Sensorimotor recalibration reverses the temporal constraints of somatosensory attenuation
Author
Houborg, Christian
Term
4. term
Education
Publication year
2018
Abstract
Denne afhandling undersøger, om hjernen kan lære en ny tidsmæssig sammenhæng mellem handling og sansning, og om ændringerne afspejler en opdatering af et internt fremadrettet (forward) model. Baggrunden er, at selvfrembragte berøringer normalt opleves dæmpede, når hjernen korrekt forudsiger deres sensoriske konsekvens, og at denne dæmpning er tidsfølsom. 120 deltagere gennemførte fire eksperimenter med en tvungen-valg opgave: Ved at tappe på en sensor med højre hånd udløste de et standardiseret tryk (2 N) på venstre pegefinger, som enten kom straks eller med forsinkelse i eksponeringstrials, responsetrials eller begge. I responsetrials blev der samtidig givet et andet, eksternt tryk (1–3 N), og deltagerne angav, hvilket tryk der føltes stærkest. Før diskriminationsopgaven modtog deltagerne en kort træning med enten 50, 200 eller 500 eksponeringstrials. Resultaterne viser, at efter eksponering for en forsinkelse ophæves den sædvanlige dæmpning af umiddelbar berøring, mens dæmpning af cirka 100 ms forsinket berøring først fremkommer efter 200 eller flere eksponeringer og tiltager med mere eksponering. De modsatrettede skift i dæmpning af umiddelbar og forsinket berøring var desuden korrelerede. Samlet tyder fundene på en omkalibrering af den forudsagte tidsmæssige relation mellem handling og konsekvens i en intern forward model, hvilket diskuteres i lyset af sensorimotorisk læring og cerebellar bearbejdning.
This thesis examines whether the brain can learn a new timing relationship between action and sensation and whether this reflects updating of an internal forward model. Self-generated touch typically feels weaker when the brain correctly predicts its sensory consequences, and this attenuation is temporally precise. Across four experiments with 120 participants, a forced-choice task was used in which tapping a sensor with the right hand triggered a standardized tap (2 N) on the left index finger, delivered either immediately or with a delay during exposure trials, response trials, or both. In response trials, a second, external tap (1–3 N) was applied, and participants indicated which tap felt stronger. Before the discrimination task, participants completed brief training with either 50, 200, or 500 exposure trials. Results showed that after exposure to a delay, the usual attenuation of immediate touch was abolished, while attenuation of approximately 100 ms delayed touch emerged only after 200 or more exposure trials and increased with further exposure. The opposite shifts in attenuation for immediate versus delayed touch were correlated. Overall, the findings indicate recalibration of the predicted temporal relationship between action and feedback within an internal forward model, discussed in the context of sensorimotor learning and cerebellar processing.
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