Chapter 157: Amygdala, Hypothalamus, Hippocampus: Emotions Are a Joint Function of the Brain
"Four men and two women. The genders aren't balanced, but it doesn't matter."
Kenichi stood in his laboratory, looking at the bound Uchiha laid out before him. A satisfied smile tugged at his lips.
Six Uchiha were enough to run his experiments. The only real issue was deciding who would go first.
He knew a little about the brain, but not enough to pretend his knowledge was complete. Which meant the first consumable had the highest chance of failing.
So Kenichi did what tradition demanded and played a crude game of picking carrots. In the end, he selected a lucky one, a handsome male shinobi.
He strapped the man down on the operating table and studied him with a thoughtful gaze.
"The part of the brain that controls emotion should be the amygdala… but that position…"
The human brain was astonishing. Even in the shinobi world, brain research was rare. It was far too easy to kill someone by accident. Tsunade might understand more, but Kenichi only had what he remembered.
He remembered it because an old classmate in his previous life studied medicine, specifically neurology. During casual conversations, Kenichi had heard him mention it.
"If it's under the brain, opening from above won't be convenient. I remember that area is below the brain."
Kenichi reached for a book his teacher had given him.
He had seen several texts about ninjutsu used for human experimentation. One of them contained a technique his teacher had developed, something strangely specialized.
He flipped pages quickly.
"Found it. This one."
Kenichi nodded, genuinely impressed. His teacher really was his teacher. The talent was absurd. Developing a technique like this was not something ordinary shinobi could do. Kenichi could not help wondering how it had been created in the first place.
He examined the technique carefully. The hand seals were not complicated. The main caution was preparing a special nutrient solution.
Fortunately, he already had it.
Kenichi picked up a scalpel and tested the edge. As expected, the blade sliced through scalp easily, but it barely bit into the skull.
"No wonder my old classmate said craniotomy feels like carving stone."
He clicked his tongue, set the scalpel down, and took out a small circular saw. The blade whined as he began cutting through the Uchiha's skull.
Before long, Kenichi lifted away a large section of bone.
Now came the crucial step.
Hand seals formed. Chakra flowed.
The technique activated, extracting the Uchiha's brain and placing it into the nutrient solution, while chakra based structures spread densely from the container and linked down into the man's empty head.
When the nutrient solution was fully added, the Uchiha shuddered.
The brain itself trembled.
Kenichi recorded it immediately.
It suggested the brain had not fully adapted to the new environment. Blood vessels and nerves were now transmitting signals through chakra formed connections, so instability was possible.
Still, it was the first time Kenichi had ever witnessed something like this.
A unique scene.
The fact that a human brain could be removed without immediately destroying normal function made Kenichi dispel the Uchiha's genjutsu at once. He needed to confirm it directly, or there was no point continuing.
"Where… am I…?"
The lucky Uchiha woke up, blinking blankly as he tried to understand his surroundings.
[Log: Cognition and the five senses appear unaffected.]
Pain caught up a heartbeat later. The Uchiha instinctively raised a hand toward his head, only to touch something hard and cold.
Glass.
[Log: Motor nerves appear normal. The brain affecting technique shows minimal impact, consistent with the teacher's notes.]
Kenichi felt satisfied. With results like this, the experiment could proceed cleanly.
"You're awake?" Kenichi said while checking the equipment. "Don't move around. If you mess up the connections, you'll actually die."
He was not joking.
The equipment monitoring brain fluctuations was expensive, and Kenichi had no desire to replace it.
[Log: Brainwave recording device operational. Subject shows no clear awareness of the current condition.]
Kenichi adjusted the device with careful hands.
It mattered.
Still, to prevent the subject from panicking too hard and causing trouble, Kenichi kept talking, even though the man's whole body was restrained and he could not do anything strenuous.
Then Kenichi held up a mirror.
Instantly, the brainwaves spiked violently.
Kenichi's eyes narrowed in delight. The reaction was that strong?
The Uchiha stared into the mirror with pure horror.
Everything above his eyebrows was gone. There was only empty space, and above that sat a glass container filled with deep blue liquid.
Inside the liquid floated a pale brain, covered in densely packed attachments. Those attachments stretched downward, linking into the hollow space where his head should have been.
"Don't panic," Kenichi said evenly. "This is a sterile lab."
The man shook as tears pooled in his eyes. His emotions surged, and his eyes opened reflexively, revealing a Sharingan with a single tomoe.
Kenichi watched carefully.
Even that level of stimulation did not push it into two tomoe. That made sense. If it were that easy, it would not be called a cursed eye.
So did Sharingan evolution require a connection to sadness?
Kenichi frowned.
Sadness looked simple on the surface, but it was actually complex brain activity.
First, humans had to perceive, identify, and recognize sadness. That involved the amygdala.
Then, people needed memory. They needed learned knowledge of emotion and stored emotional experiences. That involved the hippocampus, which stored long term memories and memories tied to feelings. Only with those foundations could a person truly understand something invisible like sadness.
An infant, for example, cried because it was hungry or uncomfortable. Pain made it wail. But an infant could not truly feel sadness.
Even if a loved one died in front of the infant, the infant would not understand what death meant, and therefore could not experience that kind of grief.
Only after growing up, learning, forming memories, and then encountering a sorrowful event, could a person recognize the emotion and be overwhelmed by it.
Sadness also had physical responses. That involved the hypothalamus. Once sadness was perceived, the brain triggered bodily changes, making the chest ache, tears spill uncontrollably, breathing tighten, and more.
So even though the amygdala was a key region for recognizing and regulating emotions, sadness itself was more like the entire brain working together to produce an intense experience.
The most fascinating part was that sadness began in the brain, yet it could affect the whole body.
People said heartbreak like it was only a metaphor, but sometimes it was not.
Extreme sorrow could cause myocardial tearing and lead to a fatal heart attack.
In a brutal way, heartbreak could be literal.
Kenichi turned back to the Uchiha, who was crying silently, eyes red, face twisted with terror.
"All right," Kenichi said flatly. "Stop crying. You're not dead yet."
He reached out and wiped the tears from the man's face, not gently, but efficiently, as if clearing moisture that might interfere with observation.
You could not die now.
Not until the experiment was finished.
Kenichi sent a thread of Yang Release chakra into the Uchiha's brain, aiming to stimulate the amygdala.
Then he realized what he had overlooked.
When Yang Release acted on the brain, it carried a stimulation effect, something close to a forced excitation.
And when it acted directly on the amygdala…
The Uchiha began laughing uncontrollably.
It was immediate. Violent. Impossible to suppress.
Even in a so called wise calm state, the man could not stop. The lab filled with a horrible mix of giggling and sobbing.
The Uchiha's mind was drowning in despair, and he wanted to sink into it, but the unnatural joy boiling up from inside him would not allow it. The laughter forced its way out, twisting his face into something obscene.
He was going crazy.
Kenichi inhaled slowly, forcing himself not to curse.
"…Fine. Fine. My fault."
He used ninjutsu to clean the subject, who was now flushed and shaking on the operating table, his laughter still spasming through him.
If someone saw this without context, they would misunderstand everything.
Only Kenichi knew the truth.
He was genuinely conducting an experiment.
"It seems Yang Release can't stimulate sadness in the way I expected," Kenichi muttered, thinking quickly. "Then should I use Yin Release instead?"
Yin and Yang chakra were not discussed much in the early years of shinobi history people liked to repeat, but in practice, mastering chakra's transformations was essential for any shinobi who wanted to climb higher.
The only problem was that Kenichi did not have much Yin chakra in his body. He had more than the average shinobi, but not enough to waste.
Kenichi suspected that the Yin chakra was connected to the birth of his Sharingan.
At least for now, it would provide him some convenience.
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