Effects of healthy aging on the regional cerebral metabolic rate of glucose assessed with statistical parametric mapping

Age-related cognitive decline, mild cognitive impairment or preclinical Alzheimer's disease?

With the promising development of effective treatment, significant improvement in the very early diagnosis of Alzheimer's disease (AD) is required. There is vast agreement that a decline in memory, especially in verbal episodic memory, is the earliest and perhaps the most sensitive sign of incipient AD at the preclinical stage. However, this review offers evidence that impairment in episodic memory can be observed in normal elderly people as well as in aged subjects with mild cognitive impairment (MCI), a large proportion of whom will, however, not convert to dementia. Quantitative measurement of atrophy and brain activation in the hippocampal-parahippocampal formation by using structural and functional magnetic resonance imaging may help to distinguish the MCI decliners from the nondecliners. Cerebrospinal fluid levels of tau protein and Abet1-42 peptide, together with the presence of an apolipoprotein (apo)E epsilon4 allele may also increase our confidence in the early positive diagnosis of AD. This review concludes, however, that while adequate for constituting groups of patients in a research perspective, the extensive diagnostic procedure based on specific cognitive testing, neuroimaging and biological investigations is still out of reach for the practitioner.

The functional neuroanatomy and long-term reproducibility of brain activation associated with a simple finger tapping task in older healthy volunteers: a serial PET study

We examined long-term reproducibility of the functional organization of the brain associated with a simple finger tapping movement using positron emission tomography (PET). Repeat measurements of regional cerebral blood flow were obtained in 10 individuals, ages 35 to 82 years (mean 52 years), at scanning sessions separated by 6 months. Although the functional neuroanatomy of hand movements has previously been investigated with PET by a number of groups, none has reported systematic investigation of the consistency of brain activation over an extended time. As expected, we found significant activation in the left precentral gyrus [Talairach coordinate (-32, -34, 52)], postcentral gyrus (-22, -48, 56), and supplementary motor area (SMA) (-2, -18, 52) at the initial study, consistent with previous studies in younger subjects. For the follow-up study we also found significant activation in the left precentral (-36, -28, 52) and postcentral (-28, -36, 52) gyri and in the SMA (2, -16, 56). Our group results demonstrate consistent anatomical location and extent of motor activation over time. More importantly, analysis of individuals confirmed the presence of consistent sites of activation in primary sensorimotor cortex and SMA over the 6-month interval in most subjects. A high degree of consistency in location of activation in the group, and within individuals, over time suggests that changes in loci of activation may be confidently monitored using the PET method. Evidence of individual differences in extent of activation over time highlights the need for caution when interpreting similar changes in patient studies.

Serotonin, cerebral blood flow, and cerebral metabolic rate in geriatric major depression and normal aging

While there is substantial evidence for abnormalities in serotonin (5-HT) neurotransmission in major depressive disorder (MDD), almost all of the findings derive from studies of young adults. Moreover, relatively little research has assessed brain 5-HT transmission in vivo. Neuroendocrine studies do not permit evaluation of a range of brain regions, but only the limited circuitry associated with hormone release. Data from autopsy studies are limited by the difficulties of assessment of the acute clinical picture before death, and by post-mortem artifacts. In vivo neuroimaging techniques overcome many of the methodological limitations of both these approaches. There is a large body of imaging data indicating regional cerebral blood flow (rCBF) and cerebral metabolic rate (rCMR) decrements both with aging and in patients with MDD. While the physiological bases for these phenomena are largely unknown, changes in brain 5-HT function may be involved. Neuroanatomical studies have revealed an intricate network of 5-HT-containing neurons within the cerebral microvasculature, with physiological evidence for serotonergic control of both rCBF and rCMR. Acute pharmacological challenges are available to probe brain 5-HT function. Such paradigms, using neuroendocrine responses as endpoints, have been of some utility in predicting outcome with antidepressant treatment. The role of 5-HT dysregulation in geriatric MDD takes on more importance given concerns regarding putative reduced efficacy of serotonin-specific reuptake inhibitors (SSRIs) in this population. If this is due to diminished responsivity of 5-HT systems, then the ability to identify antidepressant nonresponders via 5-HT challenge in combination with neuroimaging measures may have important clinical utility.