Sleep spindle density and morphology are resilient to post-traumatic gray matter volume loss.

Moderate to severe traumatic brain injury (TBI) leads to gray matter volume (GMV) loss, cognitive dysfunction, and persistent sleep-wake complaints. Given the link between GMV and sleep spindles in healthy adults and the role of spindles in neural plasticity and protecting sleep against disturbances, we investigated GMV-spindle associations following TBI. In this cross-sectional study, 27 adults with chronic moderate to severe TBI (32.0 ± 12.2 years old) and 32 healthy controls (29.2 ± 11.5 years old) underwent full-night polysomnography and 3-Tesla MRI. Spindle density, amplitude, frequency, duration, and sigma spectral power (11-16 Hz) were computed. We tested GMV-spindle associations in 1) clusters with GMV loss following TBI (right and left frontotemporal and left temporal) and 2) regions previously linked to spindles in healthy adults (hippocampus, insula, cingulate, supplementary motor area, cerebellum, Heschl's gyri, thalamus, medial prefrontal cortex, putamen, and pallidum). Multiple regression analyses were performed with Group as a moderator, controlled for age. Across all participants, higher spindle amplitude and sigma power were associated with larger GMVs in the left frontotemporal, left temporal, thalamic, and medial prefrontal regions. Faster spindle frequency was associated with larger GMV in most regions, though for the left and right frontotemporal regions and hippocampus, these associations were observed only in controls. No Group effects were found for spindle characteristics. The lack of stronger GMV-spindle associations following TBI and the absence of Group effects for spindle characteristics suggest spindles' resilience to post-traumatic GMV loss.