Probing the link between central and autonomic markers of error processing via Midfrontal Theta transcranial Alternating Current Stimulation (MFT - tACS)

The ability to monitor one’s own performance is fundamental to the effective regulation of goal-directed behaviour. In both cognitive and motor tasks, errors consistently elicit midfrontal theta oscillations (MFΘ) and transient autonomic responses, such as cardiac deceleration. These electrocortical and physiological markers have been closely associated with the activation of the anterior cingulate cortex (ACC), a ventral area of the medial frontal region within the Central Autonomic network, which monitors and integrates behavioural and visceral outcomes. However, whether the ACC causally mediates the link between MFΘ activity and autonomic responses during error processing is still unclear. In this study, we tested the hypothesis that boosting MFΘ activity would modulate the performance monitoring system and, in turn, affect autonomic responses to errors during a cognitive task. To investigate this, we delivered transcranial Alternating Current Stimulation (tACS) targeting the ACC at theta frequency (6 Hz), gamma frequency (30 Hz, as a control), or sham stimulation in healthy participants performing the Letter-Flanker task. Autonomic responses were indexed by changes in inter-beat intervals (IBIs) and skin conductance responses (SCR) following correct and erroneous trials. In Experiment 1 (N = 30 participants, 19 females, age = 25 +/- 2.5), we applied tACS at 2mA of intensity using a high-definition montage (HD-tACS) with a central electrode placed on FCz and four returns placed over FPz, Pz, FC5and FC6. Results confirmed the typical increase in reaction times and errors in incongruent compared to congruent trials. Nevertheless, no significant effect of stimulation frequency on behaviour was observed. Physiological data indicate that – as expected – participants’ IBIs length increased following errors with respect to correct responses. Interestingly, error-related cardiac deceleration was stronger in participants who made fewer errors than in low-performers. This effect may suggest a possible role of participant’s expectations concerning their performance. Moreover, SCR was higher in incongruent compared to congruent errors. Overall, tACS did not influence physiological responses to errors, possibly due to the ineffectiveness of the stimulation montage in directly targeting ACC To overcome this potential limitation, we designed a new experiment (Experiment 2; N = 30 planned), using a similar paradigm but with a different tACS montage (bipolar: F3–F4) aimed at targeting the dorsolateral prefrontal cortex, which has direct and reciprocal connections with the ACC. In this way, we expect to better establish the role of ACC in linking central (MFΘ) and autonomic signatures of error processing .