Reaction Time in a Visual 4-Choice Reaction Time Task: ERP Effects of Motor Preparation and Hemispheric Involvement

Reaction time (RT), the most common measure of CNS efficiency, shows intra- and inter-individual variability. This may be accounted for by hemispheric specialization, individual neuroanatomy, and transient functional fluctuations between trials. To explore RT on these three levels, ERPs were measured in a visual 4-choice RT task with lateralized stimuli (left lateral, left middle, right middle, and right lateral) in 28 healthy right-handed subjects. We analyzed behavioral data, ERP microstates (MS), N1 and P3 components, and trial-by-trial variance. Across subjects, the N1 component was contralateral to the stimulation side. N1-MSs were stronger over the left hemisphere, and middle stimulation evoked stronger activation than lateral stimulation in both hemispheres. The P3 was larger for the right visual field stimulation. RTs were shorter for the right visual hemifield stimulation/right hand responses. Within subjects, covariance analysis of single trial ERPs with RTs showed consistent lateralized predictors of RT over the motor cortex (MC) in the 112–248 ms interval. Decreased RTs were related to negativity over the MC contralateral to the stimulation side, an effect that could be interpreted as the lateralized readiness potential (LRP), and which was strongest for right side stimulation. The covariance analysis linking individual mean RTs and individual mean ERPs showed a frontal negativity and an occipital positivity correlating with decreased RTs in the 212–232 ms interval. We concluded that a particular RT is a composite measure that depends on the appropriateness of the motor preparation to a particular response and on stimulus lateralization that selectively involves a particular hemisphere.     

Prefrontal modulation of visual processing in humans

Single neuron, evoked potential and metabolic techniques show that attention influences visual processing in extrastriate cortex. We provide anatomical, electrophysiological and behavioral evidence that prefrontal cortex regulates neuronal activity in extrastriate cortex during visual discrimination. Event-related potentials (ERPs) were recorded during a visual detection task in patients with damage in dorsolateral prefrontal cortex. Prefrontal damage reduced neuronal activity in extrastriate cortex of the lesioned hemisphere. These electrophysiological abnormalities, beginning 125 ms after stimulation and lasting for another 500 ms, were accompanied by behavioral deficits in detection ability in the contralesional hemifield. The results provide evidence for intrahemispheric prefrontal modulation of visual processing.     

Impairment of movement initiation and execution but not preparation in idiopathic dystonia

Imaging studies have reported impaired activation of the striatum and their frontal projection sites in dsytonia, areas which are considered to play a role in motor preparation, movement initiation and execution. The aim of this study was to investigate the processes of motor preparation, response initiation and execution in patients with idiopathic torsion dystonia (ITD). We assessed 12 patients with ITD and 12 age-matched controls on a number of reaction time (RT) tasks that differed in degree of motor preparation possible. Subjects performed a visual simple RT (SRT) task, an uncued four-choice reaction time (CRT) task and a fully precued four-choice RT task. A stimulus 1-stimulus 2 (S1-S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 ms (no warning signal or precue) 200 ms, 800 ms, 1,600 ms or 3,200 ms. The patients with ITD had significantly slower RTs and movement times than normals across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, precued CRTs were significantly faster than the uncued CRTs. The results show that while response initiation and execution are significantly slower in patients with ITD than normals, movement preparation is not quantitatively or qualitatively different. The results are discussed in relation to previous imaging, behavioural and electrophysiological studies and models of fronto-striatal dysfunction in ITD.     

Testing asymmetries in noncognate translation priming: Evidence from RTs and ERPs

In this study, English–French bilinguals performed a lexical decision task while reaction times (RTs) and event related potentials (ERPs) were measured to L2 targets, preceded by noncognate L1 translation primes versus L1 unrelated primes (Experiment 1a) and vice versa (Experiment 1b). The prime–target stimulus onset asynchrony was 120 ms. Significant masked translation priming was observed, indicated by faster reaction times and a decreased N400 for translation pairs as opposed to unrelated pairs, both from L1 to L2 (Experiment 1a) and from L2 to L1 (Experiment 1b), with the latter effect being weaker (RTs) and less longer lasting (ERPs). A translation priming effect was also found in the N250 ERP component, and this effect was stronger and earlier in the L2 to L1 priming direction than the reverse. The results are discussed with respect to possible mechanisms at the basis of asymmetric translation priming effects in bilinguals.     

Electrophysiological Explorations of the Cause and Effect of Inhibition of Return in a Cue–Target Paradigm

Facilitation and inhibition of return (IOR) are, respectively, faster and slower responses to a peripherally cued target. In a spatially uninformative peripheral cueing task, facilitation is normally observed when the interval between the cue and target stimulus, the stimulus onset asynchrony (SOA), is shorter than 250 ms, while IOR is normally observed when an SOA greater than 250 ms is used. Since Posner and Cohen’s (Attention and performance X, 1984) seminal study, IOR has become an actively investigated component of orienting. In this study, using ERPs and the source localization algorithm, LORETA, we seek to examine the brain mechanisms involved in IOR by localizing the different stages of processing after the appearance of a cue that captures attention exogenously. Unlike previous ERP investigations of IOR, this study analyzes the neural activity (via EEG) produced in response to the cue, prior to the appearance of the target. Neural activations were approximately divided into three stages. In the early stage (110–240 ms), involved activations are in the prefrontal cortex, the bilateral intraparietal cortex, and the contralateral occipito-temporal cortex. In the middle stage (240–350 ms), activations are primarily found in the frontal cortex and the parietal cortex. In the late stage (350–650 ms), the main activations are in the occipito-parietal cortex, but unlike in the early stage, the activation areas have shifted to the hemisphere ipsilateral to the cued location. These findings indicate that IOR is related to both attentional and motor response processes and suggest that the time course of initial facilitation and IOR is concurrent and mediated by two neural networks. Building upon our results, electrophysiological, electroencephalographic, and behavioral results in the literature and extending previous spatial theories of IOR, we propose here a spatio-temporal theory of IOR based upon post-cue dynamics.     

Sport is not always healthy: Executive brain dysfunction in professional boxers

We measured ERPs of professional boxers in a Go/No‐Go task, comparing them to fencers and non‐athletes. Results showed that fencing improved attention and motor response control, but boxing did not. More strikingly, in boxers, as in brain trauma patients, the P3 component was delayed and reduced. The P3 delay of boxers was correlated with the amount of performed sport exercise. Furthermore, in terms of behavior, boxers showed increased intra‐individual variability and switch cost. Results were consistent with the hypothesis of specific impairment at the level of response inhibition processing. We suggest that this impairment is derived from the cumulative effect of blows to the head. The changes found in boxers suggest that ERPs and reaction times may be a tool for early detection of specific brain dysfunction.     

Interplay of neuronal processes during response inhibition: Results from a combined event-related potentials (ERPs)/transcranial magnetic stimulation (TMS) study on methylphenidate

The neuronal processes underlying response inhibition are often studied using either event-related potentials (ERPs) or by applying transcranial magnetic stimulation (TMS) to investigate excitatory and inhibitory processes in the motor system. We performed a more refined analysis of response inhibition by combining both approaches with the aim of identifying an interplay between ERPs and TMS parameters.During a go/nogo task, motor system excitability was measured using TMS single and double pulses and brain electrical activity was recorded in healthy adults (n = 14). Each participant completed two testing sessions, once on placebo and once on methylphenidate (double-blind, crossover design). Studying the effects of methylphenidate served as an example application for this combined approach.Developing regression models, inhibition-related TMS measures (e.g., short intracortical inhibition) and the contingent negative variation explained about 85% of the variance of the nogo-P3 under both MPH and placebo medication. The smaller the inhibitory effect in the motor system, the more terminal response control was required and the more resources were allocated for the evaluation of the inhibitory process, respectively, as indicated by a larger P3.Thus, an interplay between processes in the motor system (cortex) and control processes with sources in the prefrontal cortex and the anterior cingulate cortex (ACC) may take place, acting complementarily to facilitate a correct nogo-response.While ERPs rather represent initiation and monitoring of inhibitory processes and response control, motor inhibition may be best analyzed using TMS. A combined ERP/TMS analysis may allow for the development of distinct models concerning the interplay of processes involved in response inhibition.     

How to stop or change a motor response: Laplacian and independent component analysis approach

Response inhibition is an essential control function necessary to adapt one's behavior. This key cognitive capacity is assumed to be dependent on the prefrontal cortex and basal ganglia. It is unresolved whether varying inhibitory demands engage different control mechanisms or whether a single motor inhibitory mechanism is involved in any situation. We addressed this question by comparing electrophysiological activity in conditions that require stopping a response to conditions that require switching to an alternate response. Analyses of electrophysiological data obtained from stop-signal tasks are complicated by overlapping stimulus-related activity that is distributed over frontal and parietal cortical recording sites. Here, we applied Laplacian transformation and independent component analysis (ICA) to overcome these difficulties. Participants were faster in switching compared to stopping a response, but we did not observe differences in neural activity between these conditions. Both stop- and change-trials Laplacian transformed ERPs revealed a comparable bilateral parieto-occipital negativity around 180 ms and a frontocentral negativity around 220 ms. ICA results suggested an inhibition-related frontocentral component which was characterized by a negativity around 200 ms with a likely source in anterior cingulate cortex. The data provide support for the importance of posterior mediofrontal areas in inhibitory response control and are consistent with a common neural pathway underlying stopping and changing of a motor response. The methodological approach proved useful to distinguish frontal and parietal sources despite similar timing and the ICA approach allowed assessment of single-trial data with respect to behavioral data.     

Contributions from eye movement potentials to stimulus preceding negativity during anticipation of auditory stimulation

Cognitive anticipation of a stimulus has been associated with an ERP called "stimulus preceding negativity" (SPN). A new auditory delay task without stimulus-related motor activity demonstrated a prefrontal SPN, present during attentive anticipation of sounds with closed eyes, but absent during distraction of attention and during attention with fixed gaze. ERP maxima found near the eyes required examination of eye movement interference, wherefore six monopolar EOG electrodes were included. Similarities between ERPs and potentials evoked by voluntary eye movements with respect to spatial distribution and polarities of amplitudes around the eyes and over the frontal cortex suggested that, in the closed-eyes condition, small involuntary downward eye movements occurred during attentive anticipation of sounds. Analyses of single trials corroborated this interpretation. On this basis it is suggested that the SPN was caused by such eye movements.     

Prefrontal brain magnetic activity: effects of memory task demands

Changes in spatiotemporal profiles of brain magnetic activity were investigated in healthy volunteers as a function of varying demands for phonological storage of spoken pseudowords. Greater activity for the phonological memory task was restricted to the dorsolateral prefrontal cortex (DLPFC) in the left hemisphere. During performance of the memory task, activity was initially found in the left superior temporal gyrus (between 100 and 200 ms), followed by activity in the ventrolateral prefrontal, motor, and premotor cortices (between 200 and 300 ms). Activity in DLPFCs was first observed consistently across participants later, between 300 and 400 ms. The data are consistent with the purported role of posterior temporal cortices in phonological analysis and in the online storage of phonological information, the contribution of ventrolateral and motor processing areas in establishment and short-term maintenance of articulatory representations through rehearsal, and the role of DLPFCs in the executive control of the maintenance operation.     

Brain potentials index executive functions during random number generation

The generation of random sequences is considered to tax different executive functions. To explore the involvement of these functions further, brain potentials were recorded in 16 healthy young adults while either engaging in random number generation (RNG) by pressing the number keys on a computer keyboard in a random sequence or in ordered number generation (ONG) necessitating key presses in the canonical order. Key presses were paced by an external auditory stimulus to yield either fast (1 press/800 ms) or slow (1 press/1300 ms) sequences in separate runs. Attentional demands of random and ordered tasks were assessed by the introduction of a secondary task (key-press to a target tone). The P3 amplitude to the target tone of this secondary task was reduced during RNG, reflecting the greater consumption of attentional resources during RNG. Moreover, RNG led to a left frontal negativity peaking 140 ms after the onset of the pacing stimulus, whenever the subjects produced a true random response. This negativity could be attributed to the left dorsolateral prefrontal cortex and was absent when numbers were repeated. This negativity was interpreted as an index for the inhibition of habitual responses. Finally, in response locked ERPs a negative component was apparent peaking about 50 ms after the key-press that was more prominent during RNG. Source localization suggested a medial frontal source. This effect was tentatively interpreted as a reflection of the greater monitoring demands during random sequence generation.     

Preparatory ERPs in visual,auditory, and somatosensory discriminative motor tasks

Previous event-related potential (ERP) studies mainly from the present research group showed a novel component, that is, the prefrontal negativity (pN), recorded in visual-motor discriminative tasks during the pre-stimulus phase. This component is concomitant to activity related to motor preparation, that is, the Bereitschaftspotential (BP). The pN component has been reported in experiments based on the visual modality only; for other modalities (acoustic and/or somatosensory) the presence of the pN warrants further investigation. This study represents a first step toward this direction; indeed, we aimed at describing the pN and the BP components in discriminative response tasks (DRTs) for three sensory modalities. In experiment 1 ERPs were recorded in 29 adults in visual and auditory DRT; an additional group of 15 adults participated to a somatosensory DRT (experiment 2). In line with previous results both the pN and the BP were clearly detectable in the visual modality. In the auditory modality the prefrontal pN was not detectable directly; however, the pN could be derived by subtraction of separate EEG traces recorded in a “passive” version of the same auditory task, in which motor responses were not required. In the somatosensory modality both the pN and the BP were detectable, although with lower amplitudes with respect to other two sensory modalities. Overall, regardless of the sensory modality, anticipatory task-related pN and BP components could be detected (or derived by subtraction) over both the prefrontal and motor cortices. These results support the view that anticipatory processes share common components among sensory modalities.     

Missing the Target: the Neural Processing Underlying the Omission Error

The omissions are infrequent errors consisting in missing responses to the target stimuli. This is the first study aimed at investigating the brain activities associated with omissions in a decision-making task. We recorded event-related potentials (ERPs) in 12 subjects which reported a suitable number of omissions in a visual go/no-go task. We investigated both the pre- and post-stimulus brain activities associated with correct and omitted trials. The electrical neuroimaging technique (BESA) was adopted to extract the anterior insula (aIns) activity associated with the prefrontal P2 component (pP2) peaking about 300 ms after the stimulus and reflecting the stimulus–response mapping process. We found that omissions were predicted by a delayed onset (about half a second) of two pre-stimulus components, i.e. the prefrontal negativity (pN) and the Bereitschaftspotential (BP) associated with the top-down control and the motor preparation, respectively. Further, at the post-stimulus stage the omission trials were characterized by the suppression of the pP2 (and the aIns activity as measured by BESA). No differences between omission and correct trials were detected at the level of the P1 and N1 visual components, as well as the P3. These findings would suggest that omissions are attentional lapsebased errors, as indicated by the delayed brain preparation before the stimulus onset. The reduced cortical activity during the preparation phase did not affect the visual processing; in contrast the stimulus categorization process at the level of the anterior insula did not start at all, resulting in the inability to reach a decision.     

Differentiation of neuronal operations in latent components of event‐related potentials in delayed match‐to‐sample tasks

The goal of this study was to decompose ERPs into latent components associated with hypothetical processes of category discrimination, comparison to working memory and action‐related operations. In five variants of the delayed match‐to‐sample s1‐s2 task, instructions were varied for manipulation of the processes. The blind source separation was applied to the collection of ERPs. The category discrimination operation is attributed to three latent components with peak latencies of 130 to 170 ms, which are generated in different parts of the prestriate cortex. The comparison to working memory operation is attributed to a latent component that is generated in the temporal cortex and manifested in a positive deflection with a peak latency of 250 ms after s2. The category discrimination and comparison to working memory effects were dissociated spatially and temporally from attention and action selection effects.     

The ERP correlates of target checking are dependent upon the defining features of the prospective memory cues

In some contexts, prospective memory (PM) is thought to be dependent upon strategic monitoring of the environment for relevant cues. Behavioral data reveal that strategic monitoring is associated with slowing of response time for ongoing activity trials when a prospective component is added to the task, and functional imaging data reveal that monitoring is associated with recruitment of the anterior prefrontal cortex and other cortical structures. In the current study, event-related brain potentials (ERPs) were used to examine the neural correlates of target checking, one process underlying strategic monitoring. Consistent with previous research the behavioral data revealed a Stimulus Specific Interference Effect, wherein slowing of response time varied depending upon whether PM cues were words or nonwords. The ERP data also revealed that the neural correlates of target checking were sensitive to the defining features of the PM cues (i.e., were a word or nonword). When PM cues were words, the effect of target checking was associated with variation in ERP amplitude beginning around 100 ms after stimulus onset. In contrast, when PM cues were nonwords, the effect of target checking on the ERPs did not emerge until around 200 ms after stimulus onset. These data provide support for the multi-process view of PM by demonstrating that the pattern of neural recruitment related to target checking is sensitive to the defining characteristics of the PM cues.     

Visual attention task performance in Wistar and Lister hooded rats: response inhibition deficits after medial prefrontal cortex lesions

The prefrontal cortex has traditionally been implicated in a variety of cognitive processes, including memory, attention and decision making. The detection of effects of prefrontal cortex lesions on attention has been shown to depend on the procedure used to assess the attentional process. We therefore investigated the effects of lesions of the prefrontal cortex in two different visual attention tasks, i.e. a three-choice serial reaction time task involving sustained and divided attention processes and a visual timing task involving sustained attention and response inhibition processes. In two rat strains that are frequently used in behavioural analysis, i.e. albino Wistar rats and pigmented Lister Hooded rats, lesions of the medial prefrontal cortex caused a deterioration of performance in both tasks, although the effect lasted much longer in the visual timing task. This latter task proved to be especially sensitive to detect the consequences of medial prefrontal cortex lesions, consisting of a loss of both attention control and response inhibition. In both attention tasks, Wistar rats performed less accurate and made more anticipatory responses than Listers. Strain differences could not entirely be attributed to possible visual deficits in albinos, which was also evident when locomotor activity in an open field and food-motivated behaviour in a hoarding paradigm were assessed. Due to slower habituation rates, Lister rats were more active and displayed little food hoarding behaviour. In Wistar rats, hoarding was disrupted by medial prefrontal cortex lesions, showing the effectiveness of the lesion. The results indicate that, although different rat strains provide different baseline levels of behaviour for testing lesion- or drug-induced behavioural changes, lesions of the medial prefrontal cortex do not only disrupt sustained attention processes, but also induce a strong impairment in response inhibition in both Wistar and Lister rats.     

Source Localization of Early Stages of Face Processing

Summary: Recent studies using ERPs in face recognition revealed that face processing starts around 100 ms after stimulus onset, 70 ms earlier than suggested before. While the neural sources of the N170 component have repeatedly been found to be localized in the gyrus fusiformis and the inferior occipital cortex, sources have not yet been investigated for the P100 component during face processing. Therefore, we measured the ERPs elicited by faces and control stimuli in 72 subjects in order to localize the neural sources of both the P100 and the N170 component. We observed significantly higher P100 and N170 amplitudes to faces compared to control stimuli. LORETA source localization revealed significantly higher brain activity in the left and right gyrus fusiformis for the N170 component, with additional regions of increased brain activation in a parieto-temporal-occipital network. For the P100, faces activated the left and right gyrus fusiformis significantly stronger than control stimuli. This study reveals that the first step of face processing (about 100 ms after stimulus presentation) is localized in the gyrus fusiformis. The second step of face processing around 170 ms involves the gyrus fusiformis, with additional activation in a more distributed network, including the occipital cortex.     

The role of medial prefrontal cortex in context-specific inhibition during reversal learning of a visual discrimination

Rats with medial prefrontal cortex or sham lesions were trained on a visual discrimination task designed for the eight-arm radial maze. After reaching asymptotic performance on this task, both groups were divided into sub-groups that would experience reversal learning in the same or different context from original training. The results showed that both groups reversed in the different context had accelerated learning compared to the groups reversed in the same context. Reversal learning in rats with medial prefrontal cortex damage was faster than sham animals in the same context. These and other results from a transfer test suggest that the medial prefrontal cortex participates in the behavioral effects of a context-specific inhibitory association acquired during visual discrimination learning.     

Fos expression in the prefrontal cortex and nucleus accumbens following exposure to retrospective timing tasks

The dorsal striatum and prefrontal cortex have been implicated in interval timing. We examined whether performance of temporal discrimination tasks is associated with increased neuronal activation in these areas, as revealed by Fos expression, a marker for neuronal activation. In Experiment 1, rats were trained on a discrete-trials temporal discrimination task in which a light (22 cd/m2) was presented for a variable time, t (2.5-47.5 s), after which levers A and B were presented. A response on lever A was reinforced if t < 25 s, and a response on lever B was reinforced if t > 25 s. A second group was trained on a light-intensity discrimination procedure, in which a light of variable intensity, i (3.6-128.5 cd/m2) was presented for 25 s. A response on lever A was reinforced if i < 22 cd/m2, and a response on lever B was reinforced if i > 22 cd/m2. In Experiment 2, bisection procedures were used to assess temporal (200-800 ms, 22 cd/m2) and light-intensity (3.6-128.5 cd/m2, 400 ms) discrimination. The increase in proportional choice of lever B as a function of stimulus duration or intensity conformed to a two-parameter logistic equation. Fos expression in the prefrontal cortex and nucleus accumbens was higher in rats performing temporal discrimination tasks than in those performing light-intensity discrimination tasks, indicating greater neuronal activation in these areas during temporal discrimination tasks. Fos expression in the dorsal striatum did not differ between rats performing temporal and light-intensity discrimination tasks. These results suggest that the prefrontal cortex and nucleus accumbens are involved in temporal discrimination.     

Response preparation and inhibition: the role of the cortical sensorimotor beta rhythm

Paradigms requiring either a GO or a NO-GO response are often used to study the neural mechanisms of response inhibition. Here this issue is examined from the perspective of event-related beta (14-30 Hz) oscillatory activity. Two macaque monkeys performed a task that began with a self-initiated lever depression and maintenance (sustained motor output) and required a visual pattern discrimination followed by either a lever release (GO) or continued lever-holding (NO-GO) response. Analyzing simultaneous local field potentials (LFPs) from primary somatosensory, frontal motor, and posterior parietal cortices, we report two results. First, beta oscillation desynchronized shortly after stimulus presentation, the onset of which was approximately the same for both the GO and NO-GO conditions ( approximately 110 ms). Since it is well known that beta desynchronization is a reliable indicator of movement preparation, this result suggests that early motor preparation took place in both conditions. Second, following the GO/NO-GO decision ( approximately 190 ms), beta activity rebounded significantly ( approximately 300 ms) only in the NO-GO condition. Coherence and Granger causality measures revealed that the dynamical organization of the rebounded beta network was similar to that existing during the sustained motor output prior to stimulus onset. This finding suggests that response inhibition led to the restoration of the sensorimotor network to its prestimulus state.