אלה עללות

פחד עשוי להיות קשור לחוש הריח, ואפשר להפסיק אותו פשוט על-ידי חסימה של רצפטורים מסויימים במוח.

במסגרת ניסוי בעכברים, מדענים יפנים זיהו והסירו רצפטורים מסויימים באזור במוח האחראי על חוש הריח - והתוצאה היתה קבוצה של מכרסמים חסרי פחד.

כדי להוכיח את הממצאים, הראו החוקרים תמונות של עכברים חומים קרובים מאד לחתול, מרחרחים את אוזנו, מלקקים אותה ומשחקים בצווארו.

הסקרנות החליפה את הפחד

החוקרים הסבירו כי העכברים הבחינו בריח של טורפים - כמו חתול, ובריח שתן של שועל או נמר השלג, אך לא הביעו כל פחד. הם אפילו הראו סקרנות גדולה למדי אך לא הצליחו להבין כי הריח הוא סימן לסכנה.

* החוקרים - מהפקולטה לביופיסיקה וביוכימיה באוניברסיטת טוקיו.

"So these mice are very happy with cats. They play with cats. But before taking the picture, we had to feed the cat," he told Reuters in a telephone interview.

Experts have long thought that fear in animals may be prompted by their keen sense of smell.

But this is the first time scientists have discovered that smell detection and how that translates to fear take place in different parts of the olfactory bulb.

"How do our brains interpret the odorous information? What we found is that in the mammalian system, there are two circuits, one is innate and one is associative learning for detecting smells," Sakano said.

Sakano and his colleagues created two lines of mice - one lacking the receptors to translate odours and the other lacking receptors for smell detection. They were then exposed to the urine of predators such as snow leopards and foxes.

Can’t tell danger
"(The first group) keeps smelling and they turn around and they show very strong curiosity but they never can tell any danger," Sakano said.

As for the second group, Sakano said: "They are very poor in detecting smell, but as soon as they detect the fox urine, they would freeze and they will pretend to be dead.

"They are very poor in detecting smell, discriminating them and associating their memory with detecting information. They are very slow. But when they do, they can immediately tell the danger."

Mice have about 1 000 smell receptor genes, while humans have only 400 functioning ones and about 800 non-active ones, he said.

"Our sense of smell in us is bad. We can't detect this year's wine from last year's," he said. - (Tan Ee Lyn/Reuters)

Read more:
Fear may be in the genes
Wired to spot fear?
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