Background: The hippocampal formation is damaged early in Alzheimer's disease (AD). An association between temporal lobe volume and cognitive function has been shown in several studies. Increased limbic-hypothalamic-pituitary-adrenal (LHPA) axis function has been suggested to be related to hippocampal atrophy and cognitive impairment. Our hypothesis was that there is a clear link between hippocampal volume -- notably of the CA1 region -- memory (episodic and visuospatial) and decreased feedback sensitivity in the LHPA axis in AD.
Methods: Sixteen medication-free outpatients with mild to moderate AD were included. Hippocampal volume was measured with magnetic resonance imaging. Dexamethasone suppression tests were performed using .5 mg and .25 mg dexamethasone. Three different components in the neuropsychological battery -- Rey 15 item memory test, Alzheimer's Disease Assessment Scale (ADAS) word recall and spatial span from Wechsler Adult Intelligence Scale - Revised neuropsychological instrument (WAIS-R NI) -- were found to represent episodic and visuospatial memory.
Results: Low hippocampal CA1 volume and high post-dexamethasone cortisol levels in combination were significantly associated with Rey 15 item memory and spatial span test outcomes. No association was found between LHPA feedback and hippocampal volume.
Conclusions: Low hippocampal volume and a disturbed negative feedback in the LHPA axis link to specific cognitive impairments in Alzheimer's disease.