From late 2016, American diplomats assigned in Havana, Cuba have reported mysterious neurological symptoms after hearing strange sounds in their homes and hotel rooms.

A total of 21 cases have been reported until August 2017, with the patients experiencing headaches, vertigo, memory impairment and other symptoms that all point to head trauma. What baffled doctors, though, was that test results did not show even the slightest sign of injury.

What could have caused this phenomenon which the U.S. government considered as a health attack? A new study conducted by American scientists from Philadelphia may just hold the answer.

Cuban Scientists: Stress, Not Sonic Weapon

Back in December 2017, a group of Cuban scientists explained that the symptoms resulted from stress, not a sonic weapon as what media reports around that time claimed.

Since the U.S. government restricted access to the patients' medical records, the group conducted audiometric testing on neighbors and domestic workers of the affected diplomats.

Of the 20 people tested, three were found to possess abnormalities in the cochlea, eardrum and inner ear. However, all 20 participants had pre-existing hearing problems before the intriguing phenomenon occurred.

Although they withheld medical information, American officials provided some sound recordings obtained from around the personnel's homes during nighttime.

They were then compared with recordings made by Carlos Barcelo Pérez, an environment physicist from Cuba's National Institute of Hygiene, Epidemiology, and Microbiology.

He notes that insects created most of the evening sounds, particularly the Jamaican field cricket. The chirping, which reached a maximum of 74.6 decibels, matched the grating sounds in recordings from the U.S. government. Such frequency, though, is not loud enough to result in any ear damage.

After nine months of investigation and considering an insecticide as a potential cause, the Cuban scientists could only conclude that stressful conditions caused the diplomats' symptoms.

The group stressed that around the time of the intriguing phenomena, the U.S. embassy in Havana was preparing for a significant transition as President Donald Trump had just been elected.

American Scientists: Artificial Source

While such conclusion could be entirely possible, new clinical findings published Feb. 15 in The Jama Network state the audible sounds heard by patients before falling ill may not have triggered the neurological symptoms.

Nonetheless, American scientists still linked these sounds to the event, this time as results of head trauma from exposure to a non-natural and still-unidentified source.

They also indicated the possibility that cases they studied were severe ones and that other individuals could have suffered symptoms that were too subtle to be noticed.

In conclusion, the research team from Philadelphia raised their concern about an artificial mechanism that could cause brain injury upon exposure.

Such a theory only validates the State Department and federal investigators' statements last January, asserting that symptoms could be associated with head trauma from a "non-natural source."

Fortunately, a report says that the affected U.S. personnel have already shown signs of improvement.

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