Western Larch

Steve no offense but have you tried Googling

https://www.google.com/?gws_rd=ssl#q=Western+larch+indoors

Actually i have tried to search for the answer to this question in many ways, shapes and forms, but still cannot find anything

no offense to you, but what you searched has nothing on what happens to WL kept indoors during the winter

The larch is a deciduous tree.

If it's kept indoors without the right lighting/temperature changes to signal a change in seasons, why would it drop its leaves?

Think of the work people do to get poinsettias / lilies etc to bloom at the right time when kept indoors. Same thing for an indoor larch.

Which triggers the signal to drop the needles? the light or the temperature? i realise that it is possible that it is a combination of both. not to mention that blooming and dropping needles are not the same thing. the dropping of the needles is to avoid the snow piling up on the needles and breaking the branches, not to reproduce. my question is not whether the cones would open at the right time while indoors

You've missed my point. It's not a question of the purpose - bloom vs drop. It's about signals.

http://garden.lovetoknow.com/wiki/What_Causes_Plants_to_Shed_Their_Leaves_in_the_Fall#GMuKTPKyEzaSpFOR.97

If you're not providing the right signals for an outdoor plant moved indoors, it will not follow its outdoor habits.

This is very basic science project stuff.

so on the flip side, if you kept a western larch in a cold room with very little sun, you could prompt the needles to fall?

Sorry Steve, was sure it'd be in Google. Best luck otherwise

If you time it properly.