US scientists have identified two genes responsible for macular degeneration, the gradual deterioration of eyesight in the elderly that can lead to blindness, a study showed this week.The research published 24 April 2007, in the Journal of the American Medical Association also showed that smoking and being overweight carry a strong risk of the condition, in which the central part of the eye's retina degenerates.
KAREN BLEIER/AFP/Getty Images
US scientists have identified two genes responsible for macular degeneration, the gradual deterioration of eyesight in the elderly that can lead to blindness, a study showed this week.The research published 24 April 2007, in the Journal of the American Medical Association also showed that smoking and being overweight carry a strong risk of the condition, in which the central part of the eye's retina degenerates.
Now playing
02:08
Your brain on déjà vu
CNN
Now playing
02:13
Why losing weight might protect you from Covid-19
A selection of fruit ready to eat are displayed at a fruit and vegetable shop on April 12, 2016 in Lille, northern France. / AFP / DENIS CHARLET        (Photo credit should read DENIS CHARLET/AFP/Getty Images)
DENIS CHARLET/AFP/AFP/Getty Images
A selection of fruit ready to eat are displayed at a fruit and vegetable shop on April 12, 2016 in Lille, northern France. / AFP / DENIS CHARLET (Photo credit should read DENIS CHARLET/AFP/Getty Images)
Now playing
01:27
New diet can save lives and the planet, study says
this is your brain on pain health orig_00001025.jpg
CNN
this is your brain on pain health orig_00001025.jpg
Now playing
01:39
This is your brain on pain
Now playing
01:42
Here's why you can't stop eating pizza, ice cream and chocolate chip cookies
Now playing
01:10
Trouble sleeping? This may be why
CNN
Now playing
02:40
The reality of wine's health benefits
shutterstock
Now playing
01:49
These foods aren't as healthy as you think
Americans are still too fat according to a new study from JAMA. Two in three of Americans are registering as overweight or obese.
Shutterstock
Americans are still too fat according to a new study from JAMA. Two in three of Americans are registering as overweight or obese.
Now playing
01:15
What is obesity?
CNN
Now playing
01:17
Why your BMI matters
LONDON - MAY 16:  In this photo illustration a cigarette is seen burning on May 16, 2007 in London. Businesses and shops are gearing up for the introduction of the smoking ban on July 1 in England after similar bans have been introduced in Ireland, Scotland and Wales.  (Photo Illustration by Bruno Vincent/Getty Images)
Bruno Vincent/Getty Images Europe/Getty Images
LONDON - MAY 16: In this photo illustration a cigarette is seen burning on May 16, 2007 in London. Businesses and shops are gearing up for the introduction of the smoking ban on July 1 in England after similar bans have been introduced in Ireland, Scotland and Wales. (Photo Illustration by Bruno Vincent/Getty Images)
Now playing
01:07
What tobacco does to your health (2017)
Photo Illustration/Thinkstock
Now playing
01:12
World blood pressure rises (2016)
Woman pointing to area on mammogram x-ray, close-up
Getty Images/File
Woman pointing to area on mammogram x-ray, close-up
Now playing
01:19
Breast cancer: Know the facts
A surgeon sitting in front of screens of a Focal One device performs a robot-assisted prostate tumorectomy using ultrasound imaging on April 10, 2014 at the Edouard Herriot hospital in Lyon, center France. Focal One is the first robotic HIFU (high intensity focused ultrasound) device dedicated to the focal approach for prostate cancer therapy. According to EDAP TMS SA, a leader in therapeutic ultrasound, it combines the three essential components to efficiently perform a focal treatment: state-of-the-art imaging to localized tumors with the use of magnetic resonance imaging (MRI) combined with real-time ultrasound, utmost precision of robotic HIFU treatment focused only on identified targeted cancer areas, and immediate feedback on treatment efficacy utilizing Contrast-Enhanced Ultrasound Imaging. AFP PHOTO / JEFF PACHOUD        (Photo credit should read JEFF PACHOUD/AFP/Getty Images)
JEFF PACHOUD/AFP/AFP/Getty Images
A surgeon sitting in front of screens of a Focal One device performs a robot-assisted prostate tumorectomy using ultrasound imaging on April 10, 2014 at the Edouard Herriot hospital in Lyon, center France. Focal One is the first robotic HIFU (high intensity focused ultrasound) device dedicated to the focal approach for prostate cancer therapy. According to EDAP TMS SA, a leader in therapeutic ultrasound, it combines the three essential components to efficiently perform a focal treatment: state-of-the-art imaging to localized tumors with the use of magnetic resonance imaging (MRI) combined with real-time ultrasound, utmost precision of robotic HIFU treatment focused only on identified targeted cancer areas, and immediate feedback on treatment efficacy utilizing Contrast-Enhanced Ultrasound Imaging. AFP PHOTO / JEFF PACHOUD (Photo credit should read JEFF PACHOUD/AFP/Getty Images)
Now playing
01:21
What is prostate cancer?
Argosy
Now playing
00:53
What is Parkinson's disease?
Now playing
01:38
How Alzheimer's destroys the brain

Story highlights

From the French for "already seen," déjà vu is one of a group of related quirks of memory

About two-thirds of healthy people have experienced it at some point

"Déjà vécu" involves the sensation that a sequence of events has been lived through before

One drab afternoon a few years ago something very unusual happened to me.

I was lounging under a tree in a packed east London park when I experienced a sudden feeling of vertigo, followed immediately by an overwhelming and intense sense of familiarity.

The people around me vanished and I found myself lying on a tartan picnic blanket amid a field of high golden wheat. The memory was rich and detailed. I could hear the sway of the wheat ears as a gentle breeze brushed through them. I felt warm sunlight on the back of my neck and watched as birds wheeled and floated above me.

It was a pleasant and extremely vivid recollection. The problem was that it never actually happened. What I was experiencing was an extreme form of a very common mental illusion: déjà vu.

Living with persistent déjà vu

For the past five years I have been suffering epileptic seizures resulting from the growth and eventual removal of a lemon-sized tumour from the right-hand side of my brain. Before my diagnosis I appeared fit and healthy: I was in my mid-30s and displayed absolutely no symptoms. Until, that is, the afternoon that I woke up on the kitchen floor with two black eyes after suffering my first recorded seizure.

Seizures, or fits, occur after an unanticipated electrical discharge in the brain. They are usually preceded by something called an ‘aura’, a sort of minor foreshock lasting anything up to a couple of minutes before the main event begins. The nature of this aura differs greatly from patient to patient. Some people experience synaesthesia, extreme euphoria and even orgasm at the onset of a seizure. My own aren’t nearly as exciting-sounding, being distinguished by sudden shifts in perspective, a rapidly increased heart rate, anxiety, and the occasional auditory hallucination.

By far the most significant trait of my aura is the striking sense of having lived through that precise moment before at some point in the past – even though I never have. During my most intense seizures, and for a week or so afterwards, this feeling of precognition becomes so pervasive that I routinely struggle to discern the difference between lived events and dreams, between memories, hallucinations and the products of my imagination.

I don’t remember déjà vu happening with any kind of regularity before the onset of my epilepsy. Now it occurs with varying degrees of magnitude up to ten times a day, whether as part of a seizure or not. I can find no pattern to explain when or why these episodes manifest themselves, only that they usually last for the length of a pulse before vanishing.

Many of the estimated 50 million people in the world with epilepsy experience long-term memory decline and psychiatric problems. And it’s hard for me not to worry whether the blurring of fact and fiction that I experience might one day engender a kind of mania.

Exploring the déjà experience

Taken from the French for ‘already seen’, déjà vu is one of a group of related quirks of memory. Research from 50 different surveys suggests that around two-thirds of healthy people have experienced déjà vu at one time or another. For the majority, it is dismissed as a curiosity or a mildly interesting cognitive illusion.

While déjà vu is instantaneous and fleeting, déjà vécu (already lived) is far more troubling. Unlike déjà vu, déjà vécu involves the sensation that a whole sequence of events has been lived through before. What’s more, it lacks both the startling aspect and instantly dismissible quality of déjà vu.

A defining feature of the normal déjà vu experience is the ability to discern that it isn’t real. On encountering déjà vu, the brain runs a sort of sense check, searching for objective evidence of the prior experience and then disregarding it as the illusion that it is. People with déjà vécu have been known to lose this ability completely.

Professor Chris Moulin, one of the foremost experts on the déjà experience, describes a patient he encountered while working at a memory clinic at a hospital in Bath, England. In 2000, Moulin received a letter from a local GP referring an 80-year-old former engineer known as AKP. As a result of gradual brain-cell death caused by dementia, AKP was now suffering from chronic and perpetual déjà vu: déjà vécu.

AKP claimed that he had given up watching television or reading the newspaper because he knew what was about to happen. “His wife said that he was someone who felt as though everything in his life had happened before,” says Moulin, now at the Laboratoire de Psychologie et NeuroCognition CNRS in Grenoble. AKP was resistant to the idea of visiting the clinic because he felt as though he’d already been there, despite the fact that he never had. On being introduced to Moulin for the first time, the man even claimed to be able to give specific details of occasions that they had met before.

AKP did retain some self-awareness. “His wife would ask him how he could know what would happen in a television programme if he’d never seen it before,” says Moulin, “to which he would respond, ‘How would I know? I have a memory problem.’”

On that day in the park, my vision of the picnic blanket and the wheat field disappeared when a paramedic began to shake my shoulder. Despite the fact that my memories had been hallucinations, they still felt as valid as any truly autobiographical memory. Moulin classes this as a form of déjà experience in which an image is somehow imbued with a sense of reality.

“Our feeling is that déjà vu is caused by a sense of familiarity,” he says. “Rather than just feeling like something has a feeling of ‘pastness’ about it, something comes to mind that has a phenomenological characteristic, so that it appears to be a real reminiscence.”

After his first encounter with AKP, Moulin began to become interested in the causes of déjà vu and how subjective feelings can interfere with day-to-day memory processes. Discovering that there was very little credible literature describing the causes of déjà vu, Moulin and colleagues at the Language and Memory Lab at the Institute of Psychological Sciences, University of Leeds, began to study epileptics and other sufferers of profound memory defects in order to draw conclusions about déjà experiences in the healthy brain and explore what déjà vu means for the workings of consciousness generally.

They were faced with an immediate problem: déjà vu experiences can be so transitory and short-lived that they are almost impossible to recreate in clinical conditions. The job that they faced, then, was one of trying to catch lightning in a bottle.

The causes of déjà vu

In his book The Déjà Vu Experience, Professor Alan S Brown offers 30 different explanations for déjà vu. According to him, any one alone may be enough to trigger a déjà experience. As well as a biological dysfunction like epilepsy, Brown writes that stress or tiredness could cause déjà vu.

Brown is also a proponent of what is called the divided perception theory. First described in the 1930s by Dr Edward Bradford Titchener, divided perception refers to the times when the brain isn’t quite paying enough attention to its surroundings. Titchener used the example of a person about to cross a busy street before being distracted by a shop window display. “As you cross,” he wrote, “you think, ‘Why, I crossed this street just now’; your nervous system has severed two phases of a single experience, and the latter appears as a repetition of the earlier.”

For much of the last century this idea was accepted as a plausible trigger of déjà vu. Another common explanation was one offered by a doctor working at the Boston veterans’ hospital. In 1963 Robert Efron suggested that déjà vu could be caused by a sort of processing error: he believed that brains were responsible for assimilating events through the temporal lobe before then adding a sort of timestamp to them to determine when they happened.

Efron saw déjà vu as resulting from the lag between seeing and adding that timestamp: if the process took too long, the brain would think that an event had already happened.

But Alan Brown and Chris Moulin both agree that the way that the hippocampus indexes memories by cross-referencing them according to familiarity is a more likely cause of déjà vu.

“My belief is that a per-seizure déjà vu experience is triggered by spontaneous activity in that area of the brain that handles familiarity evaluations,” says Brown. Probably, he says, in the area surrounding the hippocampus, and most likely on the right side of the brain. The precise point at which I have a lemon-shaped hole.

Brown suggests that déjà vu happens to healthy people only a few times a year at most, but can be stimulated by environmental factors. “People experience it mainly when they are indoors,