Thomas C.J. Quettier

Embodied cognition, a theoretical framework that emphasises the influence of the body and sensorimotor processes on cognition (Barsalou, 2008; Wilson, 2002), has garnered significant attention in t...

Transcranial magnetic stimulation (TMS) is a widely used tool in the field of clinical and cognitive neuroscience. To exploit its excellent temporal properties, TMS usually relies on triggerbox devices, which temporize the delivery of magnetic pulses according to the paradigm requirements. However, a main limitation of most of the widely used triggerbox devices is that they rely solely on the experimental computer processor, which might add temporal uncertainty in delivering the TMS pulse when the computer’s resources are drained by other experimental devices or by task execution itself, especially during repetitive TMS or dual-coil protocols. We aimed at developing a low-cost and easily reproducible triggerbox device which could overcome these limitations by relying on an external processor to handle the timing precision. We used an Arduino Uno R4 Minima to build Silicon Spike, a low-cost ($60) triggerbox device. We tested the device’s precision in delivering the TMS pulses under different working load conditions, and the impact over time. All of the tests were ecological, delivering real TMS pulses during dual-coil, repetitive, and patterned TMS protocols. We obtained extremely high precision (< 0.022 ms) in all of the tests. This means that, for smaller or longer latencies, the error remains negligible for TMS studies. Thus, the Silicon Spike device demonstrated microsecond precision in handling the TMS pulse delivery, establishing itself as a simple and yet precise device. We freely provide the source code and the hardware schematics, allowing anyone to reproduce our work.

Fearful body expressions convey critical information that is rapidly and preferentially processed, facilitating swift motor reactions to potential dangers. Consistent evidence has shown that even the subliminal presentation of fear-related expressions can impact visual processing and autonomic responses, increasing sensory vigilance for monitoring potential threats. However, it remains unclear whether the presentation of non-visible emotional bodies modulates corticospinal excitability (CSE) in the observer. To investigate this, we asked 22 healthy participants to perform a sex discrimination task involving neutral target body postures, preceded by the brief subliminal presentation of fearful, happy, or neutral body postures. CSE was tested using Transcranial Magnetic Stimulation (TMS) at early time points (70, 90, and 110 ms) after target stimulus onset. Results showed a significant CSE reduction in the dominant hemisphere for subliminal fearful primes compared to happy and neutral primes. This CSE suppression was independent of the time of stimulation, participants’ subjective or objective awareness, metacognitive sensitivity, or personality traits. Our findings highlight an early automatic activation of the motor system in response to subliminal fearful stimuli, supporting the view that fearful expressions, even when not consciously perceived, activate basic survival mechanisms for monitoring and preparing fast motor responses to potential threats.