无影无形又无处不在，记忆之谜至今未解

几十年前，美国神经科学家卡尔·拉什利就开始找寻行踪不定的记忆轨迹。确切地说，他想了解，大脑中是不是有类似保险箱的地方储存每段记忆？大脑皮层上有有专门的存储记忆区域，可以即时提取？

为了解开这个谜，拉什利训练一群老鼠走迷宫，把食物放在迷宫尽头刺激老鼠找到重点。然后，科学实验嘛，他的办法是分别切除每只老鼠大脑皮层中的不同区域，康复后再走迷宫。拉什利想借此找出老鼠脑中哪个区域负责记住走出迷宫的路。结果他得到了惊人的发现：无论他切除哪块区域（或者哪个区域因为病变而损伤），老鼠都能找到食物。真正影响结果的不是切除哪个部位，而是切掉多少。实际上，只要老鼠熟悉了路径，哪怕脑部失去一大块灰质，仍然能顺利走完迷宫。

拉什利得到这样一个结论：记忆并不存储在任何一处神经元组成的保险箱里，某种意义上说，记忆无影无形却又无处不在，以不为人知的方式分布在大脑内部。

事实证明，拉什利是对的，只是稍微有点错：功能性磁共振成像等测试显示，记忆在大脑内部的确分区域存储。不过，时至今日人们还是相信记忆是非常复杂的集合功能。

其实记忆的复杂之处以及难于明确和界定的难点在于：记忆到底有多“鲜活”。记忆决定了我们是谁。“对人类记忆的研究最为接近系统研究心灵。”著有记忆方面教材的圣母大学教授加百利·雷万斯基说。在题为《神经学未能解决的问题》的精彩文章中，加州理工学院教授拉尔夫·阿道夫采用了另一种表述方式：“记忆可能是通过学习预知未来的能力。”

这正是深度学习的一大挑战。在10月1日《财富》刊发的文章中，我的同事罗杰·帕罗夫也详细写过这个问题，见解深刻。虽然目前无解，但深度学习终将解开的人类生理和身心健康之谜，包括衰老后记忆变差的残酷现实。（财富中文网）

译者：Pessy

审校：夏林

Decades ago American neuroscientist Karl Lashley went looking for the elusive engram: the trace of memory. Where precisely, he wanted to know, was the safe deposit box that held each memory in the brain? Was there a specific spot in the cortex that stored this precious data and kept it ready for retrieval at a moment’s notice?

To find out, he trained rats to complete a maze, drawing them to the end with a food reward. Then—science being science—he methodically snipped out discrete parts of the animals’ cortical tissue and, once healed, had them run the maze again. The aim was to see if, by process of elimination, he could discover which piece of a rat’s brain held the memory of the correct path. What he found was surprising: No matter which part he surgically removed (or destroyed by lesion), the rats still found the food. What mattered wasn’t where he cut, but rather how much. And indeed, the rodents could lose a substantial portion of their gray matter and still complete the maze, once it was learned.

Among his many conclusions: Memory isn’t held in any one storage locker of neurons; in a sense, it is both nowhere and everywhere, distributed across the brain in untold ways.

Lashley was right, it turns out, and a little wrong: We know from functional MRI studies, among other tests, that memory does have a regional component, too. But the idea that memory is a phenomenally complex collective function remains with us today.

Indeed, its complexity—and difficulty to pinpoint or characterize—speaks to how “alive” memory is. Our memories are what make us who we are. “The study of human memory is the closest one can get to a systematic study of the human soul,” writes Gabriel Radvansky, a professor at Notre Dame who has authored textbooks on memory. Caltech professor Ralph Adolphs frames it another way in a fascinating article entitled “The Unsolved Problems of Neuroscience”: “Memory may be the ability to predict the future by learning.”

This is where a big challenge for deep learning comes in, a topic on which my colleague Roger Parloff wrote about eloquently and insightfully in Fortune’s October 1 issue. Ultimately, deep learning will enable us to solve riddles of biology and well-being that may now seem just out of reach—including the sad problem of failing memory as we age.