I just started playing Mass Effect 1 and I'm a little confused about the conversation system. I understand that during regular conversation, the top right spoke leans towards the paragon alignment and the bottom right spoke leans towards the renegade alignment. Does this same system apply to choices on the left in an investigation branch? Meaning, if I choose to investigate something listed in the upper-left of an investigation branch, does that count towards paragon and vice-versa
The left-side conversation options are always "tell me more" dialog choices, and will simply expand the conversation. They should never give paragon or renegade points.
They exist to give more story and lore to those who enjoy such things.
If we look at this image we see an example of a dialog wheel:
On the right side we have the standard conversation options. These usually correspond to (from top to bottom) Paragon, Neutral, Renegade; you will sometimes receive points for these options.
On the left side you have the special conversation options. These correspond to (from top to bottom) Charm, Neutral, Intimidate. Their effect is based on your Charm/Intimidate skills respectively. While standard conversation options will sometimes give you points, special options (with the exception of neutral) will always give you points.