Human Cognition During Surgery: Stimulation-based and Cholinergic Modulation

Consenting: Prior to conducting any research related tests / procedures, the patient will be consented. At least 24 hours before scheduled surgery (most commonly the week before surgery), prospective participants for our study are contacted by a member of the study team via phone, to inform them of their candidacy to participate in our study, explain study details and answer questions and ultimately ask about their interest in participation. Once in the operating suite, the patient will be put under anesthesia for clinical purposes for surgery.

Prepare the OR before patient arrival: Before the patient is in the room, we will have at least one research team member go to the OR to set up the NeuroOmega recording system, which is also used as standard-of-care.

Pharmaceutical Preparation and Administration: Drug administration will be prepared by the pharmacy. We will obtain the drug from the pharmacy during the pre-operative phase in a single dose of 50 mg/20 mg orally BID of xanomeline and trospium chloride (COBENFY) or placebo pill. Patients will be given the dose as part of pre-operative preparation if part of the group randomized to receive the drug by members of the study team qualified for drug administration. As patients will receive a single dose of the medication during their participation, we do not anticipate serious side effects which occur from prolonged use, nor anticipate that cholinergic mechanisms activated at the lowest dose will result in issues such as seizures or nausea. However, should the patient pass the pre-screening process and consent to participation, safety measures will be in place for monitoring patients during participation. Administration will target intraoperative peak concentration of the xanomeline component at 2 hours. Oral intake status has little impact on kinetics.

Risk mitigation for drug administration will include:

1. A preop checklist for possible side effects or contraindications.
2. Discussion with neuroanesthesia partners regarding suitability for administration.
3. Use of low dosages of medicines in line with previous cognitive experiments, not expected to have substantial effects on CV systems.
4. Assess patient for side effects from initial administration every 20 minutes. Immediate monitoring and potential to reverse effects of the medicines during surgery.
5. Continuous monitoring of vital signs in surgery.
6. Inquire at 20 minute intervals about nausea, vomiting, abdominal cramping, blurred vision, dry mouth.

Preparation in the OR after patient arrival and after the patient is draped: The designated team member to work in the sterile field (Dr. Pouratian or Dr. Hitti for DBS surgeries and Dr. Lega for epilepsy surgeries) will prepare one of the sterile bowls by filling it with saline, ensuring that the hemostats will clip to the rim without tipping it over. The circulating nurse will open the sterile packaging of the NeuroProbe container. We will then carefully remove the probe from the sterile packaging and make a final inspection of the probe's condition. We will then have a team member connect the headstage board connector to the NeuroProbe. We will check the probe by using AlphaOmega system software to confirm that the connector was fitted properly. We will then perform another probe check and possibly record briefly in sterile saline. The NeuroProbe can then be secured by using a clamp to the edge of the saline bowl until used.

Insert the NeuroProbe into the brain and record baseline neural activity (Essential Tremor and Epilepsy patients). Only regions that would normally be recorded from based on clinical indications will be targeted with the probe. In all cases of brain stimulator electrode insertion, a guide cannula is used. The NeuroProbe is inserted through the guide cannula and only the tip is exposed at target. As such, use of the NeuroProbe does not add any additional risk to the surgery. No additional trajectories through the brain will be used besides any that are indicated for surgery. The NeuroProbe and its connecting cables are shipped in sterilized packaging (see supporting documents for details about sterilization). To prepare for recording, a sterile team member takes the NeuroProbe out from its sterile packaging and connects it to sterile cable. The end of the sterile cable (>6ft in length) then is passed to a sterile member and connected to the Intan acquisition system. We will then check the probe by using AlphaOmega data acquisition GUI to confirm that the connector was fitted properly. The connector is secured with Tegaderm if necessary. The NeuroProbes are inserted in the same locations as the microelectrodes that traverse the dorsal lateral surface of the prefrontal cortex on the way to the target nucleus. One to two cannula is placed in a AlphaOmega manipulator. The NeuroProbe is inserted into the cannula. The NeuroProbe is then advanced by the AlphaOmega Microdrive system, using fine millimeter steps to traverse the cortical layers. The average cortex thickness is ~3mm, we will then advance the Microdrive slowly and carefully in steps of 0.2mm. We will start recording as the NeuroProbe is affixed to the manipulator. Ensure that insertion of the electrodes is done under direct visual guidance for the entire process. Importantly, the recording is on for the whole process of insertion because the real-time recordings and probe testing during placement and insertion provide real-time confirmation if the electrode has any mechanical stress or strain (which can result in an error message in the software) or if the electrode or the ground and referencing are inserted. If, at any point, a deflection is noticed, the insertion will be halted, and the probe will be retracted immediately. We will place sterile ground and recording reference needle electrodes (Medtronic) in nearby scalp as deemed safe by the neurosurgical team. For the team member working on the electrophysiological rig computer: we will monitor the deepest channels of the LFP so as to have feedback of when the probe has entered brain tissue.

Run behavioral tasks (Essential Tremor patients only): At an appropriate time during the surgery (coordinated with the attending neurosurgeon), the research team may approach the patient from the bedside to run tasks during the recording. Details about the motor tasks and cognitive tasks are detailed in the previous sections. Select tasks that best prioritize the area of the brain from which the probe is recording. Note the time at which tasks are started. This portion of the task-related stimuli may vary in terms of individual hospital setups and research goals, such as the use of audio stimuli, visual cues or motor tasks. All of these paradigms require synchronization with the neural signal. We use a shared TTL-based wired system to do this. This also allows for concurrent comparisons with clinical recordings. Here, we present our approach for a task-related setup that is, for the most part, wired, but this approach can be highly variable and flexible across laboratories and hospital settings. Coordinate with the neurosurgeon and the clinical team at all times, being cognizant that whether or not the task is run depends on clinical necessities during surgery and patient engagement. After completion of the tasks, or after 30 min, remove all task-related equipment from the bedside and signal to the surgical team that you are ready for device extraction.

Cognitive task testing:

The cognitive tasks will be performed by the subject during the awake component of the DBS surgery for individuals capable of participating. Across all the cognitive tasks designed and implemented in this study, subjects will receive visual and auditory stimuli presented to them via a computer system. These stimuli are neutral in nature and do not contain aversive information. Subjects are asked to attend to these stimuli and form their judgements or decisions about them, while we present distracting information. Below are examples of the types of paradigms used to assay memory. In combined control/memory paradigms, a distraction condition (such as tones) are used to generate a "divided attention" state for subjects.

1. Recognition Memory: In the Recognition Memory Study, participants study lists of items. Later, at the time of test, they are shown a mix of old items (viewed during the study period) and new items (not previously viewed during the experiment). Participants are asked to judge whether or not the items have been presented in the previous list(s).
2. Paired Associates: In the Paired Associates Task, participants will study lists of paired items (e.g., the word pair fountain-piano, or a picture of a face paired with a name). At the time of test, one member of each pair will be shown as a cue and participants will attempt to recall its mate. Pairs may be tested in both the forward and the backward direction, counterbalanced across trials. Recall accuracy and reaction time data will be recorded for subsequent analysis.
3. Spatial and Verbal Working Memory: Working memory refers to the capacity of holding multiple items in mind for relatively brief periods of time (for a review, see Baddeley, 2003). The Spatial and Verbal Working Memory Experiment aims to compare recognition memory for verbally rehearsable and nonrehearsable items. Participants are tested with stimuli from different modalities. Some examples are single letters, pictures of objects, words, single dots that appear at different positions, gray-scale plaid gratings, and pictures of faces. Stimuli are displayed on a computer monitor. Each trial begins with a fixation cue, followed by a study set of between one and five stimuli. Following a short delay, a probe item appears. Participants are instructed to judge whether or not the probe is part of the preceding study set. Feedback on accuracy and response time is given at the end of each block of trials.
4. Spatial Navigation and Memory: The Spatial Navigation Task is a virtual-reality game that encourages participants to find efficient paths between arbitrary locations in a virtual environment. Participants learn the layout of a computer-generated virtual town and the locations of landmarks by navigating through the environment from a first-person perspective using a game controller. Participants memory for the locations of environmental landmarks is tested in several ways: 1) by assessing the time spent and the distance traveled when they are asked to navigate between environmental landmarks; 2) by asking them to adjust a virtual compass to point in the direction of a probed landmark; 3) by assessing the degree to which their memory for environmental stimuli is organized according to the positions of those stimuli within the environment (this organization is measured by asking participants to free recall environmental stimuli).
5. Cognitive control and attentional control tasks: The tasks will involve switching between different cognitive tasks and/or motor action and/or switching attention in between different features. Common components of the tasks: Subjects will typically view an image (neutral, non-affective) and are asked to attend to or make judgements about features of the image (e.g., whether the image is smaller or larger than a shoe box), and the questions alternate and repeat by design. The alternation versus repetition of judgements will cause subjects' reaction times to lengthen or shorten. Subjects are asked to indicate their answers to the judgement questions either by pressing buttons on a button box or by vocal response, or by eye movements.