6. Basic Circuitry Flashcards
cerebellum: how does it connect the CS and US inputs with CR outputs?
3 techniques to study this:
- neuroanatomy
- electrophysiology
- manipulation
- neuroanatomy
- what connects what with what
- for any connection of neurons, where to they project and what regions project to them?
- tract-tracing (anterograde and retrograde)
tract-tracing (anterograde)
anterograde - around cell body, travels down axon to terminal buttons
- can use different colours to see where the cell bodies project substances to
tract-tracing (retrograde)
retrograde - inject substance around cell body, substance is transported up through axons of a neuron
- usually transported back into the cell body of another neuron
- electrophysiology
physiology - what signals are carried by these connections?
- recording from the individual neuron while animal is presented with sensory stimuli, and/or performing a motor response (to establish their properties)
e. g. orientation specificity for neurons in visual cortex
- manipulation
- what happens when a particular region is removed, activated or stimulated?
- try to predict effects from anatomy and physiology
- standard systems neuroscience
circuitry
can be broken down into 5 parts:
- unconditional reflex pathway
- conditional reflex circuit
- conditioned reflex pathway
- conditioned reflex circuit: CS pathway
- conditioned reflex circuit: US pathway
unconditional reflex pathway
- periorbital shock (skin around eye) is input > unconditioned blink = output
- corneal stimulation (from air puff - register from sensory neurons) - cell bodies outside of the brain itself in the Gasserian gangloin
- after stimulation, information travels down trigeminal nerve V, synapsing onto the spinal trigeminal nucleus (STN) in the brainstem (first synapse)
- neurons in STN synapse onto neurons in the accessory abducens nucleus (second synapse)
- axons leave the nucleus and travel down abducens nerve VI (6) - retractor bulbi muscles
- UR delay = 2-3 ms (from corneal stimulation to accessory abducens nucleus) - 3 synapse reflex
conditioned reflex circuit
conditioned response (shutting NM)
- Yeo et al., (1985) - lesions of deep cerebellar nucleus block CR
- how does signal get from anterior interpositus nucleus to abducens nucleus?
- goes via the CONTRALATERAL RED NUCLEUS (inactivation blocks CR)
- thought to coordinate the general face flinch
conditioned reflex pathway: cerebellar cortex
where does input from the interpositus nucleus come from?
- LOBULE VI (HVI) of cerebellar cortex - inhibits interpositus nucleus whilst others are excitatory
- Yeo et al., (1987) - lesions here affect CR
- Heiney et al., (2014) - cortical output is tonically active - for NMR you need to silence cortical output
- he inhibited Purkinje cell firing through optogenetics altering eye lids response (duration, intensity, rise time)
conditioned reflex circuit: CS pathway
where might the HVI get its input?
- Yeo et al (1985) - anatomy: relevant region of cerebellum receives from pons
- this connection is carried by MOSSY FIBRES .
- lesions of the pontine nucleus abolish conditioning
can pair stimulation of pontine nucleus with US and get conditioning - sound > pontine nucleus > mossy fibres > cerebellum: cortex and interpositus
conditioned reflex circuit: US pathway
cerebellum also requires input about US - Yeo et al (1987)
- neurons in the spinal trigmental nucleus send a branch of axons to the inferior olive (base of brain below cerebellum)
- this sends climbing fibres to cerebellum
- Yeo et al., (1986) - lesions in relevant regions of inferior olive abolish conditioning and prevent learning
- Thompson and Krupa (1994) - can use electrical stimulation of climbing fibres as the US = conditioning
> oral subdivision of STN send branch of axons > inferior olive > climbing fibres > cerebellum: cortex and interpositus
