Functional connectivity MR imaging reveals cortical functional connectivity in the developing brain

Abstract

Background and purpose: Unlike conventional functional MR imaging where external sensory/cognitive paradigms are needed to specifically activate different regions of the brain, resting functional connectivity MR imaging acquires images in the absence of cognitive demands (a resting condition) and detects brain regions, which are highly temporally correlated. Therefore, resting functional MR imaging is highly suited for the study of brain functional development in pediatric subjects. This study aimed to determine the temporal and spatial patterns of rfc in healthy pediatric subjects between 2 weeks and 2 years of age.

Materials and methods: Rfc studies were performed on 85 children: 38 neonates (2-4 weeks of age), 26 one-year-olds, and 21 two-year-olds. All subjects were imaged while asleep; no sedation was used. Six regions of interest were chosen, including the primary motor, sensory, and visual cortices in each hemisphere. Mean signal intensity of each region of interest was used to perform correlation analysis pixel by pixel throughout the entire brain, identifying regions with high temporal correlation.

Results: Functional connectivity was observed in all subjects in the sensorimotor and visual areas. The percent brain volume exhibiting rfc and the strength of rfc continued to increase from 2 weeks to 2 years. The growth trajectories of the percent brain volume of rfc appeared to differ between the sensorimotor and visual areas, whereas the z-score was similar. The percent brain volume of rfc in the sensorimotor area was significantly larger than that in the visual area for subjects 2 weeks of age (P = .008) and 1-year-olds (P = .017) but not for the 2-year-olds.

Conclusions: These findings suggest that rfc in the sensorimotor precedes that in the visual area from 2 weeks to 1 year but becomes comparable at 2 years. In contrast, the comparable z-score values between the sensorimotor and visual areas for all age groups suggest a disassociation between percent brain volume and the strength of cortical rfc.

Fig 1.

A and B, The anatomic locations for defining the sensorimotor and visual areas are shown, respectively. The crosses, filled circles, squares, asterisks, left triangles, and right triangles represent the right motor, right sensory, left motor, left sensory, left visual, and right visual cortices, respectively. C and D, Representative processed MR signals at the sensorimotor and visual areas by using the approaches outlined in the “Materials and Methods” section for a neonate (upper row) and 1- (middle row) and 2-year-old (bottom row) children are shown, respectively. E and F, The percent signal intensity difference between the maximum and minimum signals for the sensorimotor and visual areas are shown for each age group. The error bars represent the SDs. max indicates maximum; s, second; wk, week; yr, year.

Fig 2.

The averaged group results demonstrate the brain regions exhibiting rfc when the right and left sensorimotor regions of interest are used to obtain the reference functions for correlation analysis and are superimposed on the brain surface for neonates and the 1- and 2-year-old groups. The color bar represents the z-score values. L indicates left hemisphere; R, right hemisphere; wk, week; yr, year.

Fig 3.

The averaged group results demonstrate the brain regions exhibiting rfc when the right and left visual regions of interest are used to obtain the reference functions for correlation analysis and are superimposed on the brain surface for neonates and the 1- and 2-year-old groups. The color bar represents the z-score values. L indicates left hemisphere; R, right hemisphere; wk, week; yr, year.

Fig 4.

Quantitative comparisons of the percent brain volume exhibiting rfc (A and B) and the z-score values (C and D) and histograms (E and F) for the 3 age groups at both the sensorimotor and visual areas are shown. A–D, The error bars represent the SDs. E and F, The y-axes represent the normalized populations. yr indicates year; wk, week.

Fig 5.

A comparison of 2 different TRs for obtaining rfc at the sensorimotor area is shown. The left and right sensorimotor regions of interest are used to obtain the reference functions for correlation analysis for both TRs. The color bar represents the z-score values. L indicates left hemisphere; R, right hemisphere; wk, week; yr, year.