Find out more about EEG
The EEG lab
Location: Department of Psychology Social Sciences Building Level 4, Room D401/402 Tel: +44 (0)20 7040 4211. EEG lab2 is located on the ground floor in room DG08A.
The EEG labs are purpose-built units in the Department of Psychology. EEG enables the measuring of electrical brain activity occurring during all kinds of externally and internally triggered cognitive processes such as sensory perception, selective attention, action preparation, executive control processes, learning, working memory, etc. We employ a 64- / 32-channel EEG setup and all recordings are performed in an acoustically and electrically shielded chamber.
A brief introduction to EEG researchGroups 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 procedureIn 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.
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.