Brain lesion network mapping has been used to identify common brain networks disrupted in patients with heterogeneous lesions causing apraxia, parkinsonism, hallucinations – even altruism and criminal behavior.
This emerging neuroimaging technique “challenges the assumption that neuropsychiatric symptoms should localize to one brain region, and instead shows that these symptoms localized to interconnected brain networks,” said Ryan Darby, M.D., assistant professor of neurology at Vanderbilt University Medical Center. Darby helped design some of the first studies applying brain lesion network mapping to clinical scenarios.
Movement Disorders and Free Will-associated Brain Networks
Most recently, Darby has been using brain lesion network mapping to understand brain networks that underlie expression of free will. Darby breaks free will into two components: volition (a desire to act) and agency (a sense of responsibility for that action).
People with certain movement disorders can have disruptions in their volition, agency or both. People with akinetic mutism lack volition to move or speak. Similarly, those with alien limb syndrome lack agency, and feel their movements are generated by someone else.
“By studying neurological diseases that disrupt agency and volition, we can begin to understand what brain regions are involved in free will perception,” said Darby.
“The challenge is that damage to different locations can cause each of these symptoms. We hypothesized that lesions were occurring in different parts of the same connected brain network.”
Commonalities in Brain Network Disruptions
In a study published in the Proceedings of the National Academy of Sciences, Darby and colleagues examined how free will may be related to the distinct brain network disruptions associated with movement disorders. The researchers collected 3D functional brain images from 28 patients with akinetic mutism and 50 patients with alien limb syndrome. They focused on images of the patients’ brain lesions, assessing how each lesion aligned with normal brain network map data. The researchers then overlapped lesion-associated networks to find those universally affected across a significant number of patients.
Although the patients had a range of different brain injuries and lesions, there were commonalities. “Lesion locations causing akinetic mutism all fell within one network, defined by connectivity to the anterior cingulate cortex. Lesion locations causing alien limb fell within a separate network, defined by connectivity to the precuneus,” wrote the authors.
The initial results showed that complex processes like free will occur because of brain activity in distinct brain networks, not any single lesion location. Darby and colleagues went one step further to compare their findings to existing neuroimaging data.
Complex processes like free will occur because of brain activity in distinct brain networks, not any single lesion location.
In the second part of the study, the team found that the two brain networks matched those identified by other studies as brain stimulation locations that disrupt free will. The networks also aligned with neuroimaging abnormalities in patients with psychiatric disorders of free will, such as motor conversion disorder and catatonia.
The consistent findings provide some of the first neuroanatomical insights into brain networks associated with free will. Said Darby, “Our study shows the promise of using our network localization method in neurological patients to better understand symptoms in psychiatric patients. That being said, it’s the first time we have used this technique with neuroimaging abnormalities in psychiatric patients.”
Darby plans additional studies to validate the technique in the context of free will, in partnership with Michael Fox, M.D., Ph.D., associate professor of neurology at Harvard University.