Biomedical Engineering Reference
In-Depth Information
interacting with or superimposing onto the habituation. Since cerebellar patients
did not benefit from the occurrence of the CS, and thus hardly established CR
either in the muscles or in the CVP, and since UR decay was smaller in US-
alone trials and particularly in paired trials, the cerebellum is assumed to be
critically involved in both associative and non-associative processes.
3.
THEORETICAL APPROACHES
3.1. Hypotheses and Considerations on Cerebellar Functions
Our ideas on cerebellar function are based on our early experimental find-
ings in well-trained behaving monkeys with characteristic Purkinje cell activity
during active (pursuit) and passive hand movements (7). The complex spike
activity representing climbing fiber activity, recorded from a Purkinje cell in the
intermediate part of the cerebellum, responds most sensitively to the beginning
of passive hand movements, whereas during active moments the same unit stops
any increased complex spike activity preceding the movement at onset. This
canceling of the feedback signal from the periphery seen during passive move-
ments led to an assumption that the inferior olive, the origin of climbing fibers,
could be one site at which information about "intended" (efference copy) and
"ongoing" (reafference signal) movements are compared and nullified if both
signals are equal according to the "Reafferenz" hypothesis (28). If both signals
are not equal, the olivary cell would inform the cerebellum about an error in the
performance of the movement (38). This coincided well with a comparator hy-
pothesis of the inferior olive suggested by Miller and Oscarrson (50). The con-
cept of the climbing fiber system as an "event marker" (61) seemed to us to be
too restrictive since this system is able to transmit precise information about
parameters up to the third derivative of passive hand movements (39). An error-
detecting system may receive, while an error-correcting system (55)
must
re-
ceive all this detailed movement-related information. This will not exclude other
preolivary (peripheral, or more central) structures involved in error detecting.
Although there are numerous hypotheses on how error or control error signals
may look, or how they are compiled (31), the common denominator is that the
inferior olive, and thus the climbing fiber system, is involved in handling errors
occurring during voluntary or reflexive movements.
The concept of interaction between the descending motor commands and
feedback information ascending from the periphery at the level of the intermedi-
ate part of the cerebellum coincides well with one part of Allen's and Tsuka-
hara's cerebral-cerebellum cooperative hypothesis (3). The intermediate
cerebellum is assumed to update ongoing movement on the basis of sensory
feedback information, whereas the lateral cerebellum, receiving information
from association areas and (almost) none from the periphery, and linked within
