Emotions directly influence processes of learning and memory in the brain, which could explain why first impressions last in our minds, a new study has found for the first time.
For the study, the researchers examined the electrical activity in the brains of rats during social behaviour.
They discovered strong rhythmical activity reflecting a state of excitement in the animal. This activity was particularly strong and synchronous between areas of the brain associated with social memory during the first encounter between two previously unfamiliar rats.
This rhythmical brain activity declined in strength and in the level of coordination between different brain areas as the encounter between the two rats was repeated.
"In other words, during the first encounter between the two animals, the distinct brain areas worked intensively and at a high level of coordination," said Shlomo Wagner of the University of Haifa in Israel.
"As the two animals got to know each other, the rhythmical activity declined in strength and the coordination between the different parts of the network trailed off," Wagner said.
The researchers compared the brain activity during this social behaviour with the activity sparked by non-emotional stimuli, such as an encounter with an inanimate object.
Although on the behavioural level the rats also showed a high level of interest in such stimuli, their brain patterns did not show the same level of coordinated rhythmical activity seen in the encounter with an unfamiliar rat.
The researchers also found that the brain continued to work at a high level of coordination for some time, even after the encounter had ended.
"In other words, we found a connection between the feeling of excitement, rhythmical activity in specific brain areas, and the cognitive process of memory formation," Wagner said.
"In essence, this finding explains why people tend to remember in particular their first encounter with a future friend or partner," Wagner said.
Having found the connection between social excitement and social memory, the researchers then sought to examine whether a different emotion would also influence the same network of brain areas in the same way.
The researchers duly exposed the rats to a different emotion - a negative one associated with exposure to a frightening stimulant.
It emerged that the brain works differently in this instance. Once again, strong rhythmical activity and coordination between the different areas associated with social memory was seen.
However, this took place on a different frequency and at a slower rhythmical pattern.
"It seems that when the emotion is social and positive, the brain tells the different areas to work according to one communication protocol," Wagner said.
The study was published in the science journal eLife.
