Biomedical Engineering Reference
In-Depth Information
Cerebellar patients, however, were able to reduce decision times as much as
controls in control conditions that did not require associative learning. There-
fore, deficits in cerebellar patients' ability to reduce decision times in the asso-
ciative learning part were not due to a general inability to further reduce
decision times based on motor performance deficits.
Moreover, motor performance deficits were not related to deficits in asso-
ciative learning. First, there was no significant interaction between motor de-
mands (one vs. three key presses) and the effects of learning. Second, the effects
of impaired visuomotor learning in the cerebellar group were most prominent
when reaction times were normalized for motor performance deficits. Finally,
the findings of our previous study were confirmed: background motor vari-
ables—i.e., simple reaction times, visual scanning times, and clinical ataxia
scores—did not relate to impaired associative learning.
In monkey cerebellar lesions studies, however, Passingham and his group
found that visuomotor associative learning was not impaired when controlling
for motor performance deficits (53,54). Likewise, a recent fMRI study in healthy
human subjects showed that cerebellar activation during learning a visuomotor
sequence was due to motor performance but not learning itself (66). Our studies
required the association of two visual stimuli and the linkage of the correct color
pair and motor response. In Nixon and Passingham's (53,54) and Seidler's (66)
studies, discrete associations of one visual stimulus and a motor response were
learned. The role of the cerebellum may be different in stimulus-stimulus-
response and stimulus-response associations.
In sum, the findings of the two studies by our group suggest that the cere-
bellum is not only involved in conditional learning of avoidance reactions but
also in visuomotor associative learning tasks. Further experiments are needed to
differentiate between the role of the cerebellum in sequencing incoming visual
stimuli and its role in helping to build an association between them and/or the
motor response.
2.2. Tests for Non-Associative Processes
2.2.1. Habituation during Startle
Both animal and human lesion data suggest that the cerebellum is involved
in habituation of unspecific aversive reaction, i.e., the acoustic startle response.
The acoustic startle response is a protective behavioral reaction consisting of
muscle contractions of the eyelid, the neck, and the extremities that is elicited by
sudden loud acoustic stimuli. Lesion studies in the rat have shown an involve-
ment of the cerebellar vermis in long-term habituation of the acoustic startle
response, but not in short-term habituation (45-47). Similar findings were ob-
served in a human lesion study of our group (49). Patients with midline cerebel-
Search WWH ::




Custom Search