Could a Newly Discovered Brain Network Explain Parkinson’s Disease?
Yes. A brain imaging study built on 863 participants found that a network called the somato-cognitive action network (SCAN) is central to Parkinson’s disease. When transcranial magnetic stimulation targeted this network instead of effector-specific motor regions, its efficacy doubled.
Parkinson’s disease has always been hard to explain. It often begins insidiously with sleep disturbances and somatic symptoms such as constipation. Then come tremor, rigidity, incoordination and trouble walking, along with slowed and diminished voluntary behavior. No single effector-specific motor region, the patches of cortex that control the hand, the foot, or the mouth, can account for all of that, and that has puzzled researchers for decades.
This study offers an explanation. The SCAN is thought to control action execution by coordinating arousal, organ physiology and whole-body motor plans with behavioral motivation. In people with Parkinson’s, this network becomes hyperconnected to deep brain structures. Treatments that work reduce that hyperconnectivity.
What the Data Show
Researchers assembled a large, multimodal, multi-intervention clinical imaging dataset totaling 863 participants. That total is not 863 Parkinson’s patients: it combines people with Parkinson’s, healthy control individuals, and three other movement disorder cohorts studied as comparisons (essential tremor, n = 45; dystonia, n = 42; amyotrophic lateral sclerosis, n = 30). Here is what they found:
- Network specificity: Six subcortical structures long implicated in Parkinson’s (substantia nigra, subthalamic nucleus, ventral intermediate/centromedian thalamus, globus pallidus internus and externus, and putamen) were all more strongly connected to the SCAN than to effector-specific foot, hand and mouth motor regions, and more strongly than to other functional networks
- Hyperconnectivity: In 65 patients with Parkinson’s compared with 60 age-matched healthy control individuals, connectivity between the SCAN and those six subcortical structures was significantly elevated (p = 0.002). The finding replicated in the full precision imaging sample and in a separate deep brain stimulation imaging dataset
- Specific to this network: The hyperconnectivity was not seen in other canonical brain networks, and it was absent in essential tremor, dystonia and ALS
- Treatment response: Targeting the SCAN instead of effector regions doubled the efficacy of TMS treatment. Focused ultrasound benefits increased when the target sat closer to the thalamic SCAN sweet spot
- Across therapies: Six patient cohorts undergoing deep brain stimulation, adaptive deep brain stimulation, TMS, focused ultrasound and levodopa were followed, and efficacious treatments reduced SCAN-to-subcortex hyperconnectivity
How It Works
Think of the SCAN as a master switchboard. It does not control just your hand or your foot. It coordinates whole-body motor plans, organ physiology, arousal, and behavioral motivation, and its regions sit interleaved with the classical effector-specific motor regions along the central sulcus.
The pathophysiological hallmark of Parkinson’s is the degeneration of dopamine-producing neurons in the substantia nigra, which disrupts a cortico-basal ganglia-thalamic circuit. This study shows that circuit is wired preferentially to the SCAN rather than to individual motor effectors, and that in Parkinson’s the connection between them runs too strong. Higher subcortex-to-SCAN connectivity tracked with higher motor symptom scores on the MDS-UPDRS part III (r = 0.162, p = 0.037), higher cognitive scores on the MMSE (r = 0.161, p = 0.038), and lower anxiety (r = -0.186, p = 0.017) and depression scores (r = -0.177, p = 0.023), though those correlations are weak.
Every effective Parkinson’s treatment studied here, whether a pill, implanted electrodes, magnetic stimulation or focused ultrasound, reduced that same hyperconnectivity.
Dr. Kumar’s Take
This is one of those studies that reframes how I think about a disease. For years, Parkinson’s has been treated as a movement disorder and the motor system has been the target. But the motor system alone could never explain why people with Parkinson’s also get constipation, or why their sleep falls apart, or why motivation drops.
The SCAN concept ties all of that together into one framework. As a surgeon who thinks about targets, the treatment data matters to me most. Doubling TMS efficacy by aiming at the right network is a significant result, and it suggests current therapies could get better through more precise targeting rather than new hardware. The deep brain stimulation sweet spots that already work in the subthalamic nucleus, globus pallidus and thalamus turned out to be the ones most strongly connected to the SCAN, which reads as retrospective confirmation that we have been hitting this network by trial and error for years.
I would not call this a cure, and nothing here shows the underlying degeneration slowing. It is a shift in how the disease is understood and where treatments should aim. The authors put it as targeting functionally defined subcortical SCAN nodes to improve existing therapies, while cortical SCAN targets offer non-invasive or minimally invasive options.
Practical Takeaways
- If you or a family member has Parkinson’s, ask your neurologist how your treatment targets are chosen and whether network-based mapping is used at your center
- TMS is a non-invasive option, and this work found its efficacy doubled when aimed at the SCAN rather than at effector-specific motor cortex
- Current treatments including levodopa and deep brain stimulation already appear to work partly through this mechanism, even though they were not designed around it
- Non-motor symptoms such as sleep disturbance and constipation fit within the same network disruption rather than sitting outside the disease
- For focused ultrasound, how close the target lands to the thalamic SCAN sweet spot was associated with greater benefit, which makes precision targeting a practical question to raise
Related Studies and Research
Understanding brain networks is a growing area of research, especially in neurological and mental health conditions. Here are related articles:
- Weakened Brain Network Connectivity in Adolescent Depression explores how disrupted brain networks contribute to mood disorders in young people
- How TMS Rewires Your Brain: The Science Behind Depression Recovery covers the same TMS technology used in this Parkinson’s study, applied to depression
- Mindfulness-Based Cognitive Therapy for Major Depressive Disorder examines another approach to changing brain network activity
- Brain Network Changes in Depression: Frontostriatal Salience Network Expansion looks at how brain networks expand abnormally in depression, similar to the overconnectivity seen in Parkinson’s
FAQs
What is the somato-cognitive action network (SCAN)?
The SCAN is a recently described brain network thought to control action execution by coordinating arousal, organ physiology and whole-body motor plans with behavioral motivation. Its regions alternate with the classical effector-specific motor regions along the brain’s central sulcus. Unlike regions that control a specific body part such as the hand, foot or mouth, the SCAN handles actions involving the whole body.
Does this mean Parkinson’s is not really a movement disorder?
Not exactly. Parkinson’s does cause movement problems. But this work supports understanding it as a disorder of a network that spans whole-body movement, arousal, organ physiology and motivation at once. That fits why symptoms extend well beyond tremor and rigidity into sleep, autonomic function such as constipation and orthostatic hypotension, and apathy.
Is TMS available as a treatment for Parkinson’s right now?
TMS has shown therapeutic effect in Parkinson’s but remains underexplored, possibly because precise cortical targets have been lacking. The SCAN-targeted approach described here is research, not established care. Further trials will determine whether this targeting becomes a standard option.
How many people were in this study?
The dataset totaled 863 participants across multiple cohorts. It includes people with Parkinson’s, healthy control individuals, and patients with other movement disorders including essential tremor, dystonia and ALS, so it is not a count of Parkinson’s patients. The core imaging comparison of Parkinson’s against healthy controls used 65 patients and 60 control individuals, and separate treatment cohorts followed patients through deep brain stimulation, adaptive deep brain stimulation, TMS, focused ultrasound and levodopa.
Bottom Line
This study shifts where Parkinson’s treatment should aim. By identifying the SCAN as the network the disease circuit actually connects to, the researchers explain why Parkinson’s reaches so far beyond movement, and they show that the deep brain stimulation targets already approved for the disease are the ones most tied to this network. Aiming TMS at the SCAN doubled its efficacy, and focused ultrasound worked better the closer it landed to the thalamic SCAN target. For people living with Parkinson’s, the practical promise is not a new device but better placement of the ones already in use, alongside non-invasive options that address the full scope of the disease rather than only its most visible symptoms.
