(Example) Class Presentation: John Desmond
Blakemore, S. J., Wolpert, D. M., & Frith, C. D. (1998). Central cancellation of self-produced tickle sensation. Nat Neurosci, 1(7), Introduction We are constantly bombarded by sensations from multiple sources It is adaptive to be able to disregard sensations arising from our own movements Introduction This ability to predict consequences of our actions may result in differential perception of identical sensory inputs For example, it is very difficult to tickle oneself Previous Investigations
Introducing delay (200 ms) between movement of left hand and receiving tactile stimulation of right hand increased tickle rating Thus, attenuation of self-produced tactile stimulation may be due to a temporally precise cancellation based on sensory predictions Possible Mechanism: Forward Model
Forward models receive an efference copy of motor commands and generate a corollary discharge that predicts the consequences of movements Comparing this prediction with actual sensory feedback could provide the basis for distinguishing self-generated vs. external sensory signals Forward Model Likely Site of Forward Model: Cerebellum Purpose of Present Experiment
Compare functional brain activation for self-produced versus externally produced tickle sensation Hypothesis: Cerebellar activation will distinguish these two types of stimulation Methods 6 right handed healthy subjects Mean age 33 years
fMRI scanning during 4 conditions of a 2x2 factorial design Methods Methods Each condition lasted 32.8 sec
Each subject was scanned for all 4 conditions Each condition was replicated 12 times Condition order was counterbalanced Subjects instructed to keep eyes closed fMRI Methods: Data Acquisition
2 Tesla Siemens Scanner 48 axial images per volume Inplane resolution: 3 mm x 3 mm One volume collected every 4.1 s Thus, one block (32.8 s) = 8 volumes fMRI Methods: Data Analysis
SPM97 Volumes were motion corrected Normalized into Talairach space Spatial Smoothing with 6 mm FWHM Statistical analysis using general linear model Weighted contrasts performed to create statistical t maps overlaid onto anatomical scan Results: Main Effects of Self-generated Movement
(A+B) (C+D) Results: Main Effects of Tactile Stimulation
(A+C) (B+D) Results: Interaction of Tactile Stimulation with Self-generated Movement
(C-D) (A-B) Results: Parietal Operculum
Interaction (C-D) (A-B) A-B not different from 0: ie., any movement attenuates activation Results: Cingulate Interaction (C-D) (A-B) A-B not different
from 0: ie., any movement attenuates activation Results: Cerebellum Interaction (C-D) (A-B) A-B is different from 0 Discussion Differential sensory responses to a self-generated movement do not occur at the level of somatosensory cortex. Results suggest that specific sensory predictions occur at the level of the anterior cerebellar cortex. Conclusion We conclude that decrease of activity in somatosensory cortex to self-produced tactile stimuli occurs because such stimuli match the predicted sensory feedback of the movement and that this prediction occurs in the cerebellum. Conclusion Self-generated tickle External tickle ++