Summary: Deep brain stimulation (DBS) in the subthalamic nucleus, a treatment for Parkinson’s disease, can influence more than just motor control. This treatment, which alleviates Parkinson’s symptoms such as tremors, also appears to affect patients’ ability to shift their attention between tasks.
The study conducted experiments with Parkinson’s disease patients, tracking how their attention changed when the DBS device was active or inactive. The results indicate that although DBS facilitates motor function, it may hinder the brain’s ability to redirect thoughts and attention, perhaps explaining why some patients experience cognitive and behavioral side effects.
Highlights:
- Deep brain stimulation in the subthalamic nucleus is effective in controlling symptoms of Parkinson’s disease, but may also impact cognitive functions related to attention and impulse control.
- The study used auditory distractions to measure shifts in attention in patients with Parkinson’s disease, revealing that those with active DBS had difficulty changing focus.
- This research suggests that the subthalamic nucleus plays a critical role in motor and non-motor systems, including the management of thought and attention.
Source: University of Iowa
In a new study, researchers at the University of Iowa have linked a region of the brain to how humans redirect their thoughts and attention when distracted. This link is important because it offers insight into the cognitive and behavioral side effects of a technique used to treat patients with Parkinson’s disease.
The subthalamic nucleus is a pea-sized region of the brain involved in the motor control system, i.e. our movements. In people with Parkinson’s disease, these movements have been compromised: researchers believe that the subthalamic nucleus, which normally acts as a brake on sudden movements, exerts too much influence. According to researchers, this overactive brake is what contributes to the tremors and other motor impairments associated with the disease.
In recent years, clinicians have treated Parkinson’s patients with deep brain stimulation, an electrode implanted in the subthalamic nucleus that rhythmically generates electrical signals, causing a release of braking in the brain region, thus freeing the movement. The deep brain stimulation system is like a pacemaker for the heart; once implanted, it operates continuously.
“Frankly, the technique is truly miraculous,” says Jan Wessel, associate professor in the departments of psychology, brain sciences and neurology at Iowa.
“People come in with Parkinson’s disease, the surgeons turn on the electrode and their tremors disappear. Suddenly they can keep their hands steady and go play golf. It’s one of those blockbuster treatments where, when you see it in action, it really makes you believe in what the neuroscience community is doing.
Yet some patients treated with deep brain stimulation have experienced an inability to focus attention and impulsive thoughts, sometimes leading to risky behaviors such as gambling and substance use. Researchers began to wonder: Did the subthalamic nucleus’s role in movement also mean that this same region of the brain could handle thoughts and impulse control?
Wessel decided to find out. His team designed an experiment assessing the attention of more than a dozen Parkinson’s patients when deep brain stimulation treatment was on or off.
Participants, equipped with a skull cap to track their brain waves, were asked to fixate their attention on a computer screen while brain waves in their visual cortex were monitored.
About one in five times, in random order, participants heard a chirp intended to divert their visual attention from the screen to the newly introduced auditory distraction.
In a 2021 study, Wessel’s group established that brain waves in participants’ visual cortex decreased when they heard a chirp, meaning their attention had been diverted by the sound.
By swapping instances where there was a chirp or no sound, the researchers were able to see when attention had been diverted and when the focus of visual attention had been maintained.
The team focused on groups with Parkinson’s disease for this study. When the deep brain stimulation was inactive and the chirp sounded, the Parkinson’s patients shifted their attention from the visual system to the auditory system, just as the control group had done in the previous study.
But when the chirp was presented to participants with Parkinson’s disease with deep brain stimulation activated, these participants did not divert their visual attention.
“We found that they can no longer interrupt or suppress their attention in the same way,” says Wessel, the corresponding author of the study.
“The unexpected sound occurs and they are still fully attentive to their visual system. They didn’t take their attention away from the visual.
This distinction confirmed the role of the subthalamic nucleus in how the brain and body communicate not only with movement, as previously known, but also with thoughts and attention.
“Until now, it wasn’t really clear why people with Parkinson’s disease had thinking problems, for example why they performed worse on attention tests,” says Wessel.
“Our study explains why: although removing the inhibitory influence of the subthalamic nucleus on the motor system is useful in the treatment of Parkinson’s disease, removing its inhibitory influence on non-motor systems (such as thoughts or attention) may have undesirable effects.”
Wessel strongly believes that deep brain stimulation should continue to be used for patients with Parkinson’s disease, citing its clear benefits in facilitating motor control functions.
“There may be different areas of the subthalamic nucleus that shut down the motor system and the attentional system,” he says.
“That’s why we’re doing fundamental research, to figure out how to fine-tune them to get the full benefit for the motor system without generating potential side effects.”
The study, “The human subthalamic nucleus transiently inhibits active attentional processes,” was published online March 4 in the journal Brain.
The first author is Cheol Soh of the Iowa Department of Psychological and Brain Sciences. Contributing authors, all from Iowa, include Mario Hervault, Nathan H. Chalkley, and Cathleen M. Moore, of the Department of Psychological and Brain Sciences; Jeremy Greenlee and Andrea Rohl, from the Department of Neurosurgery; and Qiang Zhang and Ergun Uc, from the Department of Neurology.
Funding: The National Institutes of Health and the National Science Foundation, through a CAREER award to Wessel, funded the research.
About this neuroscience research news
Author: Richard Lewis
Source: University of Iowa
Contact: Richard Lewis – University of Iowa
Picture: Image is credited to Neuroscience News
Original research: Closed access.
“The human subthalamic nucleus transiently inhibits active attentional processes” by Jan Wessel et al. Brain
Abstract
The human subthalamic nucleus transiently inhibits active attentional processes
The subthalamic nucleus (STN) of the basal ganglia is key to inhibitory control of movement. Therefore, it is a primary target for neurosurgical treatment of movement disorders like Parkinson’s disease, where modulation of the STN via deep brain stimulation (DBS) can release excessive inhibition of thalamo-cortical motor circuits. .
However, the STN is also anatomically connected to other thalamo-cortical circuits, including those underlying cognitive processes like attention. Notably, STN-DBS can also affect these processes.
This suggests that STN could also contribute to the inhibition of non-motor activity and that STN-DBS could modify this inhibition. Here we tested this hypothesis in humans.
We used a novel wireless ambulatory method to record intracranial local field potentials (LFPs) from STN DBS implants during a visual attention task (Experiment 1, N = 12). These ambulatory measurements allowed simultaneous recording of high-density EEG, which we used to derive steady-state visual evoked potential (SSVEP), a well-established neural index of visual attentional engagement.
By linking STN activity to this neural marker of attention (instead of overt behavior), we avoided possible confounds resulting from the driving role of the STN. We aimed to test whether the STN contributes to the momentary inhibition of the SSVEP caused by unexpected and distracting sounds.
Furthermore, we tested this association causally in a second experiment, in which we modulated STN via DBS over two sessions of the task, spaced at least one week apart (N = 21, no samples overlapped with the experiment). 1).
LFP recordings from Experiment 1 showed that reductions in SSVEP after distracting sounds were preceded by sound-related γ-frequency (>60 Hz) activity in the STN. Trial-by-trial modeling further showed that this STN activity statistically mediated the suppressive effect of sounds on the SSVEP.
In Experiment 2, modulation of STN activity via DBS significantly reduced these sound-related SSVEP reductions. This provides causal evidence for the role of the STN in inhibition of surprise-related attention.
These results suggest that the human STN contributes to the inhibition of attention, a non-motor process. This supports a general view of the field of the inhibitory role of the STN.
Furthermore, these results also suggest a potential mechanism underlying some of the known cognitive side effects of STN-DBS treatment, particularly on attentional processes.
Finally, our novel ambulatory LFP recording technique facilitates testing the role of subcortical nuclei in complex cognitive tasks, alongside recordings from the rest of the brain, and in a much shorter time frame than perisurgical recordings.
News Source : neurosciencenews.com
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