This wave known as "cortical spreading depression" activates nerve cells as it goes, and the symptoms sufferers report typically correspond to the area of the brain the wave is passing over.
Interestingly, body based attention to touch sensations, and more generally the sense of touch, are disordered in chronic pain and IBS. And the disorder seems to be mediated by a cortical mechanism.
An ectopia is a collection of several hundred nerve cells that have pushed their way up from the lower cortical layers into the outermost one, where they are not found in normal circumstances.