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The readiness potential is an ongoing negativity in the EEG preceding a self-initiated movement by approximately 1.5s. So far it has predominantly been interpreted as a preparatory signal with a causal link to the upcoming movement. Here a different hypothesis is suggested which we call the selective slow cortical potential sampling hypothesis. In this review of recent research results we argue that the initiation of a voluntary action is more likely during negative fluctuations of the slow cortical potential and that the sampling and averaging of many trials leads to the observed negativity. That is, empirical evidence indicates that the early readiness potential is not a neural correlate of preconscious motor preparation and thus a determinant of action. Our hypothesis thereafter challenges the classic interpretation of the Libet experiment which is often taken as proof that there is no free will. We furthermore suggest that slow cortical potentials are related to an urge to act but are not a neural indicator of the decision process of action initiation.
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Intuitively, being aware of one's inner processes to move should be crucial for the control of voluntary movements. However, research findings suggest that we are not always aware of the processes leading to movement execution. The present study investigated induced first-person access to inner processes of movement initiation and the underlying brain activities which contribute to the emergence of voluntary movement. Moreover, we investigated differences in task performance between mindfulness meditators and non-meditators while assuming that meditators are more experienced in attending to their inner processes. Two Libet-type tasks were performed; one in which participants were asked to press a button at a moment of their own decision, and the other one in which participants' attention was directed towards their inner processes of decision making regarding the intended movement which lead them to press the button. Meditators revealed a consistent readiness potential (RP) between the two tasks with correlations between the subjective intention time to act and the slope of the early RP. However, non-meditators did not show this consistency. Instead, elicited introspection of inner processes of movement initiation changed early brain activity that is related to voluntary movement processes. Our findings suggest that compared to non-meditators, meditators are more able to access the emergence of negative deflections of slow cortical potentials (SCPs), which could have fundamental effects on initiating a voluntary movement with awareness.
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Research findings link rolandic beta-band activity to voluntary movements, but a linkage with the decision time to move remains unknown. We found that beta-band (16-28Hz) activity shortly before the movement onset is relevant for the decision time to move: the more pronounced the decrease in beta-band synchronization, the earlier the subjective experience of the decision to move. The linkage was relevant regarding 'decision', but not regarding 'intention' timing that has been often applied in the study of free will. Our findings suggest that oscillatory neural activity in the beta-band is an important neural signature pertaining to the subjective experience of making a decision to move.
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When a voluntary action is causally linked with a sensory outcome, the action and its consequent effect are perceived as being closer together in time. This effect is called intentional binding. Although many experiments were conducted on this phenomenon, the underlying neural mechanisms are not well understood. While intentional binding is specific to voluntary action, we presumed that preconscious brain activity (the readiness potential, RP), which occurs before an action is made, might play an important role in this binding effect. In this study, the brain dynamics were recorded with electroencephalography (EEG) and analyzed in single-trials in order to estimate whether intentional binding is correlated with the early neural processes. Moreover, we were interested in different behavioral performance between meditators and non-meditators since meditators are expected to be able to keep attention more consistently on a task. Thus, we performed the intentional binding paradigm with 20 mindfulness meditators and compared them to matched controls. Although, we did not observe a group effect on either behavioral data or EEG recordings, we found that self-initiated movements following ongoing negative deflections of slow cortical potentials (SCPs) result in a stronger binding effect compared to positive potentials, especially regarding the perceived time of the consequent effect. Our results provide the first direct evidence that the early neural activity within the range of SCPs affects perceived time of a sensory outcome that is caused by intentional action.
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The belief in free will has been frequently challenged since Benjamin Libet published his famous experiment in 1983. Although Libet's experiment is highly dependent upon subjective reports, no study has been conducted that focused on a first-person or introspective perspective of the task. We took a neurophenomenological approach in an N=1 study providing reliable and valid measures of the first-person perspective in conjunction with brain dynamics. We found that a larger readiness potential (RP) is attributable to more frequent occurrences of self-initiated movements during negative deflections of the slow cortical potentials (SCP). These negative deflections occur in parallel with an inner impulse reported by an expert meditator which may in turn lead to a voluntary act. We demonstrate in this proof-of-principle approach that the first-person perspective obtained by an expert meditator in conjunction with neural signal analysis can contribute to our understanding of the neural underpinnings of voluntary acts.
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It has been repeatedly shown that specific brain activity related to planning movement develops before the conscious intention to act. This empirical finding strongly challenges the notion of free will. Here, we demonstrate that in the Libet experiment, spontaneous fluctuations of the slow electro-cortical potentials (SCPs) account for a significant fraction of the readiness potential (RP). The individual potential shifts preceding self-initiated movements were classified as showing a negative or positive shift. The negative and positive potential shifts were analyzed in a self-initiated movement condition and in a no-movement condition. Comparing the potential shifts between both conditions, we observed no differences in the early part of the potential. This reveals that the apparently negative RP emerges through an unequal ratio of negative and positive potential shifts. These results suggest that ongoing negative shifts of the SCPs facilitate self-initiated movement but are not related to processes underlying preparation or decision to act.
Erkunden
Team
- Wittmann (6)
Eintragsart
Sprache
- Englisch (6)
Thema
- Acoustic Stimulation (1)
- Adult (3)
- Attention/physiology (1)
- Awareness/*physiology (1)
- Beta oscillation (1)
- *Beta Rhythm (1)
- Brain Mapping (1)
- Brain/physiology (1)
- Brain Waves/*physiology (1)
- Cerebral Cortex/*physiology (2)
- Consciousness/*physiology (1)
- *Contingent Negative Variation (1)
- Contingent Negative Variation/*physiology (2)
- Decision (1)
- *Decision Making (1)
- Electroencephalography (2)
- Electroencephalography/instrumentation/*methods (1)
- Event-related desynchronization (1)
- Female (3)
- First-person data (1)
- *Free will (1)
- Humans (5)
- *Intention (2)
- Intention (2)
- Intention to act (1)
- intentional binding (1)
- Libet experiment (2)
- *Libet task (1)
- Male (4)
- Meditation (1)
- meditation (1)
- Middle Aged (4)
- Movement (1)
- *Movement (1)
- Movement/physiology (1)
- Movement/*physiology (1)
- Neurophenomenology (1)
- Psychomotor Performance (1)
- *Reaction Time (1)
- *Readiness potential (1)
- Readiness potential (2)
- readiness potential (1)
- sense of agency (1)
- *Slow cortical potential (1)
- slow cortical potential (1)
- Slow cortical potential (1)
- Volition (2)
- Volition/physiology (1)
- Volition/*physiology (2)
- *Voluntary action (1)
- Young Adult (1)