The electron density ne of turbulent coherent structures (blobs) has been measured at the edge plasma of the TJ-II stellarator using the helium line ratio technique. A spectroscopic high-speed camera set-up allowed 2D imaging of ne with spatial resolutions of a few millimetres and exposure times down to 15 µs. The turbulent plasma density structures have been compared with the raw helium emission structures, which in principle should be similar due to the expected relation between both, and although generally positive (negative) emission structures correspond to ne blobs (holes), we see that the shape is different and that in some cases there is even no correspondence at all. A possible explanation could be that the neutral distribution, which relates the intensity emission with the ne, varies on the same spatio-temporal scale as the plasma turbulence. This would be the case if the local ne variations of blobs and holes regulated the neutral density through ionisation, making it also turbulent within our experimental frequency (<100 kHz) and spatial scale (>1 cm). To study this point we simulate the neutrals with a simple transport model to reconstruct the corresponding measured emission profiles using the experimentally obtained ne and Te radial profiles. We do this for two cases: one where the neutral distribution is stationary and another where the atoms respond to the measured ne blob and get locally depleted through ionisation. Comparing the simulated and experimental emission profiles and looking at the characteristic ionisation times we find clear indications that point to the fact that slow thermal neutrals could react to the plasma fluctuations in the 10–100 kHz frequency range, also becoming turbulent.