On occasion stimuli may be given deliberately. As an example common stimuli administered to comatose patients are a noise such as a hand clap; the speaking of the patient's name by a close relative and alternately by a stranger; a pain stimulus. These are given under as controlled conditions as possible. Typically there will first be a period of some minutes silence during which the CFAM trace is allowed to stabilise. The stimulus is then applied and the trace observed to see if it changes, typically within the next 10 seconds. Such procedures are repeated at intervals of the order of 5 to 10 minutes to acquire confidence that any changes observed are repeatable responses. Changes may be transient of the order of 10 seconds or a change of state (possibly an arousal) lasting for many minutes.
