Mr. Kennedy said, speaking over a crowd of cheering supporters at American University. "It is time now for Barack Obama."

Seizures, like the one Sen. Edward M. Kennedy reportedly suffered yesterday, are a fairly common occurence affecting about 10 percent of the population and often are precipitated by a stroke, according to a stroke expert.

“Stroke is probably the most common cause of seizure in American adults,” said Dr. David Thaler, director of Tufts Medical Center Comprehensive Stroke Center.

According to Epilepsy Foundation figures, 22 percent of stroke survivors will have seizures. Two or more after a stroke is labeled a seizure disorder or epilepsy.

Last October, Kennedy underwent an hourlong procedure to remove a blockage from his left carotid artery. The procedure often is performed to prevent stroke.

Seizures are divided into two major categories: generalized and partial, Thaler said.

A partial seizure is an electrical discharge that affects one part of the brain. A generalized seizure is caused by an electrical discharge that affects both sides of the brain simultaneously. It’s a more serious condition that causes convulsions.

Patients can undergo an MRI, CAT scan or electroencephalogram (EEG) to determine the cause of the seizure, Thaler said.

He described anti-seizure medications as “safe and effective.”

WASHINGTON -- Sen. Edward M. Kennedy, hospitalized Saturday after apparently suffering a seizure at his home on Cape Cod, Mass., was awake and joking with family members later in the day, a spokeswoman said. The Democratic senator is undergoing tests at Massachusetts General Hospital in Boston to determine the cause of the seizure. The 76-year-old Kennedy, leader of a storied political dynasty and a liberal icon, was rushed from the family compound at Hyannis Port, Mass., to Cape Cod Hospital at 9 a.m. He was evaluated there, then airlifted to Massachusetts General. Kennedy suffered what first appeared to be "stroke-like symptoms," a Democratic Party aide said. The longtime senator experienced one seizure in Cape Cod and a second while aboard the helicopter flight to Boston, the Boston Globe reported. By the end of the day, however, Kennedy was "conscious, talking, joking with family," said Kennedy's spokeswoman, Stephanie Cutter. Nonetheless, news of his illness sent shudders through the Democratic establishment and commanded wide national attention, in part because he so vividly embodies the Kennedy legacy, with even his voice and appearance potently reminiscent of his two slain brothers. Family members said they remained "guardedly optimistic" that he would recover soon, and hospital officials said he was resting comfortably. Relatives gathered at the hospital, joined by Kennedy's Massachusetts colleague, Sen. John F. Kerry. The 76-year-old Kennedy, leader of a storied political dynasty and a liberal icon, was rushed from the family compound at Hyannis Port, Mass., to Cape Cod Hospital at 9 a.m. He was evaluated there, then airlifted to Massachusetts General. Kennedy suffered what first appeared to be "stroke-like symptoms," a Democratic Party aide said. The longtime senator experienced one seizure in Cape Cod and a second while aboard the helicopter flight to Boston, the Boston Globe reported. By the end of the day, however, Kennedy was "conscious, talking, joking with family," said Kennedy's spokeswoman, Stephanie Cutter. Nonetheless, news of his illness sent shudders through the Democratic establishment and commanded wide national attention, in part because he so vividly embodies the Kennedy legacy, with even his voice and appearance potently reminiscent of his two slain brothers. Family members said they remained "guardedly optimistic" that he would recover soon, and hospital officials said he was resting comfortably. Relatives gathered at the hospital, joined by Kennedy's Massachusetts colleague, Sen. John F. Kerry. The hospital canceled plans for a news briefing. Experts said a seizure is caused by the abnormal firing of neurons in the brain, producing an excess of electrical activity. Although frequently thought to lead to a loss of consciousness or convulsions, seizures can produce symptoms as mild as numbness, nausea or a sensation of fear. Many of those symptoms also are associated with stroke, making it difficult at times to distinguish between the two. Nearly everybody is at some risk of seizures, according to Dr. Marc R. Nuwer of UCLA's David Geffen School of Medicine. They can be triggered by sleep deprivation, stress, alcohol consumption or medications. It is unlikely that Kennedy will suffer any long-lasting aftereffects. But Nuwer said he would probably have a headache and a sore body for several days, "like he ran a marathon."