Abstract: Language disorders afflict 6 to 8 million people in the United States. One common symptom in language disorders is difficulty comprehending the grammatical structure of sentences. Understanding that the sentence “The car at the stoplight is blue” refers to a blue car requires recognizing “at the stoplight” as a distinct phrase that modifies the preceding noun phrase “the car”. People with grammatical comprehension disorders have difficulty with this. With intracranial recordings in human neurosurgical patient volunteers with normal language function we previously described the patterns of phrase-structure building in neural activity observed in the left inferior frontal gyrus (IFG) and superior temporal sulcus (STS). This is hypothesized to play a causal role in the comprehension of sentence structure, but such a role has never been demonstrated. Aim 1 will test this hypothesis by directly electrically stimulating and thus transiently disrupting the left IFG and STS of neurosurgical patient volunteers at key phrasal boundaries in a sentence and observing how this affects sentence comprehension accuracy. Aim 2 will investigate a direct link between neural activity and the resulting behavior for each trial using a self-paced reading task while we record neural activity directly from key language network sites, specifically the left IFG and STS. We will correlate neural activity with per-word reaction times, which reflect the processing requirements for each word. Also, for the experiments in Aim 1 we will simultaneously record activity from one language network area (IFG or STS) while stimulating the other area to demonstrate how disrupting each area affects activity elsewhere in the language network. Altogether, we expect that disrupting fronto-temporal phrase-merging activity will reliably create comprehension errors, and that this neural activity will be tied to behavioral markers of phrase processing and affected by the intracranial stimulation in a way that we can predict given the result that the stimulation has on behavior. Our team is uniquely qualified to accomplish these aims. This proposal will provide me with training in the technique of intracranial stimulation with simultaneous recording in human patient volunteers performing a task, in deepening my understanding of theoretical linguistics through formal instruction and mentoring, and in communication disorders, specifically aphasia. In summary, the proposed studies and training plan will lead to a better understanding of grammatical deficits in language disorders, leading to improved treatments and interventions, and will expand my impact as a neuroscientist, serving as a bridge to independent funding.