How did Henri Bergson study memory before writing Matter and Memory?

Before writing Matter and Memory, Henri Bergson spent five years conducting an intensive study of the available literature concerning memory and the psychological phenomenon of aphasia, which is the loss of the ability to use language.1

Consistent with his philosophical method, Bergson began by analyzing empirical, observed facts supported by the most up-to-date scientific opinion of his time. He specifically investigated the doctrine of psychophysiological parallelism, which posited that every psychological fact is strictly determined by a corresponding physiological fact. By examining cases of aphasia, Bergson argued that patients often retained their understanding and intent despite an inability to speak, suggesting that the underlying memory remained intact while the bodily mechanism required for expression was impaired. This research led him to conclude that the mind is independent of the body, utilizing it as a tool to carry out its purposes.1