Neurophysiological evidence of motor preparation in inner speech and the effect of content predictability.

Self-generated overt actions are preceded by a slow negativity as measured by electroencephalogram, which has been associated with motor preparation. Recent studies have shown that this neural activity is modulated by the predictability of action outcomes. It is unclear whether inner speech is also preceded by a motor-related negativity and influenced by the same factor. In three experiments, we compared the contingent negative variation elicited in a cue paradigm in an active vs. passive condition. In Experiment 1, participants produced an inner phoneme, at which an audible phoneme whose identity was unpredictable was concurrently presented. We found that while passive listening elicited a late contingent negative variation, inner speech production generated a more negative late contingent negative variation. In Experiment 2, the same pattern of results was found when participants were instead asked to overtly vocalize the phoneme. In Experiment 3, the identity of the audible phoneme was made predictable by establishing probabilistic expectations. We observed a smaller late contingent negative variation in the inner speech condition when the identity of the audible phoneme was predictable, but not in the passive condition. These findings suggest that inner speech is associated with motor preparatory activity that may also represent the predicted action-effects of covert actions.

More than fulfilled expectations: An electrophysiological investigation of varying cause-effect relationships and schizotypal personality traits as related to the sense of agency.

The sense of agency (SoA) is central to human experience. The comparator model, contrasting sensory prediction and action feedback, is influential but limited in explaining SoA. We investigated mechanisms beyond the comparator model, focusing on the processing of unpredictable stimuli, perimotor components of SoA, and their relation to schizotypy. ERPs were recorded from 18 healthy participants engaged in button-pressing tasks while perceiving tones with varying causal relationships with their actions. We investigated the processing of non-causally related tones, contrasted this to causally related tones, and examined perimotor correlates of subjective expectancy and experience of agency. We confirmed N100 attenuation for self-generated stimuli but found similar effects for expectancy-dependent processing of random tones. SoA also correlated with perimotor ERP components, modulated by schizotypy. Thus, neural processes preceding actions contribute to the formation of SoA and are associated with schizotypy. Unpredictable events also undergo sensory attenuation, implying additional mechanisms contributing to SoA.

Connectivity of neural signals to the primary motor area during preparatory periods for movement following external and internal cues.

PURPOSE: We investigated the connectivity of neural signals from movement-related cortical areas to the primary motor area (M1) in the hemisphere contralateral to the movement side during the period of movement-related magnetic fields before movement. MATERIALS AND METHODS: Participants were 13 healthy adults, and nerual signals were recorded using magnetoencephalography. Spontaneous extension of the right wrist was performed at the participant's own pace and following a visual cue in internal (IC) and external (EC) cue tasks. The connectivity of neural signals to M1 from each movement-related motor area was assessed by Granger causality analysis (GCA). The GCA was performed on the neural activity elicited in a frequency band between 7.8 and 46.9 Hz during the pre-movement periods, which occurred durng the readiness field (RF) and the negative slope prime (NSp). F-values, as connectivity values obtained by GCA, were compared between the EC and IC cue tasks. RESULTS: For NSp periods, the connectivity of neural signals from the left superior frontal area (SF-L) to M1 was dominant in the IC task, whereas that from the left superior parietal area (SP-L) to M1 was dominant in the EC task. The F value in the GCA from SP-L to M1 was greater in the EC task during RF than in the IC task during equivalent periods. CONSLUSIONS: In the present study, there were differences in the connectivity of neural signals to M1 between IC and EC tasks. The present results suggested that the pattern of pre-movement neural activity that resulted in a movement was not uniform but differed between movement tasks just before the movement.

Movement-related cortical magnetic fields were assessed with Granger causality analysisConnectivity of neural signals to M1 was different between internal and external cue tasks.Connectivity of neural signals from the frontal area was dominant to M1 in the internal cue task.Connectivity of neural signals to M1 from the parietal area was observed in the external cue task.

The place of Free Will: the freedom of the prisoner.

Debates about the concept of Free Will date back to ancient times. About 40 years ago, Benjamin Libet designed an experiment showing that the conscious intention to move is preceded by a specific pattern of brain activation. His finding suggested that unconscious processes determine our decisions. Libet-style experiments have continued to dominate the debate about Free Will, pushing some authors to argue that the existence of Free Will is a mere illusion. We believe that this dispute is because we often measure Free Will using arbitrary human decisions rather than deliberate actions. After reviewing the definition of Free Will and the related literature, we conclude that the scientific evidence does not disprove the existence of Free Will. However, our will encounters several constraints and limitations that should be considered when evaluating our deeds' personal responsibility.

Pre-movement event-related potentials and multivariate pattern of EEG encode action outcome prediction.

Self-initiated movements are accompanied by an efference copy, a motor command sent from motor regions to the sensory cortices, containing a prediction of the movement's sensory outcome. Previous studies have proposed pre-motor event-related potentials (ERPs), including the readiness potential (RP) and its lateralized sub-component (LRP), as potential neural markers of action feedback prediction. However, it is not known how specific these neural markers are for voluntary (active) movements as compared to involuntary (passive) movements, which produce much of the same sensory feedback (tactile, proprioceptive) but are not accompanied by an efference copy. The goal of the current study was to investigate how active and passive movements are distinguishable from premotor electroencephalography (EEG), and to examine if this change of neural activity differs when participants engage in tasks that differ in their expectation of sensory outcomes. Participants made active (self-initiated) or passive (finger moved by device) finger movements that led to either visual or auditory stimuli (100 ms delay), or to no immediate contingency effects (control). We investigated the time window before the movement onset by measuring pre-movement ERPs time-locked to the button press. For RP, we observed an interaction between task and movement. This was driven by movement differences in the visual and auditory but not the control conditions. LRP conversely only showed a main effect of movement. We then used multivariate pattern analysis to decode movements (active vs. passive). The results revealed ramping decoding for all tasks from around -800 ms onwards up to an accuracy of approximately 85% at the movement. Importantly, similar to RP, we observed lower decoding accuracies for the control condition than the visual and auditory conditions, but only shortly (from -200 ms) before the button press. We also decoded visual vs. auditory conditions. Here, task is decodable for both active and passive conditions, but the active condition showed increased decoding shortly before the button press. Taken together, our results provide robust evidence that pre-movement EEG activity may represent action-feedback prediction in which information about the subsequent sensory outcome is encoded.

Bridging Neuroscience and Robotics: Spiking Neural Networks in Action.

Robots are becoming increasingly sophisticated in the execution of complex tasks. However, an area that requires development is the ability to act in dynamically changing environments. To advance this, developments have turned towards understanding the human brain and applying this to improve robotics. The present study used electroencephalogram (EEG) data recorded from 54 human participants whilst they performed a two-choice task. A build-up of motor activity starting around 400 ms before response onset, also known as the lateralized readiness potential (LRP), was observed. This indicates that actions are not simply binary processes but rather, response-preparation is gradual and occurs in a temporal window that can interact with the environment. In parallel, a robot arm executing a pick-and-place task was developed. The understanding from the EEG data and the robot arm were integrated into the final system, which included cell assemblies (CAs)-a simulated spiking neural network-to inform the robot to place the object left or right. Results showed that the neural data from the robot simulation were largely consistent with the human data. This neurorobotics study provides an example of how to integrate human brain recordings with simulated neural networks in order to drive a robot.

Motor cortical signals reflecting decision making and action preparation.

Decision making often requires accumulating evidence in favour of a particular option. When choices are expressed with a motor response, these actions are preceded by reductions in the power of oscillations in the alpha and beta range in motor cortices. For unimanual movements, these reductions are greater over the hemisphere contralateral to the response side. Such lateralizations are hypothesized to be an online index of the neural state of decisions as they develop over time of processing. In contrast, the lateralized readiness potential (LRP) is considered to selectively activate a response and appears shortly before the motor output. We investigated to what extent these neural signals reflect integration of decision evidence or more motor-related action preparation. Using two different experiments, we found that lateralization of alpha and beta power (APL and BPL, respectively) rapidly emerged after stimulus presentation, even when making an overt response was not yet possible. In contrast, we show that even after prolonged stimulus presentation, no LRP was present. Instead, the LRP emerged only after an imperative cue, prompting participants to indicate their choice. Furthermore, we could show that variations in sensory evidence strength modulate APL and BPL onset times, suggesting that integration of evidence is represented in these motor cortical signals. We conclude that APL and BPL reflect higher cognitive processes rather than pure action preparation, whereas LRP is more closely tied to motor performance. APL and BPL potentially encode decision information in motor areas serving the later preparation of overt decision output.

Lateralized Readiness Potentials Recorded with Near-Threshold Auditory Stimuli in Subjects Simulating Hearing Loss.

INTRODUCTION: Preparatory motor cortical responses like the lateralized readiness potential (LRP) may be useful in revealing persistent attempts to feign hearing loss. Previous studies suggest only a marginal effect of stimulus intensity on the amplitude of the LRP. However, this has not been investigated using low-intensity auditory stimuli to cue NoGo trials. We address this in an experiment where subjects were instructed not to give a manual response to low-instensity stimuli, a situation that is akin to simulating hearing loss. METHODS: The LRP was recorded from normal hearing listeners (N = 10) with 500 and 4,000-Hz pure tones and trains of 4,000 Hz (2-1-2) tonebursts. Electrophysiologic data underwent processing to (i) analyze the effect of the stimulus type on the LRP, (ii) classify results according to manual response with both logistic regression and linear support vector machine (SVM) models, and (iii) derive auditory brainstem responses (ABRs) from the tonebursts. RESULTS: The amplitude of the LRP did not differ between the 3 stimuli used to elicit the response. Single-trial electrode data from Go and NoGo trials were submitted to supervised binary classification, and the logistic regression model gave a mean accuracy of close to 0.7. The Jewett wave V latencies of the resultant ABRs from some subjects were found to increase between the high (Go) and low (NoGo) intensity tonebursts. CONCLUSION: This study shows that auditory stimulus type does not affect the amplitude of the LRP and that the response can be recorded with stimuli that are near the auditory threshold. It can also be recorded with transient stimuli, and this allows for the possibility of simultaneously recording other confirmatory measurements, like ABR.

Neural mechanisms of response priming do not support veridical unconscious processing.

Studies using the priming paradigm often infer that unconscious processes have more veridical access to the world than conscious processes. These interpretations are based on a standard reasoning that erroneously infers good sensitivity of indirect measures from a clear priming effect. To correct for this fallacy, researchers should explicitly compute the sensitivities from indirect measures and compare them against the sensitivities of direct measures. Recent results suggest that indirect behavioral measures are not more sensitive than direct measures and challenge interpretations about veridical unconscious processing. We add to these behavioral results by focusing on neurophysiological indirect measures. In two EEG experiments, we investigate whether event related potentials (ERPs) are more sensitive to different visual stimuli than direct measures. The results show the opposite effect: higher sensitivities for direct than indirect measures. Therefore-contrasting commonly held belief-we find no evidence for more veridical unconscious than conscious processes in ERP measures.

The Readiness Potential reflects the internal source of action, rather than decision uncertainty.

Voluntary actions are preceded by a Readiness Potential (RP), a slow EEG (electroencephalogram) component generated in medial frontal cortical areas. The RP is classically thought to be specific to internally-driven decisions to act, and to reflect post-decision motor preparation. Recent work suggests instead that it may reflect noise or conflict during the decision itself, with internally driven decisions tending to be more random, more conflicted and thus more uncertain than externally driven actions. To contrast accounts based on endogenicity with accounts based on uncertainty, we recorded EEG in a task where participants decided to act or withhold action to accept or reject visually presented gambles, and used multivariate methods to extract an RP-like component. We found no difference in amplitude of this component between actions driven by strong versus weak evidence, suggesting that the RP may not reflect uncertainty. In contrast, the same RP-like component showed higher amplitudes prior to actions performed without any external evidence (guesses) than for actions performed in response to equivocal, conflicting evidence. This supports the view that the RP reflects the internal source of action, rather than decision uncertainty.

Affordances, response conflict, and enhanced-action tendencies in obsessive-compulsive disorder: an ERP study.

BACKGROUND: Obsessive-compulsive disorder (OCD) is characterized by recurrent, intrusive thoughts and/or behaviors. OCD symptoms are often triggered by external stimuli. Therefore, it has been suggested that difficulty inhibiting responses to stimuli associated with strong action tendencies may underlie symptoms. The present electrophysiological study examined whether stimuli evoking a strong automatic response are associated with enhanced action tendencies in OCD participants relative to healthy controls. METHODS: The lateralized readiness potential (LRP) and the N2 event-related potential (ERP) components were used as measures of action tendencies and inhibition, respectively. ERPs were recorded while 38 participants diagnosed with OCD and 38 healthy controls performed a variation of the Stroop task using colored arrows. RESULTS: The OCD group presented with larger LRP amplitudes than the control group. This effect was found specifically in the incongruent condition. Furthermore, an interaction effect was found between group and congruency such that the OCD group showed a reduced N2 in the incongruent condition compared to the congruent condition, whereas the control group demonstrated the opposite effect. Results support the hypothesis that OCD is characterized by stronger readiness-for-action and impaired inhibitory mechanisms, particularly when the suppression of a dominant response tendency is required. Our results were supported by source localization analyses for the LRP and N2 components. These findings were specific to OCD and not associated with anxiety and depression symptoms. CONCLUSIONS: The present results support the notion of stronger habitual behavior and embodiment tendencies in OCD and impaired inhibitory control under conditions of conflict.

Conscious intention and human action: Review of the rise and fall of the readiness potential and Libet's clock.

Is consciousness-the subjective awareness of the sensations, perceptions, beliefs, desires, and intentions of mental life-a genuine cause of human action or a mere impotent epiphenomenon accompanying the brain's physical activity but utterly incapable of making anything actually happen? This article will review the history and current status of experiments and commentary related to Libet's influential paper (Brain 106:623-664, 1983) whose conclusion "that cerebral initiation even of a spontaneous voluntary act …can and usually does begin unconsciously" has had a huge effect on debate about the efficacy of conscious intentions. Early (up to 2008) and more recent (2008 on) experiments replicating and criticizing Libet's conclusions and especially his methods will be discussed, focusing especially on recent observations that the readiness potential (RP) may only be an "artifact of averaging" and that, when intention is measured using "tone probes," the onset of intention is found much earlier and often before the onset of the RP. Based on these findings, Libet's methodology was flawed and his results are no longer valid reasons for rejecting Fodor's "good old commonsense belief/desire psychology" that "my wanting is causally responsible for my reaching.".

Inferior parietal lobule involved in representation of "what" in a delayed-action Libet task.

Intentional motor action is typically characterized by the decision about the timing, and the selection of the action variant, known as the "what" component. We compared free action selection with instructed action, where the movement type was externally cued, in order to investigate the action selection and action representation in a Libet's task. Temporal and spatial locus of these processes was examined using the combination of high-density electroencephalography, topographic analysis of variance, and source reconstruction. Instructed action, engaging representation of the response movement, was associated with distinct negativity at the parietal and centro-parietal channels starting around 750 ms before the movement, which has a source particularly in the bilateral inferior parietal lobule. This suggests that in delayed-action tasks, the process of action representation in the inferior parietal lobule may play an important part in the larger parieto-frontal activity responsible for movement selection.

Preparation and execution of voluntary action both contribute to awareness of intention.

How and when motor intentions form has long been controversial. In particular, the extent to which motor preparation and action-related processes produce a conscious experience of intention remains unknown. Here, we used a brain-computer interface (BCI) while participants performed a self-paced movement task to trigger cues upon the detection of a readiness potential (a well-characterized brain signal that precedes movement) or in its absence. The BCI-triggered cues instructed participants either to move or not to move. Following this instruction, participants reported whether they felt they were about to move at the time the cue was presented. Participants were more likely to report an intention (i) when the cue was triggered by the presence of a readiness potential than when the same cue was triggered by its absence, and (ii) when they had just made an action than when they had not. We further describe a time-dependent integration of these two factors: the probability of reporting an intention was maximal when cues were triggered in the presence of a readiness potential, and when participants also executed an action shortly afterwards. Our results provide a first systematic investigation of how prospective and retrospective components are integrated in forming a conscious intention to move.

Exploring the Relationship of Transdiagnostic Mood and Psychosis Symptom Domains with Motor Dysfunction.

BACKGROUND: A number of motor abnormalities have been reported in psychotic disorders, including dyskinesia and psychomotor slowing. There is also evidence for many of the same motor abnormalities in biological first-degree relatives and accruing evidence for motor abnormalities in bipolar disorder. In addition to motor dysfunction, there are also shared symptom domains amongst these populations. OBJECTIVES: We explored the associations of (1) current and lifetime psychosis and mood symptom domains and (2) domains of psychosis proneness with various domains of motor function in a transdiagnostic sample (n = 149). METHOD: Individuals with schizophrenia, schizoaffective disorder, or bipolar disorder, biological first-degree relatives of individuals with a psychotic disorder, and controls completed measures of psychomotor speed and movement fluidity, and neural activity related to motor preparation (stimulus-locked lateralized readiness potential, S-LRP) and execution (response-locked LRP) was assessed using EEG. All participants completed the Brief Psychiatric Rating Scale; patients were additionally assessed for lifetime psychosis and mood episode symptoms, and relatives and controls completed the Chapman psychosis proneness scales. RESULTS: Multiple regression revealed levels of current negative symptoms and mania were significantly positively associated with psychomotor slowing even after accounting for current antipsychotic medication dosage and duration of illness. S-LRP onset latency was significantly positively associated with magical ideation. CONCLUSION: Domains of motor function are associated with various mood and psychosis symptom domains in a transdiagnostic sample, which may provide insight into brain abnormalities relevant to the expression of symptoms across disorders.

The volition, the mode of movement selection and the readiness potential.

A growing body of evidence suggests that the mode of movement selection is relevant for the readiness potential, namely, internal (or free) selection of movements is associated with increased readiness potential amplitudes compared to predetermined or externally guided selection. It is little acknowledged, however, that this finding may be ascribed to the different expression of volition (i.e., conscious experience of choice) rather than to the mode of movement selection per se. To probe this issue, we conducted two experiments: in Experiment 1, a mental task was employed to distract sixteen volunteers from the selection and performance of incidental movements, which consisted of pressing one of two buttons according to either free or externally guided modes of movement selection; in Experiment 2, another sixteen individuals performed the same motor task, however, they were encouraged to attend to their intention to act. As result, the increased readiness potential amplitude before freely selected movements was found exclusively in Experiment 2. More detailed analysis suggested that the attention to the initiation of movements was associated with greater readiness potential in its medial and late portion, while the attention to the movement selection, with more global increase of the component. The study suggests that much of the higher demands on motor preparatory activities ascribed to the internal selection of movements in previous studies actually depends on individual's attention and, thus, probably corresponds to volitional processes.

Individual differences in motor development during early childhood: An MEG study.

In a previous study, we reported the first measurements of pre-movement and sensorimotor cortex activity in preschool age children (ages 3-5 years) using a customized pediatric magnetoencephalographic system. Movement-related activity in the sensorimotor cortex differed from that typically observed in adults, suggesting that maturation of cortical motor networks was still incomplete by late preschool age. Here we compare these earlier results to a group of school age children (ages 6-8 years) including seven children from the original study measured again two years later, and a group of adults (mean age 31.1 years) performing the same task. Differences in movement-related brain activity were observed both longitudinally within children in which repeated measurements were made, and cross-sectionally between preschool age children, school age children, and adults. Movement-related mu (8-12 Hz) and beta (15-30 Hz) oscillations demonstrated linear increases in amplitude and mean frequency with age. In contrast, movement-evoked gamma synchronization demonstrated a step-like transition from low (30-50 Hz) to high (70-90 Hz) narrow-band oscillations, and this occurred at different ages in different children. Notably, pre-movement activity ('readiness fields') observed in adults was absent in even the oldest children. These are the first direct observations of brain activity accompanying motor responses throughout early childhood, confirming that maturation of this activity is still incomplete by mid-childhood. In addition, individual children demonstrated markedly different developmental trajectories in movement-related brain activity, suggesting that individual differences need to be taken into account when studying motor development across age groups.

Libet's intention reports are invalid: A replication of Dominik et al. (2017).

In the "Libet experiment" the onset of movement-related brain activity preceded the reported time of the conscious intention to move, suggesting that conscious intention may not play a role in initiating voluntary movements (Libet, Gleason, Wright, & Pearl, 1983). Dominik et al. (2017) provided evidence that the intention reports employed in the Libet experiment, which Libet et al. (1983) found to precede movement reports, are invalid. In the study by Dominik et al., intention reports preceded movement reports only when participants had prior experience making movement reports. Individuals without such experience reported intention around the same time as movement. These findings suggest that Libet's intention reports do not reflect experiences of intention, but, rather, inferences based on prior experience with movement reports. Our study replicated the core findings of Dominik et al. We argue that Libet's intention reports are invalid and explore the phenomenology of intention in the Libet experiment.

The point of no return in vetoing self-initiated movements.

In humans, spontaneous movements are often preceded by early brain signals. One such signal is the readiness potential (RP) that gradually arises within the last second preceding a movement. An important question is whether people are able to cancel movements after the elicitation of such RPs, and if so until which point in time. Here, subjects played a game where they tried to press a button to earn points in a challenge with a brain-computer interface (BCI) that had been trained to detect their RPs in real time and to emit stop signals. Our data suggest that subjects can still veto a movement even after the onset of the RP. Cancellation of movements was possible if stop signals occurred earlier than 200 ms before movement onset, thus constituting a point of no return.

Precursor processes of human self-initiated action.

A gradual buildup of electrical potential over motor areas precedes self-initiated movements. Recently, such "readiness potentials" (RPs) were attributed to stochastic fluctuations in neural activity. We developed a new experimental paradigm that operationalized self-initiated actions as endogenous 'skip' responses while waiting for target stimuli in a perceptual decision task. We compared these to a block of trials where participants could not choose when to skip, but were instead instructed to skip. Frequency and timing of motor action were therefore balanced across blocks, so that conditions differed only in how the timing of skip decisions was generated. We reasoned that across-trial variability of EEG could carry as much information about the source of skip decisions as the mean RP. EEG variability decreased more markedly prior to self-initiated compared to externally-triggered skip actions. This convergence suggests a consistent preparatory process prior to self-initiated action. A leaky stochastic accumulator model could reproduce this convergence given the additional assumption of a systematic decrease in input noise prior to self-initiated actions. Our results may provide a novel neurophysiological perspective on the topical debate regarding whether self-initiated actions arise from a deterministic neurocognitive process, or from neural stochasticity. We suggest that the key precursor of self-initiated action may manifest as a reduction in neural noise.