728124
Description
Flashcards by alexlpeart, updated more than 1 year ago
|
Created by alexlpeart
over 10 years ago
|
|
| Question | Answer |
| Describe the spatial and temporal resolution of EEG and MEG | Both high temporal resolution, poor spatial resolution. MEG better spatial resolution than EEG |
| Give some invasive variation of EEG, and describe the method of recording and spatial resolution for each. | Electrocorticography (ECoG) - subdural array, 0.5cm Local field potentials- Needle electrodes, 100-1000 cells Single unit - needle electrodes, single cell (dependant on needle size) |
| what are the major limitations of Electrocorticography (ECoG). When might it be used? Give a paper which has reveiwed ECoG in humans | Extremely invasive, would never be used unless severe life threatening need. e.g. severe epilepsy to locate source of attacks so it can be removed. Hill 2012 |
| Give a paper, and the benefits it describes linked with Electrocorticography (ECoG). What is its suggested use? | Hills et.al (2012) describes how other techniques compramise either temporal or spaital resolution, not offering both. Due to the direct contact ECoG has with the brain little interference is caused so higher spatial resolution combined with high temporal resolution. Provides info about task-related activity |
| Describe local field potentials | Needle electrode used. Records sum of activity within a volume of tissue. Represents combination of 100-1000 neurons. Commonly used in animal studies due to invasive nature Used in parkinsons patients when they have therapeutic basal ganglia stimulation (already have the needle electrode inserted) |
| What is the difference between EEG and MEG signals compared to signals from CT, PET and fMRI | EEG and MEG are the direct neural activity whereas CT, PET and fMRI measure the metabolic consequences of neuronal activity. Means EEG and MEG dont need further analysis, they are very direct |
| Give an example of a paper which combined EEG with fMRI. Summaries what they did/found | Plichta 2013. They combined EEG and fMRI to look at the brain areas affected by a well established reward anticipation method. the combination of these techniques allowed them to reveal the brain areas involved, which before were not active for long enough that the fMRI could pick up the signal. |
| Describe how the structure of the brain might affect an EEG signal | Brain is made up of folds, the valleys are called the Sulcus while the higher bits the Gyrus. Because the Gyrus is closer to the surface EEG signal will be stronger from the Gyrus than the Sulcus |
| Why does EEG have a poor spatial resolution? | Signal must pass through the skull, which is conductive and therefore dispersed the signal as it crossed the skull |
| What are we actually measuring with an EEG? what implications does this have for the signal? | Not the action potential, this is way too tiny. We actually measure the postsynaptic potential, i.e the potential of the cell which the synapse leads into. It means regardless if an AP reaches threshold we will still pick it up, meaning we effectively get the analog signal not the digital (as we would from APs) |
| What is meant by synchronised firing of neurons? Why is this important for and EEG signal? | Synconrosied firing is when all the neurons fire at the same time and direction. If a group of cells are firing all in different directions the signal will be averaged by the EEG, normally equating to zero. This means unless they are all firing in the same direction no EEG signal will be picked up. Epileptic fits are highly synchronised so give a strong EEG signal |
| Describe the difference between open field organisation and closed field organisation? | Open field is where they are all lined up nicely whereas closed field is where they all point in different directions. In relation to synchronised firing open will give a synchronised signal which EEG can pick up while closed organisation wont. |
| Describe how the placement of the electrodes might make a small difference to the signal we record? Why is this only a small difference? | When the neurones are lying parallel to the sensor then there wont be as greater difference in electrical signal as you might only fit 20 cells between the sensors , compared to when the cells lie adjacent to the sensor where there will be 100 cells between the two sensors meaning the potential difference is greater. This is only small due to the skill diffusing the signals anyway. |
| what is an event related potential/event related field? | The brains response from a specific sensory, cognitive or motor event. We can also do a similar thing with MEG however we record event related fields as we measure magnetic fields with MEG |
| How can an event related potential be used? | We can change the event ever so slightly which is causing it, and by looking at changes in the amplitude, time and scalp distribution (so looking how the signal looks different from normal) we can infer what psychological process each section of the ERP is linked to. Different ERPs originate from different areas of the brain. |
| What is device used to measure MEG ? What does it actually measure? | we use a Superconducting Quantum Interference Device (SQUID). It measures magnetic fields created by the electrical potential of the cell. |
| What orientation do neurones have to lie in relation to the SQUID during MEG for a signal to be picked up. Why is this? | tangentially (parallel) to the skulls surface. Because we are measuing the magnetic field, which is created at 90 degrees to the direction of the current, if the cells aren't parallel to the skull then the field won't be picked up by the SQUID |
| What does a SQUID use to detect magnetic fields? | Magnetometers |
| Why do we need to take 100s of trials when looking at an event related potential? | So we can average out the signal and give a smooth line |
| Why would combining EEG with another technique be useful? | EEG has poor spatial resolution, we create models of the brain applying different sources to the model and using prior brain knowledge to deduce possible locations the signal came from. We uses what we know from other methodologies to ‘constrain’ the location of the source, known as converging evidence. Normally we can generate more than one scenario on computer software which would have lead to that pattern being created |
| What is a lateralized readiness potential? | A type of ERP associated with the preparation to move |
| with regards to the lateralized readiness potential, what happens to the signal before we initiate movement? what can affect this? | We see a gradual increase in EEG activity just before a movement begins. If the movement is self-initiated we see a much sooner increase in electrical activity before movement compared to if the movement is externally stimulated (i.e. someone telling you to move) |
| Describe what the Libet clock was designed to do? | An experiment to look at if movement initiation is conscious or if we have started to initiate the movement before we know about it. He used a clock with a red dot moving around it and ask participants to move when they wanted to. He then asked them to move the red dot to the point on the clock when they first thought about moving |
| What were the results from the Libets clock? | We see EEG activity before intention of movement is even established. Subconsciously they have already decided to make that movement. Consciousness is an illusion, we construct events afterwards. |
| What is frequency analysis? | Where we look at brain rhythms and how they form patterns at certain frequencies depending what we are doing. Basically looking at specific groupings of waveforms and then looking how often they occur during certain tasks |
| what type of frequency is associated with object perception | Increased gamma activity is associated with object perception |
| Give a study which looked at increases in gamma activity, and give what was done | Keil 2001, got people to watch a rotating face while recording their brain waves, found that gamma activity increased when the face was upright as we recognized it in this position. gamma activity was thought to be binding the features together. |
| What is the binding problem? | How do we manage to stick bits of information which are related to an object to that specific object? how do we know what when looking at a red square and yellow circle, that the red is associated with the squad and yellow with the circle? |
| Describe a study which shows gamma waves contribute to object perception using infants. | Csibra et. al 2000, got babies to look at an illusion of a square. Normally you can't see a square but when the illusion is orientated in certain directions a square images. An increase in gamma activity was seen when the square was formed, but only after 6 months of age once the babies were able to perceive the square. |
| What is beta activity associated with? | Postural states, inhibition of movement |
| What disease is linked with higher beta activity? What is the treatment to reduce this activity? | Parkinsons disease. Deep brain stimulation is associated with a decrease in beta activity, therefore facilitating more movement (something parkinsons patients struggle with) |
Want to create your own Flashcards for free with GoConqr? Learn more.