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Front Neural Circuits. 2014 Aug 5;8:90. doi: 10.3389/fncir.2014.00090. eCollection 2014.

Changes in complex spike activity during classical conditioning.

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Department of Experimental Medical Science, Associative Learning Group, Lund University Lund, Sweden ; Linneaus Center CCL, Lund University Lund, Sweden.
Department of Physics, James H. Clark Center for Biomedical Engineering and Sciences, Stanford University Stanford, CA, USA.


The cerebellar cortex is necessary for adaptively timed conditioned responses (CRs) in eyeblink conditioning. During conditioning, Purkinje cells acquire pause responses or "Purkinje cell CRs" to the conditioned stimuli (CS), resulting in disinhibition of the cerebellar nuclei (CN), allowing them to activate motor nuclei that control eyeblinks. This disinhibition also causes inhibition of the inferior olive (IO), via the nucleo-olivary pathway (N-O). Activation of the IO, which relays the unconditional stimulus (US) to the cortex, elicits characteristic complex spikes in Purkinje cells. Although Purkinje cell activity, as well as stimulation of the CN, is known to influence IO activity, much remains to be learned about the way that learned changes in simple spike firing affects the IO. In the present study, we analyzed changes in simple and complex spike firing, in extracellular Purkinje cell records, from the C3 zone, in decerebrate ferrets undergoing training in a conditioning paradigm. In agreement with the N-O feedback hypothesis, acquisition resulted in a gradual decrease in complex spike activity during the conditioned stimulus, with a delay that is consistent with the long N-O latency. Also supporting the feedback hypothesis, training with a short interstimulus interval (ISI), which does not lead to acquisition of a Purkinje cell CR, did not cause a suppression of complex spike activity. In contrast, observations that extinction did not lead to a recovery in complex spike activity and the irregular patterns of simple and complex spike activity after the conditioned stimulus are less conclusive.


complex spikes; eyeblink conditioning; in vivo electrophysiology; inferior olive; interstimulus interval; nucleo-olivary pathway; oscillations; purkinje cells

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