We investigated if incongruent solutions of simple
multiplication problems would elicit similar event-related
brain potentials as inappropriate words in sentences. In
Experiment I, 12 subjects verified the appropriateness
of solutions of multiplication problems or of final words
in short sentences. Both incongruent solutions and incongruent
words evoked a phasic negative shift between 300 and 500
ms having a similar topography. In Experiment II, we tested
with another sample of 13 subjects if the amplitude of
this arithmetic N400 effect was affected differently by
different stimulus onset asynchronies (SOA = 200 and 500
ms) and by errors that were either table-related or table-unrelated
to the preceding operands. Again, incorrect solutions elicited
an arithmetic N400 effect whose amplitude depended on both
the relatedness of the solution and the SOA. The ascending
part of the N400 effect was always larger for unrelated
than for related errors independently of the SOA, whereas
the maximum of the N400 effect was larger for unrelated
errors in case of a long SOA only. This pattern of effects
was similar to that observed with semantic material varying
lexical associations. These results suggest that arithmetic
incongruencies are handled by the system in a manner functionally
similar to that of semantic incongruencies.