Traumatic brain injuries, or TBIs, are often thought of as a singular event, one whose recovery period is limited to a short, concrete period of time following the incident.

But their effects can saddle survivors with lingering effects, including things like headaches and changes in behavior and mood.

Now, a new study suggests that survivors of TBIs may see improvement —or deterioration — up to seven years after the initial injury.

In a new study published in the medical journal of the American Academy of Neurology, researchers found that those with traumatic brain injuries continue to demonstrate progress and decline across a range of areas, including their ability to function and their cognitive skills.

Researchers followed participants for seven years, including 917 people with mild TBIs and 193 people who had moderate to severe TBIs.

Each year, study participants took three tests on thinking, memory, mental health and ability to handle daily activities, starting in the study’s second year. Researchers also interviewed them on their abilities and symptoms, such as headache, fatigue and sleep disturbances.

The researchers saw the most decline in participants’ ability to handle daily activities. On average, about 29% of those with mild TBI declined in their abilities, as did 23% of those with moderate to severe TBI.

On a more positive note, 22% of those with mild TBI improved over time, and so did 36% of those with moderate to severe TBI.

Like most things, patients’ responses to TBIs vary and are highly individual. But the study points to one important conclusion — the aftermath of the injury is far from static, and merits a closer look.