Volume 17, Number 24,
Issue of December 15, 1997
pp. 9736-9745
The Cerebellum and Red Nucleus Are Not Required for In
Vitro Classical Conditioning of the Turtle Abducens Nerve
Response
Received July 14, 1997; revised Sept. 26, 1997; accepted Sept. 30, 1997.
Curtis W. Anderson and
Joyce Keifer
Department of Anatomy and Structural Biology, University of South
Dakota, School of Medicine, Vermillion, South Dakota 57069
The role of the cerebellum during motor learning is a controversial
issue. Many authors have suggested that the cerebellum and its
connections with the red nucleus are essential for the acquisition of
the conditioned eye blink reflex. Although there is little argument
that the cerebellum is an important component to the generation of the
conditioned response (CR), a number of studies have suggested that the
cerebellum is not essential for conditioning. Using an in
vitro model of the classically conditioned turtle abducens
nerve response, we investigated the effect of cerebellar and red
nucleus lesions on the acquisition, extinction, and reacquisition of
CRs. Neural discharge was recorded from the abducens nerve after a
single shock unconditioned stimulus (US) was applied to the ipsilateral
trigeminal nerve. When the US was paired with a conditioned stimulus
(CS) applied to the posterior eighth, or auditory, nerve, a positive
slope of CR acquisition was recorded in the abducens nerve. After
extinction stimuli in which the CS and US were alternated, the number
of CRs decreased to near zero. When the CS and US were once again
paired, reacquisition at a faster rate was recorded. The CRs showed
unusual timing features compared with preparations in which the
cerebellum was intact; they had significantly shorter latencies and
showed burst-like responses. These data demonstrate that it is possible
to classically condition this in vitro preparation in
the absence of the cerebellum and red nucleus. However, the latencies
of CRs were found to be dramatically altered in the cerebellar-lesioned
preparations, suggesting that the cerebellum does play a role in the
timing of the CR.
Key words:
classical conditioning;
cerebellum;
in vitro;
turtle;
brainstem;
red nucleus