Neuroscience Techniques Flashcards
What does MRI stand for
Magnetic resonance imaging
What does MRI measure? And how?
It measures the presence of water in the brain. It detects the protons making up the hydrogen atom in the water molecule. This is achieved by combining a strong magnetic field and radio pulses which has the effect of the protons emitting radio signals. These signals are then picked up by the MRI. It shows the different levels of water in different shades of gray
How much water is there in the brain tissue?
73%
What happens to the protons?
Normally they are randomly spinning around. Exposure to the magnetic field aligns their orientation. When the radio frequency pulse is applied, the axes of the protons are shifted in a predictable manner and when the pulse is turned off the protons release their energy as they spin back to the orientation of the magnetic field.
what is the difference between white and grey matter?
grey matter is cell bodies and dendrites; white matter is axons (cabling)
Does MRI have high spatial or temporal resolution?
It has a spatial resolution of 1 mm
What does DTI stand for?
Diffusion Tensor Imaging
What does DTI measure? What can it help understand?
It is a kind of MRI that measures how the water in the brain moves, and not just its presence. As water doesn’t just run freely, but rather MOSTLY along the axons > DTI can help giving high-resolution structural images of long-range axons running in white matter. It can measure white-matter connectivity
What’s the movement of water?
anisotropic > restricted by the various cell membranes. It diffuses best between the sheath and the axon.
what is in vitro measurement
making observation from outside of a living organism.
what is in vivo and what does it measure?
In vivo measures action potentials inside the living brain > this requires opening up the skull and putting electores directly onto the skull.
what do direct measures do?
They measure either the primary or volume currents in the brain
what to indirect measures do?
They measure blood flow in the brain
What are pyramidal cells?
They make up around 80% of neurons in the brain. They have two types of dendrites: APICAL DENDRITES > long that stretch towards the surface of the cortex and BASAL DENDRITES > horizontal direction and cover less distance.
How are pyramidal cells organised?
They are organised into cortical columns which are interconnected, so they seldom get activated alone. So a signal from outside the column, activates the whole column and the ones near.
What is a large number of pyramidal cells called
A neural mass.
What does EEG measure?
It measures the voltage between two locations on the scalp. (It two brain regions have a different electric potential, meaning that one has more positive ions than the other, electric current would flow between them till they become equal). The electric potential is measured in Volts and that’s what we measure.
When ions are being packed into the area underneath one electode and pulled away from another, this creates voltage difference which is measured.
So: it measures electric potential fluctuations caused by the volume currents due to neurons becoming active
what does neuronal activity change? And how can this be measured?
It changes electric potential and can be measured through EEG
Main difference between EEG and MEG
EEG measures the volume current, which MEG measures the primary current.
What does MEG measure?
It measures the magnetic field of the primary currents. It needs to be measured in a magnetically shielded chamber
What is better in MEG than EEG
It has a higher spatial resolution
What is MEG blind to?
Activity in the gyri because they reverse down, away from the measuring field.
What are the types of brain oscillations? And how is freuquency and amplitude
Gamma (high-frequency and low amplitude), Beta, alpha, theta, delta (low-frequency, high amplitude). They all refer to different brain activity.
What are the advantages of EEG and MEG
They are direct measures, are non-invasiveand have a high temporal-resolution. EEG is also relatively cheap
What are disadvantages of EEG and MEG
They have a low spatial resolution and can’t solve the inverse problem.
What is the change in bloodflow in the brain called?
Haemodynamics
What does the fMRI measure
It measures the level of oxygen in the blood: Active neurons take oxygen from the blood (so blood is deoxygenated) and this can tell you which neurons were active at the time.
what is a voxel?
A 1mm cube of neurons
What is the signal measured by the fMRI called?
BOLD signal
What are advantages of fMRI?
It is non-invasive and has a good spatial resolution as it allows to study any area of the brain. It has no inverse problem
What are disatvantages of fMRI
It has low temporal resolution as oxydation of blood takes around 2 seconds and rises to a peak at around 4-6 seconds. Also because of the nature of comparison it is difficult to see what activation is due to the stimulus and what is because of nothing. Complex Statistical analysis and complexity of equipment. Replication crisis.
What are PET and NIRS
PET is semi-invasive and older; NIRS measures oxygenation in blood through infrared light and is mainly used in infant studies. The problem is it can’t reach rubcortical regions of the brain.
What do brain perturbations question?
What is the effect of a perturbation of brain activity on task performance and stimulus processing?
What are optogenetics?
Genetically modified neuron so that the ion channels become sensitive to light and can be switched on and off at will.
What and how does TMS measure?
It’s a coil-shaped conductor that generates a magnetic field, placed next to the skull. This penetrates through the skin and generates a focal electric field in the brain, which depolarises neurons locally, changing their normal activity. This can induce plastic changes to the brain and can have long-lasting beneficial effects for clinical stuff.
What and how does tDCS measure?
It has two electrodes at the sides of the skull, the anode and the cathode.
What are advantages and disadvantages of TMS and tDCS?
They both have high spatial and temporal resolution. They are safe, portable and relatively cheap and can have major advantage. But the neurophysiological effects are not yet certain. And they don’t reach deeper than the cortex.
