Abstract
ObjectiveBlink reflexes following supraorbital nerve (SON) stimulation are typically modulated by conditioning stimuli (CS) to the index finger (D2) (low-intensity, prepulse inhibition paradigm) or SON (same intensity, paired-pulse paradigm). We aimed to disentangle whether CS-intensity or CS-induced motor responses define blink reflex modulation. MethodsIn 35 subjects, test SON stimuli (8 times sensory threshold, 8 × ST) were applied either alone or following CS. In experiment 1, CS were delivered to D2 with low (2 × ST) or high intensity (inducing a somatosensory blink reflex). In experiment 2, CS were applied to SON with low (<2 × ST) or test intensity. Test blink reflex size was correlated to CS-intensity and to CS-induced motor response size. Relative strength of their influence was determined in regression analyses. ResultsTest blink reflex size showed higher inverse correlation to CS-intensity than to CS-induced motor response size for both CS delivered to D2 or SON. Regression analyses confirmed a significantly higher relative strength of CS-intensity than of CS-induced motor response size. ConclusionsThe sensory input of CS, rather than CS-induced motor output, defines subsequent blink reflex modulation. SignificanceThis ubiquitous phenomenon calls for caution when relating the size of test responses to the size of conditioning responses particularly in paired-pulse paradigms.
Published Version
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