Bracha, V., Zhao, L., Wunderlich, D. A., Morrissy, S. J., & Bloedel, J. R. (1997). Patients with cerebellar lesions cannot acquire but are able to retain conditioned eyeblink reflexes. Brain, 120, 1401-1413. pdf version of this paper (log on first for for access outside the College)
- The purpose of these experiments was to examine the role of the
human cerebellum in the acquisition and retention of conditioned
- Normal human subjects and patients with cerebellar lesions
were tested for their capacity to acquire, retain and express
conditioned eyeblink responses.
- In acquisition tests, subjects
were trained in a delay classical conditioning paradigm using
a tone conditioned stimulus and a midline forehead tap as an unconditioned
- While normal subjects developed anticipatory eyeblinks
to the tone in one session, patients with cerebellar lesions failed
to acquire conditioned responses in four consecutive training
- The conditioning deficit was bilateral even in patients
with a unilateral cerebellar pathology.
- The same groups of subjects
were tested for the presence of eyeblinks to a visual threat.
in these experiments, both normal subjects and patients with cerebellar
lesions exhibited a high level of responding when they saw an
object approaching their face.
- These eyeblinks to the visual threat
are probably naturally acquired conditioned responses because
they extinguish in normal subjects if they are not reinforced
by the unconditioned cutaneous stimulus.
- In addition, the stimulus
of seeing an approaching object blocks the acquisition of classically
conditioned eyeblinks to a new conditioned stimulus in normal
- These data imply thar patients with cerebellar lesions
who cannot acquire new classically conditioned responses are able
to retain and express conditioned eyeblinks which were acquired
before the onset of the pathology. Consequently cerebellum-dependent
neural substrates which are involved in learning new conditioned
reflexes do not seem to be required for the storage of naturally
learned conditioned responses.