He kept a secret locked tight in his heart.
When speakers of Modern English use images such as these, which locate emotions and thoughts in the heart, we do so metaphorically. Writers of Old English texts, too, locate emotions and thought in the heart and the chest, but do they do so metaphorically?Evidence from within the Old English corpus alone does not provide a satisfactory answer to this question. However, a comparison of the Old English evidence with a vast array of cross-cultural analogues, from the Greek Presocratics to the data gleaned by modern-day transcultural psychiatrists, suggests that the Old English mind-in-the-heart was, at some point in the history of the language, used as a literal expression of everyday perceptions of the physiology of emotion.
In order to discern when the mind-in-the-heart became a metaphor, we can turn again to Old English and Anglo-Latin sources, especially homilies and medical texts, which demonstrate that Anglo-Saxons of the eleventh century increasingly associated the mind with the incorporeal soul and the mind’s faculties with the organ of the brain.