Can you lose weight when studying?

Ok, its finals week, and I've noticed that when I buckle down and study (usually for hours on end and over the course of several days), I seem a bit lighter. Granted I'm just sitting on my duff doing this, but anyone else experience this?

Only thing I can think is that using the brain=calories burned since it does take a good amount of energy. Note too that I still keep my regular feed times.