Imagine the typical office birthday party. It's after lunch, so everybody is full. Then, in comes a luscious chocolate confection. The sight, the smell -- even the sound of the word 'cake!' -- stimulate the reward-and-pleasure circuits of the brain, activating memory centers and salivary glands as well.

想像一場典型的公司同事生日派對。中餐剛吃完，大家都很飽。然後，服務員送進來一個美味的巧克力蛋糕。蛋糕的形狀和香味，甚至是「蛋糕」這個詞本身都刺激起人們腦部獎賞與快樂神經的回路，對蛋糕美味的記憶隨之開啟，唾腺也開始分泌。

Those reactions quickly drown out the subtle signals from the stomach that are saying, in effect, 'Still digesting down here. Don't send more!' Social cues add pressure and permission to indulge. Soon, everybody is having a slice -- or two.

此時，人們的胃部正發出微弱的信號：「這裏還在消化，別再吃了。」社會規範給予我們壓力及允許去享受，很快，大家就開始分而食之，一塊，或是兩塊。

Scholars have understood the different motives for eating as far back as Socrates, who counseled, 'Thou shouldst eat to live, not live to eat.' But nowadays, scientists are using sophisticated brain-imaging technology to understand how the lure of delicious food can overwhelm the body's built-in mechanism to regulate hunger and fullness, what's called 'hedonic' versus 'homeostatic' eating.

學者們早就知道，人類的進食存在著各種動機，希臘哲學家蘇格拉底有句勸誡名言：「你應該為了活而吃，而不是為了吃而活。」但現在，科學家正借助先進的腦部成像技術來探查，為何美食的誘惑能夠戰勝體內控制饑餓和飽腹感的生理機制，也就是「為了快樂而吃」和「為了需求而吃」到底孰強孰弱。

One thing is clear: Obese people react much more hedonistically to sweet, fat-laden food in the pleasure and reward circuits of the brain than healthy-weight people do. Simply seeing pictures of tempting food can light up the pleasure-seeking areas of obese peoples' brains.

有一點很清楚：肥胖人群在面對高糖分高脂肪的食品時，腦部快感體驗回路的反應要比體重正常的人群積極得多。只要看到美食的圖片，肥胖人群腦部中尋求快感的區域就馬上活躍起來。

Two conferences this week on obesity are each examining aspects of how appetite works in the brain and why some people ignore their built-in fullness signals. Scientists hope that breakthroughs will lead to ways to retrain people's thinking about food or weight-loss drugs that can target certain brain areas.

這週有兩場肥胖問題研討會都在研究人體腦部的食欲反應機制，以及為什麼有些人會忽視體內的飽腹感信號。科學家希望在該領域的突破將有助於改變人們對食物的渴求程度，或研究出能影響腦部特定區域的減肥藥。