ERP, fMRI, TMS –briefly describe these research methods. What are the differences between them? What are their weak points, what are their advantages?

ERP, fMRI, TMS –briefly describe these research methods. What are the differences between them? What are their weak points, what are their advantages?

ERP- event-related potential- measured brain response that is the direct result of a specific sensory, cognitive, or motor event; any stereotyped electrophysiological response to a stimulus; it provides a noninvasive way to evaluate brain functioning in patients with cognitive diseases. Usually ERP is measured along with EEG. Compared with behavioral procedures, ERPs provide a continuous measure of processing between a stimulus and a response, making it possible to determine which stages are being affected by a specific experimental manipulation. Another advantage over behavioral measures is that they can provide a measure of processing of stimuli even when there is no behavioral change. However, because of the significantly small size of an ERP, it usually takes a large sample size to accurately measure it correctly. Unlike microelectrodes which require an electrode to be inserted into the brain and PET scans that expose humans to radiation, ERPs use EEG, a non-invasive procedure. ERPs provide excellent temporal resolution of 1 ms or better. The spatial resolution of an ERP, however, is currently undefined making it impossible to definitively localize ERPs. This provides the ERP with a major disadvantage over hemodynamic measures (fMRI and PET) which have a spatial resolution in the millimeter range. The fact that ERPs cannot easily be localized makes it extremely difficult to isolate a single ERP component from the overall ERP component. ERP research is much cheaper to do than other imaging techniques such as fMRI and PET. This is because purchasing and maintaining an EEG system is less expensive than the other systems.

fMRI- functional magnetic resonance imaging an MRI procedure that measures brain activity by detecting associated changes in blood flow. The most common risk to participants in an fMRI study is claustrophobia and there are reported risks for pregnant women to go through the scanning process. Scanning sessions also subject participants to loud high-pitched noises from Lorentz forces induced in the gradient coils by the rapidly switching current in the powerful static field. The gradient switching can also induce currents in the body causing nerve tingling. Implanted medical devices such as pacemakers could malfunction because of these currents. The radio-frequency field of the excitation coil may heat up the body, and this has to be monitored more carefully in those running a fever, the diabetic, and those with circulatory problems. Local burning from metal necklaces and other jewelry is also a risk. MRI, in general, has better spatial resolution than EEG and MEG, but not as good a resolution as invasive procedures such as single-unit electrodes. Temporal resolution of fMRI is limited by the feedback mechanism that raises the blood flow operating slowly; having to wait till net magnetization recovers before sampling a slice again; and having to acquire multiple slices to cover the whole brain or region of interest. Advanced techniques to improve temporal resolution address these issues.

TMS- transcranial magnetic stimulation- noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain. TMS uses electromagnetic induction to induce weak electric currents using a rapidly changing magnetic field; this can cause activity in specific or general parts of the brain with minimal discomfort, allowing the functioning and interconnections of the brain to be studied. Researches can "turn off" particular parts of brain while e.g. enchancing performance in other parts. The TMS-induced MRI images matched very closely with the PET images, within 5–22 mm of accuracy. TMS has also been seen to correlate closely to MEG and also fMRI. Although TMS is often regarded as safe, the greatest acute risk of TMS is the rare occurrence of induced seizures. Besides seizures, other risks include fainting, minor pains such as headache or local discomfort, minor cognitive changes, and psychiatric symptoms (particularly a low risk of mania in depressed patients). Though other side effects are thought to be possibly associated with TMS (alterations to the endocrine system, altered neurotransmitter, and immune system activity) they are considered investigational and lacking substantive proof.

ERP is measured in EEG (ElectroEncephaloGraphy). Is an electrical activity in the brain linked to a particular stimulus (or response). It uses electrodes placed on the scalp to record fluctuations in electrical activity over time. Its advantages is the low use cost although the weak point is that it is disrupted by slight movement because muscles produce electric activity when they twitch.

fMRI records magnetic activity however, the magnetic pulse sequence is designed to reveal where oxygenated red blood cells have piled up which is an indirect measure of activity in that brain area. It’s advantage is that it has a superb spatial resolution, good temporal resolution and noninvasive. However, its drawbacks include the high cost of the machine and it requires special facilities.

TMS involves placing a coil on the participant’s skull and briefly running a large current through the coil. This method can be used to discover the duration of particular processes and their causal roles in a specific task. However, their drawbacks includes the fact that if not used accordingly to safety (rTMS) can produce seizures and also the muscles at the sides of the forehead twitches when TMS is applied which can be uncomfortable.

The ERP is a method of recording rapid electrical responses of the human brain. The event realted potenitial is recorded with small dics ekectrodes placed ona a persons's scalp. Each electrode picks up a signals from gropus of neurons that fire together. The signals are very rapid, occuring on a time scale for a fractions of seconds. This makes ERP ideal for invesitigeting a process such as understanding a conversation, in which speaker says three words per second at average. The The rapid response of ERP contrasts with the slow responses of fMRI, which takes seconds to develop. A disadventage of ERP is it is difficult to pitpoint where the where the responeses is originating in the brain. however the ability of ERP proveides nearly a continous record in the brain from the moment to moment makes it well studied for studying dynamic process such as language

fMRI is based on the measurment of the blood flow. An adventage of fMRI is that a blood flow can be measured without redioactive tracers. fMRI takes adventage on the fact, that hemoglobine, which is tranfered through the blood with an oxygen contains a ferrus (iron) and therefore has magnetic properties. If a magnetic field is present in the brain, the hemoglobin molecules line up, like tiny magnets. This techinic is the main one to determine which areas of the brain are particulary active.

TMS - transcranial magnetic stimulation - it is basicly a tachnic in which a specific brain areas are "turned off" and are not being used while the participant takes place in a experiment. Such state is achieved by placing a coil on participants's skull and running a series of current impulses. If hte behavoir is disrupted, it is conluded that the deactived area of the brain is the cause of such behavoir.