Parkinson's and the Social Mind: Can Brain Stimulation Help Without Hurting?
"A new study investigates if deep brain stimulation (DBS) for Parkinson's can affect social cognitive abilities, offering hope for maintaining social connections."
Parkinson's disease (PD) is known for its motor symptoms like tremors and stiffness, but it also brings cognitive and psychiatric challenges. Individuals with PD may find it hard to recognize emotions, understand what others are thinking (Theory of Mind), affecting daily social interactions. These challenges stem from how Parkinson's impacts the brain's dopamine levels and the connections between different brain regions.
Deep brain stimulation (DBS) has emerged as a treatment for motor symptoms when medication isn't enough. DBS involves implanting electrodes in the brain, specifically in an area called the subthalamic nucleus (STN). While DBS can improve movement, scientists have been wondering about its effects on cognitive functions, especially social skills. Some studies have reported cognitive difficulties after DBS, but the research has been inconsistent and sometimes contradictory.
A recent study published in Scientific Reports sheds light on how DBS of the STN impacts social cognitive abilities in Parkinson's patients. Researchers aimed to expand the scope of previous investigations by simultaneously examining emotion recognition, affective ToM (understanding emotions), and cognitive ToM (understanding beliefs and intentions). By exploring these various aspects of social intelligence, the study provides a more holistic view of the impact of DBS on the social mind.
DBS Utilization in Parkinson's Disease
Deep brain stimulation is most frequently indicated for Parkinson's disease, with one analysis of 104,356 DBS discharges from 1993 to 2017 finding that PD accounted for 67% of procedures and essential tremor for 24%. Another characterization of patient demographics found PD represented 34.7% of primary DBS procedures, with essential tremor at 10.9% and epilepsy at 9.4%. US data suggest approximately 2,500 to 3,000 patients undergo DBS surgery for PD and essential tremor annually at 200 to 250 centers. A study of long-term outcomes found that DBS for PD is associated with a 10-year survival rate of 51%, though survey data suggest DBS does not halt disease progression.
How DBS Works and When It Falls Short
Deep brain stimulation is a surgical treatment that helps control Parkinson's movement symptoms when medications alone are not enough. The procedure involves implanting electrodes that deliver electrical impulses to specific brain areas. As Parkinson's progresses, DBS is no longer an option if symptoms don't respond to medication, or if a patient is severely disabled even in the best 'on' state. DBS does not fully resolve the symptoms of PD, but it can decrease a patient's need for medications and improve quality of life.
The Origins of Deep Brain Stimulation
Deep brain stimulation was first developed in 1987 by a team treating patients with essential tremor and Parkinson's disease at Grenoble, France. The technology first appeared in mainstream practice in the 1980s for the treatment of PD. Alim Benabid discovered that electrical stimulation of the basal ganglia improved symptoms of Parkinson's disease in the late 1980s, establishing the foundation for modern DBS therapy. The origins of this neurofunctional technique date back to the 1940s, with early 21st century advances proving its efficacy in the treatment of tremor.
Does Deep Brain Stimulation Impact Social Skills?
The researchers conducted a cross-sectional study comparing three groups: 20 patients with PD on medication, 18 patients with PD treated with STN-DBS, and 20 healthy controls. All participants underwent tests to assess their social cognitive abilities:
- Ekman 60-Faces test: Measures the ability to recognize basic emotions from facial expressions.
- Reading the Mind in the Eyes test: Assesses affective ToM, the ability to understand others' emotions from their eyes.
- Protocol for the Attribution of Communicative Intentions: Evaluates cognitive ToM, the ability to understand intentions in communicative situations.
Evidence for DBS Effectiveness
Several randomized controlled trials have found that deep brain stimulation has facilitated advances in treating Parkinson's disease, the most common indication. The latest literature review indicates that in PD, unilateral DBS of the STN or GPi improves motor scores by up to approximately 37%, while bilateral DBS achieves up to approximately 66% improvement. Studies on adaptive DBS have shown that patients experience significant improvements in 'on' time without troublesome dyskinesias and need lower medication doses. While DBS does not fully resolve symptoms of PD, it can decrease a patient's need for medications and improve quality of life.
Risks, Complications, and Limitations
Deep brain stimulation surgery is a well-accepted and widespread treatment often utilized to address symptoms in advanced PD, but it carries risks of complications. Depression and impulsivity have been reported following DBS and may represent a consequence of stimulation or emergence of underlying symptoms. Similar to available drug treatments, DBS does not slow down the disease or restore sick and dying nerve cells affected by Parkinson's disease. DBS has been known to generate other movement-related disorders such as dyskinesias, blepharospasm, and hypokinesia.
What DBS Treats Well and What It Doesn't
DBS typically works best to lessen motor symptoms of stiffness, slowness, and tremor, but it doesn't work as well for imbalance or freezing of gait. Variable frequency stimulation (VFS) appears promising in PD, though its potential seems less promising for essential tremor with the frequency range and duty cycles previously applied. For patients living with essential tremor and Parkinson's disease, medication is often the first line of treatment before considering surgical interventions like DBS.
Reassuring Results: Social Skills Preserved After DBS
The study found no significant differences between the PD groups (those treated with STN-DBS and those on medication alone) on any of the social cognitive tests. This suggests that STN-DBS does not have a detrimental effect on social cognitive abilities in Parkinson's patients. The results indicate that this surgical procedure is safe from the standpoint of social cognition. Importantly, the study highlights the potential for STN-DBS to alleviate motor symptoms without negatively impacting a person’s ability to connect with others.
Expert Consensus on DBS Value
Deep brain stimulation surgery effectively alleviates troublesome motor symptoms of Parkinson's disease, including tremor, rigidity, and bradykinesia. A systematic review with meta-analysis found evidence of a beneficial effect of deep brain stimulation combined with antiparkinsonian drugs on quality of life. Consensus expert recommendations support DBS referral for appropriately selected patients who have inadequate symptom control despite optimal medical therapy.
Advancing DBS Technology and Market Growth
Studies have demonstrated that deep brain stimulation improves all of the cardinal parkinsonian signs, with frameless and mini-frame stereotactic systems making the procedure less invasive. Future outlooks highlight translational opportunities for network neuromodulation, moving beyond traditional stimulation targets. The deep brain stimulation devices market is expected to grow from USD 1.31 billion in 2023 to USD 2.37 billion by 2034, driven by rising neurological disorder prevalence and technological advances.
Weighing the Risks of Intervention
While deep brain stimulation is a valuable treatment option, clinicians must carefully weigh its risks against benefits for each patient. DBS has been known to generate movement-related disorders such as dyskinesias, blepharospasm, and hypokinesia as potential complications. These side effects underscore the importance of thorough patient selection and careful programming of stimulation parameters to minimize adverse outcomes.
Real-World Outcomes and Patient Experience
While DBS doesn't prevent movement disorders like Parkinson's disease from progressing, it has the potential to significantly improve a patient's quality of life and daily functioning. Real-world evidence suggests that DBS might be safe and useful in carefully selected patients with moderate cognitive impairment, a population sometimes considered contraindicated for the procedure. Case studies of asleep deep brain stimulation have demonstrated relief for patients with movement disorders, offering a less burdensome surgical experience.