|
| Return to Abstracts > | Printable Version |
| November 02,2006 – SOSI Abstract Number: 7 Odors and Pain, John Prescott, PhD It is widely believed that the smells around us (often referred to as aromas or odors) can influence our moods, and perhaps even our behaviours or our state of health. This is the basis for much of aromatherapy. While the scientific evidence for many such beliefs is not strong, one reliable effect, seen in a number of studies, is that responses to pain are reduced in the presence of certain odors. But what these odors have in common has been unclear. Certainly, odors that are able to distract attention away from pain can lower the pain experience, as can other types of distractors such as enjoyable movies or music. Alternatively, odors that are pleasant have been shown to have a positive impact on mood, which in turn can reduce pain. Again, though, odors may not differ in this regard from anything else that makes us feel better or worse. However, recent research has suggested that thre may be pain reducing effects that are quite specific to odors, especially those that are described using taste qualities such as "sweetness" or "sourness." When asked to come up with words that describe vanilla, caramel or strawberry, the most common response is ‘sweet’. Similarly, vinegar and other acidic substances are often described as ‘sour’ smelling. Over the past decade, researchers have shown that these odor ‘taste’ qualities originate in repeated pairing of an odor and taste, typically in foods or drinks. For example, unfamiliar odors can be shown to become sweet smelling after being paired in a drink together with sucrose. Through this ‘associative learning’, odors appear to take on the characteristics of the taste. Sweet tastes activate the brain’s opioid (morphine-like) reward systems. This imbues sweet tastes with two remarkable properties. Firstly, sweetness in universally liked and as such, it can encourage the development of liking in other qualities that we find in foods and drinks. Hence, we are much more likely to get to like a new drink flavor if the drink is sweet. Secondly, since the opioid reward systems also modulate pain experiences, sweet tastes have been shown to reduce pain – a finding that has even led to the use of sweet tastes as pain relief in hospital settings, and a finding that is relevant for understanding the impact of odors on pain. The possibility exists therefore that sweet-smelling odors may have similar analgesic effects if they activate the same opioid systems as a result of associative pairing with sweet tastes. This hypothesis can be easily understood in termed of Pavlovian conditioning. When the dogs used by the Russian scientist Ivan Pavlov to study the physiology of digestion started to associate certain sounds with feeding time, the flow of gastric juices became conditioned to the sound, so that eventually the sound itself had the same impact as the presence of the food. The same process is evident whenever we smell the aroma of food cooking – especially when we are hungry. The idea that sweet-smelling odors might similarly activate opioid systems as a result of prior pairing with sweet tastes was recently tested in a laboratory study in which university students inhaled odors that varied in pleasantness and sweetness while their forearms were immersed in painfully cold water. Consistent with an associative or Pavlovian learning explanation of odor pain effects, while inhaling the odor that was sweet-smelling, the students kept their arms in the cold water significantly longer than in conditions where the odor was either pleasant, but not sweet-smelling, or unpleasant. These latter two odor types had no greater impact on pain tolerance than when no odor was present. These results not only provide a plausible mechanism for the impact of odors on pain, but they also indicate why some odors – vanilla, musk, and other sweet-smelling volatiles – are so widely used in both flavours and fragrances. The presumed ability of these odors to activate the brain’s opioid reward systems means that formulations including significant sweet-smelling components will tend to be significantly more liked. As well, these research results suggest the possibility they may act on pain as well – perhaps even psychological pain. Prescott, J., The Basis of odor effects on pain: A review and investigation of conditioned odor effects (White Paper prepared for the Sense of Smell Institute). November 2006. |
|
 |
|
 |
|
|
|
 |
|
 |