Final answer:
CREB plays a key role in regulating gene expression and synaptic plasticity in long-term memory.
Step-by-step explanation:
The function of CREB (cyclic AMP response element-binding protein) in long-term memory is to regulate the transcription (gene expression) of proteins necessary for memory consolidation and storage in the brain. CREB is activated by neuronal stimulation and plays a crucial role in synaptic plasticity, which is the ability of synapses to strengthen or weaken over time. In the context of long-term memory, CREB helps to form and strengthen connections between neurons, facilitating the encoding and retrieval of new memories.