Kerry Kennedy pleaded not guilty Tuesday in a Westchester court to driving while drug impaired, blaming her erratic behavior and sideswiping of a truck Friday on a "complex partial seizure," possibly from an earlier right-brain injury.

After the brief hearing in the North Castle Town Hall on the misdemeanor charge, the ex-wife of Gov. Andrew M. Cuomo told reporters that she had no recollection of the incident.

Authorities said Kennedy hit a tractor trailer about 8 a.m. Friday on Interstate 684. She left the highway and a North Castle police officer found her slumped over the steering wheel of her 2008 Lexus on nearby Route 22, authorities said.

"I remember getting on the highway and then I have no memory until I was stopped at a traffic light and a police officer was at my car door," Kennedy told reporters Tuesday outside the courthouse. "In my discussion with the police officer, I was confused and erratic."

Kennedy, 52, said she was headed to the gym when the incident occurred. Alarmed drivers alerted police, and she said she "told the officer that it was theoretically possible that I had mistakenly taken an Ambien rather than a thyroid pill earlier that morning."

Following the accident, Kennedy said she underwent a battery of neurological tests at Mount Sinai Hospital in Manhattan. "An MRI showed an area of hyperdensity, which appears to be the result of a head injury I sustained some time ago," she explained.

Doctors told Kennedy she had "symptoms consistent with a right side of the brain injury," she said. Kennedy said she will undergo treatment for the injury that court papers said she incurred during a car accident last year.

"The lack of memory, the quick recovery, and a series of other factors led my doctors to believe that this accident was caused, not by a sleeping aid, but by a complex partial seizure," Kennedy said.

Kennedy asserted that blood and urine tests taken at Northern Westchester Hospital shortly after the incident will show that no alcohol or drugs were in her system. The mother of three daughters with Cuomo said she does not abuse drugs of any kind.

North Castle Town Justice Elyse Lazansky told Kennedy that she had to be fingerprinted within two days by state police and she set her next court date for Aug. 14.

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