Apologies if this question is trivial, I'm a neuroscientist and would hugely appreciate your help to correctly interpret my analysis.

I am recording EEG signals and am manipulating the brain using light flickering at 10Hz. I then compute the PSD of this signal using FFT of 4s long epochs. I am interested in what the manipulation does to frequencies around 5Hz.

My problem is that my 10Hz stimulation creates an artifact at 10Hz (light induces current flow). I see this clearly in the PSD and I also see higher harmonics at 20 and 30 Hz. My question is whether I should expect this artifact to affect the 5 Hz frequency as well? I don't see a clear peak but I don't fully understand the theory so I'm not sure.