A Simon-like effect in Go/No-Go tasks performed in isolation.

The present study was conducted to decipher whether a spatial correspondence effect can emerge in Go/No-Go tasks (cSE, in reference to Donders' type c task) performed in isolation (participant alone in the cubicle). To this aim, a single participant was centrally positioned in front of a device and was required to respond by a hand key-press to the color of the stimulus. Half the participants were seated in front of a table equipped with only one response key and the other half in front of a table equipped with two response keys (one active and the other one useless). Using a substantial number of subjects (48) and trials (960), the present study revealed a numerically small but statistically reliable cSE. This result contrasts with referential coding predictions and suggests that the representation of a concurrently active response is not a prerequisite for the cSE to emerge. Moreover, the presence of a second response button in the participant's peripersonal space exerted no measurable influence on the cSE. The lack of statistical power of numerous previous studies may explain why the cSE has often been considered to be nil.

Dopamine and response selection: an Acute Phenylalanine/Tyrosine Depletion study.

The role of dopaminergic system in decision-making is well documented, and evidence suggests that it could play a significant role in response selection processes. The N-40 is a fronto-central event-related potential, generated by the supplementary motor areas (SMAs) and a physiological index of response selection processes. The aim of the present study was to determine whether infraclinical effects of dopamine depletion on response selection processes could be evidenced via alterations of the N-40. We obtained a dopamine depletion in healthy volunteers with the acute phenylalanine and tyrosine depletion (APTD) method which consists in decreasing the availability of dopamine precursors. Subjects realized a Simon task in the APTD condition and in the control condition. When the stimulus was presented on the same side as the required response, the stimulus-response association was congruent and when the stimulus was presented on the opposite side of the required response, the stimulus-response association was incongruent. The N-40 was smaller for congruent associations than for incongruent associations. Moreover, the N-40 was sensitive to the level of dopaminergic activity with a decrease in APTD condition compared to control condition. This modulation of the N-40 by dopaminergic level could not be explained by a global decrease of cerebral electrogenesis, since negativities and positivities indexing the recruitment of the primary motor cortex (anatomically adjacent to the SMA) were unaffected by APTD. The specific sensitivity of N-40 to ATPD supports the model of Keeler et al. (Neuroscience 282:156-175, 2014) according to which the dopaminergic system is involved in response selection.

On-line action monitoring of response execution: An electrophysiological study.

In between-hand choice-RT-tasks, small incorrect EMG activations occurring before the correct response ("partial errors") are assumed to reflect the detection, inhibition and correction of erroneous hand selection, revealing the existence of an action monitoring system, acting "on-line". Now, EMG activations of the correctly selected hand muscles, too small to reach the response threshold, may also occur before these hand muscles produce an overt correct response ("partial corrects"). We hypothesized that partial corrects reflect incorrect execution of correctly selected responses. We found 1) that response force was smaller on trials preceding a partial correct trial and 2) that the Error Negativity, a performance sensitive ERP, assumed to reveal "on-line" action monitoring, was larger for partial corrects than for correct trials. This also suggests that the competence of the action monitoring system is not restricted to selection errors but also extends to execution errors.

Linking EEG signals, brain functions and mental operations: Advantages of the Laplacian transformation.

Electroencephalography (EEG) is a very popular technique for investigating brain functions and/or mental processes. To this aim, EEG activities must be interpreted in terms of brain and/or mental processes. EEG signals being a direct manifestation of neuronal activity it is often assumed that such interpretations are quite obvious or, at least, straightforward. However, they often rely on (explicit or even implicit) assumptions regarding the structures supposed to generate the EEG activities of interest. For these assumptions to be used appropriately, reliable links between EEG activities and the underlying brain structures must be established. Because of volume conduction effects and the mixture of activities they induce, these links are difficult to establish with scalp potential recordings. We present different examples showing how the Laplacian transformation, acting as an efficient source separation method, allowed to establish more reliable links between EEG activities and brain generators and, ultimately, with mental operations. The nature of those links depends on the depth of inferences that can vary from weak to strong. Along this continuum, we show that 1) while the effects of experimental manipulation can appear widely distributed with scalp potentials, Laplacian transformation allows to reveal several generators contributing (in different manners) to these modulations, 2) amplitude variations within the same set of generators can generate spurious differences in scalp potential topographies, often interpreted as reflecting different source configurations. In such a case, Laplacian transformation provides much more similar topographies, evidencing the same generator(s) set, and 3) using the LRP as an index of response activation most often produces ambiguous results, Laplacian-transformed response-locked ERPs obtained over motor areas allow resolving these ambiguities.

Dopamine precursors depletion impairs impulse control in healthy volunteers.

The aim of the present study was to decipher the role of the dopamine system in impulse control. Impulsive actions entail (i) activation of the motor system by an impulse, which is an urge to act and (ii) a failure to suppress that impulse, when inappropriate, in order to prevent an error. These two aspects of action impulsivity can be experimentally disentangled in conflict reaction time tasks such as the Simon task, which measures susceptibility to acting on spontaneous impulses (as well as the proficiency of suppressing these impulses). In 12 healthy volunteers performing a Simon task, dopamine availability was reduced with an amino acid drink deficient in the dopamine precursors, phenylalanine and tyrosine. Classic behavioral measures were augmented with an analysis of the electromyographic activity of the response effectors. Electromyography allows one to detect covert activations undetectable with strictly behavioral measures and further reveals the participants' ability to quickly suppress covert activations before they result in an overt movement. Following dopamine depletion, compared with a placebo condition, participants displayed comparable impulse activation but were less proficient at suppressing the interference from this activation. These results provide evidence that the dopamine system is directly involved in the suppression of maladaptive response impulses.

The N-40: an electrophysiological marker of response selection.

A frontocentral electrophysiological wave occurring before the response, the N-40, has been reported in response choice situations compared to no-choice situations. This was interpreted as reflecting response selection. The gradual sensitivity of the N-40 to the demands put on response choice was tested by manipulating stimulus-response (S-R) congruence so as to influence response selection processes. After Laplacian transformation, an N-40 clearly emerged and was larger for incongruent (more demanding) than for congruent (less demanding) S-R associations. The N-40, which possibly reflects SMA activation, thus provides information about the implementation of response selection in the brain.

To err or to guess: an ERP study on the source of errors.

Given the large contribution of human error in the failure of complex systems, understanding the source of errors is an important issue. It has been proposed that, in speeded situations, responses biases induce subjects to guess which response will be required. When the guess turns out to be wrong, a fast guess error occurs. In unbiased conditions the possible contribution of fast guess errors remains an open question. We used a response-locked event-related potential (N-40), assumed to reveal the presence of a response selection process during the reaction time, to probe the presence of a response selection in biased and unbiased situations. The N-40 was present without response bias but absent in biased situations. This lends physiological support to the idea that, in a priming paradigm as used here, most errors in biased conditions are fast guesses whereas most errors result from inappropriate response selections in unbiased conditions. This reveals different sources of errors.

Sleep deprivation affects the sensitivity of proactive and reactive action monitoring: a behavioural and ERP analysis.

We studied the impact of sleep deprivation on action monitoring. Each participant performed a Simon task after a normal night of sleep and after 26 h of awakening. Reaction time (RT) distributions were analyzed and the sensitivity of the error negativity (Ne/Ne like) to response correctness was examined. Results showed that (1) the Simon effect persisted for the longest RTs only after sleep deprivation and (2) the sensitivity of the Ne/Ne like to correctness decreased after sleep deprivation, especially on incongruent trials. This suggests that after sleep deprivation (1) the ability to inhibit prepotent response tendencies is impaired and (2) the sensitivity of a response monitoring system as revealed by the error negativity is less sensitive to performance. In conclusion, action monitoring was affected by sleep deprivation as revealed by distributional analyses and the sensitivity of the Ne/Ne like to performance, which may be attributed to the fragility of prefrontal structures to sleep deprivation.

Feedback processing in hypothesis testing: a Laplacian ERP study.

The capacity to adjust behavior and evaluate performance in a changing environment is highly related to taking feedback into account. Using feedback is, hence, crucial for different cognitive capacities. The present study focused on feedback processing in hypothetico-deductive reasoning. Electroencephalographical (EEG) activity was recorded while participants performed a hypothesis-testing task in which a feedback signal allowing the evaluation of performance was delivered at each trial. To ameliorate the spatial resolution of EEG signals, the surface Laplacian was estimated. Results showed three distinct patterns of activation. At central and centro-parietal electrodes, the activity was sensitive to participants' expectancies in a binary and a gradual way, respectively. At the parieto-occipital electrode, the activity was sensitive to the evaluation of performance itself: correct versus false. In conclusion, the processing of feedback signal depends on at least three separate processes.

Executive control and response expectancy: a Laplacian ERP study.

The event-related potential called "Error Negativity" (Ne, ERN), which appears when subjects commit errors in choice reaction time tasks, is a marker of response monitoring. By introducing a response probability bias, we show that the Ne is sensitive to response expectancy. We further show that the small negativity evoked by correct responses (Ne-like, CRN) is also sensitive to response expectancy: On unexpected responses, the former decreases while the latter increases to such an extent that the amplitudes of the two components are in the same range of magnitude. Although the sensitivity of the Ne to response expectancy is compatible with the current models accounting for the Ne, the common sensitivity of the Ne and the Ne-like supports the idea that they reflect functionally similar monitoring processes.

Motor inhibition and response expectancy: a Laplacian ERP study.

In between-hand choice reaction time tasks, the motor cortex involved in the required response (contralateral) has been shown to be activated while the motor cortex involved in the non-required response (ipsilateral) has been shown to be inhibited. The aim of the present study was to test the hypothesis that ipsilateral inhibition reflects an active mechanism aimed at preventing errors. To this end, the risk of committing errors in between-hand choice reaction time tasks was manipulated by introducing a response probability bias. The surface Laplacian transforms of electroencephalographic waves recorded over the motor cortices, contralateral and ipsilateral to the responding hand were compared. Results showed that contralateral activation was not modulated by the risk of committing errors while ipsilateral inhibition was sensitive to this risk in a gradual manner: the higher the risk, the stronger the inhibition.

A reasoning bias revealed by electrodermal activity.

The sufficiency of behavioral data supporting reasoning biases was challenged. Our objective was to test if physiological data could significantly support reasoning biases. Experiment 1: When performing a rule discovery task with feedback, participants systematically gave the same response. This was not compatible with norms referring to a formal logic system, but was insufficient to conclude there was a reasoning bias. Only the knowledge of participants' expectations of feedback would merit this conclusion. Experiment 2: Participants' expectations were indexed by electrodermal activity. The results showed that when participants displayed the behavioral bias, they considered their responses to be correct and hence committed an error of logic. However, this error of logic did not prevent them from solving the task. This argues for a theory according to which human reasoning uses more economical strategies than the simple application of formal logical rules.

Does the error negativity reflect the degree of response conflict?

The recruitment of performance control was recently explained in terms of the detection of response conflict. One recent hypothesis claims that the degree of response conflict is reflected in an electroencephalographical component, the Error Negativity (Ne). Indeed, in the framework of simulations, variations of the Ne fitted well with variations of response conflict. The objective of the present study was to test the conflict hypothesis of the Ne in a real experimental situation. The subjects performed an arrowhead flanker task with two alternative responses. The degree of conflict was measured by the degree of the co-activation of the forces exerted by the two alternative effectors. Trials with co-activations (i.e., an incorrect response activation followed by a correct one) were selected. These trials were divided into two categories, namely trials with suprathreshold error force (full errors) and subthreshold error force (partial errors). The results showed that although the degree of conflict was larger for full than for partial errors, the Ne was not different for the two categories. Our study does not support the hypothesis that the Ne amplitude reflects the degree of conflict.

The modulation of the Ne-like wave on correct responses foreshadows errors.

In reaction time (RT) tasks, event-related potentials (ERPs) reveal a response-locked negative wave when subjects commit errors. This wave, termed "error negativity" (Ne) or "error-related negativity" (ERN), is thought to index response-monitoring processes. With conventional monopolar recordings, this negativity is hardly seen on correct responses, likely overlapped by a large positive wave. Indeed, after Laplacian transformation (a spatial high-pass filter), a small Ne-like wave is unmasked. Recently, it has been shown that the positivity on monopolar recordings was larger for correct responses preceding an error than for correct responses preceding a correct trial. After Laplacian transformation, it appears that this effect is due, at least in part, to a decrease of the Ne-like wave on correct responses preceding an error. This result indicates that, as the Ne on errors, the Ne-like wave on correct responses is sensitive to performance and hence is likely related to response-monitoring processes.

On-line executive control: an electromyographic study.

In a choice reaction time (RT) task, electromyographic (EMG) recordings allowed us to fractionate RT into two subcomponents, namely premotor time and motor time. This has been done for correct trials and errors. The analysis of the EMG burst and motor time (between EMG onset and overt response) showed that the EMG burst amplitude was reduced and the motor time was longer for errors than for correct responses. In the same way as posterror slowing on the RT was interpreted as revealing between-trials changes in executive control, the present data provide direct evidence for an on-line, within-trial, executive control.