Photobiomodulation Promotes Motor Recovery Following Decompressive Craniectomy for Traumatic Brain Injury.

Background: Photobiomodulation (PBM), a noninvasive therapy using red and near-infrared light, has shown promising benefits in neuropathology. However, the transmission of PBM to the central nervous system through the scalp's soft tissues and skull is unknown. We hypothesize that decompressive craniectomy (DC) for moderate-to-severe traumatic brain injury (TBI) improves PBM penetrance and enhances neurorehabilitation. Method: Adult male and female Long-Evans rats were utilized to evaluate PBM tissue penetrance and its efficacy on motor deficit recovery following TBI and DC. TBI was induced using a hit-and-run closed-head model, which replicates clinical closed-head trauma. PBM transmittance was measured ex vivo using rat scalp soft tissue and hemicranium samples, with optical power and energy meter readings to quantify penetrance. Functional motor recovery was assessed using a beam walk test to quantify limb deficits defined by forelimb and hindlimb slips. Results: Analysis demonstrated attenuation of 660 nm and 850 nm PBM intensity during transcranial transmission, with scalp skin and cranial bone reducing irradiance from 70.5 mW/cm² to 3.96 mW/cm² for 660 nm PBM and from 82 mW/cm² to 4.96 mW/cm² for 850 nm PBM. Beam walk testing revealed significantly fewer hindlimb slips in PBM-treated rats (660 nm: 1.54, 850 nm: 1.86) compared with untreated TBI controls (4.3 slips), suggesting improved motor recovery. Conclusion: Our study indicates that both PBM are attenuated by both scalp soft tissues and the hemicranium, yet both penetrate sufficiently following DC for moderate-to-severe TBI. Our findings suggest that PBM enhances neurorehabilitation outcomes with improved motor recovery in rats with TBI.