Search

Functional magnetic resonance imaging (fMRI) was used to study memory-associated activation of medial temporal lobe (MTL) regions in 32 nondemented elderly individuals with mild cognitive impairment (MCI). Subjects performed a visual encoding task during fMRI scanning and were tested for recognition of stimuli afterward. MTL regions of interest were identified from each individual's structural MRI, and activation was quantified within each region. Greater extent of activation within the hippocampal formation and parahippocampal gyrus (PHG) was correlated with better memory performance. There was, however, a paradoxical relationship between extent of activation and clinical status at both baseline and follow-up evaluations. Subjects with greater clinical impairment, based on the Clinical Dementia Rating Sum of Boxes, recruited a larger extent of the right PHG during encoding, even after accounting for atrophy. Moreover, those who subsequently declined over the 2.5 years of clinical follow-up (44% of the subjects) activated a significantly greater extent of the right PHG during encoding, despite equivalent memory performance. We hypothesize that increased activation in MTL regions reflects a compensatory response to accumulating AD pathology and may serve as a marker for impending clinical decline.

We describe a system for parcellation of the human cerebral white matter and nuclei, based upon magnetic resonance images. An algorithm for subdivision of the cerebral central white matter according to topographic criteria is developed in the companion manuscript. In the present paper we provide a rationale for this system of parcellation of the central white matter and we extend the system of cerebral parcellation to include principal subcortical gray structures such as the thalamus and the basal ganglia. The volumetric measures of the subcortical gray and white matter parcellation units in 20 young adult brains are computed and reported here as well. In addition, with the comprehensive system for cerebral gray and white matter structure parcellation as reference, we formulate a systematics of forebrain connectivity. The degree to which functionally specific brain areas correspond to topographically specific areas is an open empirical issue. The resolution of this issue requires the development of topographically specific anatomic analyses, such as presented in the current system, and the application of such systems to a comprehensive set of functional-anatomic correlation studies in order to establish the degree of structural-functional correspondence. This system is expected to be applied in both cognitive and clinical neuroscience as an MRI-based topographic systematics of human forebrain anatomy with normative volumetric reference and also as a system of reference for the anatomic organization of specific neural systems as disrupted by focal lesions in lesion-deficit correlations.

We describe a virtually automatic comprehensive parcellation of the human cerebral central white matter, which is based upon T1-weighted MRI scans. The system, which is “rule-based,” is developed from prior anatomic studies of the human brain and experimental studies of connectivity in animals as elaborated in the companion manuscript. Boundaries which delineate anatomic subregions of the white matter are computed from the geometric features of anatomic landmarks visible in the imaging data. The fiber systems of the central white matter are ordered topographically into three compartments, reflecting the inferred arrangements of principal neural systems pathways. These include an outer radiate (fibers principally radially aligned), an intermediate sagittal (fibers principally sagittally aligned), and deep bridging (fibers bridging hemispheres or cortex and deep structures) compartments. Each of these compartments is secondarily parcellated into smaller units to increase the anatomic specificity and spatial resolution of the system. The principal intended uses for this system of anatomic subdivision are for the volumetric characterization of forebrain white matter in normal and abnormal brains and for precision and specificity of localization in focal lesion-deficit correlation studies.

Magnetic resonance imaging (MRI) has revolutionized the practical demands of clinical neurology. This technology promises now to advance neurology in theoretical and applied realms of fundamental human brain science. We emphasize here two domains in which these advances will occur. The first is volumetric morphometry of the human brain. With MRI the multiple levels of processing of the brain may be characterized in terms of their absolute volumes and their relative sizes, perspectives indispensable for our understanding of the development and operation of neural systems. Volumetric morphometry also promises substantial increases in the specificity and sensitivity of neurological diagnosis, particularly where applied to disorders where structural abnormalities will be reflected only in volumetric abnormalities. The second direction of advance considered here is application of MRI in cortical mapping in support of cognitive neuroscience. In this application MRI provides means to map at high resolution the distribution of subcomponents of neural systems activated by behavioral paradigms. This line of investigation will carry forward rapidly our understanding of how the information processing algorithms of the brain are mapped upon the coordinates of the various gray matter structures of the brain. Among the practical consequences of this application will be a reasoned design of surgical field in tumor and epilepsy surgery.

The process of forming new associations between previously unrelated items of information, such as a name and a face, likely requires the integration of activity within multiple brain regions. The hippocampus and related structures in the medial temporal lobe are thought to be particularly critical in binding together items of information. We studied eight healthy young subjects with functional magnetic resonance imaging (fMRI) during the encoding of novel face‐name associations compared to viewing repeated face‐name pairs. A consistent pattern of activation was observed in the hippocampus, pulvinar nucleus of the thalamus, fusiform and dorsolateral prefrontal cortices across individual subjects. The location of the activation within the hippocampus was more anterior than previously reported in studies using similar novel vs. repeated paradigms with stimuli that did not specifically require relational processing among unrelated items. These data suggest that the process of forming new face‐name associations is supported by a distributed network of brain regions, and provide additional evidence for the essential role of the hippocampus in associative memory processes. Hum. Brain Mapping 14:129–139, 2001. © 2001 Wiley‐Liss, Inc.