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Recent evidence suggests that exercise plays a role in cognition and that the posterior cingulate cortex (PCC) can be divided into dorsal and ventral subregions based on distinct connectivity patterns.
To examine the effect of physical activity and division of the PCC on brain functional connectivity measures in subjective memory complainers (SMC) carrying the epsilon 4 allele of apolipoprotein E (APOE 4) allele.
Participants were 22 SMC carrying the APOE ɛ4 allele (ɛ4+; mean age 72.18 years) and 58 SMC non-carriers (ɛ4–; mean age 72.79 years). Connectivity of four dorsal and ventral seeds was examined. Relationships between PCC connectivity and physical activity measures were explored.
ɛ4+ individuals showed increased connectivity between the dorsal PCC and dorsolateral prefrontal cortex, and the ventral PCC and supplementary motor area (SMA). Greater levels of physical activity correlated with the magnitude of ventral PCC–SMA connectivity.
The results provide the first evidence that ɛ4+ individuals at increased risk of cognitive decline show distinct alterations in dorsal and ventral PCC functional connectivity.
Grey matter changes have been described in individuals who are pre- and peri-psychotic, but it is unclear if these changes are accompanied by changes in white matter structures.
To determine whether changes in white matter occur prior to and with the transition to psychosis in individuals who are pre-psychotic who had previously demonstrated grey matter reductions in frontotemporal regions.
We used magnetic resonance imaging (MRI) to examine regional white matter volume in 75 people with prodromal symptoms. A subset of the original group (n=21) were rescanned at 12–18 months to determine white matter volume changes. Participants were retrospectively categorised according to whether they had or had not developed psychosis at follow-up.
Comparison of the baseline MRI data from these two subgroups revealed that individuals who later developed psychosis had larger volumes of white matter in the frontal lobe, particularly in the left hemisphere. Longitudinal comparison of data in individuals who developed psychosis revealed a reduction in white matter volume in the region of the left fronto-occipital fasciculus. Participants who had not developed psychosis showed no reductions in white matter volume but increases in a region subjacent to the right inferior parietal lobule.
The reduction in volume of white matter near the left fronto-occipital fasciculus may reflect a change in this tract in association with the onset of frank psychosis.
Objective: To compare the utility of temporal lobe magnetic resonance imaging (MRI) and single-photon emission tomography (SPET) scanning in discriminating between subjects with Alzheimer's disease (AD) and age-matched controls. Methods: Thirty subjects with NINCDS-ADRDA AD (23 probable AD, 5 possible AD, 2 definite AD) and 22 age- and sex-matched controls underwent T1-weighted coronal MRI scanning (0.3 T) and technetium 99m-HMPAOSPET scanning. MRI scans were analyzed using a digitizer system with volumes of hippocampus, amygdala, entorhinal cortex, parahippocampal gyrus, and whole cerebral cortex calculated. From SPET scans, regional cerebral blood flow (rCBF) was assessed in anterior and posterior frontal, parietal, occipital, and mesial temporal cortex using a region of interest analysis with the cerebellum as a reference area. Results: Using MRI, the areas that best separated groups were left hippocampal and left amygdala volume, resulting in correct classification (patient vs. control) in 79% of cases (sensitivity 77%, specificity 82%). Exactly the same proportion of subjects were correctly classified by SPET, with the most discriminating rCBF changes being left parietal and right posterio frontal. Combining information from both scans improved the proportion of correctly classified subjects in a discriminant function to 90% (sensitivity 93%, specificity 86%, only 2AD and 3 controls misclassified). All AD subjects had abnormalities on MRI and/or SPET (sensitivity for combined examinations 100%), while abnormalities on both MRI and SPET had a positive predictive value of 100% for dementia (including the detection of one control subject who later had dementia). Significant correlations between MRI and SPET measures were seen in control subjects but not in patients. Conclusion: Both 0.3 T MRI and single rotating gamma camera SPET were equally useful in separating AD subjects from age-matched controls, although the combination of both significantly enhanced discrimination. In particular, all AD subjects had abnormalities on either MRI or SPET and both techniques may have an important role in assisting with clinical diagnosis, though replication in other centers and examination of differentiation of AD from other causes of dementia need to be examined.
We present the case of a 23-year-old Vietnamese male with a
2-year history of a psychotic illness marked by prominent negative
symptoms, fatuousness and disturbed behavior. Neuroimaging revealed
a prominent vascular flow void affecting the middle and anterior
cerebral arteries, with associated increased collateral supply
to the frontal cortex, consistent with Moyamoya disease.
Neurological examination was unremarkable; however,
neuropsychological assessment revealed significant executive
dysfunction, including stimulus-driven behavior. Whilst the
diagnosis of schizophrenia and Moyamoya disease may be
coincidental, an interaction between the 2 diseases may have
led to some of the atypical features of this case, including
prominent executive dysfunction and marked sensitivity to
psychotropic medication. We discuss the nature of possible
interactions between the 2 conditions. This case also highlights
the importance of re-evaluating patients with atypical or
treatment-resistant psychoses for cerebral pathology.
(JINS, 2003, 9, 806–810.)
Computed tomography (CT), also known as computerized axial tomography (CAT) and CAT scanning, was developed between 1967 and 1970 by the English scientist Godfrey Hounsfield. The first clinical results were reported in 1972 (Ambrose & Hounsfield, 1972a,b). Hounsfield successfully harnessed conventional X-rays and a computer to produce cross-sectional brain images of unprecedented clarity (Hounsfield, 1973).
All CT scanners share a number of key features. A finely collimated X-ray beam moves around the patient's head within a metallic shell called a gantry. The extent of X-ray absorption by the tissues is measured by detectors which fluoresce or ionize in direct proportion to the intensity of the X-ray beam striking them after traversing the patient's head. The degree of fluorescence or ionization is converted into digital information by a computer. Using one of several suitable computer algorithms, cross-sectional images of the irradiated slices of brain are constructed in which each of the individual elements of the image, called ‘pixels’ (shorthand for picture elements), is allocated a level of brightness somewhere between black and white. Approximately 256 shades of gray are available for use in modern CT scanners. Low-density structures such as fat and water appear black and high-density structures such as bone and calcium appear white.
CT scanner types
The original CT scanners were of the ‘ctranslate–rotate’ type. While continuously emitting a finely collimated, pencil shaped X-ray beam, the tube and detectors traversed (translated) across the head in a straight line.
The technique of MRI has become an essential tool in the evaluation of neurological disease. Not only is it an important adjunct to CT but in many cases it is the imaging method of choice.
MRI has its roots in the pioneering work of Bloch, Purcell and others in the first half of the century (Bloch, Hansen & Packard, 1946; Purcell, Torry & Pound, 1946). However, more than 40 years elapsed between the first description of the phenomenon of nuclear magnetic resonance (NMR) and the production of the first images of human anatomy by groups at the University of Nottingham in 1976 and 1977. The development and widespread clinical dissemination of these devices occurred in the 1980s.
Basic physics of MRI
Human tissue contains significant amounts of water, proteins, lipids and other macromolecules, which are abundant in hydrogen atoms the nuclei of which are positively charged particles called protons. MRI relies on the fact that protons are magnetically active.
Protons can be thought of as spinning around their own internal axis (Fig. 1.21). One of the fundamental features of electromagnetism is that a moving charge creates its own small magnetic field. In the case of a spinning proton, this self-produced magnetic field is referred to as its magnetic moment.
When patients are placed in a strong magnetic field, the spinning protons inside their bodies can take up one of only two possible orientations.
An age-related dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis is well recognised in animals, but still remains controversial in humans. There is increasing interest that raised corticosteroid levels, due to activation of the HPA axis, may cause both depressive symptoms and cognitive impairments. Steroid effects on cognition may be via the hippocampus, a major site of corticosteroid action and an important structure involved in learning and memory.
To investigate this further, we examined the relationship between the dexamethasone suppression test, cognitive function, depressive symptoms and hippocampal atrophy on magnetic resonance imaging (MRI) in 32 normal controls, 49 subjects with NINCDS/ADRDA Alzheimer's disease and 51 patients with DSM–III–R Major Depression.
Controlling for differences in dexamethasone concentrations, post-dexamethasone cortisol levels were related to advancing age in controls and depressed subjects. However, among subjects with Alzheimer's disease, post-dexamethasone cortisol levels were independently associated with both minor depressive symptoms and hippocampal atrophy on MRI.
An association between advancing age and increased HPA axis dysregulation is supported for controls and depressed subjects. In Alzheimer's disease, HPA axis changes were associated with depressive symptoms and hippocampal atrophy. Longitudinal studies are now needed to determine the causal direction of these associations.
White matter changes, as revealed by magnetic resonance imaging (MRI), may occur in depression and Alzheimer's disease.
T2-weighted MRI scans were performed in 39 control subjects, 61 subjects with NINCDS/ADRDA Alzheimer's disease and 60 subjects with DSM–III–R major depression. Deep white matter lesions (DWML) and periventricular lesions (PVL) were rated on a standard 0–3 scale by two radiologists blind to clinical diagnosis.
After controlling for differences in vascular risk factors and current blood pressure, DWML were significantly more common in depressed subjects and PVL in Alzheimer's disease subjects compared to controls. DWML were most common in those presenting in late life with their first ever depression and 50% of such subjects had severe (grade 3) DWML.
An association between DWML and depression and PVL and Alzheimer's disease is supported. The increase with DWML that occurs with ageing may predispose some elderly subjects to depression.
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