Fig. 8
![Fig. 8](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs13018-022-03170-w/MediaObjects/13018_2022_3170_Fig8_HTML.png)
Four groups regarding the amplitude of SEPs at different detection times. α P < 0.05 versus Group 2 in the same month; β P < 0.05 versus Group 3 in the same month; γ P < 0.05 versus Group 4 in the same month; δ P < 0.05 versus 3 months in the same group