EEG

Method used to record an electrogram of the electrical activity on the scalp that has been shown to represent macroscopic activity of surface layer of brain underneath. Non-invasive.

EEG measures voltage fluctuations resulting from ionic current within neurons. Typically refers to recording of spontaneous electrical activity of a period of time as recorded from multiple electrodes.

Diagnostic applications: Event-related potentials or spectral content of EEG.

• ERPs: Potential fluctuations time-locked to an event (ex. ‘stimulus onset’)
• Spectral content: Neural oscillations (‘brain waves’) that can be observed in frequency domain

What is being measured in EEG?

We measure synchronized neuronal activity. Neurons act as dipoles, causing ions to move from positive sites to negative sites. If sides are oriented opposite to each other, they cancel each other out & there’s no signal. Neurons must be oriented positive-positive & negative-negative for a signal to be picked up. A mixed orientation will

Finish this part. Take from Google Doc week before 5/23 tutorial

Properties

Coherence in EEG
Power in EEG
Event-related potentials

Frequency bands in EEG

• {{c1::Delta (<4 hz)}}: {{c2::frontally in adults, posteriorly in children, high-amplitude waves}}
  • Associated with adult slow-wave sleep and found during continuous-attention tasks
• {{c1::Theta (4-7hz)}}: {{c2::found in locations unrelated to task at hand
  • Higher in young children, drowsiness in adults/teens, idling, inhibition of elicited responses}}
• {{c1::Alpha (8-12hz)}}: {{c2::posterior regions of head, both sides, higher in amplitude on dominant side. Central sites (c3-c4) at rest}}
  • Relaxed/reflecting, closing eyes, inhibition control
• {{c1::Beta (13-30hz)}}: {{c2::both sides, symmetrical distribution, most evident frontally; low-amplitude waves}}
  • Range span: active calm → intense → stressed → mild obsessive. Active thinking, focus, high-alert, anxious
• {{c1::Gamma (>32 hz)}}: {{c2::somatosensory cortex}}
  • Displays during cross-modal sensory processing (perception combining senses), short-term memory matching of recognized objects, sounds, tactile sensations
• {{c1::Mu (8-12hz)}}: {{c2::Sensorimotor cortex}}
  • Rest-state motor neurons

EEG In psychiatric disorders

EEG In psychiatric disorders

From Newson and Thiagarajan 2019

ADHD

• Age-dependent (significant in children) increase in theta and decrease in beta under eyes closed conditions (increase in theta/beta ratio)
  • Approved as a biomarker by the FDA
  • But there’s a general pattern of increase in theta or decrease in beta in other disorders incl. OCD, SCZ, internet addiction — reduced theta/beta ratio is a general marker for shared symptoms across a number of disorders rather than specific to ADHD

Schizophrenia

• Consistent and reliable increases in the absolute delta and theta band power, decreases in absolute alpha band power with eyes closed
  • In eyes open, increase in theta, alpha, beta
• Differences are higher in magnitude relative to differences reported for other disorders (avg theta increase 50%, alpha decrease 58%)

Depression

• Increase in absolute power in theta and beta for both eyes open and closed, but nonsignificant when considering relative power
• Large study of 1,344 participants using a different methodology than other studies identified increases in theta across frontal regions of the brain

Addiction

• No significant difference across addictions (opioid, alcohol, internet) except beta which has an increase for opioid/alcohol addiction & decrease for internet addiction
• Increase in theta power for alcohol addiction & decrease in alpha for opioid addiction

OCD

• Similar to ADHD & SCZ: increase in delta & theta bands and decrease in alpha band
  • High consistency for absolute, but low for relative power
• Often comorbid with other disorders & these changes are unlikely to reflect changes purely attributable to OCD. There may be overlap in symptoms with ADHD and schizophrenia.

PTSD

• Generally, no significant differences in spectral bands (reasonable consistency)
• When differences reported, they suggest decrease in all bands in disorder group for eyes open conditions, and increases/decreases for eyes closed conditions

Autism

• Little or no significant difference in the majority of bands, with exception of delta/beta eyes closed & alpha eyes open. Highly inconsistent results, no patterns can be inferred.

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Related

References

EEG

Link to original

Dipoles

Orientation of neuron dipoles with regard to gyri and sulci. Commonly, neurons are oriented perpendicularly to the skull in the gyri, which creates what’s called a radial dipole. As the layer of brain moves downward into a sulcus (valley), neurons are oriented parallel to the skull, which creates a temporal dipole. Neurons on sulci also create radial ripoles, but these are farther away from the skull and the signal must project significantly farther to be picked up by the electrode.

Advantages

• Lower hardware cost
• High temporal resolution
• Easy to use (easy to train, cheaper equipment, easy to set up)
• Tolerant of subject movement
• Silent and does not aggravate claustrophobia
• No exposure to high-intensity magnetic fields
• No exposure to radioligands
• Non-invasive

Disadvantages

• Low spatial resolution on scalp
• Poorly measures neural activity occurring below cortex
• Cannot identify specific locations at which specific neurotransmitters, drugs, etc. can be found
• Often takes a long time to set up
• Signal-to-noise ratio is very poor so it requires sophisticated data analysis and large # of subjects

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Related

References