When the brain stem sees the solution
Evolutionarily old brain structures control head and eye movements in all vertebrates. Surprisingly, they are also involved in "higher" thought processes.
Anatomically ancient structures in the brain stem are apparently involved in decision-making and thought processes, as a team led by neurobiologist David J. Freedman from the University of Chicago has discovered. This is astonishing because the cerebral cortex is usually considered the "seat of thought".
The so-called superior colliculi (the "upper hills") in the brainstem enable vertebrates to orientate themselves in space by controlling eye and head movements. This has been known for some time. Freedman and his team have now discovered that the brain areas also perform other functions. The experts monitored the neuronal activity in the superior colliculi and in a part of the cerebral cortex, the posterior parietal cortex, while the animals had to decide whether a wandering dot pattern belonged to a set of defined directions of movement.
During the month-long training phase, the researchers repeatedly rewarded the monkeys with fruit juice as soon as they assigned a pattern to the correct movement category by pressing a button. It was not possible for the animals to turn their heads during the measurements, and the stimuli were presented in such a way that the monkeys had to fixate on them. According to the authors, the smallest eye movements were not related to the cognitive task solution. Based on their experimental design, the experts were instead able to filter out the activity in the superior colliculi, which was apparently solely related to categorisation. When they chemically paralysed the brain region, the macaques' ability to correctly categorise the images also decreased dramatically and only recovered when the anaesthetic effect wore off. "Even in tasks where the animals do not have to move their eyes or focus their attention on different locations, the superior colliculus is involved in these more complex cognitive behaviours," says Freedman. "The superior colliculi are really a surprising place for these kinds of cognitive signals."
In the past, they were only associated with simple visual orientation and reflex motor functions. When it comes to correctly categorising visual information, however, the posterior part of the parietal lobe stood out. The new findings suggest that the brain stem is involved in thinking to a certain extent. Whether fish, reptiles or mammals - they all need to be able to quickly assess objects in their field of vision in order to survive: Is that an obstacle ahead, a predator or tasty prey? The superior colliculi not only allow us to orientate our head and eyes and thus our attention accordingly, but also appear to be involved in more sophisticated visual decision-making processes.
It is speculated that activation may be what gives us real "momentum" when solving problems. In fact, it is noticeable that people often use involuntary eye movements and hand gestures when trying to remember something or when deciding between alternatives. If you are asked what you had for dinner yesterday, for example, your gaze often involuntarily wanders upwards as if the answer were on the ceiling. First author Barbara Peysakhovich from Harvard University also suspects that this could be due to the fact that the superior colliculi are recruited during deliberation.
It is possible that the corresponding brain region plays an even more important role in visually driven thought processes in birds. This part of the brain stem is particularly well developed in birds. Their involvement in cognitive processes could therefore perhaps enable vertebrates to make lightning-fast decisions.
Spectrum of Science
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Original article on Spektrum.de
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