PSYC 427 Lecture Notes - Lecture 16: Purkinje Cell, Climbing Fiber, Granule Cell
14 May 2018
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PSYC 427 – LECTURE 16
CEREBELLAR SYNAPTIC ORGANIZATION
There are 5 different kinds of cells in the cerebellar cortex (all but one are inhibitory)
1. Stellate
2. Basket
3. Purkinje
4. Golgi
5. Granule (excitatory)
The cerebellar cortex is divided into three parts
1. Molecular level: ear surfae of the orte; otais…
• Inhibitory basket and stellate cells
• Excitatory parallel fibers associated with granule cells
• Purkinje cell dendrites
2. Purkinje cell level
3. Inner level: contains excitatory granule cells and inhibitory Golgi cells
The only output from the cerebellar cortex is from the purkinje neurons
• Uniquely inhibitory (neurotransmitter GABA), unlike other parts of the cortex, which have a balance of excitatory and inhibitory activities.
top: simple spike; bottom: complex spike
The action of Purkinje cells is determined by two excitatory afferent inputs
1) Mossy fibers: simple spikes
2) Climbing fibers: complex spikes
CLIMBING FIBERS
Climbing fibers have a powerful synaptic effect on Purkinje neurons.
• Each action potential results in a prolonged depolarization that produces a complex spike
PARALLEL FIBERS
Parallel fibers produce a single action potential called a simple spike
Changes to the pattern of complex and simple spike activity have been implicated in motor learning
• Climbing fiber activity may function as an error signal.
• When there is an error between what was intended to happen and what actually happens as a result of movement, there is an increase in complex spikes
• Purkinje cell discharge during learning show increased complex spike activity when performance is poor
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All activity seen above is the result of simple spikes, except the heavy dots, which are complex spikes
• Note the very low frequency of complex spike activity
Both cells have a high frequency of discharge, especially Purkinje cells, in comparison to neurons in M1.
• Purkinje cell firing rates at rest are approximately 100 spikes/second.
• This can be contrasted with tonically active cerebral cortical neurons (20 spikes per second)
Upward: flexion movement (ipsilateral)
Whenever there is movement, there is suppression of firing in both types of neurons
Deep nuclear cells maintain high spontaneous rates of firing while simultaneously receiving inhibitory input from the cerebellar cortex.
Above are recordings only from Purkinje cells
• Complex spike activity is not related to one phase of movement in an orderly manner
• There is specificity of neuron sensitivity (preference for particular movement)
Purkinje cells in lobules IV and V are tonically active, reflecting mossy fiber and granule cell simple spike input.
• Complex spike activity is not associated with the movement
GRANULE CELLS HAVE TERMINATIONS ON PURKINJE CELLS, BUT WHAT DRIVES GRANULE CELLS?
1. Somatosensory receptors in the ipsilateral arm
2. Motor and sensory arm areas in pre- and post-central cerebral cortex
Even though the action of Purkinje neurons on deep cerebellar nuclei is inhibitory, deep nuclear cells are also tonically active.
The common firing pattern of Purkinje and deep nuclei cells may reflect a common input
PURKINJE CELL ACTIVITY DURING MOTOR LEARNING
After the animal learns to make a wrist movement, a perturbation is delivered. With practice, the animal adapts and learns to correct for this perturbation.
• Simple spikes: increased activity during preferred movement
• Complex spikes: rarely seen for well-learned movements; not correlated with movement pattern
However, once a load is introduced, there is increase in complex spike activity. It is as if the complex spikes signal the error between the intended movement and
actual movement made.
Once the animal adapts to the load, there are (almost) no complex spikes, and mainly simple spikes remain.
Thus, the cerebellum is involved in corrective learning
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Location of hand in degrees
The animal learns to adapt to a sequence of predictable perturbations
• Perturbation to the right → correct for perturbation
• Perturbation to the left → correct for perturbation
Once the animal gets good at correcting for the perturbation, the magnitude of only one perturbation is changed.
Each curve is the response to a single perturbation (one trial)
• Straight line: stable limb
• Curved line: unstable limb due to perturbation
• Arrow: change in load
Note that when a perturbation was applied on the 4th trial of extensor movements, the line becomes distorted.
Over time, the animal adapts and movement becomes stabilized again.
Each row represents a single trial, aligned at movement onset (one neuron).
• Alternates between flexor and extensor directed load
• Small dots indicate a simple spike discharge and large dots indicate complex spikes.
The cell activity is load-related: higher overall discharge for flexor load
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
There are 5 different kinds of cells in the cerebellar cortex (all but one are inhibitory) The cerebellar cortex is divided into three parts: molecular level: (cid:374)ear surfa(cid:272)e of the (cid:272)orte(cid:454); (cid:272)o(cid:374)tai(cid:374)s . Inner level: contains excitatory granule cells and inhibitory golgi cells. The only output from the cerebellar cortex is from the purkinje neurons. Uniquely inhibitory (neurotransmitter gaba), unlike other parts of the cortex, which have a balance of excitatory and inhibitory activities. The action of purkinje cells is determined by two excitatory afferent inputs top: simple spike; bottom: complex spike: mossy fibers: simple spikes. Climbing fibers have a powerful synaptic effect on purkinje neurons. Each action potential results in a prolonged depolarization that produces a complex spike. Parallel fibers produce a single action potential called a simple spike. Changes to the pattern of complex and simple spike activity have been implicated in motor learning.
