To Head or to Heed? Beyond the Surface of Selective Action Inhibition: A Review

To head rather than heed to temptations is easier said than done. Since tempting actions are often contextually inappropriate, selective suppression is invoked to inhibit such actions. Thus far, laboratory tasks have not been very successful in highlighting these processes. We suggest that this is for three reasons. First, it is important to dissociate between an early susceptibility to making stimulus-driven impulsive but erroneous actions, and the subsequent selective suppression of these impulses that facilitates the selection of the correct action. Second, studies have focused on mean or median reaction times (RT), which conceals the temporal dynamics of action control. Third, studies have focused on group means, while considering individual differences as a source of error variance. Here, we present an overview of recent behavioral and imaging studies that overcame these limitations by analyzing RT distributions. As will become clear, this approach has revealed variations in inhibitory control over impulsive actions as a function of task instructions, conflict probability, and between-trial adjustments (following conflict or following an error trial) that are hidden if mean RTs are analyzed. Next, we discuss a selection of behavioral as well as imaging studies to illustrate that individual differences are meaningful and help understand selective suppression during action selection within samples of young and healthy individuals, but also within clinical samples of patients diagnosed with attention deficit/hyperactivity disorder or Parkinson's disease

It wasn't me! Motor activation from irrelevant spatial information in the absence of a response

Embodied cognition postulates that perceptual and motor processes serve higher-order cognitive faculties like language. A major challenge for embodied cognition concerns the grounding of abstract concepts. Here we zoom in on abstract spatial concepts and ask the question to what extent the sensorimotor system is involved in processing these. Most of the empirical support in favor of an embodied perspective on (abstract) spatial information has derived from so-called compatibility effects in which a task-irrelevant feature either facilitates (for compatible trials) or hinders (in incompatible trials) responding to the task-relevant feature. This type of effect has been interpreted in terms of (task-irrelevant) feature-induced response activation. The problem with such approach is that incompatible features generate an array of task relevant and irrelevant activations [e.g., in primary motor cortex (M1)], and lateral hemispheric interactions render it difficult to assign credit to the task-irrelevant feature per se in driving these activations. Here, we aim to obtain a cleaner indication of response activation on the basis of abstract spatial information. We employed transcranial magnetic stimulation (TMS) to probe response activation of effectors in response to semantic, task-irrelevant stimuli (i.e., the words left and right) that did not require an overt response. Results revealed larger motor evoked potentials (MEPs) for the right (left) index finger when the word right (left) was presented. Our findings provide support for the grounding of abstract spatial concepts in the sensorimotor system

When awareness gets in the way : reactivation aversion effects resolve the generality/specificity paradox in sensorimotor interference tasks

Interference tasks combining different distractor types usually find that between-trial adaptations (congruency sequence effects [CSEs]) do not interact with each other, suggesting that sensorimotor control is domain-specific. However, within each trial, different distractor types often do interact, suggesting that control is domain-general. The present study presents a solution to this apparent paradox. In 3 experiments, testing 130 participants in total, we (a) confirm the simultaneous presence of between-trial domain-specific (noninteracting) CSEs and within-trial “domain-general” interactions in a fully factorial hybrid prime-Simon design free of repetition or contingency confounds; (b) demonstrate that the within-trial interaction occurs with supraliminal, but not with subliminal primes; and (c) show that it is disproportionately enlarged in older adults. Our findings suggest that whereas interference (priming and Simon) effects and CSEs reflect direct sensorimotor control, the within-trial interaction does not reflect sensorimotor control but “confusion” at higher-level processing stages (reactivation aversion effect [RAE])

Controlling Your Impulses: Electrical Stimulation of the Human Supplementary Motor Complex Prevents Impulsive Errors

To err is human. However, an inappropriate urge does not always result in error. Impulsive errors thus entail both a motor system capture by an urge to act and a failed inhibition of that impulse. Here we show that neuromodulatory electrical stimulation of the supplementary motor complex in healthy humans leaves action urges unchanged but prevents them from turning into overt errors. Subjects performed a choice reaction-time task known to trigger impulsive responses, leading to fast errors that can be revealed by analyzing accuracy as a function of poststimulus time. Yet, such fast errors are only the tip of the iceberg: electromyography (EMG) revealed fast subthreshold muscle activation in the incorrect response hand in an even larger proportion of overtly correct trials, revealing covert response impulses not discernible in overt behavior. Analyzing both overt and covert response tendencies enables to gauge the ability to prevent these incorrect impulses from turning into overt action errors. Hyperpolarizing the supplementary motor complex using transcranial direct current stimulation (tDCS) preserves action impulses but prevents their behavioral expression. This new combination of detailed behavioral, EMG, and tDCS techniques clarifies the neurophysiology of impulse control, and may point to avenues for improving impulse control deficits in various neurologic and psychiatric disorders

The negative compatibility effect: A case for self-inhibition

In masked priming, a briefly presented prime stimulus is followed by a mask, which in turn is followed by the task-relevant target. Under certain conditions, negative compatibility effects (NCNCEs) occur, with impaired performance on compatible trials (where prime and target indicate the same response) relative to incompatible trials (where they indicate opposite responses). However, the exact boundary conditions of NCEs, and hence the functional significance of this effect, are still under discussion. In particular, it has been argued that the NCE might be a stimulus-specific phenomenon of little general interest. This paper presents new findings indicating that the NCE can be obtained under a wider variety of conditions, suggesting that it reflects more general processes in motor control. In addition, evidence is provided suggesting that prime identification levels in forced choice tasks – usually employed to estimate prime visibility in masked prime tasks – are affected by prior experience with the prime (Exp. 1) as well as by direct motor priming (Exp. 2 & 3)

The Simon Effect in Rats: A Comparative Study on Conflict and Error Processing Using Electrophysiology and Functional µPET Imaging

Both humans and animals have the ability to learn from past experience and to adapt their behavior to resolve future conflicts faster or avoid them entirely. Conflicts in spatial stimulus–response tasks occur when the origin of the stimulus and the response area differ in location. Those conflicts lead to increased error rates, reaction times (RT) and movement time (MT) which has been termed Simon effect. A model of dual route processing (automatic and intentional) of stimulus features has been proposed, predicting response conflicts if the two routes are incongruent. Although there are various theories related to underlying neuronal mechanisms, it is commonly assumed that the anterior cingulate cortex (ACC) plays a crucial role in conflict and error processing. The Simon task is a neuropsychological interference task commonly used to study performance monitoring. Interestingly, the resulting conflict is far from uniquely human, as it has also been observed in pigeons, rats, and monkeys. On a neural level, the on-going monitoring of correct and incorrect behavior appears in the form of eventrelated potentials (ERPs). More precisely, the error-related negativity (ERN/Ne) component of the resulting ERP, assumed to be generated in the ACC, is suggested to reflect conflict and error monitoring. Unfortunately, there is often little correspondence between human and animal studies. On this account the present study uses a modified auditory Simon task to investigate a) the anatomical basis, b) the conflict- and errorrelated electrophysiological correlates and c) the performance monitoring from a crossspecies point of view. By using positron emission tomography (PET) in combination with the metabolic tracer [18F]fluorodeoxyglucose, which accumulates in metabolically active brain cells during the behavioral task, we first aim at identifying relevant brain areas in a rat model of the Simon task. According to the dual route model, brain areas involved in conflict processing are supposed to be activated when automatic and intentional route lead to different responses (dual route model). Results show specific activation patterns for different task settings coherent with the dual route model. Our data suggest that the rat motor cortex (M1) may be part of the automatic route or involved in its facilitation, while premotor (M2) and prelimbic areas, as well as the ACC appear to be essential for inhibiting the incorrect, automatic response, indicating conflict monitoring functions. Interestingly, our findings remarkably fit the pattern of activated regions reported during conflict processing in humans. To further support our findings, we measured local field potentials (LFP) from electrodes centered in the rat ACC. LFPs showed a negative slow wave less pronounced for errors at about 250-400 ms after reaction. Stimulus-locked data revealed a compatibility effect in rats, with a negative slow wave with onset in the latency range of the reaction. To finally compare these results with a human setup, we also developed a translational task for humans. In both species, similar behavioral effects were found, including an increase in error rate, RT and MT. In humans, although no difference in EEG amplitude between errors and hits in the ERN latency range was found, a pronounced error positivity between 250 and 350 ms after reaction was seen. Humans surprisingly demonstrated a stronger negativity for compatible compared to incompatible trials. Similarly to rats, this effect started at about the time of reaction time. Thus, both species (i) showed electrophysiological responses differentiating between errors and correct in a similar latency range, (ii) demonstrated a valid occurrence of the Simon effect and seem to pursue similar response strategies, both in terms of RT and MT and (iii) displayed sustained differences in the modulation of the ERP depending on correct or incorrect responses starting at the time of response and prior to reward/no reward. It is thus tempting to speculate that the underlying cognitive error processing mechanisms are highly similar across species. In conclusion, we found remarkable behavioral, electrophysiological and functional similarities between rat and human conflict and error processing. Our paradigm offers a new approach in integrative, cross-species research and provides a useful rodent model for investigating performance monitoring