Probing Cortical Excitability and Cognitive Function With TMS

In total, 60 participants will be recruited to participate in this trial. The investigators
aim to recruit 30 patients with MCI and 30 age-matched healthy adults. The age range for
inclusion will be 18-80, and the mean age of the healthy cohort will be matched with the mean
age of the MCI cohort. The following revised Mayo Clinic criteria for MCI will be used: (1)
cognitive concern expressed by a physician, informant, participant, or nurse; (2) impairment
in 1 or more cognitive domains (memory, language, visuospatial skills, or executive
functions); (3) essentially normal functional activities; and (4) absence of dementia.
Individuals with MCI will have Mini-Mental State Exam (MMSE, Appendix 19) scores between 18
and 23 (inclusive) and have a Clinical Dementia Rating Scale score of 0.5.

This study protocol comprises a single testing visit, comprised of four separate components:
a) Resting-state fMRI, b) Single-pulse TMS paradigm, c) theta-burst rTMS paradigm, and d) a
brief motor task performed on an iPad.

These tasks will be repeated before and after the theta-burst rTMS paradigm (c). Therefore,
the testing visit is:

(a) --> (d) --> (b) --> (c) --> (b) --> (a) --> (d)

This protocol will enable investigators to study the following both before and after the rTMS
paradigm: 1) connectivity patterns comprising the functional networks of the brain, 2)
measures of cortical excitability derived from single-pulse TMS, and 3) upper extremity motor
speed & acuity.

Transcranial Magnetic Stimulation:

Magnetic stimulation will be performed with a high-power MagPro X100 (MagVenture Inc.
Denmark)(Appendix 11). When the TMS machine delivers stimuli, patients may feel and/or a
clicking/tapping sensation under the coil. Participants will be given ear buds as an
additional safety precaution to protect hearing during the TMS session. Prior to beginning
the TMS session, the research team will make sure the participant is as comfortable as
possible in the TMS chair.

Single Pulse TMS Paradigm:

First, the device will need to be calibrated for each individual because everybody has a
different sensitivity to the magnetic fields generated by TMS. The TMS device will be
calibrated to ensure the participant is receiving the lowest possible "dose". To do so, the
TMS coil will be placed on the scalp directly above the region of the brain that is
responsible for finger motions, which is a specific region of the motor cortex located on the
pre-central gyrus. The TMS coil will then deliver pulses that incrementally escalate until a
level is reached that causes their hand to twitch (specifically, thumb and pointer finger).
This will be visually observed and recorded quantitatively with electromyography (EMG)
sensors. The amount of energy required to make their hand twitch is called the "motor
threshold" and it varies for everybody. This "motor threshold" will then be used to calibrate
the machine for the TMS protocol.

A figure-of-eight TMS coil will be held over the motor cortex at the optimum scalp position
to elicit motor-evoked potentials (MEPs) in the contralateral first dorsal interosseous (FDI)
muscle. In addition to observing the finger movement visually, the investigators will also
attach surface electromyography (EMG) electrodes to the skin on the right FDI. The electrodes
will detect any activity in muscles, which will yield a more accurate measurement for
personal "motor threshold". The exact location that elicits a motor response in the
contralateral FDI is referred to as the "hot spot". This location will be recorded using the
real-time TMS 3D Neuronavigation System (Localite TMS Navigator, Germany,
http://www.localite.de/en/products/tms-navigator/#c572) to ensure testing consistency in the
following trials. Localite is a software package used in conjunction with TMS equipment. It
incorporates an infrared camera to record location of the TMS coil relative to the
participants head. This allows researchers to reliably place coil in the same precise
location throughout the session.

The resting motor threshold (RMT) is defined as the minimum stimulus intensity that produces
a liminal MEP (about 50 μV in 50% of 10 trials) at rest. The active motor threshold (AMT) is
generally defined as the minimum stimulus intensity that produces a liminal MEP (about 200 μV
in 50% of 10 trials) during isometric contraction of the tested muscle. Both RMT and AMT will
be expressed as a percentage of the magnetic stimulator maximal output. The RMT and AMT data
from individual participants will serve as a baseline measure of excitability to guide the
intensity of our following single-pulses and repetitive TMS protocols, respectively. This
will be performed for the left hemisphere. The researchers will also use the Parameter
Estimation Sequential Testing (PEST) algorithm to more efficiently identify the RMT and AMT.

After the motor threshold and "hot spot" is identified for the participant, the TMS coil will
be placed over the "hot spot" that was previously recorded by the Localite Navigator software
and set the stimulus intensity at 80% of the participants uniquely identified AMT. For
example, if the active motor threshold of a specific individual is determined to be 40% of
the MagPro's maximal output, then the device intensity will be set to 32% of maximal output
for the single pulse protocol (32 equals 80% of 40%, the AMT in this example). At this time,
8 TMS pulses are applied (separated by 6 seconds) as the TMS coil is fixed on the "hot spot".
This step is repeated in increasing increments (i.e., 10% of AMT) up to an intensity
equivalent to 150% of the participant's AMT. This protocol consists of 64 single-pulse
stimuli, which will be delivered repeatedly 6 seconds apart. This procedure is safe and
follows standard single-pulses TMS protocols that have been published previously.

This single-pulses TMS protocol will be performed twice, both before and after the rTMS
protocol. Each single-pulses TMS protocol will last approximately 30 minutes. Combined, this
equates to 128 stimuli during the "Single Pulses TMS" paradigms. Throughout the single-pulse
protocol, participants will be asked to touch their pinky and thumb fingers to provide a
subtle background voluntary contraction. This will 'facilitate' the motor pathway and lower
the threshold for stimulation intensity throughout the protocol.

rTMS:

In the repetitive TMS (rTMS) protocol, a patterned rTMS paradigm called intermittent theta
burst stimulation (iTBS) will be used. The iTBS consists of three biphasic TMS stimuli
presented at 50 Hz, repeated every 200 ms for 2 seconds at an intensity of 80% of AMT (e.g.,
if AMT is determined to be 40% of maximal output, TMS will be delivered at 32% for this
protocol). Therefore, each stimulation train will last for two seconds (30 stimuli per train)
with an inter-train interval of 8 s. This rTMS protocol is comprised of 10 iTBS trains,
totaling 300 stimuli from the magnetic coil.

During this rTMS protocol, the coil will be placed over the "hotspot" of the left hemisphere.
The rTMS protocol will only be performed once and it will last approximately 10 minutes.

MRI Protocols:

This will occur in the same building, in a room adjacent to the TMS device. For their safety,
participants will be asked to leave all metal objects and personal items (e.g., wallet,
phone, jewelry) in the waiting room of the MRI center before entering the scanner room.
Participants will be asked to lie on their backs and remain still for the duration of the MRI
scan. They will be given earplugs to dampen the noise and to protect their hearing while they
are in the scanner. A Velcro strap may also be place over the forehead and foam pillows will
be provided to minimize head movement during the scans. Every effort will be made to make
participants as comfortable as possible during the scan, including blankets for warmth and
cushions to be placed under the knees/back to reduce stress from lying on one's back.

Participants will be reminded prior to the scan that their participation is voluntary and
they may signal to stop the scan at any time. There is an intercom system in the scanner,
which will enable the participants to communicate with the MRI technician and member (s) of
the research team for the entire duration that they are in the scanner. Additionally, they
will be able to immediately stop the exam at any time, either by squeezing a signal ball
placed in their hand, which will alert the MRI technician in the control room, or by raising
their legs, which will be seen by the experimenter in the control room.

Importantly, no contrast agent will be used in our collection of MRI data. Also, all MRI data
will be acquired in "resting-state" so participants will just be asked to relax and remain
still for the duration of the scan.

More specifically, MRI data will be collected on a Siemens 3.0 Tesla Skyra Magnet equipped
with a 32-channel head coil. Total scan time will be 30 minutes. The order of sequences will
be as follows: localizer scan (62 seconds), a Structural MPRAGE (9 minutes), a resting-state
fMRI scan (5 minutes), and a diffusion-tensor imaging (DTI) scan (14 minutes). The localizer
will be collected using the following parameters - direction: inferior to superior, TR= 8.6
ms, echo time (TE)=4.0 ms, flip angle = 20, FOV=250 mm, 5 slices, 7 mm slice thickness.
High-resolution structural images will be acquired using a T1-weighted spoiled gradient
recalled (SPGR) sequence (TR= 22ms; TE= 5.4ms; FOV= 25.6cm; flip angle= 20°; in-plane matrix
size= 256 x 256; slice thickness= 1mm; number of slices= 172). Whole-brain resting-state fMRI
data will be collected using T2*-weighted echo-planar imaging (EPI) (TR= 1.5s; TE= 30ms; FOV=
25.6cm; flip angle= 90°; in-plane matrix size= 64 x 64; slice thickness= 4mm), resulting in
functional data from 39 axial slices with isotropic voxels of 4mm3. During the resting-state
fMRI scan, participants will fixate on a cross-hair with eyes open. DTI images will be
acquired in the axial plane using a diffusion sensitized parallel EPI sequence that measures
diffusion in 86 directions (b-factor= 1000 s/mm2; TR= 7s; TE= 82.5ms; field of view (FOV)=
25.6cm, matrix= 128 x 128, 2mm interleaved slices; parallel acceleration factor= 2).

The resting-state fMRI data will be preprocessed using a pipeline
(http://wiki.biac.duke.edu/biac:analysis:resting_pipeline) and tools in the Oxford Centre for
Functional MRI of the Brain Software Library (FSL version 5.0.5, www.fmrib.ox.ac.uk/fsl). The
preprocessing steps include slice-time correction, MCFLIRT for motion correction, Brain
Extraction Tool (BET) for brain extraction, and FLIRT for normalization to the MNI 152 T1
template (Montreal Neurological Institute, Montreal, Canada). The investigators will regress
out signal from white matter and cerebrospinal fluid on the basis of masks created in FSL
FAST and smoothed the data with a 5 mm kernel using FSL SUSAN. Temporal band-pass filtering
will limit the data to frequencies in the 0.001 to 0.08 Hz band. Following the recommendation
of Power et al., the investigators will perform motion scrubbing using a frame-wise
displacement threshold of 0.5 and timecourse variance threshold (DVARS) of 0.5%

Behavioral Measure: Motor Task

The researchers will use iPads equipped with the digital computer software Cantab (Cambridge
Cognition Ltd., England) for our behavioral measures. Cantab is a cloud-based, computerized
cognitive assessment software that is a well-validated tool for academic research. The
investigators intend to use 1) Motor Screening Task, 2) Paired Associates Learning Test (on a
tablet) to measure functions of motor and memory, respectively.

Motor Screening Task requires the participants to touch the flashing cross, which is shown in
different locations on the screen. The outcome measures include the accuracy of pointing and
reaction time.

Inclusion Criteria:

- The following revised Mayo Clinic criteria for MCI will be used: (1) cognitive concern
expressed by a physician, informant, participant, or nurse; (2) impairment in 1 or
more cognitive domains (memory, language, visuospatial skills, or executive
functions); (3) essentially normal functional activities; and (4) absence of dementia.
Individuals with MCI will have Mini-Mental State Exam (MMSE, Appendix 19) scores
between 18 and 23 (inclusive) and have a Clinical Dementia Rating Scale score of 0.5.

- Health controls will be screened with MMSE

Exclusion Criteria:

- Contraindications to MRI

- Contraindications to TMS

- history of stroke

- clinical diagnosis of dementia

- diagnosis of neuropsychiatric disorder

- left handed