In populations of young and older adults, it has been shown that individuals may be categorized into one of three diurnal subgroups when salivary cortisol levels are assessed over a 2-day period and compared for their consistency across days: a typical subgroup, a flat subgroup, and an inconsistent subgroup. Interestingly, recent studies have reported that the typical subgroup represents the majority of the young and older adult population, a finding that is difficult to reconcile with previous studies showing increased cortisol levels in older adults with depression or cognitive impairments. In order to assess whether a typical diurnal cortisol profile is representative across different subgroups of older adults, we assessed diurnal cortisol cycle representation in a sample of older adults with subjective complaints of depression and/or memory problems. Furthermore, given the robust relationship between cortisol and cognitive function, the present study examined the association between the three diurnal subgroups and cognitive performance. Forty-two older individuals were recruited on the basis of reporting subjective complaints of either memory problems and/or depressive mood. Participants were asked to sample their saliva over a 2-day period and were then asked to undergo a neuropsychological evaluation that taps into short-term memory, declarative memory and language. The results showed that 69% of the sample presented a Flat cycle of salivary cortisol over a 2-day period while 19% presented an inconsistent pattern and 12% presented a typical pattern. Participants in the flat subgroup were significantly impaired on letter verbal fluency. Furthermore, a relationship was found between diurnal cortisol subgroup representation and subjective complaint profile. These findings show that older adults with complaints of memory problems and/or depressive symptoms do not present the typical profile of the diurnal cortisol cycle, and they provide a preliminary view of how diurnal cortisol profile relates to cognitive function during human aging.
We tested nine patients with callosal pathology in a simple reaction time task with and without redundant targets in the same or opposite visual hemifield. Four patients showed large facilitation (redundancy gain) in the presence of a redundant target, exceeding probability summation models (neural summation). Five patients showed redundancy gain not exceeding probability models. Violation of probability models was not associated with a specific type of callosal lesion. Neural summation, which probably occurs at collicular level, may be modulated by cortical activity. To test this hypothesis, we used functional MRI. During detection of redundant simultaneous targets, activations in the extrastriate cortex were observed in a patient with callosal agenesis and redundancy gain violating probability models, but not in a patient with callosal agenesis and redundancy gain not exceeding probability models. We conclude that cortical activity in the extrastriate cortex may be a modulating factor in the magnitude of the redundancy gain during parallel visuomotor transforms.
The purpose of the present study was to investigate basic methodological issues related to the usage of an examination stress protocol in studies of psychoneuroendocrinology. In the present study, 57 undergraduate students served as participants. All subjects provided salivary samples and completed psychological inventories during a low examination stress period and again during a high examination stress period. Salivary samples were analyzed for cortisol. Three major findings were observed. First, the examination stress protocol proved to be an effective trigger of elevations in both psychological measures of stress and in cortisol levels. Second, sex differences were observed in cortisol levels, such that males showed an elevation in cortisol during the high examination stress session whereas females did not. Finally, no significant correlations were observed between elevations in psychological measures of stress and elevations in cortisol levels. These findings suggest that the examination stress protocol used in the present study effectively elevated both psychological stress and cortisol levels. Furthermore, these findings suggest that there are biological differences in how males and females respond to stress. Finally, no evidence was found to suggest a relationship between psychological and hormonal levels of stress. Together, these findings suggest the need to better define and consider the implications of both the specific measures of stress being used and individual differences in the subject samples in psychoendocrine studies.
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