Task 3 Flashcards
Name facts about EEG:
- measures electrical activity of the brain revealing some properties about mental stats (sleep memory attention)
- High temporal resolution poor spatial resolution
Name The Set up of an EEG
- Non invasive electrodes are placed on the scalp
What does the EEG meassure ?
- Synchronized synaptic activity
- > activity of large group neurons that acre active at the same time
What is the EEG used for?
- Detects abnormalities in brain function
- Ongoing EEG
- > Subjects are usually not doing anything
- > It is the search of a particular state (dowsiness)
- > Neurofeedback (sport) - EEG response to stimuli
- > ERP
What are limitations of EEG ?
- > Reveals little information about cognitive processes
- > because the recording tends to reflect the brain’s global electrical activity
What are certain measurement issues off EEG ?
- Noise / artifacts
- > External noise / Extraphysiological artifacts
- > Internal noise / Physiological artifacts
What is meant by noise ?
-> Voltage that reflects sources outside the brain
How is the noise level being meassured ?
- Signal to noise ratio
- The higher the SNR the better the Signal
What is meant by external noise ?
How can it be reduced ?
Defintion:
-> Noise produced outside the body ( wires in wall or fly)
Reduced:
-> Shielding: a piece of metal surrounding the region to be measured which cancels out electromagnetic radiation
-> Active electrodes: Using an amplifier close to the electrodes
What is meant by internal noise ?
How can it be reduced ?
Defintion:
-> Noise produced inside the body (eyeblink)
Reduction:
-> Can not be eliminated just minimized via controlling the environmental factors
Whar are other method to reduce noise ?
-> Remove very slow & very fast voltage changes, as they are likely to be due to noise (against internal noise)
-> Use an active and a reference electrode to identify how much noise exist
• Reference electrode should always be placed on the mastoid bone
-> Use a pre stimulus baseline period
Name facts about ERP:
- > Electrical potentials generated by the brain which are related to specific internal or external event
- > ERPs are extracted from the EEG signal over many trails and averaged
What are ERP being used for ?
- > identifies how brain activity changes in response to a particular task
- > temporal resolution
- > Identify cognitive processes
Where should ERP not being used?
- > Does not answer neruroanatomical questions
- > No deception
- > Averaging process must be doable
Where is a ERP Method in particularly used ?
- > infants and young children
- > these individuals have relatively poor control over their behavior, ERPs can reveal mental processes that are difficult to assess behaviorally
Which synaptic potentials are being meassured within an EEG?
- > Postynaptic potentials
- > Action potentials are to fast to be meassured
Explain how we meassure an EEG signal
-> Look at the task sheet
What is a dipole ?
-> oriented flow of energy (looks like a cycle)
Is one dipole enough for an EEG signal ?
- > no it is about summation of many dipoles
- > linear superpostion
How is a dipole constructed ?
- > Source: region of positive (extracellular) charge /negatively intracellular charged
- > Sink: region of negative (extracellular) charge / positive intracellular charged
What do the electrodes meassure ?
- The activity of the active electrodes in voltage = the weightes sum of activity from all dipoles
- The activity of the reference electrodes in volatge
- > mostly placed on mastoid bone to have no brain actvity
What are the assumption which must be met in order for an electrode to detcet the activity of a dipole ?
- Neurons must be synchrously active / have similar input
- > All neurons are negtaivley charged on the dendrites and positively charged on the cell body - Neurons must be arranged in a parallel fashion
What two types of orientaion exist ?
- Radial dipoles
- > are located in the cerebral cortex, they are perpendicular to the cortex
- Tangetial dipoles
- > are oriented parallel to surface
What and How does the signal reach the electrode ?
- Tissues of the brain, skull, and scalp passively pass on the electrical impulse
