Interrogating the nervous system

Question 1

Describe DTI

Answer 1

MRI technique. DTI stands for diffusion tensor imaging. Improve form of diffusion weighted imaging that shows diffusivity of water molecules through employing the property of the intrinsic directionality of water diffusion in the brain. This allows for examination of tissue microstructure, specifically the integrity of white-matter fiber tracts. White matter pathways can be imaged by calculating the constraints on water diffusion (fractional anisotropy) arising from a given site in the nervous system. Basically allows you to imagine connectivity of the brain.

Question 2

physiologic basis for signal recorded in EEG scans

Answer 2

EEG measures electrical potential fluctuations on the scalp. These fluctuations are produced by temporal and spatial summation of electrical currents caused by the relatively slow postynaptic potentials induced in neurons of the cerebral cortex. This summation occurs at pyramidal cells.

Question 3

physiologic basis for signal recorded in MEG scans

Answer 3

MEG measures the small magnetic fields induced by electrical current flux.

Question 4

physiologic basis for signal recorded in fMRI scans

Answer 4

fMRI signals occur because of regional changes in deoxyhemoglobin concentration associated with synaptic activity. Origin of the signal is BOLD (Blood Oxygen Level Dependent) signal. You get this signal because deoxyhemoglobin is paramagnetic (and thus distorts magnetic fields), as opposed to oxyhemoglobin. So you’re basically measuring change in ratio of deoxyhemoglobin to oxyhemoglobin.

Question 5

physiologic basis for signal recorded in PET scans

Answer 5

PET measures changes in cerebral blood flow. Radionuclide in the radiotracer decays and the resulting positrons annihilate on contact with electrons. detectors around the subject pick of photons from collision. What PET measures depends on the radioisotope (H215O = cerebral blood flow, 18-FDG = brain glucose uptake and metabolism, 18-fluorodopa/FD = provides image of where in brain dopa conversion to dopamine is maximal). So PET measures both hemodynamics and metabolic responses. This gives you a tomographic image.

Question 6

What is the difference between an EPSP/IPSP and an action potential?

Answer 6

EPSPs/IPSPs are electrical potential fluctuations produced by the relatively slow postynaptic potentials. An EPSP is the postsynaptic potential that makes the neuron more likely to fire an action potential.

Question 7

Evoked potentials, AKA event related potentials

Answer 7

An evoked potential or evoked response is an electrical potential recorded from the nervous system following presentation of a stimulus (actually tons of trials of that stimulus), as distinct from spontaneous potentials as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiological recording method.. It is a pattern/average of positive and negative peaks that occur after the repeated delivery of a stimulus (basically a waveform). Variation in these waveforms can indicate pathology at specific loci since they should be the same for everyone.

Question 8

electromyography (EMG). what it measures and its application

Answer 8

uses needles or surface electrodes placed in skeletal muscle to record membrane properties of muscle fibers, and the velocity of peripheral nerve conduction. application - usually done in conduction with nerve conduction studies to identify pathology affecting muscle, peripheral nerves, and motor neuron disease.

Question 9

what are the objectives of connectomics?

Answer 9

Goal is to comprehensively describe the structural relationships within the nervous system. Generally use MRI, EEG, and DTI.

Question 10

What is the potential for connectomics to act as a biomarker for certain disease states?

Answer 10

“brain graphs,” which graph anatomical connectivity and temporal correlations between measured activity in different brain regions are altered in a number of disease processes and psychiatric conditions.

Question 11

what is phrenology?

Answer 11

antiquated idea that you could make inferences about an individuals brain function based on skull prominences

Question 12

what is lesion analysis?

Answer 12

correlating function with region that suffers a lesion.

Question 13

what are field potentials?

Answer 13

This is what EEG/MEG measure. Represented partially synchronized electrical activity, including subthreshold synaptic potentials, among groups of neurons arranged in parallel.

Question 14

what is the origin of the fMRI signal?

Answer 14

Bloo Oxygen Level Dependent/BOLD signal. Due to magnetic properties of hemobglobin as described in other question.