With any hallucinations, if you can do functional brain imagery while they're going on, you will find that the parts of the brain usually involved in seeing or hearing - in perception - have become super active by themselves. And this is an autonomous activity; this does not happen with imagination.
Interpretation
The quote explains that during hallucinations, specific brain areas responsible for perception become highly active, distinguishing these experiences from mere imagination.
Oliver Sacks highlights the neurological basis of hallucinations, identifying that they trigger heightened activity in the brain regions typically associated with sensory perception. This points to the idea that hallucinations are not simply figments of imagination, but rather autonomous activities that can be observed and measured in the brain, providing insight into how our mind processes reality and illusions differently.
In practice
In a lecture on mental health, you can quote Sacks to explain the neurobiological differences between hallucinations and imagination.
There will be no one like us when we are gone, but then there is no one like anyone else, ever. When people die, they cannot be replaced. They leave holes that cannot be filled, for it is the fate - the genetic and neural fate - of every human being to be a unique individual, to find his own path, to live his own life, to die his own death.
In general, people are afraid to acknowledge hallucinations because they immediately see them as a sign of something awful happening to the brain, whereas in most cases they're not.
Dr. Kertesz mentioned to me a case known to him of a farmer who had developed prosopagnosia and in consequence could no longer distinguish (the faces of) his cows, and of another such patient, an attendant in a Natural History Museum, who mistook his own reflection for the diorama of an ape
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We see with the eyes, but we see with the brain as well. And seeing with the brain is often called imagination.
I rejoice when I meet gifted young people... I feel the future is in good hands.
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Those who study the stars have God for a teacher.
The unreasonable efficiency of mathematics in science is a gift we neither understand nor deserve.
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