Each morning for the past four years, the Italian man has begun his day brimming with vim and vigor. His is a particularly European sort of pep, and he throws open his windows to shout a greeting at his neighbors. He does not, however, sound a triumphant “buon giorno!” — that is, “good day” in Italian.

Instead, he greets the world with “bonjour!” The man says he is full of happiness. And, as he told a team of neuroscientists and psychologists, he feels compelled to express his euphoria in French. He now reads French magazines, enjoys French movies, loves French food and speaks his non-mother-tongue with gusto.

He calls the enthusiasm he feels, appropriately enough, joie de vivre.

But he had not always been such a Francophile, as a team of scientists, from the University of Edinburgh and the Somma Lombardo Hospital in Italy, wrote recently in the journal Cortex. The man, who is 50 and described only by his initials, JC, had a brain injury stemming from an arterial anomaly four years ago. Abruptly afterward, he began to talk in French.

JC’s previous history with French amounted to high school language classes and, as the scientists put it, a “fling” with a French woman while the man was in his 20s. This was the first time he had used the language in 30 years.

Despite his newfound desire to speak French — what the scientists call a “compulsive foreign language syndrome” — JC did not suddenly master the dialect. “JC’s French is maladroit and full of inaccuracies,” the researchers write, “yet he speaks it in a fast pace with exaggerated intonation.”

Neither divinely inspired glossolalia nor gibberish, JC’s language is simply emphatic, error-prone French. JC talks as though he were in a movie, the scientists say, “posing as a typical caricature of a French man.” JC speaks French to anyone who will listen: to his wife, to his fellow hospital patients, to his “bewildered” relatives and to his pension committee, who were, the scientists say, completely baffled.

But JC does not get irritated by the bafflement of his conversational partners, attempting to first answer questions in basic French before switching over to more accurate Italian when pressed. In fact, the scientists say he is now unusually happy — “unjustified euphoria,” they call it — even offering to teach his neighbors how to speak French. After one shopping trip, when he went out to buy a pair of coat hangers, he instead returned with 70.

JC’s case is not the first instance of brain injury prompting unusual linguistic changes. In 2010, after a Croatian teenager recovered from a 24-hour-long coma, she began to speak to her parents in German, requiring a translator. In 2013, a 61-year-old Navy vet awoke in a Florida motel, apparently having forgotten English in favor of the Swedish. Because these events are so rare — and the brain is such a mysterious organ — it remains unclear to neuroscientists why people with brain injuries may begin to talk in foreign languages.

Researchers speculate that damage to the brain’s language centers could be involved. Or, perhaps, an injury could harm parts of the brain associated with childhood learning, though leave memories of languages studied later in life intact.

“When a trauma to the brain occurs — due to a car accident or a stroke, tumor, or other causes — some parts of the network may be spared while some others temporarily or irreversibly damaged,” Regina Jokel, a speech-language pathologist told ABC News in 2010, after the Croatian teen began speaking German.

The U.K. and Italian scientists studying JC argue that speaking spontaneously in a foreign language has a long literary trail, cropping up in Geoffrey Chaucer’s “The Canterbury Tales” (specifically, “The Man of Law’s Tale”) and Herman Melville’s “Moby Dick.”

Simply because speaking in disremembered tongues is hinted at throughout history, however, does not mean the researchers could explain JC’s new affinity for French. “Perhaps, as early writers and modern popular press have handed down,” the scientists write, “previous, albeit shallow, knowledge of a foreign language, apparently long forgotten, can be switched on by a brain insult and speaking it becomes a compulsive behavior.”