Fernández López, Mª Angeles. Master´s student in Biotechnology and Bioengineering of the Miguel Hernandez University 2015-2016.
Reference: Freiherr J, Lundström JN, Habel U, Reetz K. Multisensory integration mechanisms during aging. Frontiers in Human Neuroscience 2013; 7: Article 863. doi: 10.3389/fnhum.2013.00863
Thanks to our sensorial system, we are capable of interacting with our surrounding. The senses provide subjective and complementary information of the environment, which is of vital importance for an adequate perception, cognitive processing and action control, so that the latter can be performed in a safe and autonomous matter.
The majority of everyday perceptions pass through various sensorial systems, such as olfaction, hearing, sight, taste and touch. The brain has the ability to integrate all this information and return a coherent and single signal, removing all the excess noise that can interfere with the main information. However, it has also been shown that the perception of a stimulus can be favoured thanks to the combination with other senses. In this manner, multisensorial integration plays a vital role, allowing and improving perception as well as the individual´s capacities.
In this manner, multisensorial integration follows a series of guidelines:
- Unimodal stimulus should be applied during a short amount of time.
- A spatial concordance of the senses is necessary for a correct integration.
- A semantic or contextual congruence is necessary.
- They follow the principle of inverse effectiveness; in other words, they are more efficient the less ambiguous and intense the individual stimulus is.
Preliminary studies suggest that various brain regions are implicated in the data processing for a correct multisensorial integration, such as the superior colliculus. However, more recent studies, using new techniques, have demonstrated that a larger number of regions are implicated, such as the superior temporal sulcus, intraparietal sulcus, insular cortex, orbital and ventral zones of the frontal cortex and hippocampus.
Research in this area is divided into two branches. One is dedicated to the study of multisensorial integration through the observation of objects, whereas the other is focused on emotional perception. Therefore, the main objective of this review is to improve one´s knowledge regarding multisensorial integration, with a major focus on the behavioural and neuronal responses that occur during aging, especially in age-related diseases.
Understanding these processes during aging is of great importance, as the average population grows older and the changes that appear affect our quality of life. In this manner, the first question is: What changes occur in the multisensorial integration capacity during aging of healthy individuals?
As the individual ages, the senses significantly decrease, with a cognitive and motor capacity deterioration. Current studies have shown that complex structural changes occur in the brain while aging. Specifically, a 0.2% brain volume decrease is observed every year, which accelerates to 0.5% at 60 years of age, and further increases the older the individual. Therefore, grey matter and cortex is lost while aging, including the neuronal network that control the multisensorial integration. However, several studies have shown that the maintenance (or even improvement) of the response towards certain stimuli is possible in the aging population, if they are adequately trained. This response includes the time required to react to a response, as well as the ability to remove sensorial noise. Therefore, the study of the factors that allow the maintenance of multisensorial capabilities as well as the type of stimulus is an intense area of work.
As for neurodegenerative diseases, several studies have analysed and shown that certain modifications exist in this population, and how it affects the processing of multisensorial integration. For examples, Alzheimer´s disease, the most commonly studied pathology, is a type of dementia that affect 24.3 million individuals worldwide, with an enormous social and economic impact. The studies in this population has shown that an early intervention greatly improves their quality of life.
In conclusion, due to the demographic changes that our industrialized society is experiencing, it is necessary to understand the processes associated with multisensorial integration, since its degeneration is greatly related to a loss of quality of life while aging. New lines of work seem to show that it is possible to improve or maintain this integration while aging with proper training, making this field a highly relevant study for our society.