Abstract
How the brain responds to a stimulus depends not only on external experimental conditions but also on the internal conditions, i.e. the instantaneous state of the brain at the time of the stimulus. However, the brain state continuously changes, both through endogenous dynamics of neuronal network activity and in response to previous stimuli (e.g. habituation or facilitation), which introduces variability and noise to open-loop stimulation approaches. To address this limitation, we have developed a novel closed-loop method for simultaneous EEG/TMS experiments, whereby stimulation is triggered by a pre-defined brain-state, based on real-time analysis of instantaneous window of preceding EEG data with an overall latency of 3 ms and accuracy of EEG data is recorded at 80 kHz sampling rate by a 16-channel 24-bit customizable ADC and filter stage that is connected via a fiber-optic interface to a digital signal processor unit, which in turn provides 16-bit scaled analog output at 10 kHz after a fixed latency of 2.2 ms (NeurOne, Mega Electronics). This signal is acquired by a real-time processing system (Mathworks Simulink Real-Time) through a multi-channel analog data acquisition card (PD2-MF-64-500-16H, United Electronic Industries) and processed by custom EEG analysis software executing in time-intervals of 0.5 ms. If the EEG signal matches a predefined pattern, a TMS pulse is triggered, with a trigger signal to TMS pulse latency of
Published Version
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