By: Hamid Mirhosseini. Ph.D, Assistant professor of Neuroscience In the name of God By: Hamid Mirhosseini. Ph.D, Assistant professor of Neuroscience

Electroencephalogram(EEG): objectives Understanding the basic concepts Differentiate normal and abnormal waveform Learning about wave distortion in some psychiatric and neurologic disorders AND EEG application in psychiatry

Electroencephalogram(EEG) EEG is a recording of the electrical activity of the brain from the scalp. The first recordings were made by Hans Berger in 1929

What is the origin of the EEG The summed potentials of both the EPPs & IPPs are responsible for most of the EEG waveforms. Pyramidal cells of the cortical layers are the major contributor of the synaptic potentials that make up EEG. Activity generated in the neocortex and regulated by structures in the brain stem and thalamus of the brain.

electrical activity forms waves صحبت از موج ما را به فکر امواج دریا می اندازد. در واقع به انتشار هر آشفتگی در محیط که اغلب حامل انرژی است «موج» می‌گویند. امواج دریا گونه‌ای از موج‌ها ی مکانیکی قابل روئیت می‌باشند که در محیط مادّی (آب)منتشر می‌شوند. اگر این آشفتگی در میدان‌های الکتریکی باشد، آن را «موج الکتریکی» می‌نامند که قابل روئیت نیست. در موج الکتریکی حرکت ذرات موج بر راستای حرکت آن عمود است

Electroencephalography (EEG) Why EEG became subspecialty of the field of neurology? Lack of specificity of EEG abnormalities to known psychiatric syndromes EEG abnormalities correlate with epilepsy, tumors, stroke syndromes… 6

Basic Acquisition EEG signals are a measure the potential difference between two electrodes. Just like the voltage at a battery is the difference between positive and negative poles. Thus you always need at least 2 recording electrodes to get a signal, but In practice we use many electrodes

Basic Acquisition Signals on scalp are very small - microvolt range (1/1,000,000 volts). Presents some challenges for acquisition Acquisition involves Amplification Filtering Digitizing (sampling) Storage Results in one time series per channel (64 in our lab).

Sampling Theory Filters must be set to reduce contribution of signal above the Nyquist frequency.(explain analog v/s digital) Sample Rate = 250 Hz??? Nyquist frequency = 125 Hz High pass filter – allows high frequencies to pass Low pass filter – allows low frequencies to pass Notch filter – filters specific range of frequencies Band Pass – filters all but a range of frequencies(0.5- 40 Hz in psychiatry)

Recording procedure amplification recording (20 minutes at least) storage (on CD, DVD, NAS, cloud …)  

Requirements EEG machine Silver cup electrodes/metallic bridge electrodes. Electrode jelly. Rubber cap. Quiet dark comfortable room. Skin pencil & measuring tape.

EEG instruments Amplifier and ADC (Analog to Digital Converter) USB converter Active electrodes Analog Response Device Computer storage and display Analog Input Box

Electrode Positioning system What is impedance?

Procedure of EEG recording A standard EEG makes use of 21 electrodes linked in various ways (Montage). Ask the subject to lie down in bed. Apply electrode according to 10/20% system. Check the impedance of the electrodes.

Electrode placement Typically adopt an accepted placement scheme for applying electrodes to the scalp. The International 1020 placement system is the most widely adopted. It uses a set of measurements relative to landmarks on the head. Name reflects the fact that electrodes are placed at intervals that are 10% or 20% of the distance between landmarks.

Electrode placement – the „ten-twenty“ electrode system

EEG Electrodes Electrodes Cap Sliver Electrodes

EEG Recording From Normal Adult Male

Alpha block

Montage Different sets of electrode arrangement on the scalp by 10 – 20 system is known as montage.

Montages Referential or monopolar montage Each amplifier records the difference between a scalp electrode and a reference electrode. The same reference electrode is used for all channels. There is no standard position at which this reference is always placed; it is, however, at a different position than the "recording" electrodes. Midline positions are often used because they do not amplify the signal in one hemisphere vs. the other. Another popular reference is "linked ears": reference electrode are A1, A2, the ear electrodes, or A1 and A2 linked together.

Montages Referential or monopolar montage

Montages Bipolar montage Each channel represents the difference between two electrodes. The entire montage consists of a series of these channels. For example, the channel "Fp1-F3" represents the difference in voltage between the Fp1 electrode and the F3 electrode. The next channel in the montage, "F3-C3," represents the voltage difference between F3 and C3, and so on through the entire array of electrodes.

Bipolar montage

Referential or monopolar monta versus Bipolar montage Montages

Montages Average reference montage Activity from all the electrodes are measured, summed together and averaged, and this averaged signal is used as the common reference for each channel

Quantitative Electroencephalography Montages Laplacian montage Each channel represents the difference between an electrode and a weighted average of the surrounding electrodes.

Analysis Electrical activity from the brain consist of primarily of rhythms. They are named according to their frequencies (Hz) and amplitude in micro volt (μv). Different rhythms at different ages and different conditions (level of consciousness) Usually one dominant frequency (background rhythm)

Factor influencing EEG Age Infancy – theta, delta wave Child – alpha formation. Adult – all four waves. Level of consciousness (sleep) Hypocapnia(hyperventilation) slow & high amplitude waves. Hypoglycemia similar to HV Hypothermia Low glucocorticoids Slow waves

EEG Rhythms

Dominant pattern during slow wave sleep and some forms of anesthesia. SLOW WAVES (0.3-1 Hz) Dominant pattern during slow wave sleep and some forms of anesthesia. The survival of slow oscillations after extensive thalamic lesions indicates that the slow waves are generated within the cortex.

Delta Waves (1-4 Hz) Two type: Cortical origin: unknown mechanism- increase by disconnection of the cortex from the thalamus probably associated with some slow lasting processes within the cortex Thalamus origin: Delta Rhythm of Sleep Two type: In intracellular recordings in animal preparations, it was shown that delta rhythm can be generated in a single thalamo-cortical cell

Delta Waves (1-4 Hz) Alpha rhythms appear when thalamocortical neurons are relative depolarized, Sleep spindles appear when these cells are relatively hyperpolarized, (neural network involve reticular neurons) Delta rhythms emerge at the deepest level of hyperpolarization of thalamo-cortical neurons. (single neuron)

Alpha Waves (8-13 Hz) Mu-Rhythms: sensory-motor alpha rhythms (SMR) Occipital Alpha Rhythms: High amplitude rhythms recorded from occipital electrodes Parietal Alpha Rhythm: In some rare cases high amplitude rhythms in the alpha frequency band can be found at parietal areas with maximum at Pz.

Alpha Waves (8-13 Hz) Mu-Rhythms (Rolandic Rhythms)

Alpha Waves (8-13 Hz) Occipital Alpha Rhythms

Alpha Waves (8-13 Hz) Occipital Alpha Rhythms Alpha power increases from early childhood to adulthood and decreases beyond the age of 50-60 years Children with poorer education, reading/writing disabilities, spelling disabilities, and neurological disorders show significantly less alpha power Neural modulation of alpha power is strongly affected in patients with Alzheimer’s disease

Age related change in Alpha rhythms: Alpha Waves (8-13 Hz) Age related change in Alpha rhythms: In the peak frequency of occipital rhythm: A slight increase from 7 to 20 years old, A slight decrease with later aging. The frequency of the dominant alpha rhythm in healthy elderly people is around 10 Hz, An occipital alpha frequency less than 7.5 Hz is usually regarded as abnormality

Alpha Waves (8-13 Hz) ABNORMALITY OF ALPHA RHYTHMS Complete Absence of Alpha Rhythms When alpha rhythms are absent, the EEG records look lower in voltage. Low voltage records Low voltage records are found in 4–10 per cent of normal adults Low voltage records are found in alcoholics and drug addicts

Alpha Waves (8-13 Hz) ABNORMALITY OF ALPHA RHYTHMS Alpha Rhythms in Unusual Sites Maximums of distributions of abnormal alpha rhythms: Posterior temporal areas tinnitus, Left parietal areas dyslexia, Middle temporal and anterior temporal areas aging cerebrovascular disorder.

Alpha Waves (8-13 Hz) Decrease in right hemisphere: autism ABNORMALITY OF ALPHA RHYTHMS Decrease in right hemisphere: autism Decrease in posterior sites: anxiety Decrease in C3 and C4: ADHD/Hyper-activity Increase in Frontal area: depression

Alpha Waves (8-13 Hz) ABNORMALITY OF ALPHA RHYTHMS

Alpha Waves (8-13 Hz) If the asymmetry is larger than 50% this might ABNORMALITY OF ALPHA RHYTHMS Alpha Asymmetry If the asymmetry is larger than 50% this might be an indication of pathology. Richard Davidson’s theory: asymmetrical involvement of the frontal cortex is associated with the emotional reactions Left hemisphere is biased to processing positive emotional stimuli, while the right hemisphere processes mostly negative emotional stimuli

Beta Waves (13-30 Hz) Found in various locations of the cortex in normal subjects. In the frequency between 13 and 30 Hz beta The amplitude of beta rhythms when measured in reference to linked ears is less than 20 μV Rolandic beta rhythms: maximums over the sensory-motor strip Suppress during movement or preparing to make a movement. 2) Frontal beta rhythms: beta rhythms located more frontally related to stimulus assessment and decision making.

Beta Waves (13-30 Hz) Frontal beta rhythms vs. Alpha rhythms

Beta Waves (13-30 Hz) NEURONAL MECHANISMS There is a close relationship between EEG power in beta band and metabolic activity in the corresponding cortical area of the human brain.

Beta Waves (13-30 Hz) Need for Normative Databases ABNORMAL BETA RHYTHMS Need for Normative Databases asymmetry of beta activity itself (higher than 50 per cent) must be considered as additional indication of abnormality Increase of beta activity and a corresponding over-activation may be seen in areas associated with epileptic focus, for example, during pre-epileptic auras beta activity (12.5–30 Hz) in the left auditory cortex that accompanies hallucinations Excess of beta activity has been found in less than 10 per cent of the ADHD population

Beta Waves (13-30 Hz) Increase in all area: autism ABNORMAL BETA RHYTHMS Increase in all area: autism Increase in occipital: anxiety Decrease in Frontal: ADHD/attention deficit Increase in all areas: Parkinson

Theta Waves (4-8 Hz) In 1950, Arellano and Schwab observed a 4–7 cycle/s rhythm in the midline just anterior to the vertex which occurred during problem solving.

Theta Waves (4-8 Hz) NEURONAL MECHANISMS B. Association with Hippocampal Hippocampus in mammals is the ability to generate theta rhythm. Several lines of evidence support the concept that the theta rhythm plays an important role in specific memory operations. LTP is optimal when the time interval between stimuli is approximately 200 ms, that is, in theta range

Theta Waves (4-8 Hz) ABNORMAL THETA RHYTHMS these rhythms are of short duration and appear only in task conditions, even in task conditions they can be seen in EEG spectra in a form of peaks only in some part of healthy population.

Theta Waves (4-8 Hz) ABNORMAL THETA RHYTHMS Frontal Midline Theta Subtype of ADHD very long runs of the frontal midline theta rhythm. extremely high and sharp peak on EEG spectra at Fz in frequency range from 5.5 to 8 Hz extremely low theta synchronization in response to meaningful stimuli in the two-stimulus GO/NOGO and math tasks conditions. Theta Rhythms in Non-frontal Areas Appearance of theta rhythms in other than Fz (and to some extant at Pz) electrode positions must be considered as abnormal.

Theta Waves (4-8 Hz) ABNORMAL THETA RHYTHMS Theta Rhythms in Non-frontal Areas Appearance of theta rhythms in other than Fz (and to some extant at Pz) electrode positions must be considered as abnormal. The EEG was recorded in a patient after several days of closed brain injury.

NORMAL EEG CHANGES

Desynchronization or Alpha block Cause: Eyes opening (after closure) Thinking by the subject (mathematical calculation) Sound (clapping)

Eye opening Alpha rhythm changes to beta on eye opening (desynchronization / α- block)

Thinking Beta waves are observed

Provocation test Intermittent photic stimulation Hyperventilation Increase rate & decrease amplitude Hyperventilation Decrease rate & increase in amplitude

Changes in brain waves during different stages of sleep & wakefulness