Research Insights

Effects of subthalamic nucleus deep brain stimulation and L-dopa on blinking in Parkinson

Bologna M, Fasano A, Modugno N, Fabbrini G, Berardelli A. Effects of subthalamic nucleus deep brain stimulation and L-dopa on blinking in Parkinson , Exp Neurol. 2012 Feb 14. Doi: 10.1016/j.expneurol.2012.02.004

Intro:   People with Parkinson’s disease (PWP) often have difficulties with blinking (voluntary, reflexive, and spontaneous) due to depleted dopamine as well as changes within the brain, predominately the basal ganglia.  The authors note that DBS-STN has been effective on improving motor functioning in many motor regions but some areas have received less study such as what the treatment does for blinking difficulties.
 
Methods:  Sixteen PWP (4Females/12Males; Mean age 63, Mean disease duration 19 years.) were studied that had undergone bilateral DBS-STN.  The PWP were compared to 15 age matched healthy control subjects.   The PWP were evaluated at least 1 year post DBS-STN to insure that stimulator settings and medications were at effective settings/dosages.

Infrared cameras were used to evaluate voluntary, reflexive, and spontaneous blinking. The measurements were taken at four different points across time: stimulator only, medication only, no medication/ stimulator off, and medication/stimulator on.  PWP were off of their medication for 12 hours before being studied for the no medication conditions and the stimulator was turned off three hours prior for the no stimulator conditions.    

Findings: PWP had less global motor difficulties when they were on their medication as well as when the stimulator was on.  Specific information about blinking is listed below:
Voluntary blinking:  IT was found that when the stimulator was turned on, blinking took longer and was slower.  The results also showed that the pauses between blinking were slower when the stimulator was turned on.

Spontaneous blinking:  It was found that the spontaneous blinking rate was lower for the PWP when there was no medication and no stimulator.

Reflexive blinking: General differences were not found between the PWP and the healthy controls on this measure.  However, it was found that when there were more stimuli and a longer amount of time in between the presentation of those stimuli that there were changes for the PWP with the stimulator on and with medication.  Although there was a difference, the applicability of this finding is pretty small in one’s general ability to reflexively blink to something coming at one’s eye.

Conclusion:  DBS-STN changes PWP’s ability to blink in various ways.  The authors hypothesized two reasons to explain this phenomenon:

1.  It is possible that it is due to spread of the stimulator’s charge to areas beyond the STN.

2. It is due to changes from the DBS to the basal ganglia and the involved neurotransmitters communicating with the brain stem. 

The authors favored hypothesis 2.  It is noted that the authors hoped to add information to the side effect of ocular apraxia (inability to initiate opening one’s eye) that can be seen after DBS-STN but none of the patient’s studied experienced that adverse event after their surgeries.  However, they suggest that their findings on difficulty with voluntary and spontaneous blinking and possible etiology may provide utility to the apraxia research. 

Click here to read the abstract.

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