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It can be fairly said that Collingridge et al . ' s ( 1983 ) observation was the stimulus that has led , on the one hand , to structural biological work at the atomic scale describing the key features of NMDA receptors that enables their coincidence function to happen ; and , on the other , to work with whole animals investigating the contributions that calcium signalling via this receptor can have on rhythmical activities controlled by spinal circuits , memory encoding in the hippocampus ( the topic of this article ) , visual cortical plasticity , sensitization in pain , and other functions .
 Chemical: NMDA; Chemical: calcium
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: NMDA; Chemical: calcium