Patients with a small, benign tumour on a particular part of the brain suffer from a bizarre desire to laugh, doctors report.

Three patients with a growth called a hypothalamic hamartoma also suffered from giggling bouts early in life.

The strange symptom only happened to patients with smaller hamartomas, and they also suffered from mild epileptic seizures.

However, although anti-epilepsy drugs were able to stop the seizures, the urge to laugh continued.

Often they would experience a feeling that they wanted to laugh, without actually breaking out into a chuckle.

This particular growth involves a tiny area of the brain called the hypothalamus, which is though to be linked to emotions - including the production of laughter.

The report, published in the journal Neurology, described three patients who suffered from these repressed laughing bouts.

One woman described it being like "a tickling in my head". Another was forced to bite his lip when the urge happened in inappropriate circumstances.

These desires happened as many as 10 or 15 times a day.

Dr Samuel Berkovic, from the Austin and Repatriation Medical Center in Victoria, Australia, said: "Many patients find the feeling pleasant.

"However, they are aware that sometimes a seizure may follow and this is frightening.

"How laughter occurs is not completely understood. It involves a complex relationship between the thought processes and emotional aspects of the brain as well as physical control of the muscles in the chest and voice box."

All three patients had these recurring giggling, starting at a young age, and persisting into adulthood.

Dr Berkovic said that anyone with this symptom should not dismiss it, and seek the opinion of an expert.