Impact frequency and interval modulate brain network outcomes in a rat model of repetitive mild traumatic brain injury

Repetitive mild traumatic brain injury (mTBI) is an increasing public health concern, however, how impact frequency and inter-injury interval shape long-term brain network function remains unclear. This study investigated the effects of varying impact number and interval duration on functional connectivity and neurological outcomes in a rat model of repetitive mTBI. Fifty adult male Sprague-Dawley rats were randomly assigned to five groups: sham, single impact, two impacts (1-hour interval), three impacts (1-hour interval), and three impacts (6-hour interval) of closed-head injury. At 50 days post-injury, resting-state functional MRI and behavioral assessments were performed. Rats exposed to repetitive impacts at 1-hour intervals showed widespread disruptions in functional connectivity across default mode, sensory, and motor networks, with alterations increasing according to impact number. These network changes were attenuated in rats receiving impacts spaced 6 h apart, which exhibited connectivity patterns closer to sham controls. Behavioral testing revealed significant motor impairments in the 1-hour interval group, whereas motor performance was preserved in the 6-hour interval group. Connectivity within sensory and motor networks correlated with motor outcomes. These findings demonstrate that injury frequency and timing influence brain network integrity and suggest that extending inter-injury intervals may mitigate cumulative neural dysfunction following repetitive mTBI.