Employing Transcranial Magnetic Stimulation in a Resource Limited Environment to Establish Brain-Behavior Relationships

Summary

Transcranial Magnetic Stimulation (TMS) and low-frequency TMS (lfTMS) have been demonstrated to be major contributors to brain literature. Here we highlight the methods for investigating the cortical correlates of self-deception using TMS.

Abstract

Neuroimaging is typically perceived as a resource demanding discipline. While this is the case in certain circumstances, institutions with limited resources have historically contributed significantly to the field of neuroscience, including neuroimaging. In the study of self-deception, we have successfully employed single-pulse TMS to determine the brain correlates of abilities including overclaiming and self-enhancement. Even without the use of neuro-navigation, methods provided here lead to successful outcomes. For example, it was discovered that decreases in self-deceptive responding lead to a decrease in affect. These methods provide data that are reliable and valid, and such methods provide research opportunities otherwise unavailable. Through the use of these methods, the overall knowledge base in the field of neuroscience is expanded, providing research opportunities to students such as those at our institution (Montclair State University is a Hispanic-Serving Institute) who are often denied such research experiences.

Introduction

There are a number of challenges to investigating brain-behavior correlates at research institutions with limited resources (often referred to as 'teaching universities'). According to data provided by the National Science Foundation (NSF), almost all academic research is completed by a small percentage of higher education institutions in the United States. When examining over 4,400 post-secondary degree-granting institutions, the top 115 universities/institutes perform and publish 75% of all research¹. In the United States, there are 131 research 1 (R1: The highest status level a university can achieve in terms of research ranking) universities which receive the bulk of federal funding.

This top-heavy funding disparity limits research options for many principal investigators as well as students; for example, only 1.9% of R1 universities are Hispanic-Serving institutes. Further, non-R1 institutes are limited in terms of research space, grants awarded, and time made available for research, and these schools often do not have medical school affiliations². Given these obstacles, we provide the methods that have successfully allowed for the investigation of brain-behavior relationships in deception in a resource limited environment. While these methods are suitable for any institute, we believe that those at smaller/teaching intensive universities will receive the maximum benefit from these methods.

Our laboratory has focused primarily on the brain regions responsible for producing self-deception and self-enhancement. Establishing causation in terms of the underlying cortical regions is achievable by a number of techniques, and these data help confirm correlative neuroimaging methods and experimental patient trials^3,4,5.

To investigate self-deception with causal neuroimaging techniques, a number of innovative methods have been employed, mainly with single pulse Transcranial Magnetic Stimulation (TMS) and repetitive TMS (rTMS⁶; Figure 1). While tDCS (transcranial Direct Cortical Stimulation) has been employed successfully⁷ and can be modified to replicate the methods, procedures, and results presented here, the flexibility of TMS still makes it the optimal choice for the neuromodulation of self-deception. At its most common implementation, researchers inhibit, excite, disrupt, or measure cortical excitability (not covered here, but see reference⁸).

The Medial Prefrontal Cortex (MPFC) appears to be involved in self-deceptive responding⁹. Given the role of the Cortical Midline Structures (CMS) in terms of self-awareness in general¹⁰, it is not surprising that self-deception is correlated with MPFC activity. To determine causation in terms of frontal regions, TMS was relied on to create 'virtual lesions' while measuring bouts of self-deception¹¹. Measuring self-deception has been achieved via two main methods: Self-enhancement and overclaiming⁶.

We have found that disruption of the MPFC leads to the reduction of self-deception^6,8,11,12,13. Furthermore, we have discovered that such a reduction (i.e., the lowering of self-deception) is related to a decrease in a person's affect (i.e., negative mood increases and positive mood decreases).

Because neuro-navigation/individual MRI's are not employed (due to expense, most laboratories do not have these resources), concern may be raised over positioning and accuracy in TMS targeting. We have compensated for this by occasionally doing fiducial procedures in which a contrast target (e.g., a vitamin E tablet) is placed on the cap and the participant(s) is/are subsequently scanned in a structural MRI^11,12. These methods have confirmed the accuracy of the methods outlined here, and we are targeting the medial aspect of the MPFC at the border of BA 10/9 which lies above the Medial Frontal Gyrus (0, ~40, ~30).

Clearly, higher spatial resolution can be obtained using other methods such as neuro-navigation, however, these methods are not employed without drawbacks which include participant drop-out, participant exclusion, increased length of experimental duration, additional training and screening, added expense and often multiple site visits for participants. Therefore, the methods presented here offer an excellent alternative to neuro-navigation in many circumstances.

Protocol

The research presented here was approved by the Institutional Review Board (IRB) committee of Montclair State University. All participants have been treated within the ethical guidelines of the APA.

1. Participants

1. First, obtain IRB Committee Review Approval for the protocol (see Discussion for non- Research 1 institutions). Consultation with experienced researchers is recommended. Obtain forms such as Screening (Supplementary File 1) and Side Effects (Supplementary File 2) forms from other researchers-they are readily shared across the TMS community. NOTE: For the purpose of this experiment, forms were obtained from Simone Rossi.
2. Train all investigators on consenting and informing participants of all risks, side effects, and potential adverse events. If necessary, the Principal Investigator (PI) takes a TMS course if further knowledge is needed. Prior to running participants, ensure that the PI performs a pilot test of the protocol including consent and debriefing.
3. Recruit participants through flyers around campus. Screen participants in person; initial contact need not be in person. Ensure that the flyers describe the compensation and risks in general terms only, including any special circumstances (e.g., COVID).
4. Ensure participants read the consent form aloud including specific questions including: Are you a current student of ____PI______? Do you have a: history of epilepsy, family history of epilepsy? Do you have a history of seizures? Do you have any of the following-stroke, cranial metal implants, structural brain lesion, implanted device, pacemaker, medication pump, cochlear implant, implanted brain stimulator, metal worker? Do you have a history of head trauma with loss of consciousness? Do you have a high potential for pregnancy? Are you younger than 18? Are you older than 65?
5. Excuse any participants affirming any questions from the study.
6. Before being enrolled, ensure that the Screening Checklist is administered.
7. Pay all participants $25 for their participation and treat in accordance with guidelines of the Institutional Review Board at Montclair State University and of the American Psychological Association.
8. Deliver all TMS within the parameter appropriate for the institution (see Discussion).
9. Participant safety and comfort is critical so at all points forward, ask and monitor the participants closely both verbally and visually. Nervousness can be the norm which in some cases leads to more difficult outcomes and this is monitored.

2. TMS equipment handling

1. Use a single-pulse TMS device for all stimulation. Trigger the device by simultaneous depression of hand and foot switches manually by the PI. Use the maximum stimulation rate of the stimulator (i.e., 0.75 Hz).
2. Use a 70 mm figure-of-eight coil throughout the experiment. Ensure that the coil never reaches dangerous/shut-off temperatures during the experiment. Backup coils are ready in case needed as replacements.
3. Present all stimuli using a laptop computer. Open up the software (e.g., Testable) and login to the account. Click on the appropriate experiment.
4. Scale the monitor using a credit card. Enter demographic information. Clean/sanitize the laptop before and after each participant is tested.
5. Determine the motor threshold using visual inspection (5/10 evoked Abductor Pollicis Brevis) or via an EMG (Electromyograph).
6. Use swim caps to preserve markings. Use a standard coil holder for training and as demonstration only, not for active stimulation.
7. Use cloth tape measures to take coordinates for CZ and OZ from the 10/20 system and take MPFC from a previous study on overclaiming¹⁰. To determine MPFC, take 1/3 of the distance of nasion to inion, and MPFC is 1.5 cm anterior to this location. This will focus at the BA 10/9 (Medial Frontal Gyrus).
8. Confirm measurements at the PI's discretion using the fiducial method in which a vitamin E tablet is adhered to the cap of the coil location which will contrast easily in a standard MRI. Due to the cost, this option is limited.

3. COVID - 19

1. Due to COVID-19, include the following protocols¹⁴. In the Consent Form, add a disclaimer: "As a participant in this study, you will spend time in an indoor space within close proximity of the researcher. This poses a significant additional risk to getting COVID-19. We are taking the following precautions to protect you such as: Only PI will be within 6 ft of participant; Only one assistant is allowed in the vicinity but they must stay socially distanced; The participant must wear two masks; PI must wear two masks, gloves and a face shield; The assistant must wear a mask and a face shield; All contact equipment is sanitized."
2. Perform all experiments in the lobby/hall outside of the normal lab as ventilation is significantly increased. All equipment is sanitizable and portable.
3. Once COVID-19 protocols are relaxed, use normal procedures.

4. Motor threshold

1. Mark swim caps along the nasion/inion line and the midpoint taken using a magic marker. Measure pre-auricular points and take those midpoints, as well. From here, plot 10/20 coordinates (see 2.6).
2. Using the right hemisphere pre-auricular line, then go 33% down (in the ventral direction) and begin the search for the optimal location for the Abductor Pollicis Brevis (APB) using the TMS coil. Discharge the TMS machine using the coil trigger, the footswitch, and disengaging the safety.
3. Orient the TMS coil at 45° for all searches and TMS deliveries.
4. Start the stimulation output at 30% total machine output by using the dial on the front of the machine and raise in 2% increments using the dial until a movement is noted. Here, as the stimulation is increased in terms of intensity, move the location also. There is a careful interplay between coil movement and stimulation intensity.
5. Once the optimal location is found (i.e., the site that provided the maximum APB response), determine the MT.
6. Prior to starting MT determination, mark the coil tip site on the cap to allow accurate placement. Trace the entire anterior portion of the coil on to the swim cap using a magic marker.
7. For the visual inspection method, use approximately 20 pulses (varying machine intensity) to find what stimulation level results in 5/10 (50%) APB responses. The dial should be raised and lowered in response to increased or decreased finger movements. Start at 20% of machine intensity and work up. Once 5/10 responses have been obtained, record the individual's MT by noting what the machine is displaying as the intensity.
8. For the (preferred) MEP method, place disposable electrodes on the APB and the tendon of the thumb and a ground (usually around the back of the wrist), and instead of using visual inspection, a positive MEP must be observed on the recording unit.
9. Define a positive MEP response as an MEP with ≥50 µV peak-to-peak amplitude.
10. Similar to visual inspection, stimulate until 5/10 positive MEPs are observed. The MEPs should be greater than 50 µV. If 50% of the MEPs are above (and 50% below), MT has been identified.
11. Once established, set the TMS machine to the appropriate stimulation level. 90% of the motor threshold is an ideal balance between effective active TMS and safety. Do not exceed 45% of the machine's total output. There are occasions that a person's MT is 60% of the machine's total output, but this is rare.

5. Active single-pulse TMS

1. Randomly select the order of all sites (e.g., SMA, PZ, MPFC, or Sham over CZ; Figure 5).
2. Place the coil over the active site and start a presentation software, (e.g., Testable (see below)). Stimulation should proceed automatically and in sync with stimuli.
3. Always have a spare coil in case of overheating.

6. Presentation

1. Collect all behavioral data using a presentation software (e.g., Testable) This software is easily configured, and scripts are simple.
   NOTE: Three separate blocks are created-one for each of the brain conditions. Demographics to be collected are first chosen using Testable's automatic selection routine. Then real words and fake words are placed into the scripting software. The size and duration of the words are chosen, as is the location on the screen of the stimulus words.
2. Once the script is made, collect demographics first and perform screen calibration. This is done matching the slider to a credit card. Perform all experiments on a computer. All responses are made on the built-in keyboard and sensor pad.
3. Give two practice trials and introduce the analog scale. All participants easily adjust to the equipment. The instructions are given orally, and the participants are told to rate how well they know the word.
   1. If the word is familiar to them (such as 'desk') it should be given a high rating.
   2. If they 'sort of' know the word, they are to give a medium rating (such as 'chlorophyll').
   3. If it is not that familiar to them, they will assign a low rating (such as '5HTTlpr'). A total of 144 words should be used (36 per brain site).
4. Participants have unlimited time to respond. Following the response on the analog scale, the next word is presented.

Results

Figure 2, from Taylor-Lilquist et al.¹⁴, involved four brain sites: MPFC, SMA, PZ, and a Sham site. These sites were utilized to determine the correlates of overclaiming. Overclaiming is a participant indicating that they know a word when it is actually not a word. 12 participants were tested in both social and non-social settings. The social settings represented pressure to either know a word (high-social pressure; n=6) or not know a word (low-social pressure; n=6). ...

Discussion

The protocol (and variations of) outlined here has been used in over 50 studies at Montclair State University. The entire set-up can be created for under $15,000 (US). Further, we have found our coordinates match well with underlying brain structures using fiducial procedures.

Variations of this method are often used. For example, control conditions can include stimulating different brain areas, applying TMS different timings (i.e, apply TMS at a timing that should have no effect), using ...

Materials

Name	Company	Catalog Number	Comments
Android Samsung Tablet (for MEPs)	Samsung	SM-T500NZSAXAR
Cloth Measuring Tape	GDMINLO	B08TWNCDNS(AMZ)
Figure of 8 Copper TMS Coil	Magstim	4150-00	This is the current model
Lenovo T490 Laptop	Lenovo	20RY0002US
Magstim 200 Single Pulse	MagStim	Magstim200/2	This is the current model
Magstim Standard Coil Holder	MagStim	AFC/SS	This is the current model
Speedo Swim Caps	Speedo	751104-100
Testable.Org Account and Software	Testable	NA
Trigno 2 Lead Sensor (for MEPs)	DelSys	SP-W06-018B
Trigno Base and Plot Software (for MEPs)	DelSys	DS-203-D00