tutorials

• Electroencephalography (EEG)


  Measures electrical activity of the brain, sum of inhibitory and excitatory post-synaptic potentials
• EEG


  • Non-invasive, direct and continuous measure of the changes in electrical potentials at the scalp produced by neural activity in real-time
• How do we record and quantify EEG?

  1. EEG cap or wireless device fitted with electrodes; usually multichannel

  2. Standardised EEG electrode placement according to International 10-20 system

  3. Standardised electrode placement (10-10 system) - Coronal (Left, Midline, Right) and Sagittal (Frontal, Central, Parietal, Occipital) dimensions

  4. Common artifacts: muscle activity, movement, eye movements, blinks, shoulder tension, jaw clenching, frowning, head movement, cardiac artifact, mains interference

  5. Bipolar recording: two active sites

  6. Monopolar recording: one active site and one inactive site

  7. Waveforms are the sum of activity in many frequencies, frequency of a wave = number of cycles/second (Hertz; Hz), wave magnitude decreases as frequency increases, Amplitude (microvolts; µV) or Power (microvolts squared; µV^2)
• How do we record and quantify EEG?

  1. Use frequency analyses to identify activity at each frequency, Fast Fourier Transform (FFT) used to transform EEG from time domain to frequency domain

  2. Sum the activity in the frequencies of the traditional EEG bands: Delta, Theta, Alpha, Beta

  3. Headmaps use heat-map colour coding

  4. Algorithms can estimate the source/s of the EEG activity

  5. Time-frequency analyses show how the activity in each frequency changes in time
• EEG signals


  • Vary with a person's state or mental activity, can tell us about how alert, motivated, or engaged we are, or how difficult a task is
• Traditional EEG bands and their functional correlates

  • Delta
  • Theta
  • Alpha
  • Beta
• Applications of EEG


  • Neurological diagnosis and development (e.g. epilepsy, aging and cognitive decline)
  • Examine nature of deficit in clinical groups (e.g. AD/HD, OCD, Schizophrenia)
  • Neurofeedback (e.g., attention training, relaxation training)
  • Control of prosthetic devices for patients with paralysis
• Electroencephalogram (EEG)


  Waveforms of differing frequency associated with different psychological states
• EEG


  • Pros: Non-invasive, very high temporal resolution (1 ms)

  Cons: Low spatial resolution

  Risks/dangers: Relatively cheap
• EEG is suitable for use in pain studies
• EEG may be a suitable measure for your study
• Event-Related Potentials (ERPs)


  Electrical potentials generated by the brain in response to specific events, measured using EEG
• Electroencephalography (EEG)


  Technique to measure spontaneous electrical potentials generated by the brain
• Neurons communicate through electro-chemical signals, generating electrical potentials that propagate to the scalp
• These changes in electrical potential can be measured
• Creating Event-Related Potentials (ERPs)

  1. Time-lock the EEG signal to an event

  2. Process information

  3. Respond to events
• Spontaneous EEG


  Electrical potentials generated by the brain, occurring at the same time as the event-related signal
• Event-related activity


  Activity related to the event
• Noise


  Activity unrelated to the event, e.g. muscle movement, non-task related thoughts, metabolic regulation
• Increasing signal-to-noise ratio for ERPs

  Average over repeated trials of the same type
• ERP waveforms


  Deflections (peaks and troughs) in the waveform that reflect the summation of neural activity in response to an event
• ERP components


  Described by measurements of the physical properties of the deflections, including amplitude and latency
• The onset of the event is considered time 0, or the start of processing (i.e., 0 ms)
• ERP signals


  • Contain multiple sources of neural activity that overlap in time
  • Amplitude and latency of ERP components may not perfectly reflect amplitude and latency of any one neural source
  • Topography maps reflect scalp voltage distributions, not brain locations
• Complex processes are the combined activity of simple cognitive processes, each mediated by one or more brain areas
• ERPs


  Electrical potentials elicited by an event, used to study the timing and organisation of processing related to the event
• ERP components


  Indices of sensory and cognitive processes
• Investigating ERP components


  1. Manipulate task requirements to isolate constituent cognitive processes

  2. Differences in ERP components between conditions reflect processing differences
• Early ERP components


  Reflect sensory registration of stimulus (exogenous)
• Late ERP components


  Reflect stimulus-related cognitive processes (endogenous)
• Behaviour gives the outcome of a cognitive processing stream, while ERPs allow assessment of the processes that lead to behaviour
• ERPs allow testing hypotheses about how the processing stream is organised, and studying the timing of sensory and cognitive processes
• ERPs provide insight into unconscious processes, as no response is required
• ERPs


  • Direct measure of brain activity
  • Obtained by averaging segments of EEG data time-locked to a stimulus event
  • Waveforms with deflections indexing sensory & cognitive processes
• ERPs have very high temporal resolution (1 ms) but low spatial resolution
• ERPs are relatively cheap but data analysis is complex
• ERPs are non-invasive and have longer duration (multiple trials)
• ERPs have very high data quality
• ERPs may be suitable for assessing the impact of pain on sensory, cognitive, or other processes
• Electrodermal Activity (EDA)


  Relating to electricity (more specifically its conductance), and referring to the dermis or skin