Rapid cortisol enhancement of psychomotor and startle reactions to side-congruent stimuli in a focused cross-modal choice reaction time paradigm

The stress hormone cortisol has been shown to affect hemodynamic activity of human brain structures, presumably via a nongenomic mechanism. However, behavioral implications of this finding remain unknown. In a placebo-controlled, blinded, cross-over design the rapid effects of IV hydrocortisone (5 mg) on cross-modal integration of simultaneous, unilateral visual and acoustic signals in a challenging startle and reaction time (RT) paradigm were studied. On two separate days 1 week apart, 24 male volunteers responded by button push to either up- or down pointing triangles presented in random sequence in the periphery of one of the visual hemi-fields. Visual targets were accompanied by unilateral acoustic startle noise bursts, presented at the same or opposite side. Saccadic latency, manual RT, and startle eye blink responses were recorded. Faster manual reactions and increased startle eye blink responses were observed 11-20 min after hydrocortisone administration when visual targets and unilateral acoustic startle noises were presented in the same sensory hemi-field, but not when presented in opposite sensory hemi-fields. Our results suggest that a nongenomic, cortisol-sensitive mechanism enhances psychomotor and startle reactions when stimuli occur in the same sensory hemi-field. Such basic cognitive effects of cortisol may serve rapid adaptation and protection against danger stimuli in stressful contexts.