Normal Aging Limits Cortical Network Reorganization and Behavioral Recovery after Experimental Stroke

Abstract Stroke is the leading cause of chronic disability in the United States, and advancing age is associated with worse recovery. Despite this, relatively little is known about how aging influences the repair and reorganization of neural circuits and large-scale cortical networks after stroke. To address this question, we compared cortical network dynamics and behavioral recovery after focal photothrombotic stroke in forepaw somatosensory cortex in young (3-month-old) and aged (18-month-old) Thy1-GCaMP6f mice. Both young and aged mice developed significant somatomotor deficits after stroke; however, only young mice exhibited substantial behavioral recovery despite similar infarct volumes across groups. Two age-dependent effects on cortical network function emerged. First, somatosensory-evoked activity and somatosensory functional connectivity were disrupted in both cohorts early after stroke, but their trajectories diverged over time. Forepaw-evoked GCaMP responses in the affected cortex were similarly reduced in both groups early after stroke; yet by 7 weeks, responses recovered in young mice but remained persistently depressed in aged animals. Likewise, bihemispheric somatosensory functional connectivity was initially disrupted in both groups but improved between 1 and 7 weeks only in young mice. Second, global temporal measures of network function evolved differently after stroke. At baseline, stimulus-locked fidelity and interhemispheric coherence were higher in young than aged mice, but after stroke, these measures declined in young animals to levels comparable to aged mice and did not recover by 7 weeks. Stroke also altered large-scale cortical entrainment dynamics, and reductions in cortical entrainment area between baseline and 1-week post-stroke predicted long-term behavioral recovery across animals. Together, these findings indicate that impaired behavioral recovery in aged mice reflects a failure of damaged somatosensory networks to reorganize, whereas recovery in young mice occurs despite persistent degradation of global network fidelity and coherence. These results highlight age-dependent mechanisms of circuit repair after stroke and suggest a potential network-level basis for chronic deficits in stroke survivors. Competing Interest Statement The authors have declared no competing interest. Footnotes Contact Information: Jin-Moo Lee: Washington University School of Medicine, 660 S Euclid Avenue, Campus Box 8111, St. Louis, MO 63110; 314-747-1138; leejm{at}wustl.edu