When most people think about the lingering effects of a concussion, they picture persistent headaches, light sensitivity, or forgetfulness. But a new study published in Human Brain Mapping (2025) suggests that the most telling sign of chronic mild traumatic brain injury (mTBI) may not be how slow or impaired someone is on average—but how inconsistent their brain performance becomes from day to day.

Researchers from Deakin University and St. Vincent’s Hospital in Melbourne examined eleven adults about a year after sustaining an mTBI and compared them with twenty-two healthy peers. Instead of relying on a single clinic-based test, participants completed cognitive tasks and symptom surveys every day for a month using a smartphone app called Mindtrax. This “ecological momentary assessment” approach allowed scientists to track real-world performance fluctuations—something traditional one-time neuropsychological tests can easily miss.

The findings were striking. People with chronic mTBI showed far greater intraindividual variability—that is, swings in reaction time and working-memory accuracy from one day to the next—than healthy controls. Those daily ups and downs were closely tied to fluctuating post-concussive symptoms like fatigue and dizziness. Brain imaging (DTI) revealed reduced white-matter integrity in a key communication highway, the left superior longitudinal fasciculus, which links the frontal and parietal regions responsible for attention and executive control.

Intriguingly, greater moment-to-moment inconsistency was associated with structural differences in this same tract, hinting that subtle wiring disruptions may underlie unstable cognitive performance. The study suggests that concussion recovery isn’t a straight line toward improvement—it’s a moving target.

By capturing cognition “in the wild,” mobile brain-health tracking could become an important biomarker for long-term concussion effects, helping clinicians and researchers move beyond static snapshots to understand how the injured brain truly functions over time.

(2025). Association Between Intraindividual Variability in Cognitive Performance and White Matter Organisation in Chronic Mild Traumatic Brain Injury. Human Brain Mapping. 46.