NATS 1860 Study Guide - Final Guide: Animal Communication, Electric Field, Causal Inference

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Published on 31 Mar 2013
NATS 1860
Winter Term (2013)
Final Exam Questions
The exam will consist of four questions, one drawn from each of the following four
sets (A through D). You will write your answers in exam booklets that will be
provided to you without using any information stored outside your own neurons
during the exam.
Set A
1. Draw a diagram that compares the temporal and spatial resolution limits of the
functional MRI technique to the EEG technique. Make sure to label the axes of
the graph. Describe in words the different brain structures and types of
information that can be measured by each technique.
The difference between fMRI and EEG is as follows: EEG monitors the
neurons that fire action potential through an electrochemical activity.
EEG specifically monitors the brain activity on the top of the brain due
to the electrodes being laid over a person’s head. EEG allows the
collection of specific action potentials in the form of electrochemical
activity data. It has a poor spatial resolution because it only offers the
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top-of-the-brain activity, however has very good temporal awareness
allowing for the millisecond and second observation of change in the
brain. The fMRI practice, on the other hand, allows for the
examination of more specific spatial resolution such as region maps
and neuron columns of neuron layers. It specifically reflects the flow
of oxygen-rich blood traveling to hot spots that are doing greater
work. However, despite its spatial advantage, fMRI has a slower
temporal resolution ranging from seconds to hours.
2. Briefly explain each of the following imaging techniques, including which signals
are being measured from the brain, and describe one strength and one
weakness for each.
a. fMRI this is the head-gear that monitors specific flow of oxygen-rich
blood flowing around in the brain. This monitoring allows for the
measurement of blood in response to the amount of required activity
for a specific task. An advantage of fMRI is that it is a good
combination of temporal and spatial resolution, as well as a non-
invasive method of gathering data on brain activity. One disadvantage
would be that it is an indirect inference of neural activity through
secondary blood flow, as well as there being a potential for better
spatial and temporal resolutions in comparison to other forms of
b. PET This is the process of injecting an individual with a radioactive
substance and then monitoring how that substance is attached and
spread through molecules. PET works by using gamma rays emitted
by the radioactive tracer isotope that is attached to the molecules
(such as glucose in blood). PET is used to specifically detect which
regions (maps and columns) are activated over a long period of time
(can be from hours to days). For example, if you’re seeing words your
visual cortex is active, when you’re hearing words your auditory
cortex is active, etc. An advantage of PET is that it can trace different
substances and see which sections of the brain are activated based on
the specific function. A disadvantage is that the radioactive substance
is incredibly invasive and can only be injected once a year to prevent
poisoning. It also has worse spatial and temporal resolution than MRI
and requires a PET scanner to be nearby in order to proceed with the
c. EEG This is the procedure of attaching electrodes to people’s scalps in
order to measure a small, but detectable electric field. This form of
neuroimaging specifically monitors the electrochemical activity in the
brain (disturbances in the electrical field). This electrochemical
activity is the way that the brain communicates with itself (through
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electrical waves). It specifically targets the ions present in the
electrochemical activity. Its advantages include the fact that it has
very good temporal resolution, however has very limited spatial
resolution, causing it to be difficult to accurately localize the source of
the measured signal.
d. MEG This is very similar to EEG, except instead of using electrodes
attached to the scalp, this uses a big machine that uses a magnetic
field. MEG also targets specific electrochemical activity and tracks
ionic movement in the brain. An advantage of MEG includes its very
good temporal resolution, as well as an improved setup time and
subject comfort compared to EEG, as well as less degradation of the
signal due to the magnet going past the scalp. A disadvantage of MEG
is the limited spatial resolution
e. Single unit electrophysiology this is the procedure in which a machine is
used to directly record action potentials and other electrical activity
from specific areas in the brain. It’s specifically used to measure parts
of our brain that can be affected by seizures, and allows
neurosurgeons to cut out the parts where the epilepsy has influences
on the brain. An advantage of this includes the fact that it has very
high spatial and temporal resolution, allowing scientists to directly
measure action potentials and local electrical fields. It also allows the
recording of activity of multiple individual neurons that can be
directly compared. A set of disadvantages includes the fact that the
records are only from a relatively small number of neurons, as
opposed to a greater amount, as well as the fact that electrophysiology
is very invasive because it requires cutting out certain parts of the
f. Optical imaging this is the procedure in which the top of the skull is cut
open, and it allows the optical observation of the brain surface. This
method can either measure intrinsic activity such as blood flow, or
electrical activity by injecting a voltage-sensitive dye. One advantage
of this method is that it has very precise temporal and spatial
resolution. A disadvantage, however, is the fact that it is incredibly
intrusive (where you have to physically open the skull), as well as
confining the observations only to the surface of the brain. Also
making it difficult to analyze a subjects cortex since it is hidden.
g. NIRS (Near Infrared Spectroscopy) This is a procedure in which you
shine an infrared light through the persons skull. It allows scientists to
measure the specific changes in the absorption of information due to
blood flow. One example of what it specifically measures is the In
NIRS you have a transmitter and a detector. One advantage of NIRS is
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