PSY396 Lecture 5: Introduction to electroencephalography (EEG)

What is Electro-Encephalo-Gram?

Electrical Brain Picture

Electroencephalography

The recording of electrical changes at the scalp, which are caused by the synchronous activity of thousands of neurons that are parallel to each other

inventor of EEG

Hans Berger (1873-1941)

• In 1924, first to measure electrical currents from human scalps

• Coined the term electroencephalogram (“Elektroenkephalogramm”)

• Described alpha-waves (Berger waves)

• 1924 succeeded in recording the first human electroencephalogram

• 1929 published his first paper entitled "recording the electrical activity of the human brain from the surface of the head".

• in 1935, American roboticist William Grey Walter described “Berger was not regarded by his associates as in the front rank of German psychiatrists, having rather the reputation of being a crank. He seemed to me to be a modest and dignified person, full of good humour, and as unperturbed by lack of recognition as he was later by the fame it eventually brought upon him.” (W. Grey Walter, 1953, The Living Brain)

• 1937 importance of his discoveries in EEG were finally recognized at an international forum after British electrophysiologists Edgar Douglas Adrian and others confirmed Berger's basic observations in 1934

• By 1938, electroencephalography had gained widespread recognition by eminent researchers in the field, leading to its practical use in diagnosis in the United States, England, and France.

Electroencephalography – The first

Richard Caton (1842-1926)

• 1875 First to measure electrical currents from brains of mammals

• Registered change in electrical activity in the brain to sensory stimuli

Electroencephalography - Pioneers

Adolf Beck (1863-1942) Kraków

Ernst Fleischl von Marxow (1846-1891) Vienna

Vasili Yakovlevich Danilevsky (1852-1939) Charkov

Vladimir Právdicz-Neminski (1879-1952) Kiev

Documents by year for EEG, MRI and TMS

EEG - Apparatus

Electroencephalogram - now vs then

Methods in cognitive neuroscience

Patch clamp and single-/multi-unit recording

• Directly measure neuronal activity

• Invasive

• Limited to few neurons

• Unclear information code

How does EEG work?

A non-invasive technique that records electrical activity in the brain through electrodes placed on the scalp, used to study cognitive processes.

Electrical signals from the brain – Origin

In order to understand the origins of the voltage fluctuations that we measure on the scalp, we need to understand the origins of the voltage fluctuations in the brain

• Captures post synaptic potentiation

Neuronal activity - Action potentials

• Discrete signal (voltage spike) that moves from the cell body of a neuron along its axon

• At the end of the axon it enables the release of neurotransmitters

Postsynaptic potentials

• Neurotransmitters bind to the membrane of the postsynaptic cell

• Ion channels open and close leading to gradual changes in membrane potentials

• Release of excitatory (inhibitory) neurotransmitter results in +ve (-ve) ions flow into the dendrites, and a net negativity (positivity) in the extracellular space

• Meanwhile, when one end of neuron is positively charged, the other end of the neuron starts to be charged negatively (positive ions leave the cell body)

• → creates electrical dipole between different parts of the neurons

Scalp electrodes as neural activity detectors - Action potentials

• Duration less than 1 ms (no/little temporal summation)

• Random physical distribution of axons

• Neurons fire in a different timing

• Convoluted electrical activity

➥ not detectable

Scalp electrodes as neural activity detectors - Postsynaptic potentials

• Duration of tens to hundreds of ms

• Summation possible

➥ detectable

From postsynaptic potentials to EEG

Dipole of one pyramid cell is not sufficient → Summation of many required

• Involving 103 - 106 Neurons

• Occurring at about the same time

• Neurons in the cerebral cortex are roughly aligned with each other → parallel

EEG recordings/set up

Are always bipolar

• difference in voltage between an active electrode, i.e., an electrode of interest, and an electrode that is (relatively) electrically inactive, i.e., the reference electrode

Mostly done from several electrodes that are placed at standardised positions

10-20 system and extension

Artifacts

EEG – Spontaneous activity

EEG - Clinical applications

Neurological diagnoses

Detection & diagnosis → prognosis → therapy

• Epilepsy (presence, epileptogenic zone, treatment outcome)

• Creutzfeldt–Jakob disease (periodic sharp wave complexes)

• Dementia (mild generalised background slowing)

• Functional changes connected to head injuries, poisonings, or blood flow disorders (by conducting functional network analysis)

Sleep research (sleep disorder, brain development)

Neurofeedback:

EEG in cognitive neuroscience

• Event-related potentials (ERPs):

• Even-related synchronisation and desynchronization (ERS/ERD)

• Coherence

• Source localisation

Event-Related brain Potentials (ERPs)

Brain responses time-locked to some event. This event may be:

• a sensory stimulus (such as a flash or a sound),

• a movement (such as response to a specified target stimulus),

• or the omission of a stimulus (such as an increased time gap between stimuli).

Doing an ERP experiment

• During a study the participant listens to or watches some stimuli.

• These stimuli are called events.

• Electrical activity from the brain is recorded to a number of these events

Typical ERP set up

Obtaining ERPs

• Consistent electrical changes can be seen by averaging together the electrical activity from a certain number of these events.

• This activity is seen as a series of positive and negative-going deflections.

What do ERPs tell?

The timing and size of these deflections, and can be used to make inferences about

• the time-course of processing in the brain

Why can we associate ERPs with specific cognitive processing?

EPRS: Example

Why do we get slower as we get older?

3 stages of sensorimotor information processing (e.g., Yordanova, et al., 2004)

1. Stimulus processing (P300)

2. Sensorimotor integration (LRP)

3. Motor-response generation (MRP)

Four-choice-reaction task

Results:

EEG research@murdoch

“Exploring the Relationship between Mindfulness and Fear Extinction, and the Potential Implications of this Relationship for Posttraumatic Stress Symptoms (PTSS)” (DPsych Project: Ms Auretta Kumar)

“Entrainment of brain oscillations to improve inhibitory function in people with MCI”(Dementia Research Foundation funded project)

Advantages of ERP

• ERP signal is directly related to neural activity and this electrical activity is conducted instantaneously to the scalp

→Therefore, ERP has an excellent temporal resolution

• Cost effective, relatively mobile, tolerant of movement artefact, silent (advantageous for auditory research), no issue with claustrophobia, no magnetic field involved

• Compared to behavioural paradigm, detect covert processing, does not require motor response, elucidate stage of processing

Disadvantages of ERP

• The ERP signal is derived from different sources in the brain and it is not possible to infer exactly where these sources are from

→Therefore, ERP has a poor spatial resolution

• Limited to cortical level

• Takes long time to set up

• high signal-to-noise ratio

• →sophisticated data analysis tool and large number of trials and subject are needed