Birds and mammals share common brain circuit for learning
A groundbreaking study led by scientists at the Massachusetts Institute of Technology (MIT) in the US has discovered an evolutionary connection between birds and mammals. Despite extensive anatomical differences in their cerebral cortices, birds and mammals use a common learning mechanism. The research, funded in part by a grant under the EU's Seventh Framework Programme (FP7), gives weight to speculation that such learning lessons can give human biology a boost and lead to new treatments for human disorders including Parkinson's disease. The findings are published in the Journal of Neuroscience. Researchers commonly use bird song learning as a model system in order to assess the general principles of learning, and complex actions in particular. Experts consider bird song learning as being a very stereotyped form of learning. But from a scientific perspective, it has never been easy to compare between bird and mammalian systems because of the differences found in the cerebral cortices of both groups. Thanks to their study, the MIT team, along with colleagues at Hebrew University in Israel, identified specific classes of neurons with the brains of songbirds and matched them to their mammalian counterparts. Targeted in this investigation was a region of the brain called the basal ganglia, a set of neural structures found deep inside the cortex. These tightly interconnected clusters of nerve cells play a crucial role in skill learning and habit formation. Researchers have linked the basal ganglia to various disorders like obsessive compulsive disorder and Parkinson's disease. According to the researchers, Parkinson's in particular is impacted by two key structures: the striatum and globus pallidus. These structures, located within the basal ganglia, are crucial for motor sequence learning. A growing number of research shows that birds have similar brain circuits, which underlie song learning. The major difference, however, is that anatomical divisions do not exist in birds. Their basal ganglia cell types are intermixed within a very tiny structure known as 'area X'. MIT's Dr Jesse Goldberg and Professor Michale Fee recorded electrical activity from single neurons in the brains of young zebra finches. They positioned the electrodes specifically within area X with help from a motorised microdrive. The patterns of electrical activity generated while the birds were singing allowed the scientists to pinpoint two distinct classes of neurons that reveal diverse firing patterns. Their recordings were compared with the activity patterns recorded from two known anatomical pathways in monkey globus pallidus. The researchers found that the patterns were very similar between the two species despite that birds have much faster firing rates (up to 700 spikes per second, which experts say are some of the fastest neurons). The team also established that one of the two classes in birds has the same types of connections as their primate counterparts. 'Our results strongly suggest that the same brain circuits underlie learning in birds and mammals, despite the superficial differences of anatomy,' explained Dr Goldberg, who works at MIT's McGovern Institute for Brain Research. 'This circuit must have evolved at least 300 million years ago, before birds and mammals diverged.'
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Israel, United States