“Hold it in your right hand, and press it with your thumb.”

Itae took the button and pressed it lightly once. A mechanical sound popped out, thunk.

“Good sensitivity.”

The words were rough as hell, but the motion of fiddling with the button was fairly gentle. Oreum turned his eyes away from Itae’s hand, from the prominent veins, and fixed them on the laptop screen.

“We’re starting. When a circle appears on the screen, press the button right away. If a square appears, do not press it. Even if your hand moves reflexively, you have to stop yourself.”

The upper-year students whispered among themselves.

“Looks like a Go/No-go task.”

First stimulus. Second stimulus. Third. Fourth. Fifth. All of them were correct. At last, the forbidden stimulus. Even though the square shape was clear, he pressed the button without hesitation. Itae acted as if he regretted it.

“Ah, I wasn’t supposed to press it.”

Then he snorted a laugh. The ERN waveform shot up on the monitor. Usually, when people made a mistake, their brain waves would waver and only settle down later. Itae’s recovery time was very short. Besides, the moment the alarm sounded again, his response was actually even faster.

Even after recognizing the mistake, he did not waver. No inhibitory circuit. He did not process “forbidden” as forbidden, but as a “stimulus.” Oreum scribbled a note in his notebook and turned the slide.

“This time, it’s a rare-stimulus task. We’ll look at how quickly you detect a different pattern within a repetitive sequence.”

It was a task that detected changes that suddenly appeared within a regular flow. The sequence repeated at two-second intervals. Usually, because attention was focused on the uniformity of the sequence, the brain made a kind of prediction. It assumed that if the same shape continued, the next one would be the same too. So the rare stimulus was delayed by about 0.3 to 0.5 seconds, and some people did not see it at all.

Circle, circle, circle. Circle. Repetition. Repetition. Repetition. Repetition. Then one blue star. The button sound rang out. The speed was as if the sensory organs reacted first and cognition followed after. The attentional bias was excessive. Ordinary stimuli were easily discarded, and rare stimuli were rushed toward immediately. Someone in the front row muttered,

“Wow, that’s fuck fast.”

The second rare-stimulus task was to find the “fear” images that flashed for 0.25 seconds. The visual cortex was physically overloaded, so most images were often missed, and by the time one tried to press, they were usually already gone.

But Itae was different. As if the experimental device and his nervous system were directly connected, he pressed the button the instant the screen changed. His expression was so indifferent it looked bored, but his accuracy rate reached 100 percent.

This was not a simple matter of attention. His ability to detect fear stimuli was overly developed. He would immediately notice the tiny changes that happened when the other side was overpowered by his force or tried to submit.

The students, interested only at first, soon began to slack off one by one. Only Itae kept his concentration from start to finish without once taking his eyes off the experiment.

“This time, it’s a facial expression recognition task.”

Various photos appeared on the screen. Basic emotional photos such as joy, sadness, fear, anger, and disgust. The core of this task was to see which emotions people responded to “faster and stronger.”

On average, they responded first to “sadness” and “fear.” It was the expression of a very primitive alert system that detected the danger signals other people showed and increased one’s chances of survival.

Itae’s waveform was the opposite.

Sadness, no response.

Joy, no response.

Fear was no response as well.

And anger, the graph shot steeply upward at the end and drew a hyperexcited state. He was insensitive to others’ grief and shrinkage, activated only by hostility and aggressive signals.

What the experiment was showing was not a simple preference or taste. It was a unique signature of the brain, suggesting what kind of stimulus one opened oneself to and what kind of stimulus one took interest in and approached.

At some point, the entire lecture hall went quiet. Itae was now using the lecture hall’s silence like his own weapon, dominating the experiment. Oreum brought it to a low close.

“…That’s all. Good work. Take off the cap and wipe off the gel.”

Itae stood up slowly. The gel lightly on the back of his neck flashed for a moment. The students suddenly looked somewhere else, not at him. As he passed in front of Oreum, Itae asked in a voice just barely audible,

“Teacher.”

“Yes?”

“So, what do you think my brain is like?”

“......”

Oreum could not say anything. Itae smiled faintly and went in without waiting for an answer. In Oreum’s mouth, unable to be honest, a secret word lingered.

Predator.

***

Mondays and Thursdays were absolutely exhausting because lectures and tutoring overlapped. After tutoring, Oreum took the bus, dozed off with his bag in his arms, and, while still half in a dream, barely got off. Once he crawled into the house that was not even really a house, a tiny two-room apartment, and washed up, it was nearly midnight.

He wanted nothing more than to collapse and sleep right away, but he showered with all his strength. When he turned on the laptop on the kitchen table, there was an email from an unfamiliar address. The moment Oreum saw the sender’s name, he was faintly shocked. Water droplets kept falling from the ends of his wet hair. The second hand of the wall clock was like thunder. Oreum read the email down, doubting his eyes.

「[Sender] Eom Itae

it.ae＠astravestis.ac.kr

[Recipient] Seokdal Oreum

sundreamed＠astravestis.ac.kr

[Subject] Question

[Content] It’s about my major.

Science still hasn’t fully explained the mechanism of emotion, right? It’s certain that areas like the amygdala, hypothalamus, prefrontal cortex, and insular cortex are related to emotion processing, though. But no single correspondence like ‘when this part is activated, you become sad’ has been found.

Then does that mean humans are beings who cannot accurately perceive why they are sad or why they are angry? Since the emotions we become aware of are already results processed afterward by the brain.

If emotion is something we only recognize after we’ve already felt it, then isn’t everything in this world ultimately just errors or illusions made by the brain? Even if EEGs capture waveforms, what meaning is contained in them?」

The attitude of dropping a question in without even saying hello was very much like Eom Itae. On the other hand, because the contents of the email were fairly serious, Oreum, who had unconsciously decided he was not a particularly remarkable student, felt a little sorry about that.

His body was already at its limit. If he slept like the dead now, that would be it. But he was sure he would lose sleep because he would keep thinking about Itae’s email. Oreum picked at a small hangnail on his fingernail, then put his hand on the laptop keyboard.

「[Subject] Re: Question

[Content] Hello.

Emotion is closer to ‘prediction’ than to ‘error or illusion.’

The brain does not accept the world as it is. If it interpreted external stimuli one by one exactly as they were, it would take too much energy, so it corrects most sensory information with a predictive model.

‘It should be like this in this situation.’ ‘It should have been like this earlier.’ In this way, the brain writes out a scenario first, then interprets the phenomenon to fit it.

It doesn’t matter whether that judgment is right or wrong. The brain takes that discrepancy as a signal called ‘emotion.’ So emotion is closer to a wave of prediction that the brain can accept than to an objective fact. Sadness, anger, and love are all traces of the brain trying to understand the world somehow, in the end.」

Even after sending the email, Oreum looked at the screen for a long time. He had become a little curious about what Itae would reply. Suddenly Oreum felt ridiculous. Holding onto Eom Itae’s email at this late hour and feeling anticipation like that.

Soon his eyelids dropped on their own. Oreum walked to the bed, lay down without even pulling up the blanket, and then sank deeply beyond sleep as if he had been struck.

***