Rev. Jesse Jackson receiving a form of life...

(CNN) — Civil rights leader Rev. Jesse Jackson remains hospitalized and is now receiving a form of life support to stabilize his blood pressure, a source close to Jackson’s family told CNN on Sunday.

Jackson, 84, a protégé of the Rev. Martin Luther King Jr., has been under observation for progressive supranuclear palsy (PSP), the Rainbow PUSH Coalition said Wednesday evening.

Further details about his condition have not been released.

The family source says Jackson has had moments of brief energy due to a medication he has been on it for two days. Jackson had a significant drop in blood pressure Saturday night, but a medical team responded to him immediately, the source added.

Even while under treatment, he has shown brief, but meaningful signs of responsiveness, the source said.

Last week, there had been “significant improvement” in the civil rights leader’s condition under medical care, his son Jesse Jackson Jr. said Thursday in a segment during his weekday radio show.

PSP is “a rare neurological disorder that affects body movements, walking and balance, and eye movements,” according to the US National Institute of Neurological Disorders and Stroke.

The disease typically begins in a person’s 60s and has some symptoms similar to Parkinson’s disease, it adds. Most people with PSP develop severe disability within three to five years.

Jackson “has been managing this neurodegenerative condition for more than a decade,” the organization previously said in a statement. “He was originally diagnosed with Parkinson’s disease; however, last April his PSP condition was confirmed.”

Jackson first rose to national prominence in the 1960s as a close aide to the Rev. Martin Luther King Jr. After King’s assassination in 1968, Jackson became one of the most transformative civil rights leaders in America.

In 1971, he founded Operation PUSH as a way to improve Black communities’ economic conditions across the US. Jackson later launched the National Rainbow Coalition, in 1984, with the goal of obtaining equal rights for all Americans, according to the Rainbow PUSH Coalition.

Some 12 years later, the two organizations merged to form Rainbow PUSH Coalition.

One of Jackson’s signature phrases was “Keep hope alive,” and was a force for social justice over three eras: the Jim Crow period, the civil rights era and the post-civil rights era, culminating with the election of Barack Obama and the Black Lives Matter movement.

This story has been updated with additional information.

CNN’s Amanda Musa contributed to this report.