actions.

Principle 5.

Brain disorders can be classified in associated with impairment of brain systems and diagnosed according to deviations from normality in the corresponding EEG spectral and ERP parameters.

Scientists tried to classify brain disorders for centuries.  Nowadays, there are two parallel sets of diagnostic criteria.  One is American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (the latest edition is DSM-IV).  The other one is World Health Organization’s International Classification of Disease (the latest version is ICD-10).  Any classification made on descriptive behavioral level is to some extent arbitrary.  The need for endophenotypes as objective indexes of disorders could not be overestimated.  Several components of QEEG and ERPs have be suggested as probable candidates for endophenotypes.  Although more systematic research is required the first results are very promising (see table below).

Table.  Classification of brain diseases and their endophenotypes.

Principle 6.

tDCS and neurofeedback provide electrophysiologically-based tools for activation or suppression of cortical neuronal networks. 

tDCS implies passive injection of small amount of DC currents that depolarize (anodal currents) and hyperpolarize (cathodal currents) cortical pyramidal cells under the stimulation electrode.  Neurofeedback implies active involvement of the subject in voluntarily changing the EEG parameters recorded from a given electrode.  Our recent studies have shown that the combination of these two techniques might be the best way of activating the brain.

Appendix 2.  Artifact correction by means of spatial filtration.

EEG is contaminated by various artifacts.  Eye movement artifacts are the largest ones.  They are generated by vertical and horizontal eye movements.  The main source of the artifacts is the potential of the eyeball.  The eyeball acts as an electric dipole with the positive pole oriented anteriorly.  Eye blink results in reflexive upward vertical eye movement that produces positive deflection at frontal areas with maximum at F_p1, F_p2 electrodes.  Eyes closing is associated with similar artifact, while eyes opening results in downward vertical eye movement and negative deflection at F_p1, F_p2 electrodes.  Horizontal eye movements (also called saccades) produce opposite changes of potentials at F₇, F₈ electrodes.  This figure below represents a sequence of horizontal eye movement (saccade) and eye blink. 

Fig.  Horizontal and vertical eye movements artifacts.

Left – fragment of EEG recorded in the task condition in a healthy subject of 17 years old.  Note: horizontal eye movement (at the left of recording) with a corresponding topography of potential (negativity at F7 and positivity at F8), and eye blink (at the right) with a corresponding topography (positivity at Fp1, Fp2).  Right = the model of the eye as an electric dipole with the positive pole oriented anteriorly.

One way of correcting eye movements is to record the oculogram and to compute the proportion of ocular contamination in each EEG channel.  Then the EOG signals are scaled by the estimated proportion and are subtracted from the original EEG signals. Recently, a new method was suggested which is based on ICA approach.  The basic idea is the decomposition of the EEG epoch into two components: the one that corresponds to neuronal electric activity, the other one that corresponds to artifacts.  Each component consists of a waveform, describing the time course of the modeled activity, and a topography vector, describing how the waveform contributes to each recorded signal.  Artifact activity can be reconstructed as a product of artifact topographies and waveforms.

Below is an example of application of ICA method for artifact correction.

Fig. Artifact correction by spatial filtration.

Left – a fragment of raw EEG with eye blinks, ICA topographies are presented below.  Right – the result of filtration of raw EEG by a spatial filter based on the topography of vertical eyes movements.  Maps at the bottom show topographies of the first four independent components: the largest component corresponds to vertical eye movements and the smallest component – to horizontal eye movements.

Appendix 3.  Glossary.

10-20 International system of electrode placement.  The system was accepted internationally in 1959.  The name comes from the fact that any electrode is 10 or 20 percent of some distances from another. 

ADHD is the most common developmental disorder that affects 8–12% of children worldwide and includes children displaying developmentally inappropriate levels of inattention, hyperactivity, and impulsivity that begin in childhood and cause impairment to school performance, intellectual functioning, social skills, driving, and occupational functioning. 

Affective state – is a state that is formed by drives and motivations.

Alpha rhythms –are rhythmic activities in EEG recorded from the cortex of primary or secondary sensory areas during eyes open or eyes closed rest conditions and suppressed in response to activation of these areas.  In EEG of healthy subjects alpha rhythms are found in posterior regions (occipital and parietal areas) and over the sensory motor strip (mu or sensory-motor rhythms) within the frequency range from 8 to 13 Hz.  Alpha frequencies change with age: younger and older subjects have lower alpha frequencies.

Amplifier - a basic component of any EEG machine (or electroencephalograph).   It amplifies a week (30-100 mcV) EEG signal.  1 mcV=0.001 V 

Attention is a cognitive mechanism that enables one to process a given (selected) source of sensory information in more details in comparison to unselected sources by means of limited resources of the brain processor.  Attention could be also defined as a state of readiness to receive a certain stimulus – i.e. a state for looking forward for some sensory event.  Attention must be separated from motor preparatory set as a state of readiness to make a movement. 

Barbiturates– pharmaceutical substances that bind to so called “sedative-hypnotic” sites at GABA_A receptors and promote opening Cl^- ion channels.  They belong to a class of GABA agonists.  They are used as a sleeping medication, for example, to induce anesthesia before surgery as well as minor tranquilizers or antianxiety medication.

Beta band is a band beyond 13Hz in EEG and MEG recordings.  Sometimes,  beta band is divided into smaller categories: low beta band (beta 1) from 13 to 21 Hz, high beta band (beta 2) from 21 to 30 Hz, and gamma frequency band for frequencies higher than 30 Hz.

Brodmann area is a region in the human cortex defined on the basis of its organization observed in microscope when a tissue is stained for nerve cells.  Brodmann areas were originally defined in 1909 by a German neurologist Korbinian Brodmann and referred to by numbers from 1 to 52.

Coherence is a measure of synchronization between EEG recorded in different scalp locations.  It reflects a correlation between EEG power computed for these two locations in the same frequency band.

Common average reference montage – a computational montage in which electrodes’ potentials are measured in reference to “common average” potential, i.e. a potential averaged over all electrodes.  Mathematically the montage is computed by subtracting the common average potential from any single electrode potential.

Common Mode Rejection (CMR) defines the ability of a differential amplifier to be as close to the ideal (the output is zero when V1=V2) as possible.  It is expressed as ratio of the output signal when V1=V2 (they are connected to the same source) to the output signal when only one input is non-zero.  CMR is measured in dB. 

Comparison operations – hypothetical operations performed in sensory cortical areas with the goal of detecting any deviation from the anticipatory schemata and adjusting human behavior for those deviations.  An example of such operation in auditory modality is given by so called mismatch negativity – a component of ERPs elicited in response to a deviant acoustic stimulus presented at background of repetitive standard stimulus.

DC potentials  –  potentials recorded from the scalp by non-polarizable electrodes (such as silver-silver chloride electrodes) in the frequency range from 0.04 to 0.16 Hz.  Applying to a cortical tissue DC polarizes, i.e. changes membrane potentials of cells.

Delta rhythm (cortical) – an EEG rhythm generated by intracortical thalamic mechanisms.  It dominates in the EEG when the cortical area is disconnected from the corresponding thalamic nucleus.

Delta rhythm (thalamic) – an EEG rhythm generated in the thalamus and recorded from the scalp by interplay of two ion currents in the thalamo-cortical neurons, i.e. neurons of the thalamus that project to the corresponding cortical area and receive back the excitation from this area.  One of the currents is a cation current activating in the hyperpolarization state and returning the membrane potential to a less polarized state. The second current is a transient low threshold Ca⁺⁺ current de-inactivating during the hyper-polarization state and responsible for generation of so called Ca⁺⁺ spikes.  On the top of the depolarization phase of the Ca⁺⁺ spikes the neuron generates a burst of conventional K⁺-Na⁺ spikes that are transferred to the cortex and manifested in a form of delta rhythm.

Differential amplifier amplifies the difference between two input potentials V1 and V2.

Dorsal and ventral streams in the visual system originate in segregated areas of the primary visual cortex of the occipital lobe and target correspondingly temporal and parietal cortical areas.  The ventral stream is involved in recognition of separate objects (mostly defined by shape and color) while the dorsal stream is involved in encoding spatial relationships between objects and in controlling actions with those objects such as manipulating with them and orienting towards them.

Effect size – a measure of a certain effect that is defined as the difference between the means a measured parameter for the experimental and control groups, divided by the standard deviation of the control group or both groups.  The effect size is a standardized measure and allows comparing the effects found in different studies with different parameters.

Emotion – is a behavioral response (change in heart rate, facial expression, speech) to a reward (positive emotion), punishment (negative emotion) or images of those behavioral situations.  Emotion as a psychological entity can be divided into two parts: emotional response and feeling. 

Emotional feeling is a subjective experience of the state produced by emotion-triggered stimuli.  Examples of emotions are joy and sadness, courage and fear, anger and happiness, love and hate…The cortical center for mapping emotions into separate activities is the orbito-frontal cortex.

Emotional response is defined through somatosensory (facial and body) responses as well as endocrine responses to emotion-triggered stimuli - rewards and punishers. 

Episodic memory is memory for specific events that are temporally dated; includes the relationships between different events.

ERD/ERS – stands for event related desynchronization/desynchronization.  It is a parameter that measures the percentage of decrease/increase of the EEG power in a given frequency band in a given time interval in response to a given event.

Excitatory neurons – neurons that when spiking generate a so called excitatory postsynaptic potential which depolarizes (makes it less polarizable) the post-synaptic membrane and consequently, drives the membraine potential towards the threshold of action potential and increases the probability of action potential discaharge.  Glutamate serves as a fast excitatory mediator in many cortical neurons.

Executive functions refer to operations of control and monitoring of motor, sensory and cognitive actions in goal directed behavior.  These functions thus are mostly attributed to frontal lobes however the basal ganglia and some other subcortical structures are necessarily involved. 

Explicit memory (i.e. conscious memory) is a memory which is stored and retrieved consciously.  This type of memory can be acquired during one episode and declared by the subject.  It is often is called declarative memory.

High frequency filter – analog or digital filter that suppresses lower frequencies in EEG signal and leave the higher frequencies intact.  The filter is characterized by low cut in seconds.

Human frontal midline theta rhythm – in the adult brain, spontaneous and task related short (around 1 sec or less) bursts of rhythmic (from 5.5 to 8.5 Hz) activity over the frontal leads with maximum at Fz.  This is the only theta rhythm in the human adult brain that could be considered as normal.  In the resting state it can be seen on spectrograms in a form of a distinctive peak only in 10-40 percent of adult healthy population.  This rhythm synchronizes in respond to behaviorally important events and is associated with operations such as recalling from memory or encoding memory traces.  The presence of this rhythm in rest EEG is associated with personality traits such as extraversion and neuroticism.

Implicit memory is an acquired skill or knowledge that a subject can demonstrate without explicit awareness of it.  It is often is called non-declarative memory or procedural memory.

Independent Component Analysis (ICA) is a method of solving the blind source separation problem.  In EEG the problem can be formulated as finding independent cortical generators of potentials recorded at the scalp.  ICA was first introduced in early 1980s and for EEG was applied in 1995 for artifact correction.  In general terms, ICA is a special field of mathematics and for its implementation use numerical algorithms.  These algorithms are based on optimization (finding minimum or maximum) of some objective functions.

Infra-slow activity – this type of EEG activity can be recorded only by special (so-called DC) amplifies and includes oscillations with periods from few seconds to few tens of seconds.  The mechanism of their generation is unknown but the association with slow metabolic processes of the brain is hypothesized.

Inhibitory neurons - neurons that when spiking generate a so called inhibitory postsynaptic potential which hyper-polarizes (makes it more polarizable) the post-synaptic membrane and consequently, drives the membraine potential away from the threshold of action potential and decreases the probability of action potential discaharge.  Gamma-aminobutyric acid (GABA) serves as a fast inhibitory mediator in many cortical neurons.

Inverse problem is a problem of finding multiple elemental dipoles in the cortex (sometimes named density of neuronal generators) that approximate potentials recorded by multiple scalp electrodes.  Theoretically this problem does not have a unique solution, i.e. a certain scalp distribution can be achieved by infinite number of cortical distributions. 

Lateral inhibition – is a type of connectivity in neuronal networks in which neurons inhibit the surrounding neurons and thus unable the spreading of activation in the lateral direction.  Lateral inhibition was first described in retina of the eye in the 1950^s .  The function of the lateral inhibition in the visual system is to emphasize the highest gradients of luminosity in visual images (such as Mach bands).

Limbic system – the term was coined by Paul Broca to define under the same name a group of structures that form a border around the brain stem.  Limbic system plays an important part in emotional reactions.

Local average reference montage – a computed montage in which a local average potential is averaged over a small number of electrodes in the vicinity of a target electrode and is subtracted from the potential of the target electrode.  Pci=Pi-ΣwijPj, where Pi is a potential at electrode Pi, measured in reference to some reference point (such as linked ears), Pci – is a computed potential, wij – are weights of summing potentials from local electrodes.  There are several types of local average montages (having different names: Laplacian, Lemos, Hjorth) which differ from each other by the value of wij.  A general rule for these different type of the local average montage is that nearby electrodes have the largest weighting factor, while remote electrodes have the least (or zero) weighting.

Low frequency filter – analog or digital filter that suppresses higher frequencies in EEG signal and leave the lower frequencies intact.  The filter is characterized by high cut in Hz.

Memory consolidation – at neuronal level is a process of developing irreversible changes in synaptic transmission.  At psychological level, memory consolidation is associated with forming of long-term memory which decays very slowly (comparable with a life span).

Monitoring as a newly developed concept defines a hypothetical psychological operation that enables the brain to evaluate the quality of action execution and alerts the executive control mechanisms to allocate resources for compensating the conflict between intended and executed actions.

Montage – is a rule according to which EEG potentials are computed.  The simplest rule (linked ears montage) is measuring electrodes’ potentials in reference in two linked electrodes located at left and right earlobes. 

Motivation – a need or desire or drive that directs the behavior by determining its goals.

Negative reinforcer (or punisher) is a stimulus that increases behavior pattern directed to avoid the punisher.  We don’t know whether a separate punisher system exists in the brain or not. 

Neglect is a neurological syndrome in which patients with brain lesions show a marked deficit in the ability to attend to sensory information presented in the contra-lesioned field. 

Neurofeedback is a technique of self-regulation by means of EEG-based biofeedback.  In this technique, some parameters of EEG currently recorded from a subject’s scalp (such as an EEG power in a given frequency band) are presented to the subject through visual, auditory or tactile modality with the task to voluntarily alter these parameters in a desired (leading to a more efficient mode of brain functioning) direction. 

Notch filter is a very sharp filter that attenuates a certain frequency in the signal.  In EEG a notch filter at 50 (60) Hz is used to filter out the noise from the electrical system in the room.

Oppositional Defiant Disorder (ODD) -  taking unsafe risks, breaking laws, refusing to follow instructions or directions. 

Positive reinforcer (or reward) is a stimulus that increases the frequency of a behavior pattern leading to acquisition of reward. 

Reaction of desynchronization – in the case of alpha rhythms “desynchronization” corresponds to suppression of the corresponding alpha rhythm.

Referntial recording is a recording of EEG signal when the second (reference) electrode is usually located on the earlobs, mastoids or the tip of the nose, i.e. far away from the neuronal source.  This is in contrast to sequential recording when two electrodes are located on the scalp near EEG generators in the cortex.

Sampling rate – is the rate at which raw EEG signal is sampled (quintified).  According to Naiquist theorem the sampling rate must be twice as much as the hihest possible frequency of recorded EEG signal. 

Semantic memory is a memory for factual information about the world, concepts and word meaning.

Sensory modality refers to a sensory system that processes a certain type of receptor information.  The most well studied sensory systems are: Visual System (seeing form, color, depth, motion, spatial relationships of visual objects), Auditory System (hearing and localizing sounds), Somatic Sensory or Somatosensory System (feeling touch, pain, thermal sensations, mechanical displacement of muscles and joints), 

Sensory systems include receptor organs and subcortical and cortical neuronal networks that specifically respond to activation of the corresponding receptors.

Specific learning disability (LD) - difficulty in mastering language, reading or math.

Spectra are computed by means of fast Fourier transformation that decomposes EEG signals into series of sinusoidal functions with different frequencies, amplitudes and phases.  Spectra show how amplitude, power or phase of the simusoidal harmonic depends on sinusoid’s frequency.  Relative spectra are obtained by divided a spectral parameter at a certain frequency by the parameter averaged over the whole frequency range or a part of it.

tDCS – transcranial direct current stimulation – a new neurotherapy technique of application direct current to the brain by means of electrodes placed on the head.  Because of polarizing effect on neuronal cells, tDCS in the early years was called polarization technique

Thalamus – is a subcortical brain structure that controls the flow of sensory information to the posterior parts of the cortex through sensory-related nuclei and regulates activity in the prefrontal areas though a distinct set of nuclei.

Theta band in EEG is a band from 4 to 8 Hz.

Tourette’s syndrome - having tics - uncontrolled movements, like eye blinks, facial twitches, or vocal sounds. 

Working memory – a process of storing the results of the executed actions, a plan of prepared action and associated sensory representation (called also attention) within the cortical-subcortical loops.   Working memory implies an active manipulation with the temporary stored information in order to perform sensory-motor and cognitive actions such as language, planning, decision making, etc.