A recent study estimates the number at around 6200. A day. Using a tool called fMRI (functional magnetic resonance imaging), which allowed them to actually see the brain in action, researchers measured the number of "thought worms" we have each day. While they made no attempt to identify the content of participants' thoughts, the researchers could identify when the subjects jumped from one thought to another.
I am fascinated by this, and it certainly sheds light on how engaging in seemingly physically non-demanding tasks like studying, writing and planning can leave us feeling tired. Though our bodies aren't moving, our brains are still whirring away, using up energy in mental exercise rather than the physical variety.
This leaves me wondering things like how many calories mental activity burns and whether or not I really want to know how many thoughts I have on any given day. If I have 9000 on Monday, does that explain my need to slack off and have only 4500 on Tuesday? If I stay focused on a task, which, if I understand it correctly is one thought worm, does that use up less energy than creating a variety of thought worms? Am I more productive when I create fewer focused thought worms or when I get the thought worm factory up and running at full speed?
Inquiring minds want to know.