Plural of activation; the processes or instances of making something active or functional.
From 'activate' (Latin activus + '-ate' verb suffix) + '-tion' (suffix for nouns of action) + '-s' (plural). The term became prominent in neuroscience and chemistry in the 20th century.
Brain imaging studies now show 'activations' in different regions—patterns of neurons firing up when you think or feel something. It's fascinating that we can now literally see thoughts as physical patterns of brain activation.
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