Monday, 2 September 2013
Things are normal when he wakes up each day, but as time progresses he comes to experience an increasingly intense smell of skunk excrement mixed with onion. Stranger still, he's found that on a 0-10 scale the stench intensifies from 0 to 7-10 in the few hours preceding a storm. Writing in the International Journal of Biometeorology, S.R. Aiello at the University of Michigan-Ann Arbor and Alan Hirsch at the Smell and Taste Treatment and Research Foundation state that this is the "first reported case of weather-induced exacerbation of phantosmia."
Apart from a pending storm, other factors that intensify the man's odour hallucinations include "coughing, nasal congestion, and tiredness". Relief comes not just from eating but also "watching TV, nasal irrigation ... occluding the nostrils ... snorting salt water, blowing of the nose, laughing ... humming and talking."
Aiello and Hirsch conducted extensive tests of the patient's smelling abilities and found him to be significantly impaired. This is consistent with a diagnosis of Parkinson's Disease and makes sense in terms of his hallucinations, the researchers explained, because "impaired ability to smell allows disinhibition of spontaneous olfactory discharge."
The researchers present several possible explanations for why the man's phantom smells intensify prior to a storm: a drop in atmospheric pressure could further impair his sense of smell, thus disinhibiting his phantosmia; if his olfactory nerves (involved in smell) are damaged in some way, a lower atmospheric pressure may cause contractions of the scar tissue, exacerbating the hallucination that way; or the weather changes prior to a storm could lower the man's mood, perhaps intensifying his focus on his unpleasant hallucinations.
Unfortunately, Aiello and Hirsch didn't actually test the veracity of the man's claims about his storm predicting abilities. This leads them to admit: "the weather dependent phantosmia may not truly exist, but rather may be a misattribution error."
Just as we tend to remember all those times that we received a phone call from a friend or relative just when we were thinking of them - but none of the more numerous times when we weren't - perhaps this patient's purported forecasting ability is a trick of memory. This explanation is supported by the fact that twenty years earlier the patient claimed to predict the weather based on worsening of pain in a torn cartilage. This history may have led him to expect other sensory experiences to be weather-related and to seek out meteorological associations with his phantom smells that may not be real.
Aiello SR, and Hirsch AR (2013). Phantosmia as a meteorological forecaster. International journal of biometeorology, 57 (5), 813-5 PMID: 23456373
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.