Do you see what I see? (Hallucinations: Oliver Sacks)

     Oliver Sacks. Hallucinations (2012) A posthumous work assembled from Sacks’s notes and drafts. The result is a somewhat gappy discussion and occasionally rough style, but it still adds up to what to me appears a thorough survey of what’s known and unknown about hallucinations.
     Hallucinations are illusions, but they are almost always known to be illusions. Neurological research shows subtle differences between perception, illusion, hallucination, and memory. All involve the brain areas of sensory perception, but the limbic system and the frontal cortex behave differently. While we generally think first of visual hallucinations, hallucinations happen for every sense, as do illusions. Sacks as usual uses case histories to demonstrate the nature of different types of hallucination.
     I learned much. One thing is that the zig-zagged glittering visual aura that precedes most migraines is probably more common as the sole symptom of migraine. (Variations of it also precede epileptic seizures.) Since I experience that aura myself roughly once every other month or so, this information is somewhat reassuring.
     Another interesting fact is that people deprived of sight (even temporarily) experience visual hallucinations. These are oddly similar both in the content and in how the content changes over time.
      But mostly what I learned reinforces the hypothesis that the brain constructs the experience of what we are pleased to call reality. The centre of that experience is the self, the “I”. Sensory deprivation changes the “I”, not merely what the “I” sees or doesn’t see. Many people who lose their sight eventually are no longer able to remember their past visually, for example. But memories are at the core of our sense of self. We are not only our present experience, we are our memories.
     Another very good read. Recommended. ***½