Among the different brain imaging techniques, electroencephalography (EEG) is classically considered as having an excellent temporal resolution, but a poor spatial one. Here, we argue that the actual temporal resolution of conventional (scalp potentials) EEG is overestimated, and that volume conduction, the main cause of the poor spatial resolution of EEG, also distorts the recovered time course of the underlying sources at scalp level, and hence degrades the actual temporal resolution of EEG. While Current Source Density (CSD) estimates, through the Surface Laplacian (SL) computation, are well known to dramatically reduce volume conduction effects and hence improve EEG spatial resolution, its positive impact on EEG temporal resolution is much less recognized. In two simulation studies, we first show how volume conduction and reference electrodes distort the scalp potential time course, and how SL transform provides a much better spatio-temporal description. We then exemplify similar effects on two empirical datasets. We show how the time courses of the scalp potentials mis-estimate the latencies of the relevant brain events and that CSD provides a much richer, and much more accurate, view of the spatio-temporal dynamics of brain activity.

Falkenstein et al. (1991) first described a negative wave occurring just after an erroneous response in choice Reaction time tasks ("Error Negativity"-Ne or "Error Related Negativity"-ERN). Thanks to Laplacian transform of the data, Vidal et al. (2000Vidal et al. ( , 2003a described a wave on correct trials with similar topography and latency, although of smaller amplitude compared to the errors. A critical question is whether the Ne observed on errors and the negativity reported on correct trials reflect the same (modulated) activity, or whether they reflect completely different mechanisms. These two alternative possibilities were tested thanks to Independent Component Analysis (ICA) and source localization. ICA results showed that the waves recorded on errors and correct trials can be accounted for by the same independent component, corresponding to a dipolar source located within the Rostral Cingulate Zone. Source localization on the raw data also confirmed a common generator for correct and error trials. These data suggest that the waves on errors and correct trials reflect the same brain activity, whose amplitude varies as a function of the correctness of the response. The implications of this result for cognitive control are discussed.

Abstract& Our ability to detect and correct errors is essential for our adaptive behavior. The conflict-loop theory states that the anterior cingulate cortex (ACC) plays a key role in detecting the need to increase control through conflict monitoring. Such monitoring is assumed to manifest itself in an electroencephalographic (EEG) component, the ''error negativity'' (N e or ''error-related negativity'' [ERN]). We have directly tested the hypothesis that the ACC monitors conflict through simulation and experimental studies. Both the simulated and EEG traces were sorted, on a trial-by-trial basis, as a function of the degree of conflict, measured as the temporal overlap between incorrect and correct response activations. The simulations clearly show that conflict increases as temporal overlap between response activation increases, whereas the experimental results demonstrate that the amplitude of the N e decreases as temporal overlap increases, suggesting that the ACC does not monitor conflict. At a functional level, the results show that the duration of the N e depends on the time needed to correct (partial) errors, revealing an ''on-line'' modulation of control on a very short time scale. &

Metacognition, the ability to know about one’s thought process, is self-referential. Here, we combined psychophysics and time-resolved neuroimaging to explore metacognitive inference on the accuracy of a self-generated behavior. Human participants generated a time interval and evaluated the signed magnitude of their temporal production. We show that both self-generation and self-evaluation relied on the power of beta oscillations (β; 15–40 Hz) with increases in early β power predictive of increases in duration. We characterized the dynamics of β power in a low-dimensional space (β state-space trajectories) as a function of timing and found that the more distinct trajectories, the more accurate metacognitive inferences were. These results suggest that β states instantiate an internal variable determining the fate of the timing network’s trajectory, possibly as release from inhibition. Altogether, our study describes oscillatory mechanisms for timing, suggesting that temporal metacognition relies on inferential processes of self-generated dynamics.

(150 words)Metacognition, the ability to know about one's thought process, is self-referential. Here, we studied the brain mechanisms underlying metacognitive inferences in a self-generated behavior. Human participants generated a time interval, and evaluated the signed magnitude of their timing (first and second order behavioral judgments, respectively) while being recorded with time-resolved neuroimaging. We show that the first-and second-order judgments relied on the power of beta oscillations (β; 15-40 Hz), while error monitoring subsystems engaged alpha oscillations (α; 8-14 Hz). The spread of an individual's β power state-space trajectories during timing was indicative of the individual's metacognitive inference. Our results suggest that network inhibition (β power) instantiates a state variable determining future network trajectory; this naturally provides a code for duration and metacognitive inferences would consist in reading out this state variable. Altogether, our study describes oscillatory mechanisms for timing suggesting that temporal metacognition relies on inferential processes of self-generated dynamics.

Intentional actions are executed with the peculiar experience of "I decide to do that." It has been proposed that intentional actions involve a specific brain network involving the supplementary motor areas (SMAs). Here, we manipulated the internal representation participants attended to (intention vs. movement) in order to (1) examine the activity of SMAs and of the primary motor cortex (M1) during intentional action preparation and execution, and (2) investigate the temporal relationship between activity in these structures and intention awareness. Participants performed self-paced key presses. After each key press, participants were asked to report either the time they had the first intention to press the key (W-condition) or the time they actually started the movement (M-condition). We then estimated surface Laplacians from brain electrical potentials recorded while participants were performing the task. Activity in SMAs was greater in the W-condition than in the M-condition more than 1 s before electromyographic (EMG) activation, suggesting that this region is indeed associated to the formation of conscious intention. Conversely, activity in primary motor cortex (M1) contralateral to the responding hand was larger in the M-condition than in the W-condition, revealing that this region is also modulated by top-down processes. In addition, waveforms time-locked to the W-judgement revealed that M1 as well as EMG activation preceded the time at which participants become aware of their intention by about 0.3 s. This observation argues against the possibility that the temporal delay between motor-related activation and intention awareness results from smearing artifacts.

Inhibiting actions when they are no longer appropriate is essential for adaptive goal-directed behavior.In this study, we used high-density EEG and a standard flanker task to explore the spatio-temporal dynamics of cognitive control and inhibitory mechanisms aimed to prevent the commission of errors.By recording hand-related EMG activity, we could disentangle successful from unsuccessful inhibition attempts. Our results confirm that (i) the latency of the ERN (or Ne) component is too late to be associated with these online inhibitory mechanisms; (ii) instead, a frontal slow negative component with an earlier time-course was associated with the implementation of online inhibition. These findings are consistent with single-cell recordings in monkeys showing that the supplementary motor area (SMA)provides cognitive control signals to the primary motor cortex to exert online inhibition and in turn rectify the course of erroneous actions.

Behavioral estimates of time discrimination threshold on animals might be contaminated by the conditioning procedure used and by attentional effects. To avoid such side effects, we measured time discrimination by recording the rat electroencephalographic response to small temporal variations. Freely moving rats were presented with repetitive sounds, some of them being occasionally shorter than the standard, to produce a Mismatch Negativity (MMN) which is known to primarily involve preattentive processes. The smallest difference eliciting a MMN located the discrimination threshold between 16% and 33% of the standard, without attentional confound. Being observed in several species, MMN can be used to decipher both the phylogenetic and ontogenetic evolution of time discrimination, without attentional confound.