Résumé public
Projet rTMS
General rationale of the project:
(1) Movement and speech monitoring are both based on forward modeling
(2) The generation of forward models is likely to involve the cerebellum
(3) Disrupting cerebellar activity might impair forward modeling and thus speech monitoring
performance
The ability to produce and understand language is a complex cognitive skill whose intricate processes
are often thought to be unique to humans, and it is sometimes selectively impaired following brain
damage. Therefore, it has mainly been approached as an isolable faculty within the cognitive system,
investigated separately from more basic faculties such as sensori-motor skills that are shared with
other species. Nonetheless, recent evidence shows that sensori –motor information forms integral
part of how we represent and access words. Building upon such findings, this project aims at testing
whether this also holds for other aspects of language processing. In particular, we will test whether
speech monitoring makes use of the same processes dedicated to control our motor actions. In the
domain of motor control it is widely held that we use internal forward models to predict and correct
motor commands before their effective output as physical actions. More concretely, it has been
proposed that this is done by having motor actions produce expectations of their sensory
consequences (i.e., forward modeling). These sensory outcome predictions are compared with the
actual sensory input; whatever matches the outcome predictions is inhibited (i.e., reafference
cancellation). In that way, a means is provided to detect any unpredicted sensorial data that should
be attended to. Here we will seek to obtain evidence that forward modeling is the basis of speech
production error monitoring by investigating the role of the cerebellum –hypothesized center of
forward modeling– in the monitoring of speech production.
Our goal will be to test the presence of a causal link between the cerebellum, forward modeling and
speech monitoring. As a result of previous research, it has been proposed that the cerebellum plays a
central role in the forward modeling of movement. Therefore, in the same way as the cerebellum
regulates the rate, force, rhythm and accuracy of movement, it may also be involved in monitoring of
the speed, capacity, consistency and appropriateness of cognitive and linguistic processing. Indeed,
certain studies already suggest a functional connection between the cerebellum, forward modeling
and sound monitoring. For example, an abnormal pattern of cerebellar activation leads to a deficient
forward model used to monitor self-generated speech sounds from externally generated speech
sounds. Furthermore, patients with focal cerebellar lesions showed an attenuated Self Induced
Sound Auditory Suppression N100 effect in comparison with healthy controls. To our knowledge, so
far no study has explored the role of the cerebellum in the monitoring of language production
proper. We aim at doing so by applying rTMS to the cerebellum before the performance of
psycholinguistic tasks known to reflect monitoring processes.
Elin Runnqvist, Mireille Bonnard, F.-Xavier Alario (LPC)