I have wrote this code
new Ajax.PeriodicalUpdater('ChatDiv', '/index/newChatMessage',{method:'get',frequency:10,asynchronous:true, evalScripts:true, insertion:function(request){return false;},parameters:'lastId='+lastChatMessageId});

My problem is that the value of parameters not change if i change lastChatMessage.
Parameters is ever set to initial value.

Is possible change it from insertion option?how?
Thanks