[Abstract Title]. - Society for Neuroscience

Abstract: In the influential Marr-Albus-Ito model, climbing fiber input from the inferior olive
provides an error signal that shapes cerebellar processing to produce the correct output (see
Albus 1971). This model has provided a mechanistic account of cerebellar function across a wide
range of error-based learning tasks. A neurophysiological investigation of the inferior olive in
cats, however, argues that olivary discharge is linked to unexpected somatosensory stimulation,
independent of movement error (Horn et al. 2004).
We suggest a third hypothesis, building on the premise that there may be two distinct types of
on-line errors. Filled errors are directly conveyed by an unexpected sensory event; for example,
stepping onto a sidewalk that is higher than expected may cause a person to trip on the curb. In
contrast, empty errors occur when an expected sensory event is absent; when a boxer throws a
punch, the lack of contact with his opponent indicates an error. We propose that the
olivocerebellar system may be more sensitive to filled errors, perhaps because the time of the
error is precisely defined.
To test this prediction, human participants used an MR-compatible robotic manipulandum to
move a cursor during an fMRI scanning session. In one condition, the goal was to pass through a
virtual window. Contact with the surrounding walls was felt as a bump, a situation in which
unexpected sensory information conveys an error. In a second condition, the goal was to hit a
bump the same size as the window. Errors for this condition would be indicated by the absence
of an expected sensory signal. Both conditions required identical reaching movements for correct
performance. To ensure comparable error rates, we randomly rotated the cursor's trajectory.
When participants made errors, activation was observed in the inferior olive, as well as motor
regions of the cerebellum (ipsilateral lobule V and bilateral VIII). In a direct contrast of the two
error types, filled errors were associated with greater activation in vermal lobule III and
contralateral VIII, as well as the caudal aspect of the olive. Empty errors evoke activation in the
rostral olive, as well as ipsilateral lobule V and bilateral Crus I. The olivocerebellar system, then,
seems to react to both empty and filled errors, although with different subregions.
Disclosures: J.E. Schlerf, None; J. Diedrichsen, None; R.B. Ivry, None.
Poster
262. Visually-Guided Reaching II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 262.4/CC18
Topic: D.05.d. Visually guided reaching
Support: CIHR Grant 74634
Title: Oscillatory activity in different monkey premotor areas during a dissociated reaching task