Research Methods

A brief introduction to EEG research

Groups of neurons firing synchronously create electrical potentials that can be measured by electrodes placed on the scalp. When the electrical signals from a given electrode are graphed over a period of time, the resulting representation is called an EEG (electroencephalogram). The EEG ultimately provides information about the time course and location of the neural firing, allowing researchers to draw conclusions about the underlying brain activity and its relation to cognitive functions.

The image below shows EEG traces from commonly used electrodes, all placed on the scalp. Although such information is the basis of the conclusions researchers in the lab make about brain function, a fair amount of analysis must be performed before many interesting conclusions can be made. Very little can be concluded by simply looking at these traces, as one can usually only see noise not related to brain activity (e.g. eye blinks), or alpha waves when a person becomes very sleepy!

Experimental procedure

In order to record the electrical signals indicating brain activity, participants must wear a cap with embedded electrodes. The person above is modeling one such cap, and sometimes participants also wear facial electrodes in order to record eye movements, as such movements affect the readings from the electrodes monitoring brain activity. The facial electrodes and the electrodes in the cap must be filled with a conductive gel (a saline solution that easily washes off skin and out of hair) in order to obtain good electrical signals.

An experiment consists of a participant repeatedly performing a specific cognitive task while one of the lab's computers records the electrical signals from the electrodes. During the experiment, the signals from the electrodes are relayed through the amplifiers to the computer via the wires and connectors that are visible in the back of the head of the participant on the photo.

Data analysis

Since just looking at the raw EEG data does not relay much useful information to the researcher, they must be mathematically transformed in order to answer the questions a given study has posed. The most frequent analysis technique is to average the EEG recordings across multiple trials, where a trial is defined in relation to some event such as a subject response or the appearance of a visual stimulus. Such averaging reduces the effects of electrical signals not related to the brain activity evoked by the event in question. The waveform produced after averaging across trials is called an event related potential (ERP). Below is an example of averaged ERPs in response to tactile stimuli applied to one of the hands recorded over ipsilateral (same side as tactile stimulation) and contralateral (opposite side as tactile stimulation) somatosensory cortex.

Are you interested in participating in an EEG study? The following description will give you an idea of a typical EEG study in our lab. Please, read this information before participating in a study.

What will you be doing?

Basically you will be sitting in front of a computer screen doing a simple task. For example: On the screen you see a circle flashing in different colours, every time the triangle turns green you press a button (this is a very basic example). In most of our experiments we measure changes in your brain's activity while you are performing the task - that is we measure your electroencephalogram (EEG). In order for us to do this, you need to wear a cap with electrodes on your head during the experiment. We use the same equipment to do this as is used in hospitals for monitoring patients.

How long will it take?

On average an experiment takes about 2 to 3 hours. About half an hour is needed to put the cap on and ensure that a good measurement is possible. Also, you will want to wash your hair afterwards, to remove the left-behind bits of conductive gel from your hair. We have a hand-held shower, clean towels, hair-care products etc. for you to use.

Reward

We pay each participant £7 per hour in cash (or £20 for a 2.5 - 3 hour session). We do not pay for your travelling expenses.

Who are we looking for?

We are looking for healthy people between the age of 18 and 45. The experiments take place in a small cabin and for this reason it is not wise to take part in an experiment if you are claustrophobic. It is important to be fit and well-rested when you take part in an EEG experiment. Also, it helps if you do not use any hair-care products like conditioner, oils or wax in your hair. Finally, if you are wearing contact lenses but also have a pair of spectacles you could wear, it is advisable to bring your spectacles, because some participants complain of dry eyes when they are doing our experiments.

The cap

The electrodes we use to record the EEG are fitted in a cap, which looks like a bathing cap with a lot of wires coming out. To make a good contact between the skin and the electrodes we clean the skin underneath the electrodes with some alcohol and then fill the electrode with a conductive paste (this is a completely harmless saline solution). Some of this paste will be left behind in your hair after we take the cap off, so you will probably want to wash your hair afterwards and we have all the necessary facilities in our lab.
Interested?

Interested?

If you are interested in taking part in an EEG experiment or have any further queries, sign up to the SONA participant database or email to cscn@city.ac.uk.

What is TMS?

Transcranial magnetic stimulation, or TMS, is a relatively recent technique for stimulating the outer layer of the brain, particularly the cerebral cortex. Brain cells, known as neurones, pass messages by generating spikes of electrical activity, known as action potentials. In TMS, a rapidly changing magnetic field is induced in a hand-held coil in order to electrically activate the neurones in a small area of cortex located under the coil.

What different kinds of TMS are there?

Broadly speaking, TMS comes in three varieties. In single-pulse TMS, stimulation is delivered once every few seconds. In paired-pulse TMS, two TMS pulses are fired very close together in time to see how they interact. Finally, in repetitive TMS or rTMS, a train of pulses are delivered at a rate varying from once per second to 50 or even 100 times per second.

What is TMS used for?

TMS is used for both clinical and research purposes. Clinically, TMS can be used as a diagnostic tool to assess whether the nervous system is working properly. TMS is applied to the part of the brain that sends commands to the muscles of the body (the primary motor cortex) and the speed with which a muscular response occurs is measured. TMS has also been used to treat conditions such as depression. Research investigating the usefulness of TMS for treating neurological and psychiatric conditions is ongoing, but please note that we do not run clinical trials or provide TMS as a therapy/treatment at City.

In cognitive neuroscience research, TMS is used to determine how the brain controls our behaviour. Paired-pulse TMS is used to figure out the ways in which different parts of the brain are connected together. Single-pulse TMS is used to activate muscles of the body and assess the state of the motor system in different experimental conditions. Finally, both single-pulse and repetitive TMS can be used to briefly interfere with the activity of a small area of the brain, so we can see how behaviour is affected. By temporarily turning off a small part of the brain, this approach yields insights that are similar to those obtained by neuropsychologists, who study patients with lesions (damage) to particular areas. Hence TMS is sometimes described as a "virtual lesion" technique.

Are you interested in participating in an TMS study? The following description will give you an idea of a typical TMS study in our lab. Please, read this information before participating in a study.

What does TMS feel like?

TMS feels a little like being tapped on the head. Most people don't really notice it after the first few pulses. However, because TMS can activate muscles on the scalp, it is sometimes experienced as being uncomfortable. In these cases, it may give rise to a short-lived headache. Our participants are encouraged to tell us immediately if they don't feel comfortable.

Are there any risks associated with receiving TMS?

TMS has a good safety record, and is not believed to have any long-term health effects. The biggest concern for most participants is that at high intensities and high stimulation rates there is a possibility of inducing a seizure akin to those experienced by epileptic patients. There are published safety guidelines about what levels of stimulation are safe, and we adhere to these guidelines closely. We discuss the risks associated with TMS with our participants, and we ask a series of questions to make sure that these risks are not elevated for them.

Should I participate in a TMS study?

TMS is generally safe, but there are some people who should never have TMS, and there are some people who should only have it in special cases where there is a potential benefit for them, like a clinical trial. We will generally not test you if:

• You have a pacemaker, or any other electronic device inserted in your body
• You have any kind of neurological history, for example a stroke or a serious head injury
• You have epilepsy, or a family history of epilepsy
• You are currently taking prescription medication (with the exception of the contraceptive pill)
• You are pregnant.

What will a TMS study involve?

In a typical experiment, you will be seated in front of a computer doing a straightforward (but sometimes challenging) task. Examples include reacting as fast as possible to lights or sounds, or making judgements about things like whether a weak light has been presented, or how long it was presented for. Before you begin the task, we will apply some pulses of TMS to work out the right strength and location of stimulation for you. During the task, we will apply TMS from time to time to see how it affects your performance.

Experiments may last anywhere from one to three hours. You will have opportunities to take breaks, and you will be paid for your participation at a rate of around £7.50 per hour. We are happy to talk about the purpose of the experiment, although we may withhold some details until afterwards to keep you "naïve". Unfortunately, we cannot pay transport costs.

If you would like to participate in a TMS experiment or have any queries regarding participation, sign up to the SONA participant database or email to cscn@city.ac.uk.