# Sex-Related Variations in the Brain Motor-Network Connectivity at Rest during Puberty
## 1 Introduction  
Puberty and adolescence mark a child's transition into adulthood. Biologists have typically viewed puberty from an endocrine standpoint since the characteristic signs of reproductive maturation are driven by hormonal changes that occur throughout this stage of development. Although puberty and adolescence are commonly used interchangeably, the term puberty is related to the stimulation of the hypothalamic-pituitary-gonadal axis, whereas adolescence refers to the period between childhood and adulthood when there is a significant physical, psychological, cognitive, and social transformation [1].  
motor response, known to be a more challenging task, has been observed to peak at around age 16 [6]. Furthermore, it has been demonstrated that the ability to self-regulate proactive or reactive inhibition connected to movement is highly established during puberty [7]. After all, motor control is a very complex mechanism of neural circuitry and integrity of skeletal muscle's mechanical and sensorial functions, tissue that comprises almost 50% of the body weight.  
Myelin production in the central nervous system regulates conduction velocity, which is a critical component of rapid and efficient information processing and functional connectivity in the brain [8,9]. White matter is the main substance in the sensory/somatomotor cortex composed of long myelinated axons, which transfer information between various cortical and subcortical gray matter regions and with distant connections to the cerebellum and spinal cord. Myelination begins during early fetal life and brain size increases rapidly during the first three years [10]. White matter mass increases more than gray matter mass during childhood peaking around puberty [11], which is related to increased gonadal and Glia cell synthesis of sex hormones [12]. Testosterone increases oligodendrocyte proliferation favoring myelination as well as cerebellar cell volume increases in males [13], while estradiol delays the exit of oligodendrocyte progenitor cells from the cell cycle [14], allowing oligodendrocyte to undergo additional rounds of cell division and increase proliferation but reducing the rate of myelination in females.  
The brain is connected to the cerebellum via afferent and efferent pathways, whose myelination is completed early in childhood, through the Superior and Inferior Cerebral Peduncles. On the other hand, the Middle Cerebellar Peduncle ends development in puberty and only allows afferent information from the ponte nuclei (PN) to reach the cerebellum [15]. The cerebellum contains more than 100 billion neurons, accounting for more than 80% of total brain neurons [16]. The cerebellum and motor cortex network actively participate in the inhibition of voluntary movement, emotional behavior, and cognition. Together, the cerebellum and motor cortex network constitute the motor-subnetwork, a major portion of the resting brain. The resting state brain consumes 20% of the glucose available for all metabolism, therefore, motor-subnetwork connectivity at rest must be highly active. It can particularly be observed when comparing 12-year-old to 16-year-old individuals. Different expressions and responses to sex hormones related to the motor network in the resting brain will be analyzed.  
The present work aims to study connectivity on the motor network while awake with eyes closed, providing evidence on the default activity of this network. This network is notable for its extensive connectivity to the rest of the brain involved in decision-making and motor control in a body subjected to continuous sex hormonal changes, particularly during puberty. The motor network is also receiving constant proprioceptive information, the sense that lets us perceive the location, movement, and action of parts of the body. This fMRI analysis would provide a potential standard to compare fMRI data obtained to analyzed behavioral disorders that often occur during puberty and adolescence.