Please enable JavaScript.
Coggle requires JavaScript to display documents.
methods of brain investigation - Coggle Diagram
methods of brain investigation
correlational
EEG
signal primarily originates from the depolarization of pyramidal neurons.
measures Local Field Potentials (LFPs)
result of synchronized synaptic input activity into the dendrites of neurons.
Measures electrical potential differences on the scalp
extremely high temporal resolution (ms)
Large numbers of neurons must be active simultaneously to create a sufficiently strong dipole
(signal summation) / synchronization
.
Neurons must have the same orientation so their fields do not cancel each other out
Gyri
Sensitive to radial dipoles (neurons oriented perpendicular to the cortical surface)
Uses electrodes and conductive gel placed on the scalp
volume conduction
causes smearing/blurring
low spatial resolution
"inverse problem,"
difficult and underdetermined to pinpoint exactly where a 3D source in the brain is located based on 2D measurements taken at the surface
intracranial EEG
eCog
eliminates blurring
requires a surgical opening to place a grid of electrodes directly onto the cortical surface
primarily used to find the focus of epilepsy and for functional mapping during awake brain surgery
functional MRI
*T2
Echo Planar Imaging (EPI)
tracks the Blood Oxygenation Level Dependent
(BOLD)
response
deoxygenated blood is paramagnetic (signal loss)
oxygenated blood is diamagnetic (no signal loss)
By detecting these local changes in signal loss, fMRI creates a 4D model of brain activation over time
MEG
Measures magnetic activity generated by electrical currents
Sensitive to tangential sources (neurons oriented parallel to the skull)
sulci
Uses SQUID sensors (superconducting quantum interference devices) in a helmet
structural / connectivity
structural MRI
hardware/mechanisms
excitation
An RF coil sends a pulse (the B1 field), moving protons out of alignment (orthogonally).
relaxation
When the RF pulse stops, protons relax back to the B0 alignment.
alignment
A strong magnetic field (B0) aligns protons in the direction of the field.
signal detection
protons release energy picked up by the RF head coil to form a 3D image.
Image weighting
T1
Measures longitudinal relaxation (spin-lattice)
how fast protons realign with the B0 field.
used for structural images
fat appears bright
water appears dark
T2
Measures transverse relaxation (spin-spin)
the loss of phase alignment due to interactions with the surrounding tissue.
fat appears dark
water appears bright
used for pathology
Diffusion Tensor Imaging (DTI)
to map white matter connectivity in the brain.
Fractional Anisotropy (FA)
0 = random diffusion (no directionality).
1 = highly directional diffusion (healthy white matter tracts).
Measures the anisotropic diffusion of water along axons
reconstruction of fibre pathways
Voxel-Based Morphometry (VBM)
Estimating grey matter volume and neuron density in specific locations
purely structural method focused on the morphology (volume/thickness) of grey matter
Tracers
Uses physical markers to follow the path of fiber
stimulation
Brain stimulation (Penfield)
Direct electrical stimulation of the cortex via bipolar electrodes
tDCS (anodal)
Application of low-intensity direct electrical current via a negatively charged pole
Transcranial magnetic stimulation (TMS)
Uses a magnetic field to induce electrical currents in the brain (Right hand grip rule)
inhibition / interference
reversible
TMS
Uses a magnetic field to induce electrical currents that can create a "virtual lesion" to temporarily interfere with brain areas
cooling
Uses a methanol pump to lower the temperature of a brain regio
tDCS (cathodal)
Application of low-intensity direct electrical current via a positively charged pole
permanent
strokes
tumors
lesions
