In 1997, Kagerer et al. did an interesting study: they exposed subjects to a visual feedback rotation that was either abruptly or gradually introduced, and found those exposed to the abrupt adaptation had smaller aftereffects:

 

Kagerer, F. A., Contreras-Vidal, J. L., & Stelmach, G. E. (1997). Adaptation to gradual as compared with sudden visuo-motor distortions. Exp Brain Res, 115(3), 557-561. (link to pdf of this article)

 

If visual feedback is discordant with movement direction, the visuo-motor mapping is disrupted, but can be updated with practice. In this experiment subjects practiced discrete arm movements under conditions of visual feedback rotation. One group was exposed to 10 degree-step increments of visual feedback rotation up to a total of 90 degrees, a second group to a 90 degree visual feedback rotation throughout the experiment. After the first group reached the 90 degree visual feedback rotation, its subjects performed faster, with less spatial error, and showed larger aftereffects than the subjects who practiced constantly under the 90 degree visual feedback rotation condition. Results suggest that gradually increasing feedback distortion allows more complete adaptation than a large, sudden distortion onset.

 

The results suggest the possibility that two different brain systems were engaged by the abrupt versus the gradual feedback alterations. What are these different brain systems? Robertson and Miall suggest the cerebellum is especially involved in adaptation to gradual feedback changes, and did a cerebellar inactivation experiment to test their claim:

 

Robertson, E. M., & Miall, R. C. (1999). Visuomotor adaptation during inactivation of the dentate nucleus. Neuroreport, 10(5), 1029-1034. (link to pdf of this article)

 

Recent experiments have suggested that the process of visuomotor adaptation depends on how a visual distortion is introduced. The cerebellum is thought to be involved in adapting to rapidly introduced visual distortions; however its role in adapting to a gradually introduced distortion is unknown. We tested adaptation to a sudden or a gradual introduction of a visual distortion, during reversible inactivation of a monkey's dentate nucleus. There was significant adaptation in both of these tasks without any lignocaine infusion and during saline infusions. However after inactivation the ability to adapt to either visual distortion was slightly impaired, This dysfunction was significant when the visuomotor distortion was introduced over several trials, suggesting that the cerebellum has a differential contribution to visual adaptation depending on the type of visuo-motor disturbance encountered.

 

If the cerebellum is involved in gradual adaptation and less so in abrupt adaptation, what system is engaged by abrupt feedback changes? Contreras-Vidal and Buch hypothesize the basal ganglia are a key part, and they use results from an experient with Parkinsons patients to argue for their view:

 

Contreras-Vidal, J. L., & Buch, E. R. (2003). Effects of parkinson's disease on visuomotor adaptation. Experimental Brain Research, 150(1), 25-32. (link to pdf of this article)

 

Visuomotor adaptation to a kinematic distortion was investigated in Parkinson's disease (PD) patients and age-matched controls. Participants performed pointing movements in which the visual feedback of hand movement, displayed as a screen cursor, was normal (pre-exposure condition) or rotated by 90degrees counterclockwise (exposure condition). Aftereffects were assessed in a post-exposure condition in which the visual feedback of hand movement was set back to normal. In pre- and early-exposure trials, both groups showed similar initial directional error (IDE) and movement straightness (RMSE, root mean square error), but the PD group showed reduced movement smoothness (normalized jerk, NJ) and primary submovement to total movement distance ratios (PTR). During late-exposure the PD subjects, compared with controls, showed larger IDE, RMSE, NJ, and smaller PTR scores. Moreover, PD patients showed smaller aftereffects than the controls during the post-exposure condition. Overall, the PD group showed both slower and reduced adaptation compared with the control group. These results are discussed in terms of reduced signal-to-noise ratio in feedback signals related to increased movement variability and/or disordered kinesthesia, deficits in movement initiation, impaired selection of initial movement direction, and deficits in internal model formation in PD patients. We conclude that Parkinson's disease impairs visuomotor adaptation.

 

Their evidence is not particularly strong, but the hypothesized separate functions of cortico-cerebellar and cortico-striatal systems is an interesting one to consider. What do you think? Come to Sensorimotor Journal Club this Tuesday and we’ll discuss.