The impact of low-frequency stimulation of the pedunculopontine nucleus region on reaction time in parkinsonism.
OBJECTIVE
Attentional augmentation and enhanced motor function are potential mechanisms by which stimulation of the region of the pedunculopontine nucleus (PPN) may improve gait in parkinsonism. Here, the authors assess the impact of stimulation of this region on attentional and motor aspects of reaction task performance in patients with parkinsonism.


METHODS
Eleven patients implanted with PPN stimulators underwent computerised assessment of simple, choice and digit vigilance reaction tasks. Patients were assessed 'off medication' during stimulation at different frequencies (0 Hz, 5 Hz, 10 Hz and 'therapeutic' 20-35 Hz). There were two primary endpoints: 'Speed of Reaction' (sum of the mean task reaction times) and 'Accuracy of Reaction' (reflecting omissions and percentage of correct responses). Baseline performance was compared with age- and sex-matched healthy controls. Clinical effects of stimulation were assessed using the Unified Parkinson's Disease Rating Scale and a falls frequency scale.


RESULTS
Compared with healthy controls, subjects had significant deficits in 'Speed of Reaction' and in all mean task reaction times. 'Accuracy of Reaction' was not different from healthy controls and did not improve with stimulation. 'Speed of Reaction' significantly improved with stimulation at therapeutic frequencies (20-35 Hz). Of the individual tasks, only simple reaction time improved significantly. Simple reaction time distribution analysis revealed a general speeding of responses rather than a selective reduction in outliers. Acute PPN stimulation improved gait and balance but not akinesia scores. Chronic PPN stimulation significantly improved falls frequency. Falls score improvement significantly correlated with changes to simple reaction time with therapeutic stimulation.


CONCLUSIONS
The pattern of reaction time improvement with stimulation of the PPN area suggests a benefit on motor performance, rather than augmentation of attention.
Thevathasan
Wesley
W
Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK.
Silburn
Peter A
PA
Brooker
Helen
H
Coyne
Terry J
TJ
Khan
Sadaquate
S
Gill
Steven S
SS
Aziz
Tipu Z
TZ
Brown
Peter
P
D000368:Aged; D046690:Deep Brain Stimulation / Q000379:methods*; D006801:Humans; D008875:Middle Aged; D020734:Parkinsonian Disorders / Q000503:physiopathology* / Q000628:therapy; D045042:Pedunculopontine Tegmental Nucleus / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology*