A river of water cannot be altered by the man on the bank. But thought and reason and curiosity do cause the stream of consciousness to alter its course and even change its content completely.

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– Wilder Penfield, The Mystery of the Mind (1975)

As a neurosurgeon in the 1930s, Penfield was applying a 2-volt electrode to various sites in an epileptic patient’s brain when he discovered a problem with the stream of conscious metaphor.

The patient, who was conscious during the procedure, reported that she was re-experiencing a remembered scene in which she was looking at her young son in the yard. The memory included sensory inputs from different sources – in addition to what she saw, she also heard neighborhood sounds, such as car traffic – and it was clear from events within the memory that it was a record in which time was passing (it was not a still picture). Being both a convergence and a flow, the memory was very much like a stream or river.

However, the patient was aware at the same time that she was in an operating room and talking with a neurosurgeon. The consciousness embedded in the memory was her own, experiencing the scene as real, but some other aspect of her consciousness was like the man on the riverbank, watching it all go by, knowing it was not happening right now. The man on the bank changed the content of the river, polluting it with self-aware self-awareness.

Alternatively, there is no man on the riverbank; memories may instead be undercurrents in the overall stream of consciousness. Currents and undercurrents may interact and change the course and content of streams.

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