The brain’s backup system: Staying connected
Over a quarter million people suffer a stroke every year in Germany, often affecting important brain regions that were previously capable of processing crucial cognitive functions. In many cases the brain finds a way of compensating for these disturbances and recovers. How the brain manages this, even when serious damage has resulted in failure of the entire original network, has remained unclear. Gesa Hartwigsen from the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) may have found an explanation.
Together with her team, Gesa Hartwigsen has discovered a new way in which the brain manages to compensate for a completely impaired network. Following disruption of the network for language comprehension, the brain activated neighbouring regions which were previously devoted to other functions. The newly engaged regions had previously been responsible for processing general cognitive functions such as attention, working memory and cognitive control, the latter of which refers to processes that allow flexible goal-directed behaviour.
Through these additionally activated control mechanisms language processing was able to carry on nearly unaltered. The scientists therefore propose that specific disturbances can be compensated for through the recruitment of additional ‘domain-general’ cognitive resources. Moreover, the neuroscientists also suspect that this mechanism is generally how the brain responds to serious injuries.
This and other known brain plasticity mechanisms, that compensate for lesions within or beyond a network, are described by Hartwigsen in a new article published in the journal Trends in Cognitive Sciences. Her model is mainly based on transcranial magnetic stimulation studies, where certain brain areas in healthy participants are targeted, and interrupted, by magnetic pulses. Thereby it was possible to speculate as to how the brain would respond in the case of a stroke or other events which disrupt function of certain areas—and importantly, to predict which processes might be switched on to help handle the disturbance.
Based on her studies neuroscientist Hartwigsen presumes that for specific cognitive abilities such as language compensation can be achieved in two ways. On the one hand the still intact areas of the network, which are specialized in that specific function, can take on more responsibility. On the other hand, nearby networks which normally may not contribute to that function, could be activated. “It’s still unlikely that these additional resources could lead to a full recovery of function. In the case of language some deficits would likely remain”, she says. This kind of compensatory adaptation is an example of neuroplasticity: a collection of mechanisms our brains engage in to allow us to handle disturbances but also to adjust to our continually changing environment.
Hartwigsen’s observations have been based on healthy persons and need to be verified in larger samples and eventually in patients with brain lesions. Her goal is to first understand the healthy brain networks underlying several cognitive functions in order to more fully appreciate what occurs following a stroke. She hopes this will lead to new knowledge concerning how the injured brain can best be supported during rehabilitation. If the group’s findings can be verified it might mean that after a stroke not only specific functions such as language should be fostered, but also general processes, especially when the specific process is seriously affected. Next to practising language this might mean training in working memory, for instance.