PSYC20006 Lecture Notes - Lecture 3: Telepathy, Meninges, Depolarization
10 May 2018
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Lecture 3
- EEG: electroencephalography: method of detecting neural activity by placing
electrode on the scalp; electrodes pick up small fluctuations of electrical signals,
originating from activity of (mostly cortical) neurons
- Raw signals recorded are very noisy and might not look like much → systematically
related to cognitive processes; can use signals to learn something about cognition
when people perform tasks
- EEG recorded at the scalp is non-invasive: don’t open scalp, don’t stimulate brain
(just listening); also possible to record intra-cranial EEG by measuring activity directly
at the exposed cortex (record from inside the brain, stick electrodes inside brain)
- EEG is cheap and relatively easy to connect
- Hans Berger (1873 -1941): detected the first EEG signal in 1924 with electrodes
attached to the scalp of a human (his wife) and reported the results in 1929; initially
studied medicine because he was convinced that there is “psychic energy”
(something to study in brain that explains cognitive phenomenon), which might allow
for telepathy; wanted to discover the objective activity in the brain and “psychic
phenomena”, but he did not realise the basis and potential of his discovery at the
time
- Two electrodes on the scalp → measured the difference in signal in electric activity
- Alpha rhythm: when people relax and closed their eyes, electrical signal was not
constant but varied with a characteristic frequency of 8-13 Hz, regular, slower
- Frequencies that are dominant in signal strongly depend on cognitive state
- Initially used two electrodes, one attached to front of the head and one to the back of
head, recorded the potential (voltage) difference between them; electrodes were
silver wires placed under the scalp → later silver foil placed on scalp
- EEG: temporal resolution is great (how fast is signal, how often can you pick up one
signal after the other, can be recorded every millisecond or faster), but spatial
resolution is not so good (rough measure, can’t say this is one neuron doing
something, one area of brain doing stuff, spatially very rough signal because of cap
over entire head) ;
find more resources at oneclass.com
find more resources at oneclass.com
-
- Signals are very tiny, electrodes have small amplifiers
- EEG comes from neurons: pick up incoming signals
- EEG activity does not reflect action potentials but originates mostly from post-
synaptic potentials – voltages that arise when neurotransmitters bind to receptors on
the membrane of the post-synaptic cell
- This causes ion channels to open or close, leading to graded changes in the potential
across the membrane (depolarisation)
- Neuron can be understood as a small “dipole” when they receive input
- Signals from single cells are not strong enough to be recorded outside of the head,
but if many neurons spatially align, then their summed potentials add up and create
the signals we can record
- Pooled activity from groups of similarly oriented neurons mostly comes from large
cortical pyramid cells
- Functional unit is >10,000 simultaneously activated neurons, in order to get a signal
that can be recorded
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Eeg: electroencephalography: method of detecting neural activity by placing electrode on the scalp; electrodes pick up small fluctuations of electrical signals, originating from activity of (mostly cortical) neurons. Raw signals recorded are very noisy and might not look like much systematically related to cognitive processes; can use signals to learn something about cognition when people perform tasks. Eeg recorded at the scalp is non-invasive: don"t open scalp, don"t stimulate brain (just listening); also possible to record intra-cranial eeg by measuring activity directly at the exposed cortex (record from inside the brain, stick electrodes inside brain) Eeg is cheap and relatively easy to connect. Two electrodes on the scalp measured the difference in signal in electric activity. Alpha rhythm: when people relax and closed their eyes, electrical signal was not constant but varied with a characteristic frequency of 8-13 hz, regular, slower. Frequencies that are dominant in signal strongly depend on cognitive state. Signals are very tiny, electrodes have small amplifiers.
