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The Inner Sense of Free Will: Conscious Intention and Neural Substrates

  • The feeling of being in control of voluntary movement is crucial for the experience of free will. However, neuroscientists have often proposed that specific brain activity can predict our voluntary action even before we have made any decision concerning the action. This seems to confirm that a conscious will to act is an additional phenomenon arising after brain activity. These findings seem hard to reconcile with the view that such an action is our ‘own’ voluntary action. The present thesis contains four empirical studies aiming to demonstrate the underlying mechanism of intentional processes and its correlates to brain dynamics. We first demonstrated that in the Libet experiment ongoing neural fluctuations of the slow 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 aThe feeling of being in control of voluntary movement is crucial for the experience of free will. However, neuroscientists have often proposed that specific brain activity can predict our voluntary action even before we have made any decision concerning the action. This seems to confirm that a conscious will to act is an additional phenomenon arising after brain activity. These findings seem hard to reconcile with the view that such an action is our ‘own’ voluntary action. The present thesis contains four empirical studies aiming to demonstrate the underlying mechanism of intentional processes and its correlates to brain dynamics. We first demonstrated that in the Libet experiment ongoing neural fluctuations of the slow 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. 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. Therefore, for the second study, we took a neurophenomenological approach in an N = 1 study providing reliable and valid measures of the first-person perspective in conjunction with the brain dynamics. We found that a larger RP is attributable to more frequent occurrences of self-initiated movements during negative deflections of SCPs. 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 demonstrated 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. For the third study, we 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 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. These findings are supported by cortical source imaging analysis on brain activity in the pre-supplementary motor area (pre-SMA), in which directing the subjective experience towards inner process to move led to a decreased activation in non-meditators, while no or less change was found in meditators. Our findings suggest that compared to non-meditators, meditators are more able to access the emergence of negative deflections of SCPs, which could have fundamental effects on initiating a voluntary movement with awareness. For the last study, we examined the general sense of being in control of an intended movement. 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 RP), which occurs before an action is made, might play an important role in this binding effect. Therefore, the brain dynamics were recorded with 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 twenty mindfulness meditators and compared them to matched controls. Although we did not observe a group effect in either behavioral data or EEG recordings, we found that self-initiated movements following ongoing negative deflections of SCPs result in a stronger binding effect compared to positive potentials, especially regarding the perceived time of the consequent effect. These 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. The present thesis enables a new perspective on the underlying neural mechanisms of intentional processes. The finding provides evidence that (i) the emergence of an conscious intention to act is associated with ongoing negative deflections of SCPs, which leads to the seeming build-up the RP. In addition, (ii) execution of voluntary movement during this ongoing negative deflection enhances the sense of agency via temporal attraction between intended action and outcome. Finally, the finding suggests that (iii) first-person experiences of phenomenal states reported by experienced meditators contribute to our understanding brain mechanisms and free will.show moreshow less

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Metadaten
Author:Han-Gue Jo
URN:urn:nbn:de:kobv:521-opus4-905
Referee:Stefan Schmidt, Harald WalachORCiD
Document Type:Doctoral Thesis
Language:English
Date of Publication (online):2014/11/28
Publishing Institution:Europa-Universität Viadrina Frankfurt
Granting Institution:Europa-Universität Viadrina Frankfurt
Date of final exam:2014/11/14
Release Date:2014/12/09
Licence (German):License LogoCreative Commons - CC BY-NC-ND 3.0 - Namensnennung-Nicht kommerziell-Keine Bearbeitung
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