GridEEG – User training EEG data preparation EEG signal quality check EEG methods Outcome evaluation

EEG data preparation Experimental conditions Subjects sit in a comfortable chair, in a dimly-lit room. Awakening resting state eyes-closed. EEG recording parameters EEG data must be acquired through a standard 10-20 International System consisting of 19 electrodes. Reference: average signal of the earlobes electrodes A1, A2. EEG sampling frequency: 128 Hz EEG pass-band: 0.3-40 Hz

EEG data preparation Data format . Dataset composition Patient_1.txt EEG data must be organized according to the standard Neuroscan ASCII format, i.e. a .txt file of numbers where columns indicate electrodes and rows indicate consecutive time samples. The order of the electrodes in the ASCII file must be the F3, F4, T3, T4, C3, C4, P3, P4, FZ, CZ, PZ, Fp1, Fp2, F7, F8, T5, T6, O1, O2 Dataset composition The dataset consists of at least 50 artifact-free EEG segments of 2 seconds, not necessarily contiguous. Each segment must be stored in a separate ASCII file. Different .txt files must be numbered progressively, i.e. Patient_1.txt, Patient_2.txt, …, Patient_50.txt Electrodes F3 F4 ... ... ... ... ... O2 1 2 . N 0.3 0.2 ... ... ... ... ... ... 0.7 0.1 0.4 ... ... ... ... ... ... 0.6 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... Time samples ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 0.5 0.1 ... ... ... ... ... ... 0.8 Patient_1.txt

EEG signal quality check Although EEG is designed to record cerebral activity, it also records electrical activities arising from sites other than the brain. The recorded activity that is not of cerebral origin is termed artifact. EEG segments contaminated by artifacts should be removed from the subsequent analysis. Artifacts can be divided into physiologic and extraphysiologic: Physiologic artifacts are generated from the patient, they arise from sources other than the brain (ie, body) Extraphysiologic artifacts arise from outside the body (ie, equipment, environment).

EEG signal quality check F3 F4 T3 T4 C3 C4 P3 P4 FZ CZ PZ Fp1 Fp2 F7 F8 T5 T6 O1 O2 Electromyogram (muscle) artifact. These waveforms represent motor unit potentials as typically observed on needle electrode examination during electromyogram, with a frequency of 20-100 Hz. Distribution varies, and in this case it is more prominent on the left side. Such artifact can be diminished by the judicious use of the high-frequency filter. (This sample has the default setting of high-frequency filter 70 Hz.) Particular patterns of electromyogram (EMG) artifacts can occur in some movement disorders. Essential tremor and Parkinson disease can produce rhythmic 4- to 6-Hz sinusoidal artifacts that may mimic cerebral activity. Another disorder that can produce repetitive muscle artifacts is hemifacial spasm. The photomyoclonic response is a special type of EMG artifact that occurs during intermittent photic stimulation. Some subjects contract the frontalis and orbicularis muscles. These contractions occur approximately 50-60 milliseconds after each flash, disappear after eye opening and use of paralyzers, are located mostly frontally, and have no concomitant EEG changes. Chewing and sucking can produce similar artifacts. These are commonly observed in young patients. However, they also can be observed in patients with dementia or those who are uncooperative. Physiologic: Muscle activity Myogenic potentials are the most common artifacts (see images below). Frontalis and temporalis muscles (eg, clenching of jaw muscles) are common causes. Generally, the potentials generated in the muscles are of shorter duration than those generated in the brain and are identified easily on the basis of duration, morphology, and rate of firing.

EEG signal quality check F7 Fp1 T3 T4 F8 C4 P3 P4 FZ Fp2 PZ Cz F4 F3 T5 T6 O1 O2 F7 Fp1 T3 T4 F8 C4 P3 P4 FZ Fp2 PZ Cz F4 F3 T5 T6 O1 O2 Physiologic: Eyes movements Vertical eye movements typically are observed with blinks. A blink causes the positive pole (ie, cornea) to move closer to frontopolar (Fp1-Fp2) electrodes, producing symmetric downward deflections. Lateral eye movements most affect lateral frontal electrodes F7 and F8.

EEG signal quality check F3 F4 T3 T4 C3 C4 P3 P4 FZ CZ PZ Fp1 Fp2 F7 F8 T5 T6 O1 O2 ECG Regular (periodic) slow waves best observed at midtemporal and posterior temporal electrodes T4-T6 and T3-T5. These clearly are related to ECG. The duration and morphology are those of pulse artifact, but as demonstrated by the marker, no delay occurs between the ECG and the artifact. Thus, this is an ECG artifact with broad QRS complexes. Physiologic: Electrocardiogram artifact Some individual variations in the amount and persistence of ECG artifact are related to the field of the heart potentials over the surface of the scalp. ECG artifact is recognized easily by its regularity and coincidence with the ECG tracing.

EEG signal quality check F3 F4 T3 T4 C3 C4 P3 P4 FZ CZ PZ Fp1 Fp2 F7 F8 T5 T6 O1 O2 Sweat artifact. This is characterized by very low-frequency (here, 0.25- to 0.5-Hz) oscillations. The distribution here (midtemporal electrode T3 and occipital electrode O1) suggests sweat on the left side. Note that morphology and frequency are also consistent with slow rolling eye movements, but distribution is not. Physiologic: Skin artifact Biological processes and/or defects may alter impedance and cause artifacts. Sweat is a common cause. Sodium chloride and lactic acid from sweating reacting with metals of the electrodes may produce huge slow baseline sways.

EEG signal quality check F3 F4 T3 T4 C3 C4 P3 P4 FZ CZ PZ Fp1 Fp2 F7 F8 T5 T6 O1 O2 Electrode (impedance) artifact at parietal electrode P3. Initially, a slow artifact is followed by a more abrupt one at the seventh second. This commonly is referred to as an electrode pop. Note again the unusual morphology of the sharp component and that it is at a single electrode. Also note an eye blink in the third second and slight electromyogram artifact in the frontal regions in the first 2 seconds. Extra-physiologic: Electrode impedance The most common electrode artifact is the electrode popping. Morphologically this appears as single or multiple sharp waveforms due to abrupt impedance change. It is identified easily by its characteristic appearance (ie, abrupt vertical transient that does not modify the background activity) and its usual distribution, which is limited to a single electrode.

EEG signal quality check F3 F4 T3 T4 C3 C4 P3 P4 FZ CZ PZ Fp1 Fp2 F7 F8 T5 T6 O1 O2 Extra-physiologic: Alternating current (50-60 Hz) Adequate grounding on the patient has almost eliminated this type of artifact from power lines. The problem arises when the impedance of one of the active electrodes becomes significantly large between the electrodes and the ground of the amplifier. In this situation, the ground becomes an active electrode that, depending on its location, produces the 50/60-Hz artifact.

Power of the cortical oscilations at different frequency bands EEG Methods Power Spectral Density of cortical regions Linear Inverse Problem b x Scalp electrodes Cortical sources A Lead field matrix MRI images Power of the cortical oscilations at different frequency bands

Network extraction at specific frequency EEG Methods Spectral coherence between scalp electrodes Elec. (i) Elec. (j) Mij = cross-spectrum minor Mii, Mjj = auto-spectra minors ordinary coherence Network extraction at specific frequency partial coherence

EEG Methods Directed Transfer Function between scalp electrodes Elec. (i) Elec. (j) H = inverse of the multivariate autoregressive matrix Network extraction at specific frequency

EEG Methods Classification through Mahalanobis distance Nold Healthy population Dm (x, Nold) Actual subject (X) AD Dm (x, AD) Alzheimer population X = EEG features of actual subject u = population mean EEG features S = Covariance matrix Dm (x, AD) Dm (x, Nold)

Data analysis through WEB portal GridEEG Physician Scientist Default parameters Customizable parameters Frequency ranges Delta (2-4 Hz), Theta (4.5-8 Hz), Alpha1 (8.5-10.5 Hz), Alpha2 (11-13 Hz), Beta1 (13.5-20 Hz), Beta2 (20.5-30 Hz), Gamma (30.5-40 Hz) EEG features PSD (Occipital, Alpha1), ( Occipital, Delta), (Parietal, Alpha1) COH (P3,C3, Alpha1), (T3,F3, Alpha2), (Pz,Fz, Alpha2) DTF (O2,P4, Alpha1), ( Cz,Pz, Beta2), (Pz,Fz, Alpha2)

Demonstration and practice: GridEEG in action https://applications.eu-decide.eu//grideeg