The term déjà vu comes from the French and means, literally, "already seen." Those who have experienced the feeling describe it as an overwhelming sense of familiarity with something that shouldn't be familiar at all.

Déjà vu is a phenomenon that by its nature as an instantaneous event cannot be scientifically proven to exist. And yet it does. The occurrence of déjà vu is actually quite common, 70% of us experience it at least once in our lifetimes.

There are many theories regarding the nature of déjà vu experiences. In recent years déjà vu has been the subject of serious psychological and neurological research. The most likely explanation, according to scientists in these disciplines, is that déjà vu is an anomaly of memory.

Basically these theories link déjà vu with a misfiring of brain signals related to memory and recollection. Connections have been found between the experience of déjà vu and disorders such as schizophrenia and anxiety. People with these disorders are more likely to experience a déjà vu phenomenon than the rest of society.

The strongest pathological association of déjà vu is with temporal lobe epilepsy. People with this form of epilepsy often report experiencing déjà vu. This correlation has led some researchers to believe that the experience of déjà vu is a neurological anomaly related to improper electrical discharge in the brain.

Most people suffer a mild, non-pathological epileptic episode regularly. The sudden jolt, or hypnagogic jerk, A hypnagogic jerk is the experience of a large jolt, usually felt just before falling asleep and often described as an electric shock or falling sensation. It may be that a similar mild neurological abnormality in the form of a jolt to our memory functions can cause the experiences of déjà vu.

It is worth noting that people in the 15 to 25 year old age group report having far more instances of déjà vu. One speculation is that déjà vu is a kind of mental misfiring that occurs as the brain is maturing or as we have more life experiences.

The study of déjà vu experiences has until recently been relegated mostly to the fields of parapsychology and paranormal research.

It is interesting to note that the symptoms of temporal lobe epilepsy involve many experiences which are common elements of paranormal studies. Seventy-five percent of people diagnosed with temporal lobe epilepsy experience partial seizures which may include such features as: déjà vu, hallucinations of voices, music, smells, or tastes, feelings of unusual fear or joy, and the appearance of auras. Patients may also describe a sense of dissociation in which they report seeing their own body from the outside, commonly referred to as astral projection.

Far from discounting the study of the paranormal, the recent theories describing déjà vu experiences as electro-chemical misfiring in the brain, and the connections with temporal lobe epilepsy highlight the importance of continued research into paranormal phenomena.

Many of the subjects of paranormal research exist as such simply because mainstream science regimes deem them unworthy of study.

Déjà vu like many other experiences, (dreams, astral projection, precognition, thought healing, etc,) have been discounted or undervalued as a topic of serious research. Nonetheless these experiences are encountered by a vast number of people and therefore worthy of study for that reason alone.

We may find that focusing serious research efforts on subjects currently within the realm of the paranormal will lead to a greater understanding of "real world" problems. We may also find that while some myths may be shattered along the way, many of the topics of paranormal research will be proven, validated and absorbed into the world of the commonplace.