By some reports, the word samurai first appeared in the 12th century. For a long time, the samurai provided the main military force used against emishi and other clans. In the 1100s, two powerful clans served the emperor of Japan: the Taira clan, and the Minamoto clan. These two families became bitter rivals, and in 1192, Minamoto Yoritomo led his clan to victory over the Taira.
EEG measures brain activity and must demonstrate regular wave patterns to be considered valid. Therefore, by this rule the onset of life would be the time when fetal brain activity begins to exhibit regular wave patterns, which occurs fairly consistently around week 25. Previous to that time, the EEG only shows small bursts of activity without sustained firing of neurons.
Gieddâs results suggest that development in the frontal lobe continues throughout adolescence and well into the early twenties. The researchers found that the number of neurons in the frontal lobe continued to increase throughout childhood until an average age of 12.1 years for men and 10.2 years for women. Scientists previously thought that gray matter production and development only occurred during the first 18 months of life. The fact changes are still occurring in the brain during adolescence provides some evidence against some popular theories that suggest that our brains are hardwired during early childhood.