Mental Depths and Shallows

In science, there's a concept of buoyancy.  Things are buoyant if they float, that is, if their average density is less than water.  On the other hand, if this average density is greater than water, they sink.  If the density is equal to water, they stay wherever they're placed, and are considered at "neutral buoyancy."

Now, what's the buoyancy of your thoughts?

No, I don't mean the buoyancy of the brain.  Although, if you're curious, the brain is actually at relatively neutral buoyancy, which is how it floats inside our heads without hitting the bottom of our skulls.

(Take a moment to consider this.  If your brain was to somehow come out of your body underwater, it wouldn't bob to the top, like the rest of your body.  Instead, it would just hang there in the water, drifting back and forth along the currents . . . )

(Now imagine a whole school (flock?  Shoal?) of brains, roaming in the depths of the ocean.  Existing without bodies, they drain the mental energies of their prey, dragging down sailors from capsized ships into the depths, where the brains will feed off the dying thoughts . . . )

But I'm getting off topic.  No, think about thoughts.  That's right, meta-thinking.  

There are definitely shallow thoughts:

• "Oh my god, look at her dress.  It totally does not look good with her body."
• "How many of these could I fit in my mouth at once?"
• "I'm sleepy."
• "I think I should watch Keeping Up With The Kardashians."
• "Is this Justin Bieber?  I love this song!"

Yep.  Pretty shallow.  Splashing around on the edge of the mental pool.

On the other hand, there are certainly deep thoughts as well:

• "What is my purpose in life?"
• "What will happen to the universe, in the end?"
• "How will I be remembered, after I'm gone?"
• "If I eat myself, will I weigh twice as much, or nothing at all?"

Now, take a moment and reflect.  Do your day-to-day thoughts tend to be towards the shallow end, or the deeper end?

Personally, I have noticed that, like a joyful minnow, my thoughts seem to enjoy alternating between surfacing and diving.  While sitting or trying in vain to fall asleep, I will find myself pondering the deepest questions in life, when all of a sudden, my deep thoughts are interrupted by an idle wondering about when the next episode of Top Gear will be on.  Bam, back in shallow territory.

Going a step further, do different people have different mental buoyancies?  Does my friend, who watches nothing but reality television, have a brain that moors in shallower waters than mine?  Does another friend, who insists on reading dry and musty poets, have a brain hiding deeper in the depths?  

And now, for the scientific part of my brain: how could this be measured?