Electroencephalography Flashcards

Question

What do the EEG measurement mean? (2+5)

Answer 1

considered to reflect certain cognitive, affective or attentional states these frequencies vary slightly dependent on individual factors, stimulus properties and internal states classify these frequencies based on specific frequency ranges, or frequency bands: - delta - theta - alpha - beta - gamma

Answer 2

(1 – 4 Hz), deepest sleep states

Answer 3

(4 – 8 Hz), generally associated with brain processes underlying mental workload or working memory

Answer 4

(8 – 12 Hz), reflecting sensory, motor and memory functions. Increased alpha during mental and physical relaxation with eyes closed and reduced, or suppressed, with eyes open.

Answer 5

(13 – 25 Hz) , plan or execute movements, particularly when reaching or grasping requires fine finger movements and focused attention. Interestingly, also noticeable when we observe others’ bodily movements. (mirror neuron activity)

Answer 6

(> 25 Hz). Some argue that gamma serves as a carrier frequency for binding various sensory impressions of an object together to a coherent form, therefore reflecting an attentional process.

Answer 7

the clinical manifestation of an abnormal and excessive excitation and synchronization of a population of cortical neurons

Answer 8

seizure induced by very high heat

Answer 9

a tendency toward recurrent seizures unprovoked by any systemic or acute neurologic insults

Answer 10

sequence of events that converts a normal neuronal network into a hyperexcitable network

Answer 11

Sleep studies monitors many body functions, including brain activity (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG), and heart rhythm (ECG), during sleep, breathing functions, respiratory airflow, and respiratory effort indicators, peripheral pulse oximetry.

Answer 12

- sleep onset latency (SOL), the REM-sleep onset latency, the number of awakenings during the sleep-period, the total sleep duration, percentages and durations of every sleep stage, and the number of arousals

Answer 13

The electrooculogram (EOG) uses two electrodes; one that is placed 1 cm above the outer canthus of the right eye and one that is placed 1 cm below the outer canthus of the left eye. These electrodes pick up the activity of the eyes in virtue of the electropotential difference between the cornea and the retina (the cornea is positively charged relative to the retina). This helps to determine when REM sleep occurs, of which rapid eye movements are characteristic, and also essentially aids in determining when sleep occurs.

Answer 14

The electromyogram (EMG) typically uses four electrodes to measure muscle tension in the body as well as to monitor for an excessive amount of leg movements during sleep (which may be indicative of periodic limb movement disorder, PLMD). Two leads are placed on the chin with one above the jawline and one below. This, like the EOG, helps determine when sleep occurs as well as REM sleep. Sleep generally includes relaxation and so a marked decrease in muscle tension occurs. A further decrease in skeletal muscle tension occurs in REM sleep. REM-sleep Behaviour Disorder (RBD).

Answer 15

a parasomnia characterized by dream-enactment behaviors that emerge during a loss of REM sleep atonia.

Answer 16

- Snoring may be recorded with a sound probe over the neck, though more commonly the sleep technician will just note snoring as "mild", "moderate" or "loud" or give a numerical estimate on a scale of 1 to 10.

Answer 17

Finally, two more leads are placed on the anterior tibialis of each leg to measure leg movements. Though a typical electrocardiogram (ECG or EKG) would use ten electrodes, only two or three are used for a polysomnogram. They can either be placed under the collarbone on each side of the chest or one under the collarbone and the other six inches above the waist on either side of the body. These electrodes measure the electrical activity of the heart as it contracts and expands, recording such features as the "P" wave, "QRS" complex, and "T" wave. These can be analyzed for any abnormalities that might be indicative of an underlying heart pathology.

Answer 18

Nasal and oral airflow can be measured using pressure transducers, and/or a thermocouple, fitted in or near the nostrils - measure the rate of respiration and identify interruptions in breathing. Respiratory effort is also measured - Looking for hypopnea, or a period of reduced airflow, or an obstructive apnea. Pulse oximetry determines changes in blood oxygen levels that often occur with sleep apnea and other respiratory problems. The pulse oximeter fits over a fingertip or an earlobe.

Answer 19

In fact, there is none – the choice of the reference only affects the absolute electrode voltages across all electrodes while the relative voltages remain completely unchanged. - This means that changing the site of the reference may make the scalp voltages look quite different, even though the relative distribution is completely identical. Imagine a landscape with mountains and valleys. Changing the reference electrode is similar to flooding the landscape with water. While the sea level changes, the absolute shape of the landscape is completely unchanged

Answer 20

Something to bear in mind when considering this question is the Nyquist Theorem. - It states that “all of the information in an analog signal (like EEG voltages) can be captured digitally as long as the sampling rate is more than twice as great as the highest frequency of interest in the signal.” In more simple terms, the highest frequency that you can analyze in an EEG signal is half the size of the sampling rate. - For example, if you sampled your data at 256 Hz, you should only analyze frequencies up to 256 / 2 = 128 Hz. Some researchers are even stricter and recommend to use only frequencies up to one third of the sampling rate (e.g., 256 / 3 = 85.3 Hz). Remember that the brain primarily generates lower frequencies (for example, from delta [1 - 4 Hz] to gamma [25 - 80 Hz]), so even with low EEG sampling rates around 100 Hz you can be quite certain to obtain interpretable data.

Answer 21

generates electric currents that are picked up by electrodes. - The closer the muscles are to the electrodes, the stronger their impact on the recording will be. Particularly the activity of facial muscles (forehead, cheek, mouth), neck muscles and jaw musculature has severe effects on EEG recordings. - Clenching should be avoided at all costs – instruct respondents to avoid chewing or tensing their jaw. As the heart is muscle, it also affects EEG data quality. Hearts cannot be simply instructed to stop, you have to rely on signal decontamination procedures to remove ECG noise from EEG recordings. Ideally, you can monitor heart rate with an optical sensor (e.g. photoplethysmography) or an ECG device.

Answer 22

Eye movements: affect the electrical fields picked up by the electrodes. - Vertical eye movements (up-down) look more sinusoidal, - while horizontal eye movements (right-left) look more box-shaped. The eye has a strong electromagnetic field that is established by the millions of neurons in the retina. Moving your eyes also shifts the electrical field generated by the eye ball. It’s recommended to record eye movements using eye trackers or by placing additional EEG electrodes surrounding the eyes.

Answer 23

Movement of an electrode or headset movements can cause severe artifacts that are visible in the affected channel or in all channels - an electrode loses contact with the socket - electrodes are securely attached to the skin Line noise (60 Hz in the US, 50 Hz in the EU) - Filters - cognitive frequencies of the brain are often below the 50 or 60 Hz range