This consists of an abrupt loss of memory, lasting from a few seconds to several hours, without any loss of consciousness. No information is stored for that period and thus there is complete loss of memory. Such attacks may be recurrent and are thought to result from temporary reductions in blood supply to specific areas of the brain (possibly presaging a stroke). Actions may continue to be performed automatically during the attack (traumatic automatism). Analogous phenomena may occur in the case of collective memory.