Cog & Bio Common Methods Lecture Flashcards
How do neurons communicate?
Through synaptic transmission
Where do neurons send messages?
At the synapse
Dendrites receive what?
The message in the 2nd neuron
What separates the two neurons?
Synaptic cleft
What happens when the presynaptic neuron sends a message?
It becomes active
What happens when a neuron becomes active?
Generates an action potential and gets ready to fire
What happens when there’s no action potential?
Neuron is negative
Is sodium iron positive or negative?
Positive
What is depolarisation?
Inside cells move from more negative to more positive
Is potassium positive or negative?
Negative
Inhibitory means?
Neuron moves further away from firing
How long does an action potential last for?
Around 1millisecond
What does electroencephalography (EEG) record?
Records synchronised post-synaptic activity (not action potentials) of similarly orientated pyramidal cells
What are pyramidal cells?
Neurons at the surface of head
What do pyramidal cells generate?
Generate largest signal - generated post-synaptic potential
Exhibitory = ?
Positive
Does EEG have high temporal resolution?
Yes - millisecond level
Does EEG have high spatial resolution?
No - skull smooths and blurs the signal
2 benefits of EEG
Relatively cheap, most common
What does Magnetoencephalograohy (MEG) measure?
Measures changes in the magnetic field generated by the same neural populations with sensors
What is temporal resolution?
How accurate can a method pick up fast pace changes in brain activity?
What is spatial resolution?
How well a method can tell you where something is happening in the brain
Positives of MEG?
High temporal resolution
High spatial resolution (3-5mm)
HOWEVER
quite expensive
What is the difference between MEG and EEG?
MEG practically blind to radio sources but is sensitive to tangential dipoles
What do frequency domains tell us?
Can look at frequency domains of activity, can transform into frequency and look how frequent that activity occurs
What does Fourier transform do?
Decomposes any waveform into its constituent frequencies - tells us which frequencies are present in the original wave and to what extent
What does a cosine wave represent in Fourier transform?
Real part
What does a sine wave represent in Fourier transform?
Imaginary part
What methods are uncommon in humans?
Electricortocograpgy (ECoG) and Stereo-EEG with depth electrodes
Methods used in certain patients e.g epilepsy
What happens when the body is placed in a strong magnetic field? 2 points
- A slim majority of H protons will line up parallel with the field (the rest anti-parallel) - this creates a longitudinal net magnetisation vector
- The protons will precess (spin around their axis)
What happens when radio frequency is applied to the system? 2 things
- Protons will get knocked into a different orientation
- Protons will start precessing at the frequency of the pulse, creating transverse magnetisation vector - start spinning together
What happens after the radio frequency pulse is applied?
- Protons return to their original orientation - recovering longitudinal magnetisation - equilibrium
- Protons go back to asynchronous precession - lose transverse magnetisation
What happens during the return to equilibrium? 2 points
- Return to starting orientation - T1 recovery or spin lattice relaxation - recovery of longitudinal magnetisation - 63% recovered
- Dephasing - T2 decay or spin lattice relaxation - loss of transverse magnetisation - 63% lost
Why do protons never spin totally simultaneously?
Due to field inhomogeneities
How do you combat T2 effects (differences in spinning doors due to magnetic field inhomogeneities)
180 degree refocusing radio frequency pulse - makes protons precess in the other direction - there will be another moment of synchrony between slower and faster protons producing an echo
What does the MRI read out?
The echo
What does TR stand for in pulse sequences that can be used to generate an image?
Time to repetition (from RF pulse to RF pulse)
What does TE stand for in pulse sequences that can be used to generate an image?
Time to echo - from centre of RF pulse to centre of echo
Why would you want to manipulate TR and TE?
Because different tissues have different T1 and T2 times based on the density of H atoms and their molecular composition - difference between relaxation times creates a contrast in the image
Shorter TRs emphasise…
T1 effects
Slower T1 = ?
Smaller longitudinal magnetisation
Faster T1 = ?
Greater longitudinal magnetisation
Long TE emphasises … ?
T2 effects - longer TE = more T2 decay, bigger difference between tissues in T2
What does the magnet do in MRI machine?
Creates the magnetic field B0
What do the gradient coils do in MRI machine?
Varies the magnetic field to localise the region to be scanned - focuses magnetic field on area of body you want to research / image
What do RF coils do in MRI machine?
Sends the RF pulse and detects the emitted signal
What do shim coils do in MRI machine?
Correct inhomogeneities in the magnetic field
What is neurovascular coupling?
Blood flow increases to active brain regions - lots of oxygenated blood to the firing neurons - increase in oxygenated haemoglobin concentration
Oxy blood magnetic properties?
Oxygenated ones bit distort field, while deoxy does, leading to signal loss - oxy will be comparatively brighter
How does fMRI differentiate between active and non-active regions?
FMRI differentiates regions that are more active based on different magnetic properties in deoxygenated blood
Name a brain stimulation method
Transracial magnetic stimulation (TMS)
What does tms use?
Electromagnetic induction to excite neurons (depolarising pyramidal cells and interneurons)
What is a tms pulse?
Electrical current passes through a coil briefly producing a magnetic field
The field travels through scalp, skill and brain tissue inducing currents in excitable media
This can trigger action potentials in neurons e.g motor-evoked potentials (MEP) after stimulation of primary motor cortex
What can be modified in pulse?
Duration, shape, intensity, frequency of pulses - have different consequences
What can TMS be combined with?
EEG
Describe Transcranial electrical stimulation
- delivers a weak electrical current (0.5-2mA) to the scalp
Thought to modulate resting membrane potentials rather than trigger action potentials
At least 2 electrodes, one of them placed over the region of interest
What is transcranial direct current stimulation?
Current is continuous in one direction - anode to cathode
What is transcranial alternating current stimulation?
Current direction alternatives between the electrodes, field oscillates
What is transcranial random noise stimulation?
Current varies according to a noise distribution
