Wordnet 3.0
NOUN (1)
1. 
 (psychology) nervousness resulting from mental stress; 
- Example: "his responsibilities were a constant strain"- Example: "the mental strain of staying alert hour after hour was too much for him"[syn: strain, mental strain, nervous strain]
WordNet (r) 3.0 (2006):
mental strain
    n 1: (psychology) nervousness resulting from mental stress; "his
         responsibilities were a constant strain"; "the mental
         strain of staying alert hour after hour was too much for
         him" [syn: strain, mental strain, nervous strain]