F. Di Russo

Effects of sustained, voluntary attention on amplitude and latency of steady-state visual evoked potential: a costs and benefits analysis

OBJECTIVE Steady-state visual evoked potentials (VEPs) were recorded to study the mechanisms that underlie visual attention. METHODS VEPs were recorded from 1 cycle/degree sinusoidal grating contrast reversed at various temporal frequencies (6-10 Hz). This was displayed in one hemifield. A letter search display was flashed at a random rate in the other hemifield. The subject performed a demanding task on the recording stimulus (attended condition) or on the opposite side stimulus (unattended condition). Alternatively, he/she passively fixated on the fixation point (passive condition). RESULTS Relative to the passive condition, attended stimuli elicited enhanced-amplitude and shortened-latency VEP (benefits). Costs (i.e. responses to passive vs. unattended stimuli) were more marked for latency. CONCLUSIONS VEP latency may be the key of a priority-based attention mechanism acting at an early level.

New insights into old waves. Matching stimulus- and response-locked ERPs on the same time-window.

We compared the effect of locking the event-related potentials (ERPs) on the stimulus vs. the response in a simple (SRT) and in a discriminative (DRT, equally probable Go/No-go) visuo-motor task. The accurate alignment of stimulus- and response-locked ERPs on the same time scale was obtained selecting a group of 27 participants with low inter-individual response time (RT) variation in the two tasks to reduce the jitter of RTs. Two-second epochs were defined for the analyses based on averaged RTs in the two tasks. Results show that the preparatory pre-stimulus activities (i.e., the pN and the BP components) were not affected by the different locking in both SRT and DRT. As expected, the exogenous post-stimulus P1 and N1 components (and the P2, present only in SRT) were larger in stimulus- than response-locked averaging; the same trend was observed for the less-known prefrontal N1 and P1 components (pN1 and pP1) that were larger in stimulus-locked averaging (the effect was not significant in SRT). The prefrontal pP2 component was only present in DRT peaking around 370 ms, and did not show an effect of locking. The frontal-central N2 component was enhanced by response-locked averaging in SRT, while it did not show effects of locking in DRT. The P3 component peaked at about 350ms over central sites in SRT, and at about 500ms over parietal sites in DRT; in both cases its amplitude was larger in response- than in stimulus-locked averaging. Overall, the amplitude of the preparatory components was independent from locking, the exogenous components were enhanced by stimulus locking, and the late components were more related to the response than to the stimulus. Concluding, to investigate action preparation, perception, and perceptual-decisional activity ERP studies should adopt stimulus-locked averaging with an appropriate baseline and longer pre-stimulus interval, or use both types of locking.

From cognitive motor preparation to visual processing: The benefits of childhood fitness to brain health

The association between a fit body and a fit brain in children has led to a rise of behavioral and neuroscientific research. Yet, the relation of cardiorespiratory fitness on premotor neurocognitive preparation with early visual processing has received little attention. Here, 41 healthy, lower and higher fit preadolescent children were administered a modified version of the Eriksen flanker task while electroencephalography (EEG) and behavioral measures were recorded. Event-related potentials (ERPs) locked to the stimulus onset with an earlier than usual baseline (-900/-800 ms) allowed investigation of both the usual post-stimulus (i.e., the P1, N1 and P2) as well as the pre-stimulus ERP components, such as the Bereitschaftspotential (BP) and the prefrontal negativity (pN component). At the behavioral level, aerobic fitness was associated response accuracy, with higher fit children being more accurate than lower fit children. Fitness-related differences selectively emerged at prefrontal brain regions during response preparation, with larger pN amplitude for higher than lower fit children, and at early perceptual stages after stimulus onset, with larger P1 and N1 amplitudes in higher relative to lower fit children. Collectively, the results suggest that the benefits of being aerobically fit appear at the stage of cognitive preparation prior to stimulus presentation and the behavioral response during the performance of a task that challenges cognitive control. Further, it is likely that enhanced activity in prefrontal brain areas may improve cognitive control of visuo-motor tasks, allowing for stronger proactive inhibition and larger early allocation of selective attention resources on relevant external stimuli.

Beyond the "Bereitschaftspotential": Action preparation behind cognitive functions

HighlightsWe review EEG literature on motor‐related cortical activity of the last 10 years.The focus is on the brain proactive cognitive control for complex interactive actions.Prefrontal, frontal, parietal and insular cortices are involved in action planning.In brain preparation phase, we can catch glimpses of cognitive functions foundation. Abstract Research on preparatory brain processes taking place before acting shows unexpected connections with cognitive processing. From 50 years, we know that motor‐related brain activity can be measured by electrocortical recordings 1–3 s before voluntary actions. This readiness potential has been associated with increasing excitably of premotor and motor areas and directly linked to the kinematic of the upcoming action. Now we know that the mere motor preparation is only one function of a more complex preparatory activity. Recent research shows that before any action many cognitive processes may occur depending on various aspects of the action, such as complexity, meaning, emotional valence, fatigue and consequences of the action itself. In addition to studies on self‐paced action, the review considers also studies on externally‐triggered paradigms showing differences in preparation processes related to age, physical exercise, and task instructions. Evidences from electrophysiological and neuroimaging recording indicate that in addition to the motor areas, the prefrontal, parietal and sensory cortices may be active during action preparation to anticipate future events and calibrate responses.

Single-epoch analysis of interleaved evoked potentials and fMRI responses during steady-state visual stimulation

OBJECTIVE Aim of the study was to record BOLD-fMRI interleaved with evoked potentials for single-epochs of visual stimulation and to investigate the possible relationship between these two measures. METHODS Sparse recording of fMRI and EEG allowed us to measure BOLD responses and evoked potentials on an epoch-by-epoch basis. To obtain robust estimates of evoked potentials, we used blocks of contrast-reversing visual stimuli eliciting steady-state visual evoked potentials (SSVEPs). For each block we acquired one volume of fMRI data and we then tested for co-variations between SSVEPs and fMRI signals. Our analyses tested for frequency-specific co-variation between the two measurements that could not be explained by the mere presence/absence of the visual stimulation. RESULTS Condition-specific single-epoch SSVEPs and fMRI responses were observed at occipital sites. Combined SSVEPs-fMRI analysis at the single-epoch level did not reveal any significant correlation between the two recordings. However, both signals contained stimulation-specific linear decreases that may relate to neuronal habituation. CONCLUSIONS Our findings demonstrate robust estimation of single-epoch evoked potentials and fMRI responses during interleaved recording, using visual steady-state stimulation. SIGNIFICANCE Single-epochs analysis of evoked potentials and fMRI signals is feasible for interleaved SSVEPs-fMRI recordings.

Effect of target probability on pre-stimulus brain activity.

Studies on perceptual decision-making showed that manipulating the proportion of target and non-target stimuli affects the behavioral performance. Tasks with high frequency of targets are associated to faster response times (RTs) conjunctively to higher number of errors (reflecting a response bias characterized by speed/accuracy trade-off) when compared to conditions with low frequency of targets. Electroencephalographic studies well described modulations of post-stimulus event-related potentials as effect of the stimulus probability; in contrast, in the present study we focused on the pre-stimulus preparatory activities subtending the response bias. Two versions of a Go/No-go task characterized by different proportion of Go stimuli (88% vs. 12%) were adopted. In the task with frequent go trials, we observed a strong enhancement in the motor preparation as indexed by the Bereitschaftspotential (BP, previously associated with activity within the supplementary motor area), faster RTs, and larger commission error rate than in the task with rare go trials. Contemporarily with the BP, a right lateralized prefrontal negativity (lateral pN, previously associated with activity within the dorsolateral prefrontal cortex) was larger in the task with rare go trial. In the post-stimulus processing stage, we confirmed that the N2 and the P3 components were larger for rare trials, irrespective of the Go/No-go stimulus category. The increase of activities recorded in the preparatory phase related to frequency of targets is consistent with the view proposed in accumulation models of perceptual decision for which target frequency affects the subjective baseline, reducing the distance between the starting-point and the response boundary, which determines the response speed.

Sight and sound of actions share a common neural network

The mirror‐neuron system (MNS) connects sensory information that describes an action with a motor plan for performing that action. Recently, studies using the repetition‐suppression paradigm have shown that strong activation occurs in the left premotor and superior temporal areas in response to action‐related, but not non‐action‐related, stimuli. However, few studies have investigated the mirror system by using event‐related potentials (ERPs) and employing more than one sensory modality in the same sample. In the present study, we compared ERPs that occurred in response to visual and auditory action/non‐action‐related stimuli to search for evidence of overlapping activations for the two modalities. The results confirmed previous studies that investigated auditory MNS and extended these studies by showing that similar activity existed for the visual modality. Furthermore, we confirmed that the responses to action‐ and non‐action‐related stimuli were distinct by demonstrating that, in the case of action‐related stimuli, activity was restricted mainly to the left hemisphere, whereas for non‐action‐related stimuli, activity tended to be more bilateral. The time course of ERP brain sources showed a clear sequence of events that subtended the processing of action‐related stimuli. This activity seemed to occur in the left temporal lobe and, in agreement with findings from previous studies of the mirror‐neuron network, the information involved appeared to be conveyed subsequently to the premotor area. The left temporo‐parietal activity observed following a delay might reflect processing associated with stimulus‐related motor preparation.

The proactive self-control of actions: Time-course of underlying brain activities

&NA; Proactive brain control optimizes upcoming actions and inhibits unwanted responses. In the present event‐related potential (ERP) study, participants freely decided in advance whether to respond or not to an upcoming stimulus, then prepared or not the action according to their decision; finally, a stimulus was delivered, and subjects had to respond (or not). During the decision‐making stage, a prefrontal negativity raised bilaterally in case no‐response was decided, reflecting the first brain signal of proactive inhibition. Simultaneously, slow activity raised over premotor cortices independently from the decision taken, and then raised during the preparation phase only in the case of response decision (as a sort of accelerator). When the decision was not to respond, the prefrontal activity remained sustained (as a sort of brake) and showed a right‐lateralized distribution during the preparation phase. Overall, we described the time‐course of a proactive accelerating‐braking system regulating self‐control of actions. HighlightsSelf‐control of responses relies on activity within frontal and prefrontal cortices.Bilateral prefrontal activity has been associated with no–response decision.Activity in premotor cortex, independent by decisions, worked as an accelerator.Right prefrontal cortex activity, as a brake, has been associated with inhibition.

Weak proactive cognitive/motor brain control accounts for poor children’s behavioral performance in speeded discrimination tasks

BACKGROUND Motor and inhibitory control rely on frontal cortex activity, which is known to reach full maturation only in late adolescence. The development of inhibitory control has been studied using event-related potentials (ERP), focusing on reactive processing (i.e. the N2 and the P3 components). Scarce information exists concerning pre-stimulus activity as that represented by the Bereinshafstpotential (BP) and by the prefrontal negativity (pN). Further, no literature exists concerning the post-stimulus components originating within the anterior insula (pN1, pP1, pP2). This study aims at associating children performance with these motor-cognitive processing in frontal brain areas. METHODS High-resolution EEG recordings were employed to measure ERPs from 18 children (12 years old) and 18 adults (28 years old) during a visuo-motor discriminative response task. Response time (RT), commission (CE) and omission errors, and RT variability were compared between groups. At brain level, two pre-stimulus (BP and pN) and seven post-stimulus (P1; pN1; N1; pP1; N2; pP2; P3) ERP components were compared between groups. RESULTS Children showed slower and more variable RTs and poorer inhibition (higher CEs) than adults. At electrophysiological level, children presented smaller BP and pN. After stimulus onset, children showed lower amplitude of N1, pP1, P3, and pP2 components. The P1, pP1, N2 and P3 were delayed compared to adults. CONCLUSIONS Our results demonstrate that children are characterized by less intense task-related proactive activities in frontal cortex, which may account for subsequent poor and delayed reactive processing and, thus, for inaccurate and slow performance.