Behavioral and Neural Measures of Speech Motor Control
Phase: NA
Conditions: Speech
Sponsor: University of Wisconsin, Madison

Title: Modulation of Sensory Acuity With Transcranial Magnetic Stimulation 
(TMS) (Exp 7) 
NCT number: NCT05723575 
Document date: 7/18/2024 
 
 

Study Protocol 
This study consists of three related behavioral paradigms aiming to test sensorimotor 
adaptation, a correlative analysis investigating the relationship between the outcome 
measurements from these three experiments, and several experiments seeking to modulate 
these outcome measures. Here we describe Experiment 7, which used transcranial magnetic 
stimulation (TMS) to modulate somatosensory acuity of the tongue. 
 
Experiment 7 specific Methods: Participants will complete three TMS sessions (iTBS, cTBS, 
sham) and a fourth behavioral-only control session. Each session will be separated by at least 
one week with the order counterbalanced across participants. The target of the stimulation is left 
primary somatosensory cortex (S1). The duration of tbTMS stimulation is short (40-190s), with 
effects that begin ~5 minutes following stimulation and persist for up to 30 minutes. In each 
TMS session, sensory acuity will be tested in two tasks (spatial and temporal) before and after 
application of theta-burst TMS (tbTMS): 
• 
Task practice: Participants first complete a brief training to familiarize them with each 
acuity task and to ensure they met performance criteria (five consecutive correct 
responses). 
• 
Baseline tests: Participants complete 3 blocks of each task, with the tasks alternating. 
• 
TMS localization and thresholding: Single-pulse TMS is used to localize the target 
stimulation site (S1) and determine the active motor threshold. S1 is localized on each 
participant’s brain surface with Brainsight neural navigation by moving the stimulator 2 
cm posterior to a motor hotspot that elicits tongue motor-evoked potentials (MEPs). 
• 
Rest: 20-minute break to allow the somatosensory cortex to recover from any potential 
disruption related to single-pulse TMS. 
• 
TBS: Delivery of TBS to S1. Stimulation intensity will be set to 80% of the active motor 
threshold. Sham stimulation will be applied with the coil rotated away from the head (coil 
facing downward). This emits the same sound as active stimulation without stimulating 
the brain. 
• 
Post tests: Performed every 5 minutes for 45 minutes following stimulation: participants 
complete 10 blocks of each task (SDT and TDT), alternating between the tasks with a 1-
minute break in between each task. 
In the 4th behavioral-only session (“control”), participants’ acuity is tested without TMS 
localization. 
 
- 
Somatosensory acuity metrics: The acuity tasks measure tactile acuity (spatial amplitude 
and temporal order judgment) with a custom corticalmetrics Brain Gauge vibrotactile 
stimulator. These measures reliably track the recovery of somatosensory function after 
neurological damage and can be modified with tbTMS. We use tactile acuity as a proxy 
for full somatosensation, given the difficulty in measuring proprioception in the oral 
system. Tactile acuity has been suggested to be important for speech production, as 
tactile contact is maintained parasagittally during vowel production and tactile 
deprivation leads to imprecise speech movements. 
- 
Data analysis and outcome measurements: Each acuity task (spatial amplitude and 
temporal order judgment) yields a threshold (spatial amplitude discrimination threshold in 
μm; temporal discrimination threshold in ms) representing the smallest difference 
detectable by the participant at a given time point. For each acuity task, we will compare 
the change in threshold from pre- to post-TMS. Post-TMS values will be normalized by 
subtracting baseline thresholds for each task on a session-specific basis, then compared 
across time windows. 

- 
Sample size with power analysis: Given previous results in the hand (d = 1.8-3.1), we 
conservatively anticipate an effect size of Cohen’s d = 1. Testing 17 participants gives a 
power of .82 with α = 0.05. 
 
Statistical Analysis Plan 
Experiment 7: We will compare the change in sensory acuity from pre- to post-TMS between 
sessions using a repeated measures ANOVA. Post-TMS values will be normalized by 
subtracting baseline thresholds for each task on a session-specific basis, then compared across 
time windows. To compare changes in thresholds across sessions, a single repeated-measures 
ANOVA will be conducted for each task with sessions (cTBS, iTBS, control, sham) and time 
windows as independent variables.