Redistribution of cerebral activity during childhood

Review : Metabolic Imaging: A Window on Brain Development and Plasticity

Various biochemical and physiological processes that undergo maturational changes during human brain development can be now studied in vivo using PET. The distribution of local cerebral glucose utilization shows regional alterations in the first year of life in agreement with behavioral, neurophysiological, and anatomical changes known to occur during development of the infant. Measurement of the absolute rates of glucose utilization with PET reveals that during the major portion of the first decade, the human brain has a higher energy (glucose) demand compared with both the newborn and adult brains. With adolescence, glucose utilization rates decline to reach adult values by age 16-18 years. This nonlinear course of cerebral glucose 'metabolic' maturation is also seen in a number of animal models and coincides with the develop mental course of transient synaptic exuberance associated with enhanced brain plasticity and efficient learn ing. Evidence of brain reorganization detected with PET is discussed in children with unilateral brain injury and early sensory deprivation. NEUROSCIENTIST 5:29-40, 1999

A multi-methodological MR resting state network analysis to assess the changes in brain physiology of children with ADHD

The purpose of this work was to highlight the neurological differences between the MR resting state networks of a group of children with ADHD (pre-treatment) and an age-matched healthy group. Results were obtained using different image analysis techniques. A sample of n = 46 children with ages between 6 and 12 years were included in this study (23 per cohort). Resting state image analysis was performed using ReHo, ALFF and ICA techniques. ReHo and ICA represent connectivity analyses calculated with different mathematical approaches. ALFF represents an indirect measurement of brain activity. The ReHo and ICA analyses suggested differences between the two groups, while the ALFF analysis did not. The ReHo and ALFF analyses presented differences with respect to the results previously reported in the literature. ICA analysis showed that the same resting state networks that appear in healthy volunteers of adult age were obtained for both groups. In contrast, these networks were not identical when comparing the healthy and ADHD groups. These differences affected areas for all the networks except the Right Memory Function network. All techniques employed in this study were used to monitor different cerebral regions which participate in the phenomenological characterization of ADHD patients when compared to healthy controls. Results from our three analyses indicated that the cerebellum and mid-frontal lobe bilaterally for ReHo, the executive function regions in ICA, and the precuneus, cuneus and the clacarine fissure for ALFF, were the “hubs” in which the main inter-group differences were found. These results do not just help to explain the physiology underlying the disorder but open the door to future uses of these methodologies to monitor and evaluate patients with ADHD.

Brain perfusion in children: evolution with age assessed by quantitative perfusion computed tomography

OBJECTIVE

The objective of this study was to assess the age-related variations of brain perfusion through quantitative cerebral perfusion computed tomography (CT) results in children without brain abnormality.

METHODS

Brain perfusion CT examinations were performed in 77 children, aged 7 days to 18 years. These patients were admitted at our institution for both noncontrast and contrast-enhanced cerebral CT. Only children whose conventional cerebral CT and clinical/radiologic follow-up, including additional investigations, were normal were taken into account for this study (53 of 77).

RESULTS

The average regional rCBF amounts to 40 (mL/100 g per minute) for the first 6 months of life, peaks at approximately 130 (mL/100 g per minute) at approximately 2 to 4 years of age, and finally stabilizes at approximately 50 (mL/100 g per minute) at approximately 7 to 8 years of age, with a small increase of rCBF values at approximately 12 years of age. The rCBF in the gray matter averages 3 times that in the white matter, except for the first 6 months of life. The global CBF represents 10% to 20% of the global cardiac output for the first 6 months of life, peaks at approximately 55% by 2 to 4 years of age, and finally stabilizes at approximately 15% by 7 to 8 years of age. Specific age-related evolution patterns were identified in the different anatomic areas of the cerebral parenchyma, which could be related to the development of neuroanatomic structures and to the emergence of corresponding cognitive functions.

CONCLUSIONS

Quantitative perfusion CT characterization of brain perfusion shows specific age variations. Brain perfusion of each cortical area evolves according to a specific time course, in close correlation with the psychomotor development.

A mathematical model for the analysis of cross-sectional brain glucose metabolism data in children

1. The authors present here a 5-parameter developmental function designed to describe quantitatively the time-course of changes in glucose metabolism with age. This function consists of a plateau phase which is described by the rate of increase with age and the height of the plateau, followed by a decline phase characterized by the rate of decrease to adult levels. These two phases are separated by a distinct point in time, at which the transition between the two phases occurs. 2. The model is designed to fit published data showing that glucose metabolic rate in frontal cortex at birth is about 60% of adult values (mean adult value is 24 mumol/100 g/min) and increases to slightly less than triple adult value by age 3. The metabolic rate remains at this level until the age of approximately 8 years when it starts the decline to adult values. 3. A procedure is presented which allows the approximate computation of the 98% confidence contours in data space for the developmental function. The computation is based on the joint probability function obtained from the model covariance matrix. 4. The newly designed 5-parameter developmental function is well suited to describe maturational changes of glucose metabolism. Due to its excellent model identifiability and the interpretability of individual parameters, this function is better suited for description of maturational changes than the gamma-function. Furthermore, this function may provide a useful framework for interpretation of other data sets during development.