Two ERP components: N2 and P300.

<p>In panels (a), (b), (d), (e) and (f), ERP analyses from a cluster of 15 electrodes around Cz in different experimental conditions are presented, with incongruent trials in red and congruent trials in blue. The gray shadings indicate time periods of statistical significance (pcorrected < 0.05) and scalp topographies of the difference between incongruent and congruent trials show the effects of congruence during these time periods. (a) In the unmasked baseline, the N2 component is modulated by congruence from 272 ms to 364 ms after the target onset. (b) In unmasked mostly-incongruent (MI) blocks, the P300 component is modulated by congruence from 404 ms to 572 ms after the target onset. (c) The amplitude of the N2 and P300 components was computed as the absolute value of the difference between congruent and incongruent trials in the time windows of interest for each component. We found a significant interaction (F(1,19) = 6.67, p = 0.02) between the amplitude of the components and the experimental condition (unmasked baseline—dotted line/unmasked mostly-incongruent blocks—continuous line). Scalp topographies of the difference between incongruent and congruent trials for the time window of interest for each component and in each condition are plotted next to the corresponding point in the plot. (d) No significant difference was observed in the EEG between congruent and incongruent trials in the masked baseline condition. (e) No significant difference was observed in the EEG between congruent and incongruent trials in the masked baseline condition. (f) Interestingly, in the masked trials included in the unmasked mostly-incongruent blocks, a modulation of the P300 by congruence was observed from 384 ms to 452 ms after the target onset, similar to the signature observed for unmasked trials in mostly-incongruent blocks.</p

Experimental paradigm.

<p>We used a modified version of the Stroop task. Subjects were first presented with a color word as a prime (blue or green) and they had to respond to the color of a meaningless string. The prime could either be masked or unmasked. There were 4 types of blocks: masked baseline (50% incongruent trials), unmasked baseline (50% incongruent trials), mostly-incongruent masked blocks (80% incongruent trials) and unmasked mostly-incongruent blocks (80% incongruent trials) which included 70% unmasked trials and 30% masked trials.</p

Experimental paradigm and effect of memory in Experiment 2.

<p>(<b>a</b>) Experimental paradigm for Experiment 2. Five stages were included: Rating 1, Choice 1, Rating 2, Choice 2 and Memory test. Each ‘Choice’ block comprised two sub-blocks: one in which the choice was immediately followed by a 2-back task and one including only the choice.(<b>b</b>) Effect of memory on spreading of alternatives. The interaction between the sequence (RCR/RRC) and the memorization of the choices was significant (* p = 0.019). The difference between the spread in the RCR and the RRC sequences was significant only in pairs for which the choice was remembered (** p<0.01, paired t test, two tailed).</p

Spreading of alternatives in experiment 1.

<p>(<b>a</b>) Results obtained by Izuma et al. 2010 (adapted from PNAS). Bars represent the change in ratings between Rating 2 and Rating 1 for chosen items (left) and rejected items (right) in each condition. The critical comparison (corresponding to the comparison between RCR and RRC sequences respectively) is between Self-Difficult and PostEx-Choice. * p<0.05, *** p<0.001 (paired t-test, one tailed). (<b>b</b>) Replication of Izuma et al’s experiment (‘Reminder’ group). *** p<0.001 (paired t-test, one tailed). (<b>c</b>) Spreading of alternatives in the ‘Reminder’ (left) and ‘No reminder’ (right) groups. The interaction between the sequence (RCR – Self-difficult/RRC – PostEx-Choice) is significant (* p<0.05, ANOVA) and the critical comparison between RCR - Self-difficult and RRC - PostEx-Choice conditions is significant in both groups (* p<0.05, *** p<0.001, paired t test, two tailed).(<b>d</b>) Effect of memory on spreading of alternatives. The difference between the spread in the RCR – Self-difficult and the RRC – PostEx-Choice was significant only in pairs for which the choice was remembered (*** p<0.001, paired t test, two tailed).</p

Experimental paradigm for the ‘Reminder’ and ‘No reminder’ groups.

<p>The experimental paradigm included 5 stages: Rating 1, Choice 1, Rating 2, Choice 2 and Memory test. The procedure differed between the ‘Reminder’ and ‘No reminder’ groups in Rating 2 and Memory test. In Rating 2, previous choice (either subject’s or computer) was indicated for the ‘Reminder’ group (left panel) but not for the ‘No reminder’ group (right panel). Additionally, subjects in the ‘No reminder’ group performed a memory test designed to check whether they have remember the information corresponding to the reminder present in Rating 2 for the ‘Reminder’ group.</p

Violating two types of auditory regularities.

<p>The Local-Global experimental design <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085791#pone.0085791-Bekinschtein1" target="_blank">[7]</a> is a variation of the auditory oddball task. It consists in presenting series of 5-sound sequences which are composed of five identical sounds (local standard) or four identical sounds followed by a deviant one (local deviant). The global regularity is established across trials by making 80% of the trials identical (global standard). The design thus dissociates the violation of local predictions (change of sound in a given trial) and global predictions (change of sequence across trials).</p

Generalization across time of the local and global responses to auditory novelty.

<p>At each time point, a classifier was trained to extract the pattern of MEG activity that distinguishes local-standard from local-deviant trials (mismatch effect, top) or to contrast global-standard from global-deviant trials (bottom). Each classifier was subsequently tested on its ability to generalize this discrimination to all other time samples. (left) Differential patterns (standard – deviant) of brain activity across subjects as well as in a single representative subject using classic univariate analyses. For simplicity purposes, only the magnetometers are plotted (n = 102/306 channels). Note that, unlike subject-specific decoding, classic event related fields (ERF) analyses are tested across subjects, and are thus insensitive to inter-individual variability of subjects' topographies. (middle) Generalization of six different classifiers trained at regularly spaced times between 100 ms and 600 ms (purple), compared to the traditional “diagonal” decoding method where a different classifier is trained and tested at the same time point (black). The thick lines indicate significant decoding scores. The yellow areas indicate when the diagonal performance was significantly different from the generalization across time. Error bars indicate the standard error of the mean (SEM) across subjects. (right) Generalization matrices. Decoding performance is plotted as a function of training time (vertical axis) and testing time (horizontal axis) for all classifiers. Decoding of the local-violation effect leads to a diagonal-shaped decoding performance from 82 ms to 508 ms (AUC over 50% in red), demonstrating that each classifier was only able to predict trials' classes for a short amount of time. Decoding of the global-violation effect leads to a square generalization matrix, suggesting that the underlying brain activity is essentially stable during this time period. Early classifiers of the global violation (<350 ms) are slightly lower than the traditional “diagonal” decoding performance, thus suggesting only a small change in the underlying pattern of activity.</p

Detecting two types of brain dynamics by assessing the ability of multivariate pattern classifiers to generalize across time.

<p>The temporal generalization method can characterize the dynamics of neural activity. (left) When the stimulus evokes a serial chain of brain activations, “diagonal classifiers”, trained and tested at each time point can extract stimulus information throughout the activation period. However, as each classifier is specific to the time point at which it has been trained, they cannot generalize across other time samples. The generalization time analysis thus reveals a diagonal generalization matrix. (right) By contrast, if the underlying activity is sustained over time, then all classifiers would capture the same pattern. These classifiers would thus generalize to one another and lead to a square generalization matrix.</p

The Cerebral Cost of Breathing: An fMRI Case-Study in Congenital Central Hypoventilation Syndrome

<div><p>Certain motor activities - like walking or breathing - present the interesting property of proceeding either automatically or under voluntary control. In the case of breathing, brainstem structures located in the medulla are in charge of the automatic mode, whereas cortico-subcortical brain networks - including various frontal lobe areas - subtend the voluntary mode. We speculated that the involvement of cortical activity during voluntary breathing could impact both on the “resting state” pattern of cortical-subcortical connectivity, and on the recruitment of executive functions mediated by the frontal lobe. In order to test this prediction we explored a patient suffering from central congenital hypoventilation syndrome (CCHS), a very rare developmental condition secondary to brainstem dysfunction. Typically, CCHS patients demonstrate efficient cortically-controlled breathing while awake, but require mechanically-assisted ventilation during sleep to overcome the inability of brainstem structures to mediate automatic breathing. We used simultaneous EEG-fMRI recordings to compare patterns of brain activity between these two types of ventilation during wakefulness. As compared with spontaneous breathing (SB), mechanical ventilation (MV) restored the default mode network (DMN) associated with self-consciousness, mind-wandering, creativity and introspection in healthy subjects. SB on the other hand resulted in a specific increase of functional connectivity between brainstem and frontal lobe. Behaviorally, the patient was more efficient in cognitive tasks requiring executive control during MV than during SB, in agreement with her subjective reports in everyday life. Taken together our results provide insight into the cognitive and neural costs of spontaneous breathing in one CCHS patient, and suggest that MV during waking periods may free up frontal lobe resources, and make them available for cognitive recruitment. More generally, this study reveals how the active maintenance of cortical control over a continuous motor activity impacts on brain functioning and cognition.</p></div

Restoration of DMN under mechanical ventilation.

<p>(A). Comparison of BOLD signal between MV and SB revealed a specific increase of activation in the default-mode network associated in awake controls in introspection and self-consciousness. No significant result was observed in the opposite contrast. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107850#pone-0107850-t001" target="_blank">Table 1</a> for detailed fMRI results. (B&C). Functional connectivity assessed with a hypothesis-driven approach revealed a larger correlation with precuneus activity in posterior mesial areas during MV than during SB (B), and a larger correlation between brainstem activity and a large anterior cortico-subcortical network during SB than during MV (C). This large network resembles the executive attention network.</p