Administration of hydrocortisone does not alter interhemispheric connectivity

Information is exchanged and integrated between the two hemispheres of the human brain via the corpus callosum. Previous work has shown that sex hormones like estradiol and progesterone can affect excitatory and inhibitory properties of the corpus callosum. Thus, it is evident that interhemispheric integration and hemispheric asymmetries are modifiable by endocrinological influences. In previous studies, our group could show an enhancing effect of acute stress on interhemispheric integration. To investigate if this effect can be attributed to an increase in the stress hormone cortisol, 50 male participants received 20mg hydrocortisone or a placebo in a double-blind crossover design. In each test session, we collected N1 ERP data while participants completed a lexical decision task and a Poffenberger paradigm. In the lexical decision task, we found shorter N1 latencies for contralateral compared to ipsilateral presentation of lexical stimuli. Similarly, we replicated the classical Poffenberger effect with shorter ERP latencies for stimuli presented in the contralateral visual field compared to the ipsilateral visual field. However, no effect of cortisol on latency differences between hemispheres could be detected. These results suggest that an increase in cortisol alone might not be enough to affect the interhemispheric transfer of information via the corpus callosum.