is center embedding, in which phrases are placed in the center of other similarly formed phrases (i.e. "The rat the cat the man hit chased ran into the trap".) Sentences with 2 or in the most extreme cases 3 center embeddings are challenging for mental parsing, again because of ambiguity of syntactic relationship.

Within neurolinguistics there are multiple theories that aim to describe how parsing takes place in the brain. One such model is a more traditional generative model of sentence processing, which theorizes that within the brain