A new study provides evidence that basic human learning systems use areas of the brain that also exist in the most primitive vertebrates, such as certain fish, reptiles and amphibians.
Researchers from the Swedish medical university Karolinska Institutet investigated the limbic striatum, one of the evolutionarily oldest parts of the brain. They explored how individuals learn movements (consciously and unconsciously) through repetition.
Many of the mundane skills that we apply every day, such as buttoning a shirt or playing an instrument, comprise a sequence of discrete movements that must be carried out in the correct order.
Scientists have long known that there are two learning systems for such patterns of movement: the implicit and explicit systems.
With the implicit system, we learn without being aware of the fact and without conscious training, such as through simple repetition.
The explicit system, on the other hand, we use when we consciously train and are aware of what we are learning.
The basal ganglia, which lie deep in the cerebral hemisphere, is involved in learning and motor control. Dopamine, a substance used in the transmission of signals between neurons, is important for learning and the plasticity of the basal ganglia.
In the present study, published in PNAS, the journal of the American Academy of Sciences, researchers have examined both the implicit and explicit learning of motor sequences in relation to the number of dopamine D2 receptors in the basal ganglia.
While they found a correlation between D2 receptor density and both forms of learning, they also noted that the evolutionarily oldest part of the basal ganglia — the limbic striatum — was involved only in implicit learning.
“In other words, we probably have certain fundamental learning systems in common not only with rats, mice and other mammals, but also with the most primitive vertebrates, which also have a limbic striatum,” says Dr Ullén.
In the future, a better understanding of how these learning systems work can be of use in developing new treatments for diseases such as Parkinson’s and Huntington’s, diseases which are characterized by disorders of basal ganglia function and impaired motor skills.
Source: Karolinska Institutet