Just stumbled over this in R. Sapolsky's "Behave".
tl; dr: Managing cognitive load is important!

"Pertinent to this is the concept of „cognitive load“. Make the frontal cortex work hard - a tough working-memory task, regulating social behavior, or making numerous decisions while shopping. Immediately afterwards performance on a different frontally dependent task declines.
1/2

Likewise during multitasking where PFC [pre frontal cortex] neurons simultaneously participate in multiple activates circuits.
Importantly, increase cognitive load on the frontal cortex, and afterwards subjects become less prosocial - less charitable or helpful, more likely to lie."

Robert Sapolsky, „Behave“, p49 ff.