With continued debate over the functional significance of adult neurogenesis, identifying an in vivo correlate of neurogenesis has become an important goal. Here we rely on the coupling between neurogenesis and angiogenesis and test whether MRI measurements of cerebral blood volume (CBV) provide an imaging correlate of neurogenesis. First, we used an MRI approach to generate CBV maps over time in the hippocampal formation of exercising mice. Among all hippocampal subregions, exercise was found to have a primary effect on dentate gyrus CBV, the only subregion that supports adult neurogenesis. Moreover, exercise-induced increases in dentate gyrus CBV were found to correlate with postmortem measurements of neurogenesis. Second, using similar MRI technologies, we generated CBV maps over time in the hippocampal formation of exercising humans. As in mice, exercise was found to have a primary effect on dentate gyrus CBV, and the CBV changes were found to selectively correlate with cardiopulmonary and cognitive function. Taken together, these findings show that dentate gyrus CBV provides an imaging correlate of exercise-induced neurogenesis and that exercise differentially targets the dentate gyrus, a hippocampal subregion important for memory and implicated in cognitive aging.hippocampus ͉ in vivo imaging ͉ cerebral blood volume ͉ angiogenesis T he hippocampal formation, a brain circuit made up of separate but interconnected subregions (1), is vital for memory function (2) and is targeted by the aging process (3). The dentate gyrus is the only hippocampal subregion that supports neurogenesis in the adult brain (4-6). Nevertheless, because neurogenesis can only be assessed in postmortem tissue, its functional significance remains undetermined. With this limitation in mind, we have explored different imaging approaches applicable to rodents and humans that might provide an in vivo correlate of neurogenesis.Although imaging radioligands designed to bind newly dividing cells is an attractive approach, positron emission tomography imaging suffers inherently poor resolution and cannot visualize the dentate gyrus. Additionally, radiolabeling newborn cells introduces potential safety concerns. For these reasons, we have focused on MRI technologies instead. Notably, a coupling has been established between neurogenesis and angiogenesis (7,8). The process of angiogenesis, in turn, gradually gives rise to the formation of new blood vessels, increasing regional microvascular density (9-12). Importantly, vascular density can be measured in vivo with imaging techniques that map regional blood volume. Numerous studies have established a tight relationship between angiogenesis and regional blood volume (13-17), including in the brain where regional angiogenesis is coupled to regional cerebral blood volume (CBV) (18)(19)(20)(21)(22)(23)(24)(25)(26).Because CBV can be measured with MRI, we hypothesized that a regionally selective increase in hippocampal CBV might provide an imaging correlate of neurogenesis. This hypothesis was tested in...

The entorhinal cortex has been implicated in the early stages of Alzheimer’s disease, which is characterized by changes in the tau protein and in the cleaved fragments of the amyloid precursor protein (APP). We used a high-resolution functional magnetic resonance imaging (fMRI) variant that can map metabolic defects in patients and mouse models to address basic questions about entorhinal cortex pathophysiology. The entorhinal cortex is divided into functionally distinct regions, the medial entorhinal cortex (MEC) and the lateral entorhinal cortex (LEC), and we exploited the high-resolution capabilities of the fMRI variant to ask whether either of them was affected in patients with preclinical Alzheimer’s disease. Next, we imaged three mouse models of disease to clarify how tau and APP relate to entorhinal cortex dysfunction and to determine whether the entorhinal cortex can act as a source of dysfunction observed in other cortical areas. We found that the LEC was affected in preclinical disease, that LEC dysfunction could spread to the parietal cortex during preclinical disease and that APP expression potentiated tau toxicity in driving LEC dysfunction, thereby helping to explain regional vulnerability in the disease.

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The dentate gyrus (DG) is a region in the hippocampal formation whose function declines in association with human aging and is therefore considered to be a possible source of age-related memory decline. Causal evidence is needed, however, to show that DG-associated memory decline in otherwise healthy elders can be improved by interventions that enhance DG function. We addressed this issue by first using a high-resolution variant of functional magnetic resonance imaging (fMRI) to map the precise site of age-related DG dysfunction and to develop a cognitive task whose function localized to this anatomical site. Then, in a controlled randomized trial, we applied these tools to study healthy 50–69-year-old subjects who consumed either a high or low cocoa–containing diet for 3 months. A high-flavanol intervention was found to enhance DG function, as measured by fMRI and by cognitive testing. Our findings establish that DG dysfunction is a driver of age-related cognitive decline and suggest non-pharmacological means for its amelioration.