▁the ▁coll ars ▁effectively ▁d eter red ▁b ark ing ▁without ▁statist ically ▁significant ▁elev ations ▁in ▁pl asma ▁cort is ol , ▁compared ▁to ▁controls , ▁at ▁any ▁of ▁the ▁time ▁points ▁measured ." ▁ ▁T ort ora ▁Study ▁( 1 9 8 3 ) ▁T ort ora ▁applied ▁a ▁method ▁called ▁" s af ety ▁training " ▁to ▁treat ▁ag gression ▁in ▁ 3 6 ▁cases ▁exhib iting ▁a ▁form ▁of ▁" inst rument al ▁ag gression ", ▁selected ▁after ▁screen ing ▁a ▁population ▁of ▁ 4 7 6 ▁cases . ▁" Inst rument al ▁ag gression " ▁was ▁defined ▁as ▁describing ▁ag gress ive ▁acts ▁that ▁" do ▁not ▁have ▁a ▁clear ▁evolution ary ▁significance , ▁are ▁not ▁directly ▁related ▁to ▁emot ional ▁ar ous al , ▁do ▁not ▁have ▁specific ▁re le asing ▁stim uli , ▁are ▁not ▁directly ▁mod ulated ▁by ▁h orm ones , ▁and ▁do ▁not ▁have ▁an ▁ident ifiable ▁focus ▁in ▁the ▁brain ". ▁T ort ora ▁states ▁that ▁in ▁the ▁context ▁of ▁the ▁article ▁" inst rument al ▁ag gression " ▁was ▁specifically ▁defined ▁as ▁" ag gress ive ▁responses ▁that ▁have ▁" a ▁spec ifiable ▁learning ▁history , ▁show ▁a ▁growth ▁function ▁over ▁time ▁and ▁are ▁mod ulated ▁by ▁their ▁consequences . ▁These ▁dogs ▁had ▁few ▁oper ant ▁alternatives ▁to ▁gain ▁rein for cement ▁by ▁comp liance ▁and ▁were ▁ch anne led ▁down ▁a ▁path ▁that ▁allowed ▁their ▁inn ate ▁ag gress iveness ▁to ▁come ▁under ▁the ▁control ▁of ▁the ▁neg atively ▁rein