When in a group, brains of mice and bats “synchronize” with others of their species

When animals socially interact with one another, a synchronization of brain activity takes place among the participants. This effect has been observed in mice, bats, and even in humans. The level of synchronization attests to the nature of the interaction.

In 2002, a group of researchers from Texas proposed a new method for measuring the coordination of brain activity among several participants, called Hyperscan. This method enables the simultaneous recording of brain activity in two different participants through fMRI scanning. The MRI system, employed extensively in medical examinations, is used to scan internal organs through magnetic resonance. A different analysis of the data generated by the system facilitates evaluation of brain activity; this is a functional examination widely used in brain research. Hyperscan involves parallel scans using two different MRI systems, which are connected to each other via the internet. The method has led to the development of a new branch of brain research, as it enables researchers to study human brain activity during social interaction, for example, while playing a computer game during the scan.

Unlike other fields in biological research, which typically begin with research on animals and evolve into research of human subjects, this field began in humans and remained exclusive to them for an extended time. This fact has left certain gaps in the researchers’ understanding, as research on humans is limited, both in terms of scanning capabilities, which must be non-invasive, and of the nature of the experiments that can be conducted, which take place in a less than “natural” environment.

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Synchronized bats

In a recently published paper, researchers in Michael Yartsev’s lab at the University of California, Berkeley, used a bat model to extend current knowledge of brain activity during social interactions. Using wireless electrodes inserted into the bats’ brains, the researchers recorded the bats’ neural activity as they were socially interacting with one another, which recorded the neurons’ electrical signals. This experiment enabled overcoming the limitations which human research poses, because the recording methods are more sensitive and accurate, and the variety of experiments that can be conducted is greater.

The researchers measured the degree of correlation in brain signals between two bats, or, in other words, to what extent were the brain cells acting similarly. They found a high degree of correlation in the brain activity of bats sharing the same environment, both when looking at averages of large cell populations and when observing local activity. The researchers were surprised to discover that even when the bats engaged in different behaviors, there still was a high degree of correlation in brain activity, but as the similarity of their behavior increased, so did the synchronization of their neural activity.

The quality of the interaction also affected the correlation in brain activity – the stronger the interaction between two bats, the stronger the correlation in their neural activity. Another interesting finding was that the level of correlation in neural activity predicted if the following interaction between the bats would be social or un-social – when the correlation was high, the probability of the next interaction to be social was also higher.

Another study published on the same day reported that a correlation in neural activity during social interaction was also found in mice also showed a correlation in neural activity while socially interacting. Similarly to the bat research, this study indicated that the correlation in the brain activity of mice can predict a subsequent social interaction. Other interesting findings were that the correlation is also observed during competitive behavior, and that the level of synchronization in brain activity could predict social dominance relationships among mice.

Many studies have been published to date in the field of human brain activity couplings, citing numerous examples for high synchronization during social interaction. The researchers suggest that the correlation seen in bats’ neural activity characterize social interactions in a natural environment, and may serve as a basis for future studies investigating the specific contribution of neural activity synchronization to social behaviors.