Monkeys’ calls – the beginnings of human language?

Rhesus macaques communicate between themselves using a complex series of sounds that can signify things as distinct as the presence of danger, particular social relationships, emotions or food alerts. Now scientists in the latest issue of Proceedings of the National Academy of Sciences of the United States of America, while analyzing the brain areas activated during the recognition of these sounds, found that not only do monkeys seem to interpret these sounds using abstract representations like humans but they also use analogue neural networks, a discovery that can help to understand the origins of language in humans.

Ricardo Gil-da-Costa, Alex Martin and colleagues at the National Institutes of Health and the Harvard University in USA and at the Gulbenkian Science Institute in Portugal used positron emission tomography, a technique which allows the measurement of the functioning of distinct areas of the human brain with the individual conscious and alert, to study in Rhesus monkeys the brain’s response to the sounds used for communication within the species.

They were particularly interested in understanding how the monkeys processed the information transmitted by these sounds and the relationship with the mechanisms for human’s conceptual representation. The team of scientists used calls known to be associated with pleasant feelings, such as food recognition and friendly approach, or unpleasant emotions, such as fear, and analysed which areas of the brain were activated in each circumstance. As controls, non-biological sounds such as those produced by musical instruments were used.

Very interestingly, Gil-da-Costa, Martin and colleagues found that when listening to other monkeys’ calls, not only the sound-processing parts of the macaque brain were activated but also those areas associated with visual and affective/emotional-processing. This did not happen when the animals listened to non-biological noises, in which case only the parts of the brain associated with the processing of sounds were activated.

The stimulation of regions used to store visual information suggested to the scientists that the monkeys retrieve visual data to “read” the system of sounds used in the communication between members of the same species, just like in human where these areas are stimulated when listening to words with meaning. Furthermore, when “unpleasant” calls were played the monkeys exhibited activation of zones in the brain usually associated, both in humans and macaques, with the recall of emotional memories and the regulation of affective responses.

Gil-da-Costa, Martin and colleagues’ results are very interesting as they show that calls by other monkeys of the same species, sounds which the animals understand, lead to the activation in macaques’ brain of areas specifically associated with the visual memories of objects and their affective properties, exactly as listening to meaningful language activates the same areas in humans. Both phenomena represent examples of conceptual representation, in this case of sounds. This suggests a similar system of processing information in both humans and non-human primates, which lead to the proposal by Gil-da-Costa, Martin and colleagues, of a common pattern of evolution where the system described in this paper could have served partially as basis for the subsequent development of language in humans.

Piece researched and written by: Catarina Amorim (catarina.amorim@linacre.ox.ac.uk)