Altered tonic and phasic cortisol secretion following unilateral stroke.

Evidence is accumulating that cerebral laterality appears to be an important feature in the regulation of the stress response with the right hemisphere being closely linked to stress-regulatory systems, including the hypothalamic-pituitary-adrenal (HPA) axis. Although some animal and human data support this hypothesis, studies on brain damaged patients yet failed to substantiate laterality effects on cortisol secretion. The aim of this study was to examine whether unilateral stroke differentially affects tonic and phasic response characteristics of the HPA axis, and to evaluate the impact of intrahemispheric lesion location. Basal morning cortisol levels and phasic responses towards a mentally challenging task were examined in 32 stroke patients with left-sided (LH; n=18) or right-sided (RH; n=14) infarctions and 30 healthy controls matched for age and gender. Only LH, but not RH patients displayed increased morning cortisol levels when compared to controls. In contrast, phasic reactions were blunted in the combined patient group with RH patients showing the most distinct decline. More anterior located lesions were associated with reduced phasic, but not tonic cortisol measures. This relationship appeared to be particularly pronounced in RH patients. Results support the conclusion that the central regulation of cortisol secretion is under excitatory control of the right hemisphere and can be interpreted within a framework of asymmetrical regulation of the stress response. Left- and right-sided strokes may differentially affect response patterns of the HPA axis, a stress-regulatory system that is associated with effective protection against disease and external challenges.