A-161 Corticomedial Amygdala Volume Significantly Predicts Cognitive Fexibility in an Older Adult Sample

Objective The present study examined the relationship between anxiety, corticomedial and basolateral amygdala volume, and cognitive flexibility among older adults (OA). We hypothesized that higher subclinical Beck Anxiety Inventory (BAI) scores would be associated with lower cognitive flexibility, assessed using the Delis-Kaplan Executive Function System (D-KEFS) verbal fluency. Additionally, we hypothesized that basolateral amygdala volume would negatively correspond to anxiety scores and exhibit a positive relationship with cognitive flexibility. Method Sixty-three OA (M age: 65; SD: 9; 59% female) were recruited via community advertising and cardiac clinics for a parent study on cardiovascular disease. Participants completed the D-KEFS and BAI as part of a comprehensive neuropsychological assessment prior to magnetic resonance imaging (MRI). Amygdala segmentation was completed with FreeSurfer version 6.0, using T1-weighted MPRAGE and T2-weighted FLAIR images. Data was analyzed using hierarchical multiple regression, controlling for age, sex, years of education, and intracranial volume. Results No significant relationship emerged between basolateral amygdala volume and BAI scores (r = .11, p = .41) or cognitive flexibility (r = .04, p = .76). However, a significant positive relationship was observed between corticomedial amygdala volume and cognitive flexibility after controls (β = 0.37, p < .01). Conclusions The previously reported relationship between high anxiety and basolateral amygdala volume does not appear to extend to subclinical levels. We conjecture that the significant relationship between the corticomedial amygdala and cognitive flexibility represents the upward slope between arousal and cognitive performance on the Yerkes-Dodson curve. These findings newly implicate corticomedial amygdala volume as a representative measure linking emotional arousal and cognitive performance in OA.

Electrophysiological effects of testosterone on the medial preoptic–anterior hypothalamus of the rat

Castration in the rat significantly lengthened the refractory period of medial preoptic–anterior hypothalamic neurones with outputs into the medial forebrain bundle but not of those with outputs to the lateral septum. Treatment with testosterone propionate reduced the neuronal refractory period to its lowest level at the same time as it restored mounts and intromissions (after 5 days). Equally, when treatment was ended at 15 days, mounts and intromissions were no longer shown when the refractory period lengthened again 14 days later. The sub-population of neurones which also received inputs from the contralateral fimbria (through the corticomedial amygdala) showed the same results as the overall population. Castration also significantly increased the baseline firing rates of medial preoptic–anterior hypothalamic neurones receiving inputs from the medial forebrain bundle. The same effect was observed for the sub-population of neurones which also had inputs from the contralateral fimbria, but castration significantly reduced the percentage of neurones responding to this additional input. The neurones having inputs with the fastest conduction velocity were responsible for these changes in firing rate and the input neurones were therefore probably non-dopaminergic.