Degree centrality and voxel-mirrored homotopic connectivity in children with nocturnal enuresis: A functional MRI study
Keywords: Children, degree centrality, fMRI, nocturnal enuresis, voxel-mirrored homotopic connectivity
Nocturnal enuresis (NE) is defined as the condition in which children over 5 years are not able to wake up to control urination at night time during sleeping. The prevalent morbidity of NE in children is 6–10%. The condition can last until the adult stage in 0.5–2% of the cases., Patients of NE usually display deficits of memory and attention, which are often accompanied by attention deficit hyperactivity disorder.,
Using an electroencephalogram, Hallioğlu et al., found that alpha waves of children with NE decreased in the left temporal lobe. However, the delta waves increased in the right temporal lobe. The study of the regional homogeneity (Reho) of functional magnetic resonance imaging (fMRI) indicated that the Reho values were obviously different between children with NE and normal controls. Although these studies have led to some progress in eliciting local neural mechanisms responsible for the development of NE, the changes occurring in the brain functional connectivity in children with NE are not yet clear.
fMRI, is a new functional imaging technique that has the advantage of being noninvasive, with the children not being exposed to radiation, and the images have a high spatial resolution. fMRI has been widely used in research related to cognitive understanding and in eliciting neural mechanisms responsible for clinical diseases. Resting state fMRI (rs-fMRI) can exclude the influence of results obtained during the conduction of a task by the subject, and has become one of the most efficient tools for research on brain function.
Degree centrality (DC) of fMRI reflects the role of the node in information transmission in the brain functional network. Higher values of DC imply that connections within the brain network are more complete and quicker, and thus, information integration becomes more efficient. Therefore, DC can well-reflect the brain functional connectivity.
Voxel-mirrored homotopic connectivity (VMHC) is a method developed in the recent years to analyze the collaborative activities between the two hemispheres using fMRI data. VMHC can quantify the functional connectivity of every voxel. Zuo et al., reported that, with increasing age, brain regions present different developmental levels and gain more extensive homotopic functional connectivity. Children with NE exhibit dysplasia of functional brain regions, which is related to urination control. Therefore, VMHC is appropriate for studying the neural mechanisms responsible for the occurrence of NE.
NE can influence the children's psychology and cause various emotional and behavioral problems, for example, anxiety, inferiority, irascibility, unsociability, social failure, as well as unwillingness to participate in group activity (especially in outdoor activities, such as a summer camp). The children's self-concept reflects the recognition of their own status in the society. It plays an important role in the merging of an individual into the society as well as in the perfection of personality traits. If the children develop unhealthy self-concepts due to the harmful influences of intrinsic and extrinsic factors in the process of their growing, the phenomena will have a negative effect on their behavior, study capacity, and social ability, as well as on their personality development. To our knowledge, there is no report in the literature of investigating the network patterns and the mechansims responsible for NE by the technique of DC and VMHC. The present work aims at analyzing the behavior of children with NE using the two methods of DC and VMHC. We also investigated the functional brain network, particularly the intensity of functional connectivity, both among the nodes in the brain network and between the two hemispheres of the brain. Furthermore, the scale analysis for psychological testing in children was also utilized in the study.
The group having NE included 23 children, aged 5–11 years, who were diagnosed by the urologists from the Changzhou Children's Hospital during September 2014 to October 2015. There were 12 boys and 11 girls (mean age: 8.55 ± 1.96 years). All children met the following criteria: (1) they were all of age more than 5-years; (2) they were bed-wetting at least twice a week, with the ailment lasting for more than 6 months; (3) they were able to control urination in the daytime but not after falling asleep; (4) they did not have any urinary system disease; (5) they had no symptoms, signs, and medical history related to the neural and mental system; and, (6) they were cooperative enough to be able to undergo an MR scan. The dataset of this study excluded children with attention deficit hyperactivity disorder (ADHD), based on the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV).
The control group included 23 children from an ordinary school. There were 12 boys and 11 girls (mean age: 8.59 ± 1.42 years). The age and gender were matched between the two groups (P > 0.05). Both NE and normal participants were right-handed and had intelligence quotient (IQ) scores of >80 (measured by the Wechsler Intelligence Scale for Chinese Children-Revised; WISCC-R). This study was approved by the ethical committee of the Changzhou Children's Hospital of Nantong University. Informed consent was obtained from the parent of each participant, and all the children agreed to participate in the study.
Images were acquired using a Siemens 1.5-Tesla Magnetom Avanto scanner. Participants were asked to lay on the back with their head fixed by a belt and foam pads to minimize head motion. During resting-state fMRI scanning, the participants were instructed to close their eyes and remain as still as possible in a calm and awake status., Resting-state fMRI data were acquired using an echo-planar imaging (EPI) sequence with the following parameters: 18 axial slices, repetition time (TR) = 2000 ms, echo time (TE) = 40 ms, flip angle = 90°, thickness/gap = 6.0/1.2 mm, field of view (FOV) = 240 × 240 mm, matrix = 64 × 64, 180 volumes (6 min). Sagittal high-resolution T1-weighted three-dimensional (3D) images were acquired, covering the entire brain using the following parameters: TR = 414 ms, TE = 11 ms, flip angle = 90°, in-plane resolution = 256 × 256, FOV = 240 mm × 240 mm and thickness/gap = 5.0/1.5 mm.
The first 10 volumes of each of the participants' functional time series data were discarded to avoid any transient signal changes before the magnetization reached a steady-state, and to allow for the participants to get used to the fMRI scanning noise. The data were then preprocessed using the Data Processing Assistant for Resting-State fMRI (DPARSF) V2.3 software package. DPARSF had been widely used to process the data of resting-state fMRI based on its functions in the Statistical Parametric Mapping (SPM8) and Resting-State fMRI Data Analysis Toolkit V1.8 (REST 1.8) [http://www.restfmri.net]. First, the slice timing and head motion correction were carried out. The data was discarded if the head motion exceeded 3 mm of translation or 3° of rotation in any direction. The functional scans were then spatially normalized to a standard template (Montreal Neurological Institute; MNI) and re-sampled to 3 × 3 × 3 mm 3. Subsequently, spatial smoothing was conducted using a Gaussian kernel of 6 mm full width at half maximum. Further preprocessing included removal of the linear trend and temporal band-pass filtering (0.01–0.08 Hz).
A corrected threshold of P < 0.05 corresponded to a combined threshold of P < 0.01 at individual voxel level and cluster size >40 mm 3. The multiple comparison correction was performed using Monte Carlo simulation , implemented with the REST software, i.e., the AlphaSim program, part of the AFNI software package (http://afni.nimh.nih.gov).
Two-tailed two-sample t-tests were performed as a measure of the resting-state DC and VMHC difference between the NE children and normal controls. The result after two-sample t-tests was overlaid on the Ch2 template.,
The children's self-concept scale (the perceived health competence scale; PHCSS) is a scale for children's self-rating which was compiled in 1969 and revised in 1974 by the American psychologists, Piers and Harris. PHCSS is used to evaluate the standard of self-concept of children with behavior, emotion, or study problems, and has been proven to be reliable and validated. Children with NE and normal children fill in the scale form themselves using the same instructions under the guidance of professionals. The scale contains 6 sections comprising 80 items in total. The 6 sections include behavior, intelligence and school condition, appearance and property, anxiety, gregariousness, happiness, and satisfaction. The scale is scored positively. It implies that the scale will be evaluated as being reflective of a better psychological condition of a subject if high scores are noted. We conducted statistical analysis on the results of the scale obtained in the two groups by the Statistical Package for the Social Sciences (SPSS, IBM, Chicago, IL).
We found four brain areas in which the DC values of the NE group were obviously lower than that of controls. These four areas were the posterior cerebellar lobe, anterior cingulate cortex (ACC), medial frontal gyrus, and superior left temporal gyrus (P < 0.05) [Table 1] and [Figure 1].
We also found two brain areas where the VMHC values of NE group were obviously lower than that of the controls. The two groups were the cerebellar lobe and anterior cingulate cortex (ACC) [P < 0.05, after correction] [Table 2] and [Figure 2].
In addition to the statistical analysis on the resting state fMRI data of the NE and the control groups of children, we also compared children with NE and the normal group on their self-concept scale. The scores of NE children were lower than that of controls on the behavior, appearance and property, anxiety, gregariousness, happiness, and satisfaction domains (P < 0.05) [Table 3].
The brain network is based on the relationship of the connectivity of brain regions. Brain network can extract and integrate information and has been one of the research hotspots of neuroscience in recent years. The methods of DC and VMHC both apply the principle of functional connectivity of rs-fMRI. DC refers to the number of the sides connecting a node to other nodes in the network. It reflects the property of the nodes. It is used to describe the direct influence of nodes in the resting state network and reflects the property of functional connectivity in the brain network from a new angle., Areas having a high DC value own a high degree of core, and their existences makes brain information more intact and the connections of network more convenient. DC makes the brain network more complete by establishing a quicker connection type.
VMHC compares the strength of the connectivity of the left hemisphere brain areas to the mirrored right hemisphere. Those areas of the brain that have a higher left–to-right hemisphere connecting strength would have a higher VMHC value, while those areas having a lower left–to-right hemisphere connecting strength would show a lower VMHC value. Our experiments reveal that the DC and VMHC values of the NE group were both lower than those of the control group in the cerebellar lobe and anterior cingulate cortex. Furthermore, the DC value of NE group was lower than the control group in the medial frontal gyrus and the superior left temporal gyrus.
Children show symptoms of incontinence when they are unable to control urination at the right time. The ‘timing function' of the cerebellum acts simultaneously on the motor processes and on the operation of perception that requires an accurate time information.
People with a weak cerebellar function are inclined to make mistakes on judging the stimulus intervals and the speed of visual movement. Therefore, experiments requiring time would invoke the cerebellum to participate. Different neural cells are activated during different tasks. We noticed that in subjects with NE, the cerebellum's node function decreased and the strength of functional connectivity of bilateral cerebellar hemispheres also reduced. In addition, we noticed the reduction of cerebellar function that is responsible for adjusting and controlling the exercise time. Therefore, NE children cannot reasonably control urination during night time, which manifests as nocturnal enuresis.
There are direct bidirectional fiber connections between the cerebellum and the hypothalamus. The projection fibres of the cerebellum–hypothalamus and the hypothalamus–cerebellum networds make up the neural circuit of cerebellum and the hypothalamus. Hypothalamus is the brain area that secretes vasopressin. In patients with NE, the degree centrality of cerebellum reduces, and the functional connectivity between the left and right cerebellum decreases. The connection between the cerebellum and other brain regions are inhibited, and the connection between the cerebellum and the hypothalamus is affected. This affects the control of vasopressin secretion of the hypothalamus. This precipitates a change in the urination behavior of children with NE leading to the demonstration of nocturnal enuresis in them. Thus, the function of cerebellum in controlling the ‘timing function' of various activities and its effects on the hypothalamus that lead to a change in the vasopressin secretion patterns, may cause NE; the retardation of cerebellar functions, therefore, has a major role to play in the pathogenesis of NE.
The anterior cingulate gyrus is part of the salience network. The salience network possesses the highest classification accuracy. Its main function is to integrate various sensory information, judgments and ideas, to plan activities in the internal and external environment. It plays an important role on the process of determining the awareness of consciousness. The anterior cingulate area can monitor and control ongoing objective-directed behavior and release signals when a desired response to a conflict or a mistake is required. Our research found that the DC and VMHC values of children with NE in the anterior cingulate area were lower than that of the control children. It suggested that the functionality of this area of the brain decreases and the functional connectivity between the two hemispheres also weakens in children with NE. Children with NE cannot achieve the proper state of consciousness when perceiving urinary sensations. They cannot send out signals to the cerebrum in time to control their urination. The next step of our study is aimed to enlarge the sample size and investigate the functional mechanisms of the anterior cingulate region that may be responsible for the genesis of NE.
This study found that the DC value of NE children was lower than that of the control children in the medial frontal gyrus. The medial frontal gyrus plays an important role in the choice of the object of attention of the brain. The functional abnormality of the area leads to an attention deficit. Using structural MRI, Hill et al., found that the performance of a task that demanded a continuous attention was inversely proportional to the volume of the medial frontal gyrus; thus, the larger the volume of the frontal gyrus, the worse was the performance. This research suggested that a weakened functioning of the medial frontal gyrus would affect attention. The frontal gyrus is an important cortex responsible for executive functions, and the maturity of the frontal cortex plays an important role in more advanced cognitive activities. The decline of centrality of medial frontal gyrus causes the diminution of function of attention and control. Therefore, children with NE tend to have a higher incidence of attention deficits compared to normal children.
The temporal lobe is the main area of the brain responsible for human memory. The lesions of temporal lobe will lead to various dysfunction of memory. Xi  tested linguistic competence such as the frequent causation of faux pas in patients with temporal infarction when compared to the normal people. He found that the two groups had significant differences in their levels of intelligence and oral fluency, which suggested temporal lobe involvement in the mechanism of memory of language. Howard  investigated patients with temporal lobe epilepsy versus those in the control group using identification learning and feeling-of-knowing. Their results suggested that patients with temporal lobe epilepsy had episodic memory deficits. Our research found that in children with NE, the DC value was lower than that found in the normal group in the superior left temporal gyrus. The dysfunction of memory, which is controlled by temporal lobe, causes memory barriers in NE patients.
The result of self-concept scale of the two groups suggested that the factors of behavior, appearance, anxiety, gregariousness, happiness, satisfaction, as well as the total score were all remarkably lower in patients with NE than that found in the normal group. Multiple-factor analysis found that the appearance of children with NE was the main factor. Children with NE tend to have more behavioral, emotional and psychological problems, as well as a lower self-concept than is present in the normal group, especially with regard to body self-evaluation. The behavior and emotional problems of these children always get a bad evaluation from external sources, which in turn makes them evaluate themselves as being on a lower scale than what they actually are. Therefore, they lack confidence in themselves and find it hard to adapt to the environment they are placed in. This has a far-reaching effect on their learning and life.
The decline of DC and VMHC value of children with NE indicates a decrease in the timing function of the cerebellum, which affects the vasopressin secretion in the hypothalamic region. This, we believe, leads to the deficits of urination control. The decrease in both the function of the anterior cingulate region in the brain as well as the functional connectivity of the two hemispheres causes obstacles in sending out signals to the cerebrum in time and this manifests as the phenomenon of nocturnal enuresis. The decline of centrality of the medial frontal gyrus diminishes the child's function of attention and control. The function of memory, which is controlled by the temporal lobe, also decreases, resulting in memory barriers. The analysis of self-concept scale suggests that NE children always lack self-confidence. This study investigated the neural mechanisms related to the dysfunctioning of the core brain areas in children with NE. The results of this study offer evidence to increase the early functional training of specific areas of the brain in children with NE.
We would like to thank all the participants and researchers in this study. Funding for this study was provided by the science and technology projects of Jiangsu province (BL2014037). We especially wish to thank Professor Shan Yu from the INRIA.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]