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Synapse formation is associated with memory storage in the cerebellum
Jeffrey A Kleim1, John H Freeman, Rochelle Bruneau
1Canadian Centre for Behavioural Neuroscience, Department of Psychology and Neuroscience, University of Lethbridge, Lethbridge, AB, Canada T1K 3M4. jeffrey.kleim@uleth.ca
Summary
Eyeblink conditioning in rats increases synapse number in the cerebellum, demonstrating that synaptic growth (synaptogenesis) is key to forming memories in the mammalian brain.
Area of Science:
- Neuroscience
- Cellular Biology
- Behavioral Science
Background:
- The concept of synaptic growth encoding memory is longstanding but challenging to prove in mammals.
- Mammalian behavior and neural complexity hinder direct demonstration of memory-related synaptogenesis.
Purpose of the Study:
- To investigate the impact of classical eyeblink conditioning on synapse numbers in the mammalian cerebellum.
- To determine if synaptogenesis contributes to the formation of conditioned responses and memory.
Main Methods:
- Eyeblink classical conditioning was performed on rats.
- Synapse counts per neuron were quantified in the cerebellar interpositus nucleus.
- Comparison was made between conditioned, unpaired, and untrained control groups.
Main Results:
- Conditioned rats exhibited significantly higher synapse numbers per neuron in the cerebellar interpositus nucleus compared to controls.
- The observed increase in synapses was attributed to the addition of excitatory, not inhibitory, synapses.
- This suggests strengthened inputs from precerebellar nuclei, not cerebellar cortex.
Conclusions:
- Synaptogenesis, specifically the addition of excitatory synapses, is demonstrably linked to the formation of conditioned eyeblink responses.
- These findings provide direct evidence that modifications in neural pathways via synaptogenesis contribute to memory formation in the mammalian brain.