Thesis defense Ceci Verbaarschot (Donders series 421)

16 January 2020

Promotor: prof. dr. P. Desain 
Co-promotors: dr. P. Haselager, dr. J. Farquhar

The brain in(tending) action: Linking neural preparation and subjective experience of motor intentions

In this thesis, five independent experiments on intended movement are presented. Across these experiments, the influence of external stimuli was limited or expanded, providing different contexts in which to intend and act. Some movements were made spontaneously, in absence of any identifiable external reasons for what action to perform or when to perform it. Others were made deliberately, in a gaming context that required an action strategy based on the current game situation. The neural preparation for these movements was measured in terms of the (lateralized) readiness potential (RP) and 8-30Hz event-related desynchronization (ERD) across the (pre)supplementary motor area using EEG. Reports on the experience of an intention to move were collected post-hoc using Libet’s clock method or ante-hoc using a probe method. The probe method either measured the behavioral response to a pseudo-randomly timed probe, or requested a report on the awareness of an intention to move as soon as movement intent was detected from ongoing EEG activity. Using these methods, we investigated (a) the influence of experimental instructions and external stimuli on these brain signals and intention reports, and (b) the nature of the relation between these brain signals, the experience and report of an intention, and the action.

We suggest that our results are consistent with the interpretation of intention reports as forms of self-interpretation. Depending on the context, various sources of information may be used to construct an intention report at a given moment in time: ongoing brain processes, overt behavior, action consequences, and the absence or presence of environmental events. In a situation where there are no clear external reasons for deciding when to move, brain signals such as the (L)RP and 8-30Hz ERD may be (partially) responsible for triggering a report on an intention to move. In other words, the neuronal activity that generates these signals could be a source of information to other brain processes that lead up to intention reports. Therefore, in specific contexts, the (L)RP and 8-30Hz ERD may be considered potential instigators of intention reports, rather than causes or implementations of experienced intentions.