Lecture 2.2: Measurement of Neural Structure and Function

Question 1

STED and STORM

Answer 1

In STED: super resolution is achieved by narrowing the point spread function the diffraction disc (Airy disc) by using a laser to precisely deactivate the outmost portion of the disc.
In STORM: the random switching of fluorescence of individual molecules allows their individual contributions to be imaged: single molecules, which are stochastically switched on, imaged and localized, and then switched off. Many cycles of this allows the centre of these discs to be calculated and the image is constructed from millions of locations.

Question 2

CT scans use

Answer 2

X-rays. Varying attenuation of the x-ray comes from the different densities of the tissues encountered along the way. X-ray detectors positioned around the circumference of the scanner collect attenuation readings from multiple angles. A computer reconstructs an image of each slice

Question 3

PET scans use

Answer 3

Radio-labelled compounds that are injected in trace amounts, and their photon emissions can be detected much like x-rays in CT.
The images made represent the accumulation of the labelled compound. The compound may reflect, for example, blood flow, oxygen or glucose metabolism, or chemical concentrations (such as administered drugs), thus can provide functional or pharmacological data. The ionising radiation used in PET and SPECT studies is harmful in large doses; this limits the number of scans an individual can receive.

Question 4

fMRI/BOLD

Answer 4

The “blood oxygenation level dependent” (BOLD) imaging technique does not measure tissue perfusion or flow directly but exploits the difference in the signal decay of de-oxygenated blood.
The properties of the protons of water molecules in the brain change slightly between areas that are near blood with its oxygen exhausted relative to those near freshly oxygenated blood.

Question 5

MEG

Answer 5

Method of measuring the tiny magnetic fields produced when groups of the brain’s 100 billion or so cells, or neurons, are active.
These magnetic fields generated by electrical currents produced by coherent neural activity are a billion times smaller than Earth’s magnetic field.
Provides no structural information. Must be paired with MRI or CT scans