In our brains, tiny nerve cells called neurons constantly transmit weak electromagnetic signals in order to communicate with each other. Different regions of our brains need to communicate with each other depending on what we are currently doing, seeing or hearing. So these signals change in different areas and at different times. An electroencephalogram (EEG) uses little sensors on the surface of a person’s head to measure where and when these signals change. Similar to a thermometer, which can measure and display a temperature, the EEG’s sensors measure the brain’s signals and can then be processed using computer software and considered in relation to what the person has observed and heard. This method is particularly popular in studies using children, as it makes their thinking and the development of thinking ‘visible’.

In our research work at the Chair for Developmental Psychology: Infancy and Childhood, we use particularly flexible, child-friendly caps which are covered in sensors. We have caps in a range of different sizes. This means we can ensure that the child’s cap is the right size and can be adjusted to the shape of his or her head. Each sensor is surrounded by a little sponge. For us to be able to measure the weak signals on the surface of the child’s head, these sponges have to be wet. This is why we begin by soaking the cap in warm salty water and baby shampoo.