( Tom Ackerman, Getty Images) While you work on a task at home
or in the workplace, signals firing off inside your brain are
determining when you'll decide it's time for a break.
Researchers in Paris set out to clinically test pieces of a
theory first posed by philosopher and psychologist William James
in the early 20th century. In their report, published online in
the Proceedings of the National Academy of Sciences, they
explain James' theory: There is a signal connected to fatigue,
James proposed, that accumulates when we exert effort.  When
that signal reaches its highest possible end, we decide to stop.
Lastly, that high point can change based on varying
circumstances — like incentives. For this experiment, the
researchers added one more hypothesis: That we decide to begin
work again when the signal reaches its lowest end.  The first
point of the study was to find out whether the signal, which the
researchers called "cost evidence," actually exists in the human
brain. They recruited 39 participants to sq