When brief periods of eeg patterns are recorded in response to a specific event, the response is called a(n)

EEG stands for Electroencephalogram.  EEG measures electrical activity in the head related to the firing of a specific group of neurons reveals brain wave activity
When brief periods of EEG patterns are recorded in response to a specific event, the response is called an event-related potential or an evoked potential.
This measure the electrical activity of the brain in response to a  certain event stimulation.