Scientists have discovered the existence of a gene that appears to control whether fear reactions to impending danger are appropriate or not.
It seems that when mice lack the gene stathmin they quite daring and far less fearful in conditions that should instinctively inspire fear.
The gene is apparently present in particularly high levels in a part of the brain, called the amygdala, which is known to be important in regard to human fear.
The US team say their findings could shed light on anxiety disorders.
The team from the Howard Hughes Medical Institute had, some years previously, identified a similar gene called GPR that appeared to be important in the process of "learned fear".
In this situation animals, including humans, learn over time that something is a threat or danger, as opposed to the instinctive fear which animals are born with.
The gene GPR appeared to block the action of "circuitry" in the amygdala of the brain which learns fear; there already exists evidence that the amygdala is involved in fear.
It seems that mice which were bred with a lack of stathmin showed abnormally low levels of anxiety in situations that would normally make a mouse very afraid, such as being in large open spaces - innate fear, and they also reacted less to learned fear.
In the study, this was done by playing a neutral tone while the animals were given a mild electric shock.
These mice showed a decreased memory for the fearful situations and had difficulty recognising dangerous environments, whereas their memory for things other than fear was not affected.
According to researcher Dr Gleb Shumyatsky, from Rutgers University Piscataway, New Jersey, the mice could be used to study human phobias and anxiety-related disorders such as post-traumatic stress disorder.
He believes their work on genes and anxiety supports clinical data which indicates that anxiety is a spectrum of disorders, and it is possible that each disorder has a "unique molecular signature" and requires individually tailored drugs.