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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. (2000, 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., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

The parieto-frontal network plays a crucial role in the transformations that convert visual information into motor commands for hand reaching movements. Here we use electroencephalography to determine whether the planning of reaching movements to visual and somatosensory targets involves a similar spatio-temporal pattern of neural activity. Subjects performed reaching movements toward spatial locations defined either by visual (light-emitting diode) or somatosensory (vibration of a fingertip of the contralateral hand) stimuli. To identify the activations associated with sensorimotor transformations, we subtracted the event-related potentials recorded in a "static" task (the stimuli were presented but no movement was initiated) from those recorded in a "reach" task (a reach had to be initiated toward the spatial location of the stimuli). In the visual condition, reach-related activities were observed over parietal, premotor and sensorimotor areas contralateral to the reaching hand. Activation was first observed over parietal areas 140 ms after stimulus onset and progressed to frontal areas. The proprioceptive condition recruited a similar set of structures as for visual targets. However, the temporal pattern of activity within these cortical areas differed greatly. Activity was sustained over premotor and sensorimotor areas throughout the reaction time interval, occurring simultaneously with the parietal activation. These results suggest that a common cortical network serves to transform visual and somatosensory signals into motor commands, but that the interactions between the structures of this network differ. This raises the possibility that different coordinate frames are used to encode the motor error for the two target modalities.

The nogo potentials (N2/P3) were studied in a precuing auditory reaction time task in human subjects who had to either perform a button-press response (Press condition) or imagine they were performing it (Imagine condition). In the full precue condition (the subjects knew in advance which response they had to perform/imagine), in 25% of the trials, a nogo signal instructed the subject not to perform or not to imagine the prepared action. Clear N2/P3 components were obtained on nogo trials on the Press trials, but also on the Imagine ones: the N2 was of similar amplitude in both conditions, whereas the P3 was of smaller amplitude in the Imagine condition. The presence of nogo potential in motor imagery is discussed in terms of the functional significance of the N2/P3 complex.

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. [ABSTRACT FROM AUTHOR]

The ability to stop ongoing motor responses in a splitsecond is a vital element of human cognitive control and flexibility that relies in large part on prefrontal cortex. We used the stop-signal paradigm to elucidate the engagement of primary motor cortex (M1) in inhibiting an ongoing voluntary motor response. The stop-signal paradigm taps the ability to flexibly countermand ongoing voluntary behavior upon presentation of a stop signal. We applied single-pulse TMS to M1 at several intervals following the stop signal to track the time course of excitability of the motor system related to generating and stopping a manual response. Electromyography recorded from the flexor pollicis brevis allowed quantification of the excitability of the corticospinal tract and the involvement of intracortical GABABergic circuits within M1, indexed respectively by the amplitude of the motor-evoked potential and the duration of the late part of the cortical silent period (SP). The results extend our knowledge of the neural basis of inhibitory control in three ways. First, the results revealed a dynamic interplay between response activation and stopping processes at M1 level during stop-signal inhibition of an ongoing response. Second, increased excitability of inhibitory interneurons that drives SP prolongation was evident as early as 134 msec following the instruction to stop. Third, this pattern was followed by a stop-related reduction of corticospinal excitability implemented around 180 after the stop signal. These findings point to the recruitment of GABABergic intracortical inhibitory circuits within M1 in stop-signal inhibition and support the notion of stopping as an active act of control. [ABSTRACT FROM AUTHOR]

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 electroencepha- lographic (EEG) component, the "error negativity" (Ne 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 tempoial 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 Ne 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 Ne depends on the time needed to correct (partial) errors, revealing an "on-line'' modulation of control on a very short time scale. [ABSTRACT FROM AUTHOR]

Abstract: The objective was to test whether motor preparation can modulate the efficiency of the cortical motor command. The electroencephalogram (EEG) was recorded from electrodes located over the primary sensorimotor cortices during the performance of a between-hand choice reaction time task in which foreperiod duration (the interval between the warning and the imperative signals, 800 vs. 2800ms) was varied across blocks of trials. In order to increase the spatial resolution of the EEG traces, surface Laplacian was estimated. The amplitude of the negative wave developing over the hemisphere contralateral to the response was smaller for the short foreperiod associated with the best performance level. These results indicate that the activation of the primary sensorimotor cortex involved in the response is less pronounced for the short foreperiod, suggesting that temporal advance information increases the efficiency of the cortical motor command. [Copyright &y& Elsevier]