Inverse correlation of intracortical inhibition and brain-stem inhibition in humans.
OBJECTIVE
To determine whether intracortical inhibition and the conditioned blink reflex R2 inhibition correlate in healthy subjects.


BACKGROUND
In Parkinson's disease and in focal dystonia the intracortical inhibition and the conditioned blink reflex R2 inhibition are abnormally weak.


METHODS
In 10 healthy humans (average age 25.7 years) we investigated the intracortical excitability of the optimal representation of the abductor digiti minimi of the dominant hand using transcranial magnetic stimulation with a conditioning pulse (90% active motor threshold) followed by a pulse of 120% resting motor threshold after an interstimulus interval ranging from 1 to 30 ms. We investigated the blink reflex with two suprathreshold stimuli over the supraorbital nerve and EMG recording from the orbicularis oculi ipsilateral to electrical stimulation, the interstimulus intervals were 100, 250 and 500 ms.


RESULTS
The intracortical inhibition, but not the intracortical facilitation, was inversely and significantly correlated with the R2 inhibition on the side of transcranial stimulation, but not with the contralateral R2 inhibition.


CONCLUSIONS
The correlation of intracortical inhibitory interneurons and ipsilateral blink reflex interneurons may indicate a common influence, possibly from the basal ganglia, on either circuit, or a direct influence of cortical circuits on brain-stem circuits via corticopontine pathways.
Sommer
Martin
M
Department of Clinical Neurology, University of Göttingen, Robert-Koch-Strasse 40, D-37075 Göttingen, Germany. msommer@gwdg.de
Heise
Alexander
A
Tergau
Frithjof
F
Paulus
Walter
W
D000293:Adolescent; D000328:Adult; D001767:Blinking / Q000502:physiology; D001933:Brain Stem / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology