Objective To observe the expression of the polysialic acid neural cell adhesion molecule ( PSA-NCAM) in the hippocampus of rats after exposure to low intensity ( 16 Hz,90 dB) infrasound for different periods.Methods One hundred and twenty male Sprague-Dawley rats were randomly divided into infrasound exposure and normal groups.The exposure group was tjem further divided into 1 day,7 days,14 days and 21 days exposure groups.After exposure,the rats' brains were removed and an immunohistochemical technique was used to observe the expression of PSA-NCAM in the hippocampus after 1,7,14 or 21 days of exposure. Methods The expression of PSA-NCAM had increased significantly after exposure for 7 days. It peaked at 14 days,then had decreased by 21 days,but always remaining higher than in the normal group.After the infrasound exposure had ended,the expression of PSA-NCAM demonstrated a tendency of decrease over time,and the least was on the 21st day.The largest decrease was observed in the 14 days exposure groups. Conclusion 16 Hz,90 dB infrasound can increase the expression of PSA-NCAM in the hippocampus,at least in rats.This suggests that low intensity infrasound might initiate recovery of an injured central nervous system.Migration of neural stem cells may aid in the repair of neural injuries resulted from infrasound exposure.