Glossary


Dense array electroencephalography (dEEG)


dEEG electrode distribution across the scalp is dense compared to the standard International 10-20 system used in many research and clinical settings (see below).

Photo of Dr. Tucker wearing a dense EEG net.


Electroencephalography (EEG)

Developed in 1929, EEG electrodes are placed on the human scalp to record electric signals from the top layers of the brain. The International 10-20 system established standard electrode locations across the scalp. Note the position of electrodes F3 and F4 on either side of the head.
An image laying out scalp electrode locations for the International 10-20 EEG system.


EEG Frequencies

The brainwaves collected from the human scalp typically appear in five canonical frequencies which are correlated with resting eyes open or eyes closed, and during various tasks (movement or thinking).
An image illustrating the key frequency ranges of EEG activity.


 
 

Electromyography (EMG)
EMG measures electrical activity in selected surface muscle groups. EMG signals provide information on amount and frequency of muscle activity.

An image illustrating specific EMG electrode locations on a adult human male.

An image illustrating both raw and rectified EMG activity signals.




Geodesic Photogrammetry System (GPS)
This system utilizes 11 video cameras to record the positions of each electrode. 

An image of a foam head equipped with a dense EEG net sitting beneath a geodesic photogrammetry system.


Head modeling

The human head is composed of a number of different tissues, each with its own electrical conductivity properties including brain tissue, connective tissue (e.g., dura mater) and bone (the skull). In addition, each person’s brain has a generally similar shape compared to other people, however, each person’s brain does have unique variations on the general shape. EEG head modeling techniques allow processing of EEG signals that take tissue conductivity properties into account, as well as positioning of electrodes for recording or weak electrical current injection that optimizes data collection accuracy and intervention effects.
An image illustrating the components of the human head that are taken into account for head modeling purposes.


Iontophoresis

This procedure uses electrodes to deliver medical compounds directly into the skin.

An image illustrating how electricity may flow into skin.


Mastoid Location

The mastoid bones are located on both sides of the head just behind and below the ear.
An image of a human skull with the mastoid process highlighted in red.


Memory

Memory begins between neurons at places called synapses which are structures in the neuron membrane that receive information from other neuron synapses. Synapses are modified to permit easy sharing of information or ‘decommissioned’ such that transmission is lessened or stopped at that synapse. Memory is created in stages, as seen above. Different kinds of memory are associated with different brain regions.
An illustration of neurons firing.


Declarative Memory

Declarative (explicit) memories are those that can be reported verbally. This includes autobiographical and factual informationThis type of memory is associated with activity in deep areas of the brain in what has been called the limbic system (medial temporal lobe).
An image mapping and describing the medial temporal lobe memory system.


Procedural Memory 

Procedural (implicit) memory encodes and permits motor behaviors that do not require conscious awareness to perform such as walking, running, and riding a bike.



Memory consolidation

Memory consolidation (storage) is thought to occur during sleep when synapses are either strengthened or decommissioned. 

An image mapping the stages of memory encoding.


Sleep

Sleep is a state common to all mammals. It is characterized by loss of normal consciousness and dreaming. It is required for life and health. Memories are thought to be consolidated during sleep.
An image of a sleeping woman.


Sleep Spindles

These are characteristic of EEG signals along midline (top of the head) electrodes during slow wave sleep (NREM-non-rapid eye movement sleep). These are thought to be correlated with motor memory consolidation.

An image illustrating a sleep spindle as seen in EEG signal as compared to a K complex as seen in EEG signal.




Sleep Stages

Sleep in humans proceeds through standard stages. These stages can be visually identified in EEG data traces. Slow wave sleep is termed non-rapid eye movement (NREM) sleep stages 3-4It is thought memories are consolidated during NREM slow wave sleep. Rapid eye movement (REM) sleep can occur throughout the night and has been associated with dreaming.
An image illustrating a variety of EEG signals from a variety of states of sleep and wakefulness.


Source Localization

Use of mathematical signal analysis to determine the brain sources of electrical activity recorded at the scalp.
An image illustrating two cartoon human heads, one capped, the other with brain EEG sources illustrated.


Transcranial Direct Current Stimulation (tDCS) Electrodes

In typical tDCS neurodulation there are two electrodes, anodal (positive) and cathodal (negative). Anodal stimulation has been associated with increasing neuron probability of signaling and cathodal stimulation has been associated with lessening neuron probability of signaling.

An image illustrating a variety of transcranial direct current stimulation results.

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