What epilepsy teaches us about diversity and resilience
There is growing recognition of the importance of equity, diversity and inclusion in society and its institutions. The most progressive and forward-thinking organizations consider the diversity of people to be essential to the success, growth, innovation and development of a company.
The benefits of diversity, however, are far from exclusive to human organizations; heterogeneity and variability are design principles at the heart of all complex natural systems, whether they are ecological, cellular or genetic networks.
Whether it is an ecosystem, a society or a brain, how is this diversity related to the functioning and stability of a complex system?
As neuroscientists, our interdisciplinary research and clinical work has drawn us to the incredible complexity and richness of the human brain and natural systems. We seek not only to better understand how brain circuits work, but also to develop new treatments for neurological diseases such as epilepsy.
Diversity equals resilience
First developed by Darwinthe idea that diversity leads to stability and survival has been debated by scientists from many disciplines for over a century. The ability of natural systems to resist change is a characteristic known as resilience. This fundamental characteristic emerges from the interactions between the members of the same system — such as the species of an ecosystem, the individuals of a group or the cells of an organism — and allows it to maintain its functions over time.
Resilience is tested by change. Some ecosystems can adapt to the extinction of specific species or to drought. Some virtual communities or social networks can resist cyberattacks. Some organizations may continue to function following a conflict, war, political revolution or… a pandemic.
In light of these common examples – and many others related to the social or natural sciences – it is now more important than ever to understand the role that diversity plays in maintaining the resilience of complex systems.
What if the clues to the answer lay in the circuitry of the brain, particularly in a brain with epilepsy?
Overturning in an electrical storm
For several years, our interdisciplinary team has studied epilepsy, the most common severe neurological disorder. Epilepsy is characterized primarily by the seemingly spontaneous and recurrent occurrence of seizures, often triggered by stress or visual stimuli (such as flashing lights or specific images). Recent research has also shown that the frequency of these attacks may vary depending on the time of day or monthdepending on the individual’s sleep-wake cycle, for example.
In this light, a brain with epilepsy can be seen as fragile and non-resilient, regularly rocking in an electrical storm. So, rather than adapting normally to changes, neurons become disproportionately active and synchronous, and the resulting intense electrical activity spreads out, disrupting brain function.
Because of the significant impact these seizures have on patients and their families, our team is relentlessly studying the circuits responsible for triggering them and exploring ways to prevent them.
What does diversity have to do with epilepsy? Our team recently measured the activity of neurons in people with epilepsy. We found that neurons in brain regions responsible for triggering seizures were much less diverse than those in regions not responsible for seizures. These neurons were eerily similar to each other, showing very similar characteristics and responses.
Could this lack of diversity explain why seizure-prone brains are less resilient?
Mathematical models to the rescue
To answer this complex question, we turned to mathematics. What if, using mathematical models of brain circuitry, we could understand how neural diversity (or lack thereof) predicts resilience to seizures? Could we determine if neural diversity promotes resilience in the brain?
Using our equations, we found that when diversity was too low, seizure-like activity emerged spontaneously: the activity of neurons would become vulnerable to a sudden change in synchrony, recalling what is observed during crises. These results are unequivocal: a low diversity made these neural circuits fragile, not very resilient and unable to maintain the type of activity necessary to maintain brain functions.
What do these results mean? They provide key insights into the role different types of neurons play in maintaining brain function.
These findings help us look at neurological diseases such as epilepsy differently than before, potentially opening up new avenues of how to treat them. Our approach of using interdisciplinary methods and mathematics enables us to dig deeper and better understand how diversity increases resilience, providing invaluable clues and answering difficult questions such as: is there a optimal level of diversity? What are the different types of diversities and do they all promote stability in the same way? Could we improve resilience by promoting neural diversity through targeted therapeutic interventions?
But above all, our results are also a strong reminder of the primordial role that diversity plays in the robustness of systems in the face of change: this applies not only to neurons and circuits, but also to humans and collectives. Variety really is the spice of life.