Cognitive neuroscience Flashcards
(133 cards)
What is the principle of MRI
hydrogen is measured in the brain. The nucleus of a hydrogen atom is a single positively charged proton, a tiny spinning magnet. The huge magnet causes the external magnetic field is induced align the hydrogen in one direction. Second magnetic field is induced, direct the direction of the magnetic field for a short time. By switching off the b1 the hydrogen wants to go back to its original direction. The different tissue types have a different in time that the hydrogen goes back to the B0 direction -> this is how you see contrast.
how does fMRI work?
M0 recovers more slowly in oxygenated blood than in deoxygenated blood. To measure which brain area is active. Active brain areas are more oxygenated. You are measuring BOLD: Blood oxygen level dependent.
What is blocked design?
stimuli are often presented in quick succession in blocks between baseline periods, signal increases to plateau. -> only possible for simple tasks
o Multiple trials needed for good SNR
o No information about duration or time course of activation
o Only possible for simple tasks.
What is event related design?
between stimuli the signal goes back to the baseline.
o Complex tasks are possible.
o It gives information about duration and time course of activation.
o SNR can be worser: Small signal, less trials, more complex tasks have more conditions, fewer trials per condition.
Advantages of fMRI
o you can measure the whole active human brain
o it can be combined with many kinds of cognitive tasks
o Versatile: Anatomy, connectivity (DTI), Metabolites(fMRS), Neural activity (BOLD)
Disadvantages of fMRI
o You don’t measure neuronal activity but oxygen consumption (not all forms of neural activity consume the same amount of oxygen, action potential/ synaptic potential, excitation vs inhibition)
o Only correlational: you do not know the effect of the measured activity.
o Temporal and spatial resolution are limited.
o behavioural tasks are limited by scanner.
o expensive and time consuming: many subjects and many sessions are necessary for good signals.
LFP
combination of transmembrane currents from many neurons near the electrode: slow frequency, Excitation(sinks) and inhibition(source) occurs simultaneously at different locations of the neuron, such that the net transmembrane current is zero. Cortical LFP’s are so strong you can record them on EEG. Only possible because of elongated bipolar cells.
EEG
non invasive method to measure electric activity with electrodes on the scalp
- High temporal resolution
- Signal distortion and attenuation -> difficult to interpret the signals
ECoG
: electrocorticography: invasive, better signal. Placed surgically on top of cortical areas of brain.
- Utah array: Brain machine interface = electrical recording from motor cortex -> paralyzed patients can do some behaviour tasks by themselves.
Advantage extracellular recording
direct measure of neuronal activity, high temporal resolution
Disadvantages
invasiveness, a limited number of neurons can be studies, a limited applicability to neurons.
Optogenetics
Optogenetics is used to manipulate neuronal activity and verify the effects of such manipulations
Optogenetics principple
optogenetic and gated ion channels: light gated ion channels open when light is introduced -> initiates action potential. -> activates the constructed gene
Steps of optogenetics
- Piece together genetic construct: promotor + gene encoding opsin (light sensitive ion channel)
- Insert construct into virus.
- Inject virus into animal brain: opsin is expressed in targeted neurons
- Insert optrode plus electrode.
- Laser light of specific wavelength opens ion channels in neurons
- Record electrophysiological and behavioural results.
DREADDS principle
pharmacological on/off switch affecting only genetically modified cells.
Steps making DREADDS
- Make your desired receptor: activator or inhibitor
a. Engineered G-protein coupled receptor
b. Responding only to a specific drugs (CNO: clozapine-N-oxide)
c. Responding only with a specific action - Express that receptor in the brain(globally, locally or cell type specific
a. Inject gene for the receptor via AAV(adeno-associated virus)
b. With marker protein - Inject ligand for the expressed receptor
a. Inject the drug for the DREADD or via food, eye drops
Pro’s DREADDS
o The effect can be specific to one cell type or brain region
o The expressed receptors do nothing without CNO, only when CNO is provided, the receptors affect the cellular activity
o No need for light
Con’s DREADDS
o No strict timing control: slow the effect can be long lasting
o Side effect of injects drug?
NMDA receptor
o GluN2 is the glutamate binding domain
GLUN2B in immature hippocampal CA1 neuron
After maturing you get GLUN2A subunits.
Before birth almost all expression of GluN2B and after birth its more GluN2A
o GluN1 is the glycine binding domain
o If glutamate is released NMDA do not respond because of this. -> Depolarization of the membrane then the magnesium blockage is removed. Then NMDA receptors open their channels -> wiring of neurons
o Coincidence detector.
o Slow response
AMPA
AMPA is necessary for inflow of sodium
o LTP is an increase of AMPA receptors.
o AMPA has a faster response than NMDA receptors.
1 type contains GluA1 and GluA2
1 type contains GluA2 and GluA3?
CAMKII
- Calcium/Calmodulin dependent kinase II(CAMKII) is always switched off normally
o If calcium flows in and binds to calmodulin it binds to regulatory segment and it is phosphorylated.
o Because it is in a ring structure in can phosphorylate itself. CAMKII can stay active for over a minute.
o CAMKII can bind NMDA(GLUN2B) -> phosphorylation of AMPAs facilitates LTP -> causes the synapse to widen -> more room for AMPA receptors.
LTP
Early phase LTP: early phase is independent of protein synthesis
Late phase LTP: does require protein synthesis
Habituation
progressive decrease of the amplitude of frequency of a motor response to repeated sensory stimulation.
- Less glutamate released from presynaptic synapse= synaptic depression
- Fewer synapses : In the end there are fewer synapses between the sensory and the motor neurons but this only happens after days of continuing the stimulus.
Sensitization
repeated administration of a stimulus results in the progressive amplification of a response.
- Same number of action potential -> bigger excitatory response because of serotonin released by interneurons, changes the potassium channel causes a longer depolarization.
