Modern experimental research often relies on the synchronization of different events prior to data analysis. One way of achieving synchronization involves marking distinct events with electrical pulses (event markers or “TTL pulses”), which are continuously recorded with research hardware, and can later be temporally aligned. Traditionally, this event marking was often performed using the parallel port in standard personal computers. However, the parallel port is disappearing from the landscape of computer hardware, being replaced by a serial (COM) port, namely the USB port. To find an adequate replacement for the parallel port, we evaluated four microcontroller units (MCUs) and the LabJack U3, an often-used USB data acquisition device, in terms of their latency and jitter for sending event markers in a simulated experiment on both Windows and Linux. Our results show that all four MCUs were comparable to the parallel port in terms of both latency and jitter, and consistently achieved latencies under 1 ms. With some caveats, the LabJack U3 can also achieve comparable latencies. In addition to the collected data, we share extensive documentation on how to build and use MCUs for event marking, including code examples. MCUs are a cost-effective, flexible, and performant replacement for the disappearing parallel port, enabling event marking and synchronization of data streams.
The left posterior inferior frontal gyrus in the prefrontal cortex is a key region for phonological aspects of language processing. A previous study has shown that alpha-tACS over the prefrontal cortex applied before task processing facilitated phonological decision-making and increased task-related theta power. However, it is unclear how alpha-tACS affects phonological processing when applied directly during the task. Moreover, the frequency specificity of this effect is also unclear since the majority of neurostimulation studies tested a single frequency only. The present study addressed the question whether and how 10 Hz online tACS affects phonological decisions. To this end, 24 healthy participants received tACS at 10 Hz or 16.18 Hz (control frequency) or sham stimulation over the left prefrontal cortex during task processing in three sessions. As an unexpected finding, 16.18 Hz significantly impaired task accuracy relative to sham stimulation, without affecting response speed. There was no significant difference in phonological task performance between 10 Hz and 16.18 Hz tACS or between 10 Hz and sham stimulation. Our results support the functional relevance of the left prefrontal cortex for phonological decisions and suggest that online beta-tACS may modulate language comprehension.
Introduction: Previous work in the language domain has shown that 10 Hz rTMS of the left or right posterior inferior frontal gyrus (pIFG) in the prefrontal cortex impaired phonological decision-making, arguing for a causal contribution of the bilateral pIFG to phonological processing. However, the neurophysiological correlates of these effects are unclear. The present study addressed the question whether neural activity in the prefrontal cortex could be modulated by 10 Hz tACS and how this would affect phonological decisions. Methods: In three sessions, 24 healthy participants received tACS at 10 Hz or 16.18 Hz (control frequency) or sham stimulation over the bilateral prefrontal cortex before task processing. Resting state EEG was recorded before and after tACS. We also recorded EEG during task processing. Results: Relative to sham stimulation, 10 Hz tACS significantly facilitated phonological response speed. This effect was task-specific as tACS did not affect a simple control task. Moreover, 10 Hz tACS significantly increased theta power during phonological decisions. The individual increase in theta power was positively correlated with the behavioral facilitation after 10 Hz tACS. Conclusion: Our results show a facilitation of phonological decisions after 10 Hz tACS over the bilateral prefrontal cortex. This might indicate that 10 Hz tACS increased task-related activity in the stimulated area to a level that was optimal for phonological performance. The significant correlation with the individual increase in theta power suggests that the behavioral facilitation might be related to increased theta power during language processing.