On the one hand, the symptoms of amnesia are very basic: the inability to recall events and information from the past (retrograde amnesia), or the inability to gather and retain new information (anterograde amnesia). On the other hand, it may be difficult to determine the extent of the memory loss because a person may appear to have no difficulty remembering events and people from the past, but they are unable to form new memories. Neurological amnesia is usually associated with pressure on the brain from injury or illness; therefore, the symptoms of amnesia are connected to the condition that caused the onset. With transient global amnesia, memory of a recent event may vanish for a brief time but return. Amnesia can cause irritability and frustration, depending on how long and how severe the memory loss is.