Readiness Potential Research Articles

Influence of pain on motor preparation in the human brain.

The protective function of pain depends on appropriate motor responses to avoid injury and promote recovery. The preparation and execution of motor responses is thus an essential part of pain. However, it is not yet fully understood how pain and motor processes interact in the brain. Here we used electroencephalography to investigate the effects of pain on motor preparation in the human brain. Twenty healthy human participants performed a motor task in which they performed button presses to stop increasingly painful thermal stimuli when they became intolerable. In another condition, participants performed button presses without concurrent stimulation. The results show that the amplitudes of preparatory event-related desynchronizations at alpha and beta frequencies did not differ between conditions. In contrast, the amplitude of the preparatory readiness potential was reduced when a button press was performed to stop a painful stimulus compared with a button press without concomitant pain. A control experiment with nonpainful thermal stimuli showed a similar reduction of the readiness potential when a button press was performed to stop a nonpainful thermal stimulus. Together, these findings indicate that painful and nonpainful thermal stimuli can similarly influence motor preparation in the human brain. Pain-specific effects on motor preparation in the human brain remain to be demonstrated.NEW & NOTEWORTHY Pain is inherently linked to motor processes, but the interactions between pain and motor processes in the human brain are not yet fully understood. Using electroencephalography, we show that pain reduces movement-preparatory brain activity. Further results indicate that this effect is not pain specific but independent of the modality of stimulation.

Pre-movement planning processes in people with congenital mirror movements

ObjectivePre-movement processes were investigated in people with Congenital mirrormovement (CMM), a rare disorder in which bilateral movement (mirroring) occurs in the upper distal extremities (primarily the hands and fingers) during intended unilateral movements. Abnormal density of ipsilateral corticospinal projections is an established hallmark of CMM. This study tested whether the Lateralised Readiness Potential (LRP), which reflects movement planning and readiness, is also abnormal in people with CMM. MethodsTwenty-eight neurologically-normal controls and 8 people with CMM were tested on a unimanual Go/No-go task while electroencephalography (EEG) was recorded to assess the LRP. ResultsNo significant group differences were found in reaction time (RT). However, significantly smaller LRP amplitudes were found, on average, in the CMM group compared to Controls at central-motor (C3,C4) sites in stimulus-locked and response-locked epochs; similar group differences were also found at further frontal sites (F3,F4) during response-locked epochs. ConclusionsAbnormal brain activity in pre-movement processes associated with response planning and preparation is present in people with CMM. SignificanceAberrant bilateral activity during pre-movement processes is clearly implicated; whether part of the etiology of CMM, or as a mechanism of neuro-compensation, is not yet known.

Bereitschaftspotential preceding eyelid blinks in Parkinson's disease.

Ten PD patients in stages 1 and 2 of the Hoehn & Yahr classification were compared to 18 healthy controls. Artifact-free EEG segments of two seconds preceding the onset of the blink potential were averaged and analyzed, and the statistical significance of the measured amplitudes were evaluated by analysis of variance models. The presence of a BP in the PD patients was demonstrated. The mean amplitudes at 0 ms were respectively 0.6 µV and 3.3 µV for the BP patients and the normal controls, respectively. The BP amplitudes were significantly smaller in PD patients than normal participants. The amplitudes of the BP were not modified by levodopa.

Maternal blood contamination of collected cord blood can be identified using DNA methylation at three CpGs

BackgroundCord blood is a commonly used tissue in environmental, genetic, and epigenetic population studies due to its ready availability and potential to inform on a sensitive period of human development. However, the introduction of maternal blood during labor or cross-contamination during sample collection may complicate downstream analyses. After discovering maternal contamination of cord blood in a cohort study of 150 neonates using Illumina 450K DNA methylation (DNAm) data, we used a combination of linear regression and random forest machine learning to create a DNAm-based screening method. We identified a panel of DNAm sites that could discriminate between contaminated and non-contaminated samples, then designed pyrosequencing assays to pre-screen DNA prior to being assayed on an array.ResultsMaternal contamination of cord blood was initially identified by unusual X chromosome DNA methylation patterns in 17 males. We utilized our DNAm panel to detect contaminated male samples and a proportional amount of female samples in the same cohort. We validated our DNAm screening method on an additional 189 sample cohort using both pyrosequencing and DNAm arrays, as well as 9 publically available cord blood 450K data sets. The rate of contamination varied from 0 to 10% within these studies, likely related to collection specific methods.ConclusionsMaternal blood can contaminate cord blood during sample collection at appreciable levels across multiple studies. We have identified a panel of markers that can be used to identify this contamination, either post hoc after DNAm arrays have been completed, or in advance using a targeted technique like pyrosequencing.

The amount of recent action-outcome coupling modulates the mechanisms of the intentional binding effect: A behavioral and ERP study.

Our everyday interactions depend on the ability to maintain a feeling of control over our bodily actions, that is, the sense of agency. The intentional binding effect - a perceived temporal shortening between voluntary actions and sensory outcomes - has been shown to implicitly measure agency. We investigated the effect's underlying mechanisms: prediction and retrospective inference. First, long-term and recent action-outcome coupling were compared. Second, brain activity was recorded to uncover the neural correlates of the two mechanisms. Our results show that the recent accumulation of action-outcome coupling, but not that of a long-term accumulation, is correlated with the binding effect of actions and accounts for both mechanisms. Temporal action binding was reflected in both the readiness potential and the auditory evoked potential. The results shed new light on our understanding of the influence that immediate context of an action has on its temporal binding and the neural substrate of human agency.

Early response activation in repetition priming: an LRP study

According to recent interpretations of repetition priming, response codes are automatically bound to a stimulus and retrieved during successive presentations of the stimulus, hence, affecting its current processing. Despite a solid corpus of behavioural evidence in line with this interpretation, electrophysiological studies have reported contrasting results regarding the nature and the timing of response code retrieval. The present experiment aims to establish at which stage of information processing decision and action codes are retrieved in repetition priming. To this end, the lateralized readiness potential (LRP) was analysed for primed faces to monitor motor cortex activity related to response preparation. Congruent and incongruent responses were obtained by having identical or reversed tasks between study and test. Primed stimuli presented LRP activations with opposite polarities for the two congruency conditions in the time-window 250–300 ms, indicating response-related motor cortex activity resulting from the retrieval of correct and incorrect decision/action codes for congruent and incongruent trials, respectively. This result indicates that decision and action codes bound to a primed stimulus are retrieved at early stages of stimulus processing and that these codes are transmitted to the motor cortex.

Role of multisensory stimuli in vigilance enhancement- a single trial event related potential study.

Development of interventions to prevent vigilance decrement has important applications in sensitive areas like transportation and defence. The objective of this work is to use multisensory (visual and haptic) stimuli for cognitive enhancement during mundane tasks. Two different epoch intervals representing sensory perception and motor response were analysed using minimum variance distortionless response (MVDR) based single trial ERP estimation to understand the performance dependency on both factors. Bereitschaftspotential (BP) latency L3 (r=0.6 in phase 1 (visual) and r=0.71 in phase 2 (visual and haptic)) was significantly correlated with reaction time as compared to that of sensory ERP latency L2 (r=0.1 in both phase 1 and phase 2). This implies that low performance in monotonous tasks is predominantly dependent on the prolonged neural interaction with the muscles to initiate movement. Further, negative relationship was found between the ERP latencies related to sensory perception and Bereitschaftspotential (BP) and occurrence of epochs when multisensory cues are provided. This means that vigilance decrement is reduced with the help of multisensory stimulus presentation in prolonged monotonous tasks.

A robust beamforming approach for early detection of readiness potential with application to brain-computer interface systems.

Early detection of intention to move, at self-paced voluntary movements from the activities of neural current sources on the motor cortex, can be an effective approach to brain-computer interface (BCI) systems. Achieving high sensitivity and pre-movement negative latency are important issues for increasing the speed of BCI and other rehabilitation and neurofeedback systems used by disabled and stroke patients and helps enhance their movement abilities. Therefore, developing high-performance extractors or beamformers is a necessary task in this regard. In this paper, for the sake of improving the beamforming performance in well reconstruction of sources of readiness potential, related to hand movement, one kind of surface spatial filter (spherical spline derivative on electrode space) and the linearly constrained minimum variance (LCMV) beamformer are utilized jointly. Moreover, in order to achieve better results, the real head model of each subject was created, using individual head MRI, and was used in beamformer algorithm. Also, few optimizations were done on reconstructed source signal powers to help our template matching classifier with detection of movement onset for five healthy subjects. Our classification results show an average true positive rate (TPR) of 77.1% and 73.1%, false positive rate (FPR) of 28.96% and 28.74% and latency of -512.426 ±396. 7ms and - 360.29 ±252. 16 ms from signals of current sources of motor cortex and sensor space respectively. It can be seen that the proposed method has reliable sensitivity and is faster in prediction of movement onset and more reliable to be used for online BCI in future.

The Age Effects on the Cognitive Processes of Intention-Based and Stimulus-Based Actions: An ERP Study.

The functional decline in action among older adults is caused not only by physical weakness but also by cognitive decline. In this study, we aimed to compare the cognitive effects of age between intention-based and stimulus-based action modes electrophysiologically. Because age-related declines in cognitive function might proceed distinctly according to specific action modes and processes, four specific cognitive processes, action-effect binding, stimulus-response linkage, action-effect feedback control, and effect-action retrieval, were investigated. We recorded event-related potentials (ERPs) during a modified acquisition-test paradigm in young (mean age = 21, SD = 2) and old (mean age = 69, SD = 5) groups. A temporal bisection task and a movement pre-cuing task were used during the acquisition and test phases, respectively. Using ERP indices including readiness potential (RP), P3, N2 and contingent negative variation (CNV) to identify these four specific processes for the two action modes, we revealed the effects of age on each ERP index. The results showed similar patterns of waveforms but consistently decreasing amplitudes of all four ERP indices in the old age group compared with the young age group, which indicates not only generally declining functions of action preparation in older adults but also age effects specific to the action modes and processes that might otherwise be mixed together under confounding experimental conditions. Particularly, an interference effect indexed by the differences in the amplitudes of CNV between congruent and incongruent tasks was observed in the young age group, which is consistent with previous behavioral reports. However, this effect was absent in the old age group, indicating a specific age-related deficit in the effect-action retrieval process of intention-based action, which might be caused by an age-related deficit in associative memory. In sum, this study investigated the cognitive processes of two action modes from a developmental perspective and suggests the importance of adding associative memory training to interventions for older adults with the aim of improving intention-based action.

The role of affective evaluation in conflict adaptation: An LRP study

Conflict between incompatible response tendencies is typically followed by control adjustments aimed at diminishing subsequent conflicts, a phenomenon often called conflict adaptation. Dreisbach and Fischer (2015, 2016) recently proposed that it is not the conflict per se but the aversive quality of a conflict that originally motivates this kind of sequential control adjustment. With the present study we tested the causal role of aversive signals in conflict adaptation in a more direct way. To this end, after each trial of a vertical Simon task participants rated whether they experienced the last trial as rather pleasant or unpleasant. Conflict adaptation was measured via lateralized readiness potentials as a measure of early motor-related activation that were computed on the basis of event-related brain potentials. Results showed the typical suppression of automatic response activation following trials rated as unpleasant, whereas suppression was relaxed following trials rated as pleasant. That is, sequential control adaptation was not based on previous conflict but on the subjective affective experience. This is taken as evidence that negative affect even in the absence of actual conflict triggers subsequent control adjustments.

A Ternary Brain-Computer Interface Based on Single-Trial Readiness Potentials of Self-initiated Fine Movements: A Diversified Classification Scheme.

In recent years, the readiness potential (RP), a type of pre-movement neural activity, has been investigated for asynchronous electroencephalogram (EEG)-based brain-computer interfaces (BCIs). Since the RP is attenuated for involuntary movements, a BCI driven by RP alone could facilitate intentional control amid a plethora of unintentional movements. Previous studies have mainly attempted binary single-trial classification of RP. An RP-based BCI with three or more states would expand the options for functional control. Here, we propose a ternary BCI based on single-trial RPs. This BCI classifies amongst an idle state, a left hand and a right hand self-initiated fine movement. A pipeline of spatio-temporal filtering with per participant parameter optimization was used for feature extraction. The ternary classification was decomposed into binary classifications using a decision-directed acyclic graph (DDAG). For each class pair in the DDAG structure, an ordered diversified classifier system (ODCS-DDAG) was used to select the best among various classification algorithms or to combine the results of different classification algorithms. Using EEG data from 14 participants performing self-initiated left or right key presses, punctuated with rest periods, we compared the performance of ODCS-DDAG to a ternary classifier and four popular multiclass decomposition methods using only a single classification algorithm. ODCS-DDAG had the highest performance (0.769 Cohen's Kappa score) and was significantly better than the ternary classifier and two of the four multiclass decomposition methods. Our work supports further study of RP-based BCI for intuitive asynchronous environmental control or augmentative communication.

Time-based expectations entail preparatory motor activity

Human behavior is guided by expectations that facilitate perception of upcoming events or reaction to them. In natural settings expectations are often implicitly based on time, e.g., when making a phone call one would expect to hear either a person answering (earlier) or a voicemail greeting (later). We investigated how time-based expectations can improve performance in the absence of explicit prior information on the pending stimulus or the associated response. Visual stimuli were presented after a characteristic short or long foreperiod, and a forced-choice categorization using either the left or the right hand was required. The electroencephalogram (EEG) revealed a decrease in central 9–12 Hz power over the course of the trial. Moreover, lateralized pre-motor potentials were observed which changed polarity after the short foreperiod. At stimulus onset, amplitudes of pre-motor potentials co-varied with performance, so that higher (more negative) amplitudes were associated with slower responses to unexpected targets. Altogether, the results suggest that implicit time-based expectations entail effector-specific preparatory brain activity, which is inhibited until the expected onset time of the event. Thus, time-based expectations prepare for action.

Increased Gamma Connectivity in the Human Prefrontal Cortex during the Bereitschaftspotential.

The Bereitschaftspotential (BP) is a slow negative cortical potential preceding voluntary movement. Since movement preparation is dependent upon the synchronous activity of a variety of neurons, BP may develop through the exchange of information among motor-related neurons. However, the relationship between BP and information flow is not yet well-known. In the present study, we aimed to investigate how the connectivity in the prefrontal cortex (PFC) changes during the occurrence of BP. Electrocorticography (ECoG) was recorded in five patients with epilepsy. The subjects performed self-paced hand grasping. We compared the intraregional connectivity between PFC and non-PFC regions using partial directed coherence. In the PFC, the connectivity of beta and gamma bands in the BP period increased by an average of 24.4% compared with the baseline connectivity. Conversely, gamma connectivity in non-PFC regions decreased by 31.4%. Moreover, the intraregional connectivity in the PFC increased according to the stage of BP. The increased gamma band connectivity in the PFC implies that the increased communication among neurons in the PFC is associated with development of BP. Intraregional connectivity as one of the factors involved in voluntary movement may reflect the activation of brain networks related to movement preparation in PFC.

The Detection of the Rise to Stand Movements Using Bereitschaftspotential from Scalp Electroencephalography (EEG)

The negative-going Bereitschaftspotential (BP) is associated with the preparation and execution of dynamic movement. So far, BP for simple movements involving either the upper or the lower body has...

Neural Correlates of Semantic Prediction and Resolution in Sentence Processing.

Most brain-imaging studies of language comprehension focus on activity following meaningful stimuli. Testing adult human participants with high-density EEG, we show that, already before the presentation of a critical word, context-induced semantic predictions are reflected by a neurophysiological index, which we therefore call the semantic readiness potential (SRP). The SRP precedes critical words if a previous sentence context constrains the upcoming semantic content (high-constraint contexts), but not in unpredictable (low-constraint) contexts. Specific semantic predictions were indexed by SRP sources within the motor system—in dorsolateral hand motor areas for expected hand-related words (e.g., “write”), but in ventral motor cortex for face-related words (“talk”). Compared with affirmative sentences, negated ones led to medial prefrontal and more widespread motor source activation, the latter being consistent with predictive semantic computation of alternatives to the negated expected concept. Predictive processing of semantic alternatives in negated sentences is further supported by a negative-going event-related potential at ∼400 ms (N400), which showed the typical enhancement to semantically incongruent sentence endings only in high-constraint affirmative contexts, but not to high-constraint negated ones. These brain dynamics reveal the interplay between semantic prediction and resolution (match vs error) processing in sentence understanding.SIGNIFICANCE STATEMENT Most neuroscientists agree on the eminent importance of predictive mechanisms for understanding basic as well as higher brain functions. This contrasts with a sparseness of brain measures that directly reflects specific aspects of prediction, as they are relevant in the processing of language and thought. Here we show that when critical words are strongly expected in their sentence context, a predictive brain response reflects meaning features of these anticipated symbols already before they appear. The granularity of the semantic predictions was so fine grained that the cortical sources in sensorimotor and medial prefrontal cortex even distinguished between predicted face- or hand-related action words (e.g., the words “lick” or “pick”) and between affirmative and negated sentence meanings.

Prepotent motor activity and inhibitory control demands in different variants of the go/no-go paradigm.

Inhibitory control enables humans to stop prepotent motor activity, and is commonly studied using go/no-go or stop-signal tasks. In stop-signal tasks, prepotent motor activity is elicited by delaying stop signals relative to go signals. In go/no-go tasks, however, trials include only one signal-go or no-go. Hence, prepotent motor activity has to be ensured differently-for example, by using rare no-go trials and short trial durations. However, a literature survey shows that ∼40% of studies use equiprobable go/no-go trials and ∼20% use long stimulus-stimulus intervals (> 4 s). It is unclear whether such slow-paced, equiprobable go/no-go tasks elicit prepotent motor activity and probe inhibitory control. We recorded EEG during four go/no-go tasks, varying in no-go probability and trial duration. We quantified prepotent motor activity on successfully inhibited no-go trials using the lateralized readiness potential. Only fast-paced go/no-go tasks with rare no-go trials reliably evoked such activity. We then used a stop-signal task and independent component analysis to isolate an established neural signature of inhibitory control, and investigated this signature's activity across the go/no-go tasks. Across tasks, increased prepotent motor activity on individual no-go trials was accompanied by greater frontocentral P3 amplitudes, confirming it as an index of inhibition. Crucially, this inhibition-related activity showed a 75% reduction in slow-paced, equiprobable go/no-go tasks compared to fast-paced, rare no-go versions. Therefore, since many common go/no-go task configurations do not reliably evoke prepotent motor activity, their inhibitory requirements are greatly reduced. This has major implications for the usage of go/no-go tasks in psychological experiments.

Changes in the stimulus-preceding negativity and lateralized readiness potential during reinforcement learning.

According to reinforcement learning theory, dopamine-dependent anticipatory processes play a critical role in learning from action outcomes such as feedback or reward. To better understand outcome anticipation, we examined variation in slow cortical potentials and assessed their changes over the course of motor-skill acquisition. Healthy young adults learned a series of precisely timed, key press sequences. Feedback was delivered at a delay of either 2.5 or 8 s, to encourage use of either the striatally mediated, habit learning system or the hippocampus-dependent, episodic memory system, respectively. During the 2.5-s delay, the stimulus-preceding negativity (SPN) was shown to decline in amplitude across trials, confirming previous results from a perceptual categorization task (Morís, Luque, & Rodríguez-Fornells, 2013). This falsifies the hypothesis that SPN reflects specific outcome predictions, on the assumption that the ability to make such predictions should improve as a task is mastered. An SPN was also evident during the 8-s delay, but it increased in amplitude across trials. At the conclusion of the 8-s but not the 2.5-s prefeedback interval, a reversed-polarity lateralized readiness potential (LRP) was noted. It was suggested that this might indicate maintenance of an action representation for comparison with the feedback display. If so, this would constitute the first direct psychophysiological evidence for a popular hypothetical construct in quantitative models of reinforcement learning, the so-called eligibility trace.

The 'Innovation Radar': A New Policy Tool to Support Innovation Management

Introduction: In this paper we describe a new policy tool to support innovation management and increase the innovation impact of research and innovation programs. With nearly 80 billion Euro over a period of 7 years (2014-2020), Horizon 2020 is the largest ever publicly funded research and innovation program in the European Union. Cutting-edge technologies are being developed within the program and a significant part of these technologies could be commercialized. But not all technologies and innovation with commercial potential actually reach the market. The questions are why, and what additional actions are needed on the part of the policy makers to address this problem? To this effect the European Commission developed and successfully tested an in the part of the program that focuses on Information and Communication Technologies (ICT) and their applications. The Innovation Radar focuses on the identification of high-potential innovations and the key organizations developing these innovations in the program. Our paper presents the Innovation Radar (IR) methodology which was developed by our team jointly with the team from European Commission's Directorate General for Communications Networks, Content & Technology that manages the ICT part of Horizon 2020. The paper then presents the results of its pilot application. Approach and Data: The IR methodology is based on assessment of innovation and new technology ventures. The IR uses two composite indicators aiming at capturing the heterogeneity in innovation activities and innovators across projects. First, the Potential Indicator provides a holistic view of the innovation potential of projects. Second, the Innovator Capacity Indicator is capturing the innovator's capacity in conducting innovation activities. Each of these two indicators includes several sub-indicators. The IR characterizes innovations with respect to their technical readiness, innovation management and market potential. For innovators - usually researchers - it delivers information on their ability to innovate and their environment. We applied the OECD/JRC methodology to construct composite indicators. The data used in the paper was collected via a structured questionnaire during the IR pilot phase from May 2014 to January 2015 on the occasion of annual projects reviews conducted by external experts (projects typically run for 3 years). Results overview: Out of the 2600 projects running at the time, the IR scanned 280 projects. Over 500 innovations with market potential were identified, or on average nearly two new or substantially improved products or services within each project. The IR pilot phase provided in particular evidence that while innovators demonstrate high levels of technological expertise, they usually pay less attention to the business-related dimensions. The most common needs expressed by innovators are partnerships with other companies, business plan development and expanding to more markets. They less frequently mention needs for incubation, investment training, or participation in accelerators. More than 40% of the innovators mention lack of financing as a major external bottleneck to innovation exploitation, although interestingly only 5% have sought or are planning to seek private or public funding. Regulation and IPR issues are also considered important bottlenecks. Impact of the IR covers 3 main dimensions: 1. Providing structured and quantified intelligence on innovations and innovators in publicly funded projects and use this intelligence to design customized support to those projects and organizations. 2. Creating bridges between innovative organizations/projects and external stakeholders such as venture capitalists. 3. Providing feedback on the effectiveness of the program in funding innovation, thereby enabling the policy makers to improve its impact. Having completed the IR pilot phase and analyzed the collected information, it can be concluded that, for the first time, policy makers and project participants can obtain up-to-date structured information on the innovative output of the projects, and that the IR demonstrated its real potential as a policy tool to support innovation management.

Motor planning and performance in transitive and intransitive gesture execution and imagination: Does EEG (RP) activity predict hemodynamic (fNIRS) response?

The interplay between neural structures and processes underlying motor planning and proper movement initiation and guidance is still a matter of debate. The present study aimed at investigating cortical correlates of motor planning and production when execution and imagery of real-life gestures are performed, with an additional focus on potential specificities of meaningful transitive/intransitive gestures. Electrophysiological (Readiness Potential – RP) and functional near-infrared spectroscopy (fNIRS) measures were analyzed to investigate the relationship between processes supporting action planning, execution and imagination. Participants were instructed to observe videos presenting various gestures and then to execute or to imagine them. We observed comparable RP before gesture execution and imagination, with a “facilitation effect” of transitive gestures in particular for imagination. Further, while the supplementary motor regions showed similar O2Hb profiles during both execution and imagination of transitive/intransitive gestures, premotor and posterior parietal areas showed specificities respectively for execution processes and transitive gesture execution. Finally, regression analyses showed that RP amplitude is a predictive factor of subsequent hemodynamic brain activity during action production. Such predictive role was modulated by both task and gesture type factors.

Enhanced action tendencies in obsessive-compulsive disorder: An ERP study

Obsessive-compulsive disorder (OCD) is characterized by repeated thoughts and behaviors. This study explored the stages of motor response preparation that precede action performance or inhibition: We investigated whether OCD is related to enhanced action tendencies in response to external stimuli. Response preparation processes were assessed using the event-related potential (ERP) component of the readiness potential (RP). ERPs were recorded while 15 participants with OCD and 16 healthy controls performed a variation of the go/no-go task and the stop-signal task using schematic faces (angry and neutral). The OCD group presented with a greater RP slope gradient and amplitude over bilateral frontoparietal areas corresponding to the motor cortex. The amplitude effect was further enhanced under negative valence, compared to the neutral condition. Results support the hypothesis that stronger readiness for action might characterize OCD, especially in the presence of threatening stimuli. These findings – specifically correlated with OCD and not with anxiety and depression symptoms – may underlie habitual behavior and embodiment tendencies in OCD. This study suggests that early stages of motor preparation might be important to the etiology and maintenance of OCD.