EEG + MEG - Brain stimulation Flashcards
1
Q
Receptive field
A
- where + what a stimulus has to be for a neuron to respond
- Many neurons in visual cortex respond more vigorously to specific ornientation
2
Q
Hubel + Weisel- visual experiences
A
- visual experiences are dominant ones
- perception of world based on messages brain from eyes
- following visual impulses along path to cells of optical cortex demonstrates that messages about images falling on retina undergo analysis in nerve cells which all have specific function
3
Q
Colour, Motion + Primary visual cortex
A
- Zeki found specialisation
- V4 = colour
- v 5 /MT= motion
- within v 1 are blobs + interblobs where specialised neurons lie + project to different areas
- v 1 = primary visual cortex
4
Q
specialisation within between visual areas
A
- Blob cells selective to colour
- interblobs selective orientation
- Structural motif
- signals from blobs go thin stripe region in v 2 then colour selectively projects to V4
- selective filtering of signals in v 2
- thick stripe region in V2 leads motion selectively projecting to V 5
5
Q
Human brain measurements + faces
A
- Hippocampus can be highly specific to particular person
- measure cells responding to identity
- cells showed prominent activity to Halle Berry stimulus
6
Q
Single unit electrophysiology
A
- uses microelectrodes to record AP
- Attempts to define receptive field of neurons to understand function
- Neurons that lie together are often responsible in similar ways (blobs)
- Neurons response properties become increasingly specialised (V 1 = baselevel, v 2, V 3, v 4, v 5 )
- invasive + only possible in humans with epilepsy
7
Q
Electroncephalography (EEG)
A
- measures electrical activity in brain
- electrodes placed on scalp record brain waves
- under rest. frequencies reflect different cog States
-osciliations modulated during different cog tasks - waveform oscillates between pos+ neg voltage
- slow oscillations in deep sleep + when awake are much faster
- can determine stages of sleep
8
Q
EEG + concerted neural activation - neural basis of EEG
A
- signals mainly driven by large electric dipoles
- sensitive to electrical field changes of concentrated neurons
- single AP too fast to measure so we see concentrated in membrane potentials
- when neurons receive presynaptic inputs to dendrites, memb potential changes
- excitatory input = pos current travels to Soma + neg current travels extracellular forming dipole
- Neurons are well interconnected + snow synchronised activation patterns
- EEG signaIs reflect changes in local field potential
- magnitude of EEG don’t straight forwardly map on to neural excitation + inhibition
9
Q
EEG responses vs microelectrode recording (MEG)
A
- MEG records primary intracellular current whereas EEG records secondary volume current
- record changes of local field potentials
10
Q
Event Related potentials
A
- Relatively small electrical responses to specific events can be observed
- EEG traces are averages over series of trials
- large background oscillations of EEG trace make it impossible to detect evoked response to sensory stimulus from a single trial
- Averaging across hundreds of trials removes background EEG leaving ERP
11
Q
Time of ERP components give a clue in the pathway where the signals come from - Evoked potentials
A
- Auditory pathway has multiple neural stages
- Auditory and visual Evoked potential is a diagnostic tool
- Evoked potentials allow us to see where the input came from + we can use this to locate potential deficits
12
Q
Problems with EEG
A
- EEG responses in a single trial looks noisy + contains unrelated noise to stimulus
- solution = when averaging across many trials, noise is distributed + cancelled out
13
Q
Selectivity to objects
A
- ERPs consist of distinct components according to polarity
- pos + neg polarities cant be interpreted as pos or neg activations
- larger deflection for faces snows its preferred
14
Q
ERPs and Timing g cog processes - semantic + syntactic
A
- ERPs to semantic + (g syntactic (grammar) violation in lang processing
- Semantic violations impact processing at N400
- sensitivity to violation at 400 brain realises something isn’t right
-syntactic violation impacts processing at p600 stage - syntactic violations processed later than semantic
15
Q
Localising ERP effects
A
- localising on scalp: restricted to electrodes but scalp locations don’t correspond to brain regions
- localising effects in brain: mapping locations of dipoIe has inverse problem, pattern across electrodes can be caused by various dipole configurations
- in EEG localisation is hampered by effects of volume conduction
- Tissue changes voltages of scalp
