brain research techniques Flashcards
What does electrophysiology refer to?
the electrical potentials generated in nerve cells
Neurons generate what two kinds of electrical activity
action potentials and post-synaptic potentials
How can action potentials and post-synaptic potentials be measured?
using very thin electrodes (micro-electrodes) inserted into the brain precisely at the desired locations
How are post-synaptic potentials formed>
The communication between brain cells (neurons) leads to large amounts of ions (electrically charged particles) entering and exiting the neurons, thus resulting in the so-called post-synaptic potentials inside neurons
what is a consequence of post-synaptic potentials
in the areas outside the neurons from which ions leave or where they arrive transient (temporary) deficits or surpluses of electrical charges occur- these are referred to as Local Field Potentials (LFPs).
What can LFPs spread over
large volume of tissue and be detectable on the surface of the head – this is the voltage detected by EEG. Thus, the EEG signal is the summation of multiple LFPs recorded on the scalp.
How do ERPs work example
For instance, to compare the recognition of famous vs. unfamiliar faces, one would present the subject with a number of faces of each kind, extract the EEG segments associated with the onset of each stimulus, average separately the segments for the famous faces and the segments for the unfamiliar faces and compare the two resulting averages. The resulting two averages are the ERP for the ‘typical’ famous face and the ERP for the ‘typical’ unfamiliar face. Their amplitude can then be compares at different times.
How long is the baseline prior to the stimulus
100-200ms
what is the inverse problem
Determining the brain sources from scalp data
What is the forward problem
If one knew the set of brain regions active during some task and wanted to determine the resulting EEG (or ERP) on the scalp
what does MRI measure
the magnetic signal coming from hydrogen atoms, which are essentially very small dipole magnets
How much stronger is the magnetic filed in the MRI than the field of the earth
10,000 to 20,000
Whne do you get a greater MRI signal?
One might assume that the more active brain regions would consume more oxygen and contain more deoxy-haemoglobin thus generating a weaker MRI signal. However, this ignores the increase in blood flow into the more active region which is greater than the increase in oxygen consumption in those regions. This leads to a surplus of oxy-haemoglobin and a reduction in deoxy-haemoglobin
How do you show impaired performance in neurpsychology
showing that damage to a brain region impairs performance in condition A relative to condition B (a single dissociation) may not be sufficient evidence of qualitatively different anatomical substrates (e.g. it may just be that A is harder than B) - one must also demonstrate that damage to a another brain region leads to a greater impairment in condition B than condition A (a double-dissociation).
what is Transcranial Magnetic Stimulation (TMS)
application to the surface of the head of a strong magnetic field (originating from a electric current in a coil) in very brief (less than 10 ms) pulses.
