Cerebral activity during exposure to non - visible light
Vision is based on a protein interaction with a molecule called retinal from vitamin A.

Wavelengths of light in the visual range cause a photoisomerization of retinal (a cis- to trans- change), which is sensed by the protein that is "holding on" to the retinal.

Wavelengths that do not cause this photoisomerization cannot be sensed by the photoreceptors of the retina, so there isn't any signal produced to transmit to the brain.

However, there is some filtering done by the lens of the eye. Without the lens, humans (and other animals) can see further into the UV range. That UV light is also damaging to the retina, though, so it's best to keep the lens intact.

Note that the image in the answer by @Remi.b is actually from a psychometric experiment, so the lens is intact. The responses there are actually human perceptual sensitivity to light for each cone. The blue curve would go off to the left quite a bit further into the 300nm range if the lens were not present. The research subjects probably prefer the experiment as-is, however.

You wouldn't perceive that UV light much differently than a far violet color, however, because differences between different cones are necessary for color vision, and by that end of the spectrum only the cones responsive to the shortest wavelengths are responsive at all.