Department of Psychiatry

Research Team

Contact

Research Topics:

Tourette's Syndrome

Diabetes and the Brain

Spatial Memory Test

Subthalamic Nucleus Implants

One recently developed, significantly effective treatment of Parkinson’s Disease is the implantation of deep brain stimulator (DBS) electrodes in the subthalamic nucleus (STN) region of the brain.  These implants greatly improve motor function in patients suffering from Parkinson’s disease, but may also affect the ability to monitor and manipulate memory.  Our research focuses on the mechanisms of electrode stimulation to the STN as well as how these mechanisms may interfere with working memory.

Figure above: Illustration of the steps involved in localization of the active stimulator contacts. (A) CT image showing electrode track. (B) CT image with location of tip of electrode. (C) CT superimposed on coronal MR with the electrode track displayed. (D) Location of the calculated active contact from CT scan superimposed on the correct MR coronal slice.

How does it work?

Even though it is evident that STN stimulation remarkably improves motor function in Parkinson’s patients, it is not clear if this benefit is from increasing, decreasing, or blocking the output of neural circuits.  By using positron emissions tomography (PET) to measure cerebral blood flow while the stimulator was turned off and on in separate conditions, we attempted to gain insight into the mechanisms of STN stimulation.  We observed that stimulation increased neural activation in the left midbrain region while reducing activation in the frontal, parietal and temporal cortex bilaterally.  These results support the hypothesis that STN stimulation increases the activity of STN output (which in turn decreases cortical activity).

Blood flow decreases with STN stimulation in several cortical areas

Current Studies

Cognitive Changes with STN Stimulation  In this study, the cognitive functions that are associated with the inhibited regions of STN stimulation are being examined.  By using the Spatial Delayed Response (SDR) and Go-No-Go tasks, patients’ spatial working memory and response inhibition are being monitored with and without STN stimulation.  Preliminary analyses of the results suggest that under STN stimulation there is a decrease in both spatial working memory as well as response inhibition, which supports the hypothesis that STN stimulation negatively affects some cognitive ability.  As an extension of this study, we are examining whether changes in stimulator voltage may affect cognition.  We predict that at higher voltages, current will be more likely to spread to the cognitive areas in and around the STN and adversely affect cognitive functioning.

Prospective Memory in Parkinson's Disease  Cognitive dysfunction in non-demented patients with PD is common (30-70% of patients).  The skills most affected (such as working memory, response inhibition and planning) rely upon active monitoring and manipulation of information for short term use, called cognitive control.

Prefrontal cortical regions are critical for optimal cognitive control functioning.  It has been hypothesized that in PD, dopamine deficiency reduces the optimal functioning of these prefrontal regions, thus affecting fundamental cognitive control skills. Prospective memory, the ability to remember actions to be performed at a particular moment in the future, relies heavily on cognitive control skills and is highly relevant for everyday life (e.g. "I need to remember to buy milk on the way home").  Despite these strong associations, little is known about prospective memory in PD.  If cognitive control skills are fundamentally altered by dopamine deficiency, prospective memory tasks that emphasize active monitoring and control should be deficient in PD, particularly in an unmedicated state.

We are testing whether prospective memory with high demand on strategic, controlled processes is impaired in individuals with PD compared to controls using reliable and validated experimental measures.  To translate results from laboratory tasks to clinical relevance, we also challenge participants with naturalistic tasks resembling the memory challenges faced in everyday life.  Finally we assess the impact of dopaminergic medication on prospective memory performance in PD to better estimate prospective memory function in PD patients' everyday (chronically treated) life.

Parkinson's Links

 

American Parkinson's Disease Association http://www.apdaparkinson.com/  Information, referrals to specialists, and support groups (here is a link to the Saint Louis Chapter of APDA).

Parkinson's on WeMove.org http://www.wemove.org/par.html  A wealth of information for patients, family, and professionals.

The National Parkinson Foundation http://www.parkinson.org/  Public forums, informative articles, self tests, suggested reading material.

Disclaimer: The contents of the links listed have not been evaluated by Dr. Hershey or Washington University and should not be considered endorsed.  Always consult a doctor when making decisions that involve your health or medical treatment.