Man's memory returns

Wednesday January 30 2008

“Scientists have accidentally discovered a key to unlocking memory, which could offer hope to thousands of Alzheimer’s sufferers,” according to The Daily Telegraph. The Independent also reported the case of an obese man who had “experimental brain surgery” in an attempt to control his appetite, but whose brain was instead accidentally stimulated to induce a “déjà vu” like experience of an event from more than 30 years ago. In further experiments, the man was found to have improved memory and learning abilities when electrical current was applied to the same part of his brain.

The newspapers said that the researchers are now repeating the experiment in Alzheimer’s patients to see if it is beneficial, and, if successful, could provide hope to the thousands of sufferers by “providing a pacemaker for the brain”.

Deep brain stimulation, the technique that provoked the experience, is already widely used as a treatment for Parkinson’s disease. It involves surgically inserting electrodes into patients’ brains and stimulating parts of the brain with an electric current.

These findings will be of interest to doctors and scientists and will probably lead to further research and development in the field of deep brain stimulation. However, it is too early to say if this treatment could have any potential benefit in the improvement of memory or the management of Alzheimer’s disease. The findings are the result of a case study in one man only, who was not himself a sufferer of Alzheimer’s. Further research in Alzheimer’s patients is needed before it is known if this could be used as a treatment for the disease.

Where did the story come from?

Dr Clement Hamani and colleagues from the Toronto Western Hospital and Research Institute, University of Toronto, Canada carried out the research. The study was published in the peer-reviewed medical journal: Annals of Neurology.

What kind of scientific study was this?

Animal studies have found that electrical stimulation of the hypothalamus, (the control centre of the brain that regulates hormone levels and certain body functions such as sleep, thirst and hunger), has an affect upon feeding behaviour and memory.

In this case report, an obese man received deep brain stimulation (DBS) to the hypothalamus, in an attempt to control his appetite. DBS is a surgical procedure that is widely used to treat the symptoms of neurological illnesses such as Parkinson’s disease. The man was 50-years-old with a lifetime history of obesity that had been unresponsive to treatment. He also had several related medical problems including high blood pressure.

The patient was awake but anaesthetised during the procedure, during which DBS electrodes were implanted into both sides of his hypothalamus. The electrodes were moved to different positions to identify sites that affected the patient’s appetite and where the electrodes would be best situated. Potential sites were identified by asking the patient to score between one and 10 how hungry he was when that site was stimulated. After testing was completed, the electrodes were secured in position, and a “pulse generator” that would provide the electrical stimuli was also implanted into the brain.

At the time of surgery, and after three weeks of continuous DBS, an in-depth neurological assessment was made using a variety of standardised intelligence, verbal and memory tests. At this point, further memory stimulation was also carried out, with the patient being unsure when electrodes were randomly switched on or off. The “on or off” tests each lasted two days and were one week apart. They involved presenting the patient with a series of 80 word pairs, and then later testing whether he could remember the words in the right combinations by presenting him with word pairs that were the same as before, recombined or new pairs. 

A repeat experiment was carried out 12 months later, this time with the “on or off” tests being completed in the same day, and the man being given a series of 120 word pairs with which he had to construct a sentence.

Radiological testing was also carried out after one month of DBS to see which regions of the brain were being activated by hypothalamic stimulation.

What were the results of the study?

When the researchers placed the electrodes at one contact site on the left side of the hypothalamus, they found that the man unexpectedly reported a sensation he described as "déjà vu". The experience was of a situation from about 30 years earlier, of being in a park with friends. As the voltage was increased (from three to five volts) the details of the scene became clearer to the man. When the experiment was repeated at different electrode positions (the man being unaware of which position was receiving the stimulation) the researchers found that specific situations could be recalled with each position.

When certain positions received more than five volts, the man experienced adverse effects including flushing and sweating. The patient also experienced flashes of light in one of his eyes when the front part of the hypothalamus - located where nerve tracts between the eyes and the brain cross over - was stimulated. During these experiences, the man reported no change in his feelings of hunger on the scale of one to 10.

Two weeks after the electrodes were fixed in place, repeat testing produced similar memories to those recalled in the operating room, although these were independent of the site of the hypothalamus being stimulated. The same findings that the memory increased in detail with increasing voltage and increased side effects were also repeated.

At the time of surgery, the man scored average to high-average on all verbal, memory and intelligence tests. At three weeks, there were significant improvements on two verbal and spatial learning tests, but not across the others (14 individual tests in total).

On both word pair tests, the researchers found that the patient was more likely to remember the correct word pairs when DBS was switched on.

Radiological testing demonstrated that when the electrodes in the hypothalamus were stimulated, there were signs of increased activity in parts of the temporal lobe of the brain that is involved with memory and recall.

Further details of the effects of DBS upon appetite were not published in this report.

What interpretations did the researchers draw from these results?

The authors conclude that deep brain stimulation to the hypothalamus causes activity in a region of the temporal lobe and that “it may be possible to apply electrical stimulation to modulate memory function”.

What does the NHS Knowledge Service make of this study?

This study will be of interest to doctors and scientists and will probably lead to further research and development in the field of deep brain stimulation and the effects that it may have on memory. However, at the current time any practical applications of this treatment are a long way off.

It should be pointed out that these findings are the result of a case study in one man only and it is unclear whether the same effects would be witnessed in other people. There may also have been other hidden factors that affected the results.

The man in this study was not an Alzheimer’s sufferer and the researchers do not make any mention of this as a potential treatment for Alzheimer’s disease within the paper. It is too early to conclude from this research if this technique could be used as a treatment for Alzheimer’s disease.

Sir Muir Gray adds...

Stimulation keeps the mind fit, but I think I will stick to arguing, reading, and trying to learn a foreign language rather than deep brain stimulation.

Analysis by Bazian
Edited by NHS Choices