No two cells act the same

In physics it is often reasonable to assume that all members in a population of particles (e.g. molecules in a gas) are identical, and all individual particles behave in the same way. However, this may not be a good approach in biology. For experimental neuroscientists it was always clear that individual nerve cells exhibit considerable intrinsic differences, even if they are of the same type and situated in the same brain area. Their morphology varies strongly and their ion channel equipment may differ widely, to name just two examples. As a consequence of this heterogeneity in their intrinsic properties, the spike patterns that these neurons produce in response to identical input may differ considerably. But what is the significance of these differences for the functioning of the brain?

In a study published in the journal Physical Review E, Man Yi Yim, Ad Aertsen and Stefan Rotter from the Bernstein Center Freiburg and the University of Freiburg’s Faculty of Biology investigated two basic questions: How can scientists handle and represent this heterogeneity of neuronal properties appropriately in theory? How does it affect the response of a population of neurons? Due to the mathematical complications of this problem, this kind of cellular diversity had previously not received much attention in theoretical models. The scientists from Freiburg now tackled this problem by “rescaling” the equations that govern the dynamics of a simple model neuron in a systematic way, such that the neuronal diversity remained mathematically manageable.

Next, Yim and her colleagues simulated a population of neurons and specifically accounted for the effects of heterogeneous parameters. In doing so, they could quantify how firing rates differed between neurons and explain to which degree they tended to desynchronize their activity. Both effects had been observed recently in experiments with real nerve cells kept in petri dishes. The scientists hope that their findings will help to understand how the biological diversity of neurons contributes to the ability of neuronal networks to encode and process information efficiently – which, after all, is the primary task of the brain.
 

Original article (subscription required):

Man Yi Yim, Ad Aertsen, and Stefan Rotter (2013) Impact of intrinsic biophysical diversity on the activity of spiking neurons. Phys. Rev. E 87, 032710. doi: 10.1103/PhysRevE.87.032710

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So far, most mathematical models of neuronal populations described different cells by the same equations. A new approach, allowing for individuality regarding certain parameters (small index numbers) takes into account that in biology, no two cells behave in exactly the same way.