Given the organization of the primary somatosensory cortex, why does a slap in the face hurt more than a slap on the back? The primary somatosensory cortex is a part of the cortex (brain burier) that protects the skull. The cortex and brain are very sensitive parts of the body and it has more room to move around in its location verses the back. Due to the complexity of the brain and the space it occupies, it has more room to bounce and hit the ‘walls’ which causes more pain over a slap in the back.