How does electromagnetic radiation injure a human brain?

Electromagnetic radiation can mean many things. Short wavelength UV, X-Rays, and Gamma rays are all ionizing radiation. Ionizing radiation is energetic enough to dislodge electrons and alter molecular structure. It is widely known that ionizing radiation is harmful to living tissue. Very powerful non-ionizing radiation is known to be able to cause damage from tissue heating (e.g. microwave ovens). The danger here is determined by the frequency and strength of the radiation. Microwave frequencies in the GHz range are the most readily absorbed by tissue so they are the ones most likely to damage tissue through heating. Frequencies above and below this range mostly pass through tissue harmlessly without being absorbed. The damage Ionizing radiation causes is cumulative. X-Rays cause some tissue damage but when doctors need diagnostic images the benefits outweigh the risk. Someone being unnecessarily X-Rayed multiple times could be injured. In theory non-ionizing radiation too weak to cause tissue warming should be harmless. Currently the effects of very weak ionizing radiation and of non-ionizing radiation too weak th heat tissue are being studied. Some believe that this radiation can cause damage through some mechanism not yet understood but so far the results are inconsistent and inconclusive. For example, radiation from living under high tension power lines should be harmless because the low frequency but some researchers suspect a cancer link.