MEG correlates of empty subjects in Japanese control and raising constructions

Empty categories are unpronounced elements with syntactic properties that play a central role in theories of sentence structure. Although there are several types within these categories, the neural basis for distinguishing among them remains unclear. Using magnetoencephalography, we investigate whether the brain distinguishes between two Japanese sentence structures: Control and raising. Although these constructions appear similar on the surface, they are argued to involve different types of empty categories. In theoretical analyses, the control-type empty category, which is called PRO, is often treated as an anaphoric element, similar to reflexives such as himself and herself, whereas the raising-type empty category is a noun phrase trace. Twenty-six native Japanese speakers participated in a reading task under three experimental conditions: Control, raising, and baseline. Source estimates were computed, and condition differences were tested using spatiotemporal cluster-based permutation t-tests. We observed late left-hemispheric differences at approximately 700-800 ms after the critical verb. The control condition elicited larger responses than the raising condition, with activity centered in the temporal cortex spanning the middle temporal gyrus and the superior temporal sulcus and gyrus and extending into the anterior insula and the supramarginal gyrus. In addition, the control condition elicited larger late responses than the baseline condition in a broader left fronto-temporal distribution, including the inferior frontal cortex, anterior temporal cortex, and insula. These results provide source-level evidence that brain activity in the left language network differs between the control and raising conditions in Japanese during online sentence comprehension. Furthermore, they suggest that we can distinguish empty category types in the brain.