Robinson, Farrel R., Ph.D.
We want to understand the function of the cerebellum. It makes every movement
as fast, accurate, and consistent as possible but no one understands yet exactly
how it does this. Optimizing movements is probably important for survival since the
cerebellum represents a large investment of brain resources. It contains roughly twice as many neurons as the entire cerebral cortex.
We could use any movement to study the cerebellum but currently we use voluntary rapid eye movements,
called saccades. These movements offer several advantages. For example, the saccade-related parts of
the cerebellum are much better described than other areas, we can measure saccades very accurately,
and saccades involve only six extraocular muscles so their organization is easier to characterize than, say,
a limb movement. Every part of the cerebellum is nearly identical so we expect that what we learn about
saccades will help us understand the cerebellum's role in all movements.
The cerebellum does two jobs. It affects each movement
immediately by contributing to every motor commands with a signal that makes movements fast, accurate, and consistent.
Over a longer period it alters its contribution to motor commands so that movements remain accurate when growth
, aging, or injury render previous commands inaccurate. For example, why do limb movements remain accurate during
childhood when the limb length, weight, and strength change significantly and more or less continuously? This sustained
accuracy is not simply a consequence of a the limb becoming stronger at exactly the same rate that it is becoming heavier
. The cerebellum monitors movement accuracy and compensates when movements become inaccurate for any reason.
We study how the cerebellum does both jobs. To
understand its immediate effect on movements, we record from neurons in the cerebellum as the monkey makes
saccades and we measure saccades after small lesions in the cerebellum. We use these data to work out how the
cerebellum processes the signals that it receives into the output that makes saccades fast, accurate, and consistent.
We recently found that the cerebellum sends incoming signals through slowly-conducting fibers that act as delay
lines to provide the proper timing of saccade deceleration.
To understand how the cerebellum keeps saccades accurate
in the long term we elicit changes in cerebellar output by making saccades seem to be inaccurate. We do this by
manipulating the visual target that the monkey tracks with its eye movements. We record from neurons as the
cerebellum compensates for this apparent inaccuracy and we temporarily turn off small parts of the cerebellum with drugs.
With these data we work out where in the cerebellum compensation occurs. We have found that it occurs in the
cerebellar cortex, and not the cerebellar nuclei.
We also use neuroanatomical tracing to learn how different
parts of the cerebellum connect to each other and to the rest of the brain. The top panel in
Figure 1 shows the positions of the saccade-related part of the cerebellar cortex and the medial cerebellar nucleus. the
bottom two panels show an injection of tracer into saccade-related cerebellar cortex and the resultant
labeling of the projection to the saccade-related part of the medial cerebellar nucleus.
Finally, we have begun using immunohistochemistry to
examine the development of the cerebellum Figure 2 shows a section from the cerebellum of a developing
monkey fetus 95 days after conceptio. In this section different types of cerebellar neurons are labeled with different colors.
Together, these different techniques are starting to
provide the components of a coherent and detailed description of how the cerebellum functions.
Eggert T, Mezger F, Robinson, F, Straube A. (1999) Orbital position dependence is different for externally
and internally triggered saccades. Neuroreport,
Robinson F, Noto C, Watanabe S. (2000) Effect of visual background on saccadic adaptation in monkeys.
Vision Res. 40: 2359-2367.
Robinson F. (2000) Role of the cerebellar interpositus nucleus in saccades. I. Effect of temporary lesions.
Journal of Neurophysiology, 84: 1289-1302.
Noto C, Robinson F. (2001) Visual error is the stimulus for saccadic gain adaptation.
Cognitive Brain Research 12: 309-313.
Robinson F, Rice P, Hollerman J, Berger T. (2001) Projection of the magnocellular red nucleus to the region
of the accessory abducens nucleus in the rabbit. Neurobiology of Learning and Memory,
Seeberger T. Noto C, Robinson F. (2002) Non-visual information does not drive saccade gain adaptation in
monkeys. Brain Research 956: 374-379.
Dacey D, Peterson B, Robinson F, Gamlin P. (2003) Fireworks in the primate retina: in vitro photodynamics
reveals diverse LGN-projecting ganglion cell types. Neuron 37: 15-27.
Robinson F, Noto C, Bevans S. (2003) Effect of visual error size on saccade adaptation in monkey.
Journal of Neurophysiology, 90: 1235-1244.
Schwartz B, Li S, Bespalova I, Burnmeister M, Dulaney E, Robinson F, Leigh R. (2003) Pathogenesis of
clinical signs in recessive cerebellar ataxia with saccadic intrusions and neuropathy (SCA SI). Annals of
Dacey D, Liao H-W, Peterson B, Robinson F, Smith V, Pokorny J, Yau K-W, Gamlin P. (2005) Melanopsion
-expressing ganglion cells in primate retina signal colour and irradiance and project to the LGN. Nature
Robinson F, Soetedjo R, Noto C (2006) Distinct short-term and long-term adaptation to reduce saccade
size in monkey. Journal of Neurophysiology, 96:1030-1041.
Crook J, Hendrickson A, Robinson F. (2006) Co-localization of glycine and GABA immunoreactivity in
interneurons in Macaca monkey cerebellar cortex. Neuroscience, 141:1951-1959.
Crook J, Hendrickson A, Erickson A, Possin D, Robinson F. (2007) Purkinje cell axon collaterals terminate on
Cat-301+ neurons in macaca monkey cerebellum. Neuroscience, 149:834-844.
Kojima Y, Iwamoto Y, Robinson F , Noto C, Yoshida K (2008) Premotor inhibitory neurons carry signals
related to saccade adaptation in the monkey. Journal of Neurophysiology, 99: 220-230.