Divide and compute
In the brain, many nerve cells from the cortex (yellow) connect to the striatum (violet) in a peculiar wiring pattern. Neuroscientists from Freiburg now found an explanation why this is advantageous.
Although the cortex, the outer layer of our brain, is commonly seen as the seat of cognition, other areas are involved in thought processes and behaviour as well. Whenever we need to make a decision or select a course of action from several alternatives, communication between the cortex and a structure called the striatum plays a crucial role. The peculiar wiring between these regions has been known for some time, but a study by Man Yi Yim and colleagues from the Bernstein Center at the University of Freiburg for the first time provides an explanation how this kind of connection serves a specific purpose. Their work has been published in the latest issue of PLoS Computational Biology.
As the striatum is an important station in the processing of thoughts and movements, nerve cells from all over the cortex make connections to this relatively small structure in the centre of the brain. Thus, striatum cells receive information from many different locations in the cortex. Despite this wide projection area and large number of input nerves, oddly enough, neighbouring nerve cells in the striatum rarely receive information from the same cortex nerves. Why the brain makes such an effort to avoid an overlap in nerve cells connecting to the striatum had remained unresolved thus far.
Because it is impossible to rewire the cortex-striatum connection experimentally, Man Yi Yim from the group of Arvind Kumar and Ad Aertsen opted for a different approach: She fed the available knowledge into a computer and built a model of these structures that she could investigate and manipulate.
Yim’s simulations revealed that in the striatum, a signal does not benefit from being transmitted to many neighbouring cells – this actually weakens its impact. A signal from the cortex stands a much better chance in competing among the multitude of interactions if it is unique to one or few pathways. This uniqueness, thereby becomes a factor independent from its strength, which also determines the fate of a signal. The scientists conclude that the striatum’s specific way to process signals helps to strengthen the representation of certain alternatives, while weakening others. Dividing up the information from the cortex and feeding it to different cells with as little overlap as possible thereby helps the striatum to compute in parallel what may be, at any moment, the optimal course of action.
Full article (open access):
Yim MY, Aertsen A, Kumar A (2011) Significance of Input Correlations in Striatal Function. PLoS Comput Biol 7(11): e1002254. doi:10.1371/journal.pcbi.1002254
Press release by the University of Freiburg (English/German)