That strong emotions can make our heart beat faster is well known, but how moods affect other organs, or what effect particular physiological conditions have on human emotions, has not yet been demonstrated. Until now.

A new research project on eLife, coordinated by Sapienza in collaboration with the IIT-Italian Institute of Technology and Santa Lucia Foundation IRCCS in Rome, focused on the digestive system and, in particular, the stomach. Using ingestible pills equipped with sensors, it was found that the PH of the stomach is strongly linked to the perception of different types of emotions, paving the way for future research on the subject.

Each of the 31 participants, all men aged between 20 and 30 (to reduce the variability of the sample), was asked to ingest a millimetre-sized capsule fitted with sensors capable of measuring PH, temperature and pressure inside the digestive organs. This technology, developed for gastrointestinal medicine, is an absolute novelty in psychological studies and proves promising for future research in this field. At the same time, the participants were also monitored externally by measuring their heartbeats, the electrical (and therefore nervous) activity of their stomachs and by observing the blinking of their eyelashes.

Next, they were shown five types of videos capable of triggering different emotions: fear, disgust, happiness, sadness and a non-specific neutral state.

A questionnaire completed by the volunteers showed that the effects produced are not only concentrated in the heart or lungs but involve, already at a perceptible level, the stomach directly, especially in cases of disgust and fear.

Using the pill sensors, it was possible to capture PH data in real time. What the researchers noticed was that participants with a lower PH (and therefore a more acidic stomach) tended to feel more disgust and fear, while those with a higher PH, happiness, this happened especially when watching disgusting videos.  However, it was also observed that the volunteers' stomachs were generally more acidic when watching disgusting films than when watching frightening, happy and neutral films and less acidic when watching happy films.

With regard to the externally detectable electrical signals of the stomach, no correlation was found with the emotion experienced, apart from an increase in the speed of tachygastric cycle frequencies when participants watched happy videos.

The temperature and pressure measured by the pills did not provide any particular indication either but helped clarify the position of the device within the digestive tract.

On the other hand, the analysis of the heartbeat showed a great influence of the sensations produced by the videos and the same applies to blinking, which decreases for both positive and negative scenarios compared to neutral ones, except the sad videos. This reveals the link of the act of blinking with attention, the need to remain alert and the acquisition of information.

By revealing the complex network of relationships between gastric functions and emotions, this research paves the way for future investigations and insights into patients suffering from gastrointestinal diseases or depressive and autistic spectrum disorders. The innovative technology used, which employs sensors inserted into ingestible pills, can also be applied in new research into the relationship between internal organs and various states of mind.