Neurophysiological Mechanisms of Language Comprehension

Description

All experiments and recordings will take place in the University of Alabama at Birmingham (UAB) Epilepsy Monitoring Unit (EMU). All electrodes being used to gather data are in place through standard of care to treat the patient's epilepsy by monitoring neural activity to guide an upcoming respective surgery. In all experiments, neural activity will be recorded from the standard of care electrodes using either a high-fidelity, FDA-approved Neuralynx Atlas amplifier system (Bozeman, MT) or a standard-of-care recording system (Natus Quantum Recording System, Pleasanton, CA) that is used normally to monitor seizure activity for clinical purposes during the patient's hospital stay. In the task-related stimulation experiment, stimulation will be delivered with a standard of care electrically isolated stimulator (Nicolet Cortical Stimulator, Natus, Pleasanton, CA).

Recording-only word-by-word task. Participants are asked to read and comprehend sentences presented one word at a time. Participants advance through the sentence at their own pace by pressing a button to advance to each next word of the sentence. At the end of each sentence, participants are presented with 4 pictures, and their task is to choose which of the 4 pictures corresponds to the sentence they just read. Three sentence types are presented: Object relative sentences (e.g. "The cat that the dog chased was brown"), Subject relative sentences ("The cat that chased the dog was brown") and control sentences ("The brown cat chased the dog"). The 4 pictures simultaneously probe patient/agent assignment (i.e. "who chased whom?") and complement-noun assignment ("was the cat or the dog brown?"). 1 of the 4 pictures is correct, 1 picture reflects a patient-agent error, 1 reflects a complement-noun error, and 1 reflects both errors simultaneously.

Stimulation task. Subjects will perform a word-by-word sentence-reading task as before, only for this task on some object relative sentence trials intracranial stimulation is applied at the phrase boundary in the middle of the sentence. For example, this would be the word "chased" in the object relative sentence "The cat that the dog chased was brown". Stimulation parameters. Intracranial stimulation is delivered at 50 Hz for 1 second. This stimulation parameters are designed to interrupt local processing when delivered to areas outside of primary motor and sensory cortices. The investigators will choose which electrodes to stimulate based on the anatomical locations of recording sites for that patient and based on preliminary analyses of recorded activity in recording-only sessions before the stimulation session. Intracranial stimulation will be performed with simultaneous intracranial recording. Stimulation sessions need to be minimized in length to avoid patient fatigue and other effects from too much stimulation. In our preliminary data the investigators have found that the investigators can acquire 8 stimulation trials in 2 different stimulation locations for a given patient. The investigators ideally will choose one left Inferior Frontal Gyrus (IFG) and one left Superior Temporal Sulcus (STS) electrode to stimulate to the extent that one or both are available for a subject. The investigators stimulate the most difficult sentences, object-relative sentences, to maximize the chances of observing an effect. The investigators will pair this with an equal number (8) of non-stimulated object-relative sentences. When possible, the investigators will include 8 subject-relative and 8 control sentences, both without stimulation to include variety in the types of sentences given in the stimulation session. The stimulation task will be performed either with a constant rate of word presentation (500 ms per word) through-out all of the sentences, or performed in a "self-paced" manner as described above for the recording-only word-by-word task.

All participants will complete the same procedures. Participants will perform any recording only tasks first, which will occur when they are able and willing to after they have recovered from the surgery, typically 2 days after the implantation surgery. Participants will perform the stimulation task in co-ordination with the epileptologists at the EMU in the same sessions when stimulation mapping occurs for clinical purposes. This typically occurs at the end of the patient's stay in the EMU when the patients are on full doses of anti-seizure medication.

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