How Does Deep Brain Stimulation Affect Sensory Processing in Tourette Syndrome and OCD?

What you need to know

• The study examined how deep brain stimulation (DBS) affects sensory processing in patients with Tourette syndrome and obsessive-compulsive disorder (OCD)
• Patients with Tourette syndrome showed deficits in sensory filtering compared to healthy controls
• DBS did not significantly change sensory filtering in either patient group
• More research is needed to understand how DBS impacts brain networks involved in sensory processing

Background on sensory filtering and deep brain stimulation

Our brains are constantly bombarded with sensory information from our environment. To function effectively, we need ways to filter out irrelevant sensations and focus on what’s important. This ability is called sensorimotor gating.

Scientists can measure sensorimotor gating using a technique called prepulse inhibition. Here’s how it works:

1. A sudden loud noise normally causes a person to startle and blink.
2. But if a quieter “warning” sound is played just before the loud noise, most people startle less.
3. This reduction in startle response is called prepulse inhibition. It shows the brain is able to process the warning sound and dampen the reaction to the louder noise.

Prepulse inhibition provides a way to assess how well someone’s brain can filter sensory information. Research has found prepulse inhibition is often impaired in certain psychiatric and neurological conditions.

Deep brain stimulation (DBS) is a treatment that involves surgically implanting electrodes in specific brain regions. These electrodes deliver electrical pulses to modulate brain activity. DBS has shown promise for treating movement disorders like Parkinson’s disease as well as psychiatric conditions like obsessive-compulsive disorder (OCD) in cases that don’t respond to other therapies.

However, the exact effects of DBS on brain networks are still not fully understood. This study aimed to examine how DBS impacts sensorimotor gating in patients with Tourette syndrome and OCD.

How the study was conducted

The researchers recruited three groups of participants:

• 10 patients with Tourette syndrome who had undergone DBS
• 8 patients with OCD who had undergone DBS
• 18 healthy control subjects matched for age and gender

For the patient groups, prepulse inhibition was measured twice:

1. With their DBS device turned on
2. With their DBS device turned off

The healthy controls were tested once for comparison.

To measure prepulse inhibition, participants listened to sounds through headphones while their eye blink responses were recorded. The key comparison was how much their startle response was reduced when a quieter warning sound preceded the startling noise.

Key findings on sensory filtering

The main results of the study were:

• Patients with Tourette syndrome showed significantly lower prepulse inhibition compared to healthy controls when their DBS was turned on. This suggests impaired sensory filtering.

• There was no significant difference in prepulse inhibition between the on and off DBS conditions for either the Tourette syndrome or OCD patient groups.

• The OCD patient group did not show significant differences in prepulse inhibition compared to healthy controls.

• There was a weak correlation between improvement in clinical symptoms and prepulse inhibition levels in the OCD group, but this was not statistically significant in the main analysis.

What do these results mean?

The finding of reduced prepulse inhibition in Tourette syndrome patients aligns with previous research suggesting impaired sensory filtering in this condition. The brain regions involved in Tourette syndrome symptoms may overlap with networks that regulate sensory processing.

However, the lack of significant change between the on and off DBS conditions was somewhat surprising. The researchers suggest a few possible explanations:

1. The small sample size may have limited the ability to detect more subtle effects of DBS.

2. DBS may not directly impact the specific brain circuits involved in prepulse inhibition.

3. Long-term DBS treatment may lead to lasting brain changes that persist even when the device is temporarily turned off.

For the OCD group, the normal prepulse inhibition levels were unexpected based on some previous studies. The researchers note their OCD patients had been receiving DBS for over a year on average. It’s possible that long-term DBS treatment helped normalize sensory filtering in this group.

Limitations to consider

As the authors acknowledge, this study had some important limitations:

• The sample sizes were quite small, making it difficult to draw firm conclusions.

• Patients were taking various medications that could potentially impact prepulse inhibition.

• The study did not have pre-surgical baseline measurements to compare against.

• Factors like age, gender, and smoking status varied between groups and may have influenced the results.

Conclusions and future directions

This study provides new insights into how DBS may affect sensory processing in Tourette syndrome and OCD. The key takeaways are:

• Sensory filtering deficits were confirmed in Tourette syndrome patients
• DBS did not appear to significantly alter prepulse inhibition in either patient group
• More research is needed to understand the complex effects of DBS on brain networks

The authors suggest future studies should:

• Include larger sample sizes
• Control for factors like medication use
• Obtain pre-surgical baseline measurements
• Combine prepulse inhibition testing with brain imaging

Understanding how DBS impacts various aspects of brain function is crucial for optimizing this promising treatment approach. While many questions remain, this study takes an important step in examining the effects of DBS on a key aspect of sensory processing.