NMR Conditioning Flashcards
We have selected NMR conditioning to investigate and have determined which parts of the brain is involved, what is the next step?
Establish the circuitry
Give an overview of what lesions indicated about what brain areas are involved in NMR conditioning
A lesion between the forebrain and the brainstem in the rats brain, cutting off the cerebral cortex and hippocampus from the brainstem and cerebellum, (decerebration) did not affect delay NMR conditioning
However, such conditioning is not possible after cerebellar damage
Must be the cerebellum
What are the main questions we want to answer by establishing the circuitry?
How does the cerebellum connect with the CS and US inputs, and with the CR outputs
What techniques can be used to establish the circuitry?
3 basic techniques
1. Neuroanatomy
2. Electrophysiology
3. Manipulation
What is involved with the neuroanatomy technique?
Finding out what connects with what
For any collection of neurons:
- Where do they project?
- Which regions project to them?
Neuroanatomy techniques often cannot be seen directly, even with a microscope, how do we overcome this?
Use tract-tracing methods
What are the two types of tract-tracing methods?
Retrograde transport
Anterograde transport
What is retrograde transport?
Used to trace neural connections from their point of termination (the synapse) to their source (cell body)
A tracer substance that will be taken up by synaptic terminals is injected into a region of interest, such as a central nervous system nucleus
The tracer is then conveyed retrogradely by axonal transport to the cell bodies of the neurons that give rise to the projection being labeled
What is anterograde transport?
Used to trace axonal projections from their source (cell body) to their point of termination (the synapse)
Inject substance into the nucleus, substance is transported to terminals
What can we find out using electrophysiology?
What signals are carried by these connections?
Establish their properties e.g., by recording from individual neurons while animal is presented with sensory stimuli, and/or performing motor responses
Example = orientation specificity of neurons in visual cortex
What does manipulation tell us about circuitry?
What happens when a particular region is removed, inactivated or stimulated?
Try to predict effects from anatomy and physiology
Standard systems neuroscience
What is the NMR conditioning circuitry broken down into?
5 parts ==
- Unconditioned reflex pathway
- Conditioned reflex circuit: conditioned response
- Conditioned reflex pathway: cerebellar cortex
- Conditioned reflex circuit: CS pathway
- Conditioned reflex circuit : US pathway
What does the unconditioned reflex pathway consist of and what is an advantage of this?
Basic three neuron reflex arc
1. Sensory neuron (in Gasserian ganglion)
2. Interneuron (in trigeminal nucleus)
3. Motor neuron (in abducens nucleus)
Only 3 synapses - 2 in the CNS and the nerve-muscle synapse
Therefore, is very fast - overall about 20msec of which 16msec is mechanical, 2.5ms time for trigeminal neurons to respond to air puff, only 2.5ms in the CNS - makes sense given the importance of protecting the eye
Explain the unconditioned reflex pathway
Synapse 1 = Cornea projects to the spinal trigeminal nucleus via the trigeminal nerve 5 with cell bodies in the Gasserian ganglion
Synapse 2 = spinal trigeminal nucleus projects to the accessory abducens nucleus
Synapse 3 = accessory abducens nucleus project to the retractor bulbi muscle via the abducens nerve 6
Retractor bulbi muscle pulls eye back into the orbit, the nictitating membrane then slides over the eyeball
What do we know about the conditioned response as part of the Conditioned Reflex Circuit: CR?
Lesions of the deep cerebellar nuclei block the CR and any pre-existing conditioning is abolished and cannot be re-learned
In fact, lesions confined to the anterior interpositus nucleus are effective