INTRODUCTION: Recent models of decision making support the existence of an urgency signal shaping neural activity during deliberation (Cisek & Thura, 2022). In a past study using transcranial magnetic stimulation (TMS), we were able to show that high urgency materializes into two main adjustments of motor neural activity: a broad facilitation and a surround inhibition (around the index prime mover) (Derosiere et al., 2022). Notably, urgency is often treated as a uniform phenomenon, when in fact, it is more likely to be shaped by several influences, with potentially opposing effects modelling its ultimate strength. For instance, reward, which is known to invigorate action, is a likely promoter of urgency while influences supporting caution will rather counteract this effect. Here, we tested the hypothesis that motor adjustments observed in high urgency contexts result from these contrasting regulators, with surround inhibition boosted by influences promoting urgency, such as reward, and broad facilitation reflecting a weak recruitment, in such settings, of (inhibitory) influences promoting caution.

METHODS: 13 young healthy right-handed participants (23 ± 3.0 years old; 10 women) were tested in this ongoing study spanning over two days (target sample size n=20, planned completion Dec-2023). We recorded motor evoked potentials (MEPs) to TMS over primary motor cortex while subjects performed an index finger variant of the Tokens task with low or high reward trials (randomized low or high monetary precue), which were grouped in blocks requiring either low (majority of easy trials) or high (minority of easy trials) caution (8 or 9 blocks of 40 trials for each level of caution, in a counterbalanced order). On two separate days, the TMS coil position was adapted to obtain MEPs in finger muscles (as a probe of surround inhibition; total of 16 blocks) or in leg muscles (as a probe of broad facilitation; total of 18 blocks).

RESULTS: Behaviour in the task was clearly influenced by the reward landscape and the caution requirements. As expected, subjects were overall faster to decide in low than high caution blocks (in 13/13 subjects; paired-t₍₁₂₎=5.5, p<0.001), consistent with a greater urgency in the former block type. Yet, rather than a boosting effect, high reward generally tended to slow down decisions (in 9/13 subjects; paired-t₍₁₂₎=1.9, p=0.08 when compared to low reward trials), possibly because reward outcome was largely contingent on accuracy in our task design. Interestingly though, as evident when considering finger MEPs, high reward trials still tended to be associated with greater surround inhibition (i.e. lower ΔMEP [thumb-index]), compared to low reward trials (in 11/13 subjects; paired-t₍₁₂₎=1.345 p=0.203). Preliminary inspections of leg MEPs are consistent with a broad facilitation of motor neural activity during deliberation, although more subjects are required to determine how this effect interacts with urgency as a function of caution and reward.

CONCLUSION: Our preliminary data provide evidence for the view that surround inhibition can be increased by reward landscape and that broad facilitation can be observed during decision making, possibly related to caution level as will be further examined with a larger sample size.