Lecture 5 - introduction to EEG Questions And Answers

EEG- what does it stand for? correct answer: Electroencephalogram Electro- meaning electrical encephalo- meaning releating to the brain gram- measurement sometimes called electroencephalography Invention of EEG (who and why) correct answer: Hans Berger () A neurologist interested in extra-sensory perception Wanted to measure 'brainwaves' responsible for telepathy- this was because of a near death experience where he thought that he could telepathically communicate with his sister. Developed the technique of recording electrical activity at the scalp, published in 1929. The signals were very small and he realised that this would not permit telepathic communication. Not taken seriously for around 10 years Eventually killed himself after having his research shut down by the Nazis What does EEG measure? correct answer: Neurons are electrical devices- they send electrical signals down the axon. Cannot measure the activity of one neuron in the brain (to do that would need to do invasive procedures) However the activity of populations of neurons firing together produces a change in electrical polarization in the brain Can be measured at the scalp with electrodes People think that the EEG signal comes from the pyramidal cells that are in the top layer of the cortex, as they tend to be aligned orthogonally to the scalp and the electrical signal is going in the right direction to be detected. N and P waves stand for positive and negative waves electricity and magnetism correct answer: Electrical current flows down the dendrite So the tissue above the cell becomes positively charged and the tissue below negatively charged (so you are producing a potential voltage across part of the brain) A magnetic field is also produced at right angles (MEG can detect magnetic field. If a large number of neurons are all firing at once, this will produce an electrical dipole and an accompanying magnetic field We can measure these with EEG electrodes and MEG sensors (can see this in slide diagram of isopotential lines and isoflux lines) EEG and MEG are detecting the same activity, but in a different way. isopotential lines correct answer: lines connecting points of equal electrical potential. isoflux lines correct answer: lines connecting points of