, ▁suggested ▁that ▁the ▁a ura ▁in ▁mig ra ines ▁is ▁caused ▁by ▁con str iction ▁of ▁int rac ran ial ▁vessels ▁( v ess els ▁inside ▁the ▁brain ), ▁and ▁the ▁head ache ▁itself ▁is ▁caused ▁by ▁re bound ▁d ilation ▁of ▁ext rac ran ial ▁vessels ▁( v ess els ▁just ▁outside ▁the ▁brain ). ▁D ilation ▁of ▁these ▁ext rac ran ial ▁blood ▁vessels ▁activ ates ▁the ▁pain ▁re cept ors ▁in ▁the ▁surrounding ▁n erves , ▁causing ▁a ▁head ache . ▁The ▁v asc ular ▁theory ▁is ▁no ▁longer ▁accepted . ▁ ▁Studies ▁have ▁shown ▁mig raine ▁head ▁pain ▁is ▁not ▁accompanied ▁by ▁ext rac ran ial ▁vas od ilation , ▁but ▁rather ▁only ▁has ▁some ▁m ild ▁int rac ran ial ▁vas od ilation . ▁ ▁Currently , ▁most ▁special ists ▁think ▁mig ra ines ▁are ▁due ▁to ▁a ▁primary ▁problem ▁with ▁the ▁n erves ▁in ▁the ▁brain . ▁A uras ▁are ▁thought ▁to ▁be ▁caused ▁by ▁a ▁wave ▁of ▁increased ▁activity ▁of ▁neur ons ▁in ▁the ▁c ere br al ▁cor tex ▁( a ▁part ▁of ▁the ▁brain ) ▁known ▁as ▁cort ical ▁spread ing ▁de pression ▁followed ▁by ▁a ▁period ▁of ▁de pressed ▁activity . ▁Some ▁people ▁think ▁head aches ▁are ▁caused ▁by ▁the ▁activation ▁of ▁sens ory ▁n erves ▁which ▁release ▁pe pt ides ▁or ▁ser ot on in , ▁causing ▁infl amm ation ▁in ▁ar ter ies , ▁dur a ▁and ▁ ▁men ing es ▁and ▁also ▁cause ▁some ▁vas od ilation . ▁Tri