Activation is reflected by blood oxygen level dependence and is normally represented by colouring the activated brain region on a model of the brain.
fMRI - functional magnetic resonance imaging, can provide answers to three questions that are absolutely crucial to advertising:
does a specific ad evoke an emotional reaction?
Are elements from the ad stored in long-term memory?
Is an ad processed attentionally?
Questions such as 'which one of two TV ads is more emotionally engaging/memorable/attention
grabbing?' are best addressed through fMRI.
Brain activation is not under direct conscious control, so the risks of meta-cognitive biases that plague questionnaires are not present with this methodology.