Reading the words halitosis or jasmine activates the olfactory areas of the brain

Jul 18 2006

There are words whose power to evoke sensations has become proverbial. Just hearing them brings to mind the image, sound or feeling of that little fragment of reality they refer to. But what is the mechanism that accounts for this connection between a word and the mental imagery it conjures up?

A joint research project carried out by scientists from the Universitat Jaume I and the Cognition and Brain Sciences unit at the Medical Research Council in the UK has gone a step further towards finding an explanation for this phenomenon. With the help of magnetic resonance imaging, the team observed that reading words with strong connotations to odours not only triggers activity in the brain areas related to language, but also those linked to the sense of smell.

Garlic, stink, incense, urine, lemon, armpit, lavender… 23 people read these and another 53 words related to smells (either pleasant or unpleasant) that were jumbled up with another 60 words with no aromatic association. At the same time, images of their brain activity were registered using magnetic resonance. Findings showed that reading the words associated with a smell triggered activation of the area in the brain that processes olfactory information. More specifically, the areas involved were the primary olfactory cortex and the orbitofrontal cortex. In contrast, when the volunteers read words with no aromatic connotations, these regions of the brain remained inactive.

From these results, the researchers believe that when we acquire knowledge or experience about something that has a word to describe it, the brain connects the two pieces of information, that is, linguistic and sensory, in order to create the semantic meaning. “Given the fact that words are normally used with the objects and actions they refer to, the cortical neurons that process the information related with the words and with the objects are activated at the same time. In this way data about the referent and about the word are brought together through the cortical networks or neuronal webs”, the researchers explain in a paper that is soon to be published in the journal Neuroimage.

This concept was already put forward in the mid-20th century by Donald Hebb, one of the fathers of neuropsychology, in his well-known principle of correlation-based learning. According to this principle, any two cells or two systems of cells that are repeatedly activated at the same time will tend to become associated so that the activity taking place in one facilitates the activity of the other. Thus, when the sensory information produced by the smell of cinnamon is stored in the brain and we label it, cinnamon, a link is set up between the groups of neurons that store the two types of data. That is why, on smelling a stick of cinnamon its name suddenly comes to mind and, conversely, when we read the name we know what smell it refers to.

“The fact that primary olfactory areas are activated by words with olfactory semantic associations supports the idea that sensory information linked to the referent of a word is important for its neuronal representation”, says the research team led by Julio González, César Ávila and Alfonso Barros, who are all scientists working in the Department of Psychology at the Universitat Jaume I.

Other previous studies have obtained similar evidence that lends support to this theoretical perspective, especially for words expressing actions that are semantically related with different parts of the body. Thus, previous research has shown that reading, for example, a verb related to the legs, such as kick, activates both the classical language areas and the motor areas involved in moving the legs and feet.

According to the authors of the study, in which the radiology company Eresa also collaborated, all these data suggest that the meaning of words is not confined solely to areas of the brain concerned with language, but rather “it seems that semantic representations are distributed systematically throughout the entire cerebral cortex”.

The work carried out by the Universitat Jaume I and the Medical Research Council in Cambridge goes a long way towards furthering our understanding of the principles governing the organisation of the human brain.