Leading research would suggest that climbing fibers play a specific role in motor learning.

Each climbing fiber will form synapses with 1-10 Purkinje cells.

The climbing fibers stimulate a large increase in postsynaptic Ca levels when activated.

In fact, the function of climbing fibers is the most controversial topic concerning the cerebellum.

They terminate directly on Purkinje cells as the climbing fiber input system.

Once they enter the cerebellum, they are referred to as the climbing fibers.

The climbing fibers then send the image or projection to the part of the brain that receives electrical signals and generates movement.

Climbing fibers project to Purkinje cells and also send collaterals directly to the deep nuclei.

In this way climbing fibers (CFs) perform a central role in motor behaviors.

Purkinje cells also receive input from the inferior olivary nucleus via climbing fibers.

The idea that climbing fiber activity functions as an error signal has been examined in many experimental studies, with some supporting it but others casting doubt.

If the inferior olive it would go via excitatory climbing fiber inputs to Purkinje neurons.

Vestibular inputs are also carried through climbing fibers that project into the flocculus, stimulating Purkinje cells.

They are caused by climbing fiber activation, and can involve the generation of calcium-mediated action potentials in the dendrites.

For other investigators, the message lies in the degree of ensemble synchrony and rhythmicity among a population of climbing fibers."

There are three sources of input to the cerebellum, in two categories consisting of mossy and climbing fibers, respectively.

Both parallel fibers and climbing fibers must be simultaneously activated for LTD to occur.

Climbing fibers are the name given to a series of neuronal projections from the inferior olivary nucleus located in the medulla oblongata.

LTD in the cerebellum requires a coincident stimulation of parallel fibers and climbing fibers.

One brainstem nucelus, the inferior olivary nucleus, projects climbing fibers to innervate Purkinje cells.

The branches of a climbing fiber (usually numbering about 10) usually innervate Purkinje cells belonging to the same microzone.

Marr assumed that climbing fiber input would cause synchronously activated parallel fiber inputs to be strengthened.

A good mnemonic for this interaction is the phrase "climb the other olive tree", given that climbing fibers originate from the contralateral inferior olive.

The climbing fiber synapses cover the cell body and proximal dendrites; this zone is devoid of parallel fiber inputs.

Thus, the nucleo-olivary projection provides an inhibitory feedback to match the excitatory projection of climbing fibers to the nuclei.

Parallel fibre terminals and climbing fibres work together in a positive feedback loop for invoking high calcium release.

For best release of calcium however, it is best if parallel fibre is activated a few hundred milliseconds before the climbing fibres.

There are several sources of calcium signaling that elicit LTD: climbing fibres and parallel fibres which converge onto Purkinje cells.

In the climbing fibres, AMPAR-mediated depolarization induces a regenerative action potential that spreads to the dendrites, which is generated by voltage-gated calcium channels.

Since multiple ( 200,000) granule cells synapse onto a single Purkinje cell, the effects of each parallel fiber can be altered in response to a "teacher signal" from the climbing fibre input.

Different patterns of mossy fibre input will produce unique patterns of activity in granule cells that can be modified by a teaching signal conveyed by the climbing fibre input.

This pause response, called a Purkinje cell CR, was also obtained when direct mossy fibre stimulation was used as the CS and direct climbing fibre stimulation as the US.

It was proposed by Marr and Albus (see above) that the cerebellar Purkinje cells could learn to change their responses to particular parallel fibre inputs if these were repeatedly paired with simultaneuous inputs from the climbing fibres.

While working with the cerebellum, Kreitzer's group also discovered that depolarization of Purkinje cells could also cause a temporary reduction in excitatory input into these cells from both climbing fibres and parallel fibres (Kreitzer et al. 2001b).

Calcium signaling in the post-synaptic cell involved both spatial and temporal overlap of climbing fibre induced calcium release into dendrites as well as parallel fibre induced mGluRs and IP3 mediated calcium release.

Paired activation of the parallel and climbing fibre inputs results in long-term depression of the parallel fibre-Purkinje cell synapse, which is thought to be mediated through the mGlu receptor that is coupled to InsP 3 formation (Box 1).