HC 1 Flashcards
How do we study the relation between a structure and function of the brain and the specific cognitive functions?
Study these procesess within normal healthy people and study the breakdown of these processes with people with brain damage as a consequence of acquired or developed brain damage.
What is the difference between grey and white matter?
Grey matter consists out of cellbodies in the cerebral cortex and subcortical structures, while white matter consists out of axons.
What is hyperpolarisation and depolarisation?
Hyperpolarisation is when the potential difference between the in-and outside of the membrane of a neuron becomes more negative, depolarisation is when it becomes more positive.
When does an actionpotential occur? What then?
If enough excitory input is received, the critical level of the membranepotential is achieved.
Changes in membranepotential results in a signal that gives detailed information about what is happening in the neuron.
What is a frequency, amplitude and phase?
Frequency= Rate at which the signal changes, in EEG, cycle per second
Amplitude= How much it goes up and down
Phase= When it goes up and down
By what is the highest frequency limited?
By how many times the signal gets measured, also called the sampling frequency. Can only establish fluctuations on half the sampling frequency.
This principle is called the Nyquist sampling theoreom:
1/2 * sampling frequency
By what is the lowest frequency limited?
By how long the signal gets measured.
seconds measured
What is filtering and which types are there?
Filtering is to weaken or exclude a certain part of the frequency spectrum.
Low pass filtering= Higher/faster frequencies are weakened or deleted out of the signal. This is also called smoothing.
High pass filtering= Lower frequencies are weakened or deleted out of the signal.
Band-pass filtering= Certain range of frequencies may pass the filter. All other are weakened or deleted.
What are hemodynamics?
Blood supply adjusted to the energy needs at a certain moment, so it changes over time. If more energy is needed, higher blood supply.
Why is the amplitude of potential differences not the best predictor for energy consumption?
What should we use then?
An action potential is a passive chain of events that does not use alot of energy. If an action potential is generated, then the rest is an automatic process that requires little/or no energy. This gives no information.
The restoring of an actionpotential requires energy. Energy consumption of a neuron can correlate with the amount of actionpotentials this way.
What is clustering?
The tendency of neurons with the same functional characteristic to physically lay close to each other. The higher up in the brain, the higher the level of clustering, because there are more networks. The more clustering, the more the average signal of many neurons correspond with that of a single one (the better the signal).
So, the sensitivity of non-invasive methods depends on the amount of available clustering.
What are the three dimensions of the brain imaging methods?
Temporal resolution= smallest unit in time that can be distinguished by a method. Miliseconds is needed for individual action potentials and seconds is sufficient for reaction time.
Spatial resolution= smallest unit in space that can be determined. This resolutionh determines which scale of organisation you can pick up. Limited to systems or more detailed?
Invasiveness= Most methods are either totally invasive or not at all. The distance between neural tissue that sends out the signal and the detector.
What is the disadvantage of using non-invasive methods?
There are no methods that have a high spatial (single neuron) and temporal (ms) resolution.
What is histology?
Invasive method where the brain gets cut up into pieces (slices). These slices are processed chemically to visualize the structures of interest. Chemicals react to certain regions, depending on the type of cells and neurons.
It is the standard method to study anatomy of brain in non-human animals. It has high spatial resolution.
What are hemodynamic correlates?
Changes in oxygen supply of the blood, tissue, bloodstream and bloodvolume. Change in energyconsumption triggers this.
Why is the temporal resolution of hemodynamic imaging worse than electrical?
Hemodynamic processes are slow, because blood flow is slow, around 16 seconds.
What is optical imaging?
Uses the effect of oxygen supply of the tissue on the reflection of the light that shines through it. It is an invasive method.
Why do methods that measure electrophysiological activity vary greatly in spatial resolution?
-The distance between the electrode and the source of the signal
-The in between tissue makes the signal worse
-Due to the non-invasiveness. Highest frequencies cannot get picked up, so you are limited to the low ones. Only get part of the information of the signal.
What is patch-clamp recording?
Technique with optimal spatial resolution. Only technique that measures changes in membranepotential reliably with minimal disturbances. A hollow glass tube is filled with electrolyte solution and a recordinhg electrode is conneted with an amplifier that is brought in contact with the membrane of an isolated cell.
What is extracellular single-unit recording?
An electrode is placed in the cortex, as close as possible by a single neuron to pick up the action potential of that neuron. A term is that the electrode has a strong resistance , so only signals from nearby are picked up.
What is multi-unit recording?
If the electrode in the cortex has less resistance, this can be used. Actionpotentials of multiple nearby laying units are measured simultaneously.
What is the difference between multi-unit recordig and local field potentials?
Multi-unit has high-pass filtering, because actionpotentials are characterised by fast changes in membranepotential and high frequencies can be kept.
Local field potentials process the same signal with a low-pass filter, to get information about the slow changes in membranepotential from all nearby neurons.
Why are extracellular single-unit recordings, multi-unit recordings and local field potentials risky?
They require opening of the dura, which protects the cortex against infections.
What is intracranial recording?
Require opening of the skull, but only to place electrodes on the topside of the dura, so it stays intact. This way, the electrode is closer to the neural tissue and the signal is not disturbed by the skull.
