When binary economical rewards are offered along a temporal dimension (e.g., Do you prefer 5€ now or 15€ in 120days?) people may show decision conflicts depending on how sensitive they are to the discounting effect of time. EEG studies have shown that during conflict processing of cognitive representations, a rhythmic oscillatory activity in theta rhythm, named midfrontal theta (MFT), increases over the medial frontal cortex (MFC). MFT may index the temporal dynamics of different brain areas, operating as a synchronizer during the request of control. Despite the correlational link between MFC activation and MFT has been demonstrated, what remains unknown is the extent to which MFT causally reflects cognitive control processing during behavioural performance. The transcranial Alternating Current Stimulation (tACS) is an emerging technique that changes endogenous patterns of oscillatory activity by entraining the neural networks acting on the behavioural performance in a frequency-dependent manner. The present within-subject, sham controlled, cross-over study, aims at exploring the tendency to choose between economic offers in a temporal discounting paradigm during theta, gamma, and sham tACS, with the goal of modulating reaction times (RTs) and choice preferences when different levels of conflict, induced by combining specific delays and payoffs, occur. Hypothesis testing, sample size estimate and analysis of pilot results have been conducted using Bayesian statistics. The study received a priori peer-review (1 Stage) and In-Principle-Acceptance (IPA) as a Registered Report (RR) from the Cortex Journal (https://osf.io/x52vm/) even if data collection has not been already initiated. Importantly, the RR format guarantees publication also in case of null results or mismatch between hypothesis and results. The present proposal aims at securing for the second phase of the study (Stage 2) where data collection and analysis will be finalized.
We propose that by parametrically varying the amount of conflict inherent to a given decision, we can modulate the time taken to process the subjective value of the immediate and delayed rewards and ultimately the preferences under uncertainty.
Studies demonstrate that applying tACS while people make value-guided decisions it is possible to engage neural oscillations associated with cognitive control and cognitive processing (Polanìa et al., 2015).
In view of this, we expect to entrain theta task-related oscillations (i.e. MFT) and modulate the communication between frontal structures during information processing. The present study aims to explore how individual choices between economic offers might change during band-specific tACS. In particular, we expect that tACS modulates reaction times (RTs) at indifference points (high conflict trials) and that such modulations are different for theta and sham stimulation.
The two tasks within the experimental phase are implemented with different purposes.
In the Temporal Discounting Task, the critical hypothesis involves the modulatory effect of theta-tACS on behaviour during high conflict trials (value difference = 0). In particular, we expect that in the combinations where participants experience high decisional conflicts, the exogenous alternating current applied over the medial frontal cortex in the theta band may lead to specific changes of neuronal excitability through modulation of the firing rate effectiveness and of the temporal and computational dynamics of task-related electrocortical activity.
At the behavioural level, we expect to observe faster RTs and more immediate choices during theta-tACS than sham-tACS and y-tACS in high conflict trials. This effect may reflect the capability of the exogenous MFT in modulating the communication among specific frontal structures (ACC-MFC-DLPFC) during the emergence of decision conflicts.
However, faster RTs may decrease the probability of selecting delayed rewards, which might indicate a weaker role of the cognitive-control system in driving the behavioural choices of the participants toward future preferences. Therefore, immediate rewards should be preferred and selected more frequently since they may represent a rapid behavioural strategy to cope with high levels of conflict under uncertainty.
The possibility to modulate intertemporal choices with non-invasive methods may paves the way for improvements in clinical and traslational research (e.g. addiction, Parkinson' s Disease) and may inform theories of how neural oscillations causally influence impulsive and controlled behavior and decision processes in everyday life.
The present Registered Report (RR) has been in-principle accepted (IPA) following a long process of peer-review. This means that the Cortex journal guarantees the publication even if results do not match with the initial predictions, thus contributing toward the direction of the Open Science Framework.
Indeed, RR is a pre-registered study in which the hypothesis, sample size estimation, methodology, data analysis and expected results are publicly declared before data collection.
This scientific approach is innovative and outstanding since aims at reducing publication biases and p-hacking, and therefore, improving replicability in science.