In the spotlight: How the brainstem modulates information flow.

OBJECTIVE

The blink reflex (BR) to supraorbital nerve (SON) stimulation is reduced by either a low-intensity prepulse stimulus to digital nerves (prepulse inhibition, PPI) or a conditioning SON stimulus (SON) of the same intensity as the test (SON) stimulus (paired-pulse paradigm). We studied how PPI affects BR excitability recovery (BRER) to paired SON stimulation.

METHODS

Electrical prepulses were applied to the index finger 100 ms before SON, which was followed by SON at interstimulus intervals (ISI) of 100, 300, or 500 ms.

RESULTS

BRs to SON showed PPI proportional to prepulse intensity, but this did not affect BRER at any ISI. PPI was observed on the BR to SON only when additional prepulses were applied 100 ms before SON, regardless of the size of BRs to SON.

CONCLUSIONS

In BR paired-pulse paradigms, the size of the response to SON is not determined by the size of the response to SON. PPI does not leave any trace of inhibitory activity after it is enacted.

SIGNIFICANCE

Our data demonstrate that BR response size to SON depends on SON stimulus intensity and not SON response size, an observation that calls for further physiological studies and cautions against unanimous clinical applicability of BRER curves.