A 61 year-old lady was admitted to a Florida hospital with florid hallucinations after suffering a stroke to her thalamus. She saw curious strangers and visitors with odd clothes, but rather unusually, the ones on the right always seemed pleasant and happy, whereas the ones on the left always seemed fearful and unsettling.
The case was reported in the journal Cognitive Neuropsychiatry and is of interest because the emotional content of the hallucinations seem to match the dominant emotion of the corresponding hemisphere of the brain.
[The patient] described the right visual hallucinations as consisting of “college age boys in colourful Hawaiian shirts” that “are too happy, talk too much”, and that are somewhat “too energetic”. The patient called them the “he-haw boys,” and reported that she could hear them talking.
The left visual hallucinations were described as “men in black religious clothes that make no noises.” The patient called them “the eye drillers”, and stated that “they look a hole right through you”. The patient provided vivid drawings of the hallucinations that accentuated the positive and negative associations she had with each hallucination. The patient provided vivid drawings of the hallucinations that accentuated the positive and negative associations she had with each hallucination.
This is not the first time that hallucinations have been reported to be differing in emotional tone depending on which side of space they appear.
This is likely due to the way emotion is processed in the brain.
Perception of negative emotions often relies largely on the right hemisphere, where positive emotions are processed by both the right and the left hemispheres. In fact, this pattern of brain response has been found in children as young as 10 months old.
The woman in this case report didn’t suffer damage to the hemispheres directly, but to the thalamus. This area is often called the brain’s relay station as it is extensively connected to hemispheres, so damage in this area can often mimic damage to the cortex.
Link to PubMed abstract of case report.