Pigeon brain:RUB scientists investigate anatomy of the pigeon brain

New insights into connections between brain hemispheres

Research aims to draw conclusions about human brain

The brain of Columba livia, a close relative of the domestic pigeon, is an evolutionary precursor to the human brain; making it particularly interesting for neuroscientists. In contrast to the human brain, the brain of pigeons does not have a corpus callosum. This thick strand of nerve cells connects the brain hemispheres of humans and other mammals. In pigeons, the two halves of the brain are connected by the much smaller commissura anterior. Scientists of the Collaborative Research Center 874 at the Ruhr-University Bochum have taken a closer look at this structure. They hope to gain a better understanding of interhemispheric exchange in birds and other vertebrate classes. “The Journal of Comparative Neurology” has published the results of their neuroanatomical study.

Even without corpus callosum: birds are capable of complex behavior

Exchange of information between the brain hemispheres is key for survival. Neuroanatomists call structures, which connect the two halves of the brain “commissures”. In the brains of humans and other mammals the hemispheres are connected via the corpus callosum, the commissura anterior (“anterior commissure”) and the hippocampal commissure. Birds, similar to marsupials, lack a corpus callosum as a major interhemispheric pathway. Exchange between the brain halves occurs for the main part via the anterior commissure. Despite this, birds are capable of complex behavior and cognitive operations.

New tracing methods to investigate the anterior commissure

As early as the 1970s, scientists were able to show that the anterior commissure of pigeons connects a wide range of brain structures. Since then, methods of tracing the connections of the central nervous system have improved significantly, explains PhD student Sara Letzner: “Using current methods, we can now show much more accurately where nerve strands begin and where they end.” The team around Letzner and Prof. Dr. Onur Güntürkün has used these new tracing methods to look more closely at the anterior commissure of the pigeon – the first time in over 40 years.

Significant differences to mammals

The neuroscientists were able to show that amongst many similarities between the commissura anterior of mammals and pigeons, there are also some major differences. In contrast to humans, there are no olfactory, or smell-related, interconnections in pigeons. Apart from somatosensory information, like temperature sensitivity and pain perception, no primary sensory areas are connected at this commissure. A further significant difference on a structural level is that the anterior commissure of pigeons predominantly connects non-corresponding areas of the brain hemispheres and that these connections are mostly one-way streets. The scientists were also able to show, that only an extremely small number of neurons participate in interhemispheric exchange at the commissura anterior.