This poses the question of whether the long structural maturation process translates to changes in neuronal transmission speed. One cortico-cortical evoked potential (CCEP) study reported that conduction delays in subjects older than 15 years were only 1 ms faster compared with younger subjects 18. 10), others report no change in latency during adolescence 11, 12, others report that latency decreases up to age 20 followed by an increase 13, 14, 15, while others report that latency decreases up to age 40 years 16, 17 (Supplementary Table 2). Some studies report that evoked potential latency starts increasing after age 13 (ref. While studies consistently find decreases in the latency of the visual evoked potential at around 100 ms during infancy and early childhood (<13 years) 7, 8, 9, the developmental plateau at which latency decreases change to latency increases differs across studies. However, electroencephalography and magnetoencephalography studies that approximate transmission speed by measuring the latency of visual evoked potentials, show highly variable ages at which development plateaus. Magnetic resonance imaging (MRI) analyses have demonstrated that white matter properties change across the life-span 6, often reaching a plateau around 30 years of age. However, little is known about the maturation process of transmission speed in the human brain, partially because the axonal diameter in the adult human brain is relatively large compared with most other mammalian species 4.Īnatomical studies indicate that the structural human connectome follows a long developmental trajectory: postmortem studies have shown that myelination starts in the late prenatal period and continues into late adolescence 5. The developing axons in the human brain support rapid neuronal transmission, influencing whether electrical signals arrive at the same or at different times and shaping the timescales of functional connectivity 3. The speed of neuronal transmission is fundamental to the temporal organization of neuronal activity 1 and is a core component in many computational human brain models 2. The development of rapid communication between human brain regions is essential for cognitive function.
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