The Impact of Stimulus Presentation on Skin Conductance and Potential Implications for Neurofeedback Studies.

Real-time fMRI neurofeedback enables individuals to learn self-regulation of specific brain regions, such as the amygdala, which is often targeted for downregulation in trauma-related disorders. However, repeated exposure to emotional stimuli during lengthy sessions may lead to habituation, with amygdala activity naturally decreasing over time independent of self-regulation success. Presentation rate may influence this effect--however, empirical evidence remains limited with that rate varying widely across studies (ranging from three pictures every 4.5 s to one picture for 20 s). Therefore, prior to conducting an intended real-time fMRI neurofeedback study, we conducted this pilot to evaluate two types of presentation rate. We compared two aversive image presentation procedures and used skin conductance as an index of amygdala activation to identify an optimal presentation rate for a future neurofeedback study. The final sample included 13 healthy adults, who viewed blocks of six aversive images every four seconds (labeled "dynamic") and blocks of one aversive image for 24 s (labeled "static") while skin conductance was continuously recorded. Before the task, participants completed questionnaires assessing stress exposure and anxiety to explore their relationship with skin conductance. Skin conductance level (SCL), a measure of longer-term tonic arousal, remained higher in the dynamic condition than in the static condition. Although the static condition elicited a sharper initial peak, the response decayed more rapidly, whereas the dynamic condition yielded sustained SCL with small increases following each image onset. Further, we found that higher anxiety scores, as defined with the State-Trait Anxiety Inventory for Adults, correlated with lower SCL. These findings suggest that dynamic image presentations may mitigate amygdala habituation more effectively than static presentations, highlighting stimulus timing as a key factor for optimizing protocols such as neurofeedback.