Of all the telltale signs of aging, the scariest are those that affect the mind. I sometimes think of one word and type another, an unsettling trait for a journalist. Its usually a word thats close to the one I want, like of instead of for, or there instead of their.

Turns out theres a name for this -- a literal paraphasia -- and its just one kind of senior moment, an unscientific term for a variety of mental glitches. Most common is the temporary inability to recall a name or a number or what you were about to do.

We think the vast majority of these are probably benign, but many cases of Alzheimers do start out as senior moments, says P. Murali Doraiswamy, chief of Biological Psychiatry at Duke University Medical School and co-author of The Alzheimers Action Plan, a new book for people who are worried.

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Even in normal aging, theres a general slowing of cognitive function, starting in the 50s and 60s. Neurotransmitters, the chemicals that allow nerve cells to communicate, diminish. The brain itself shrinks. White matter -- the fiber tracks connecting the front of the brain to storage areas -- changes so that information takes longer to process. Its like a computer that freezes temporarily as it tries to call up a file.

Names and dates that take time to retrieve generally arent well-archived, says Dr. Doraiswamy. You may not have paid much attention to them in the first place -- especially if you were multitasking. Your brain has an inexhaustible amount of storage, but you cant have too many programs running at the same time, or its hard to attend to them, says Gayatri Devi, a psychiatrist and neurologist who runs the New York Memory Center. That may explain the in-one-ear-and-out-the-other phenomenon that plagues some people.

Paying attention is critical to laying down memories, which scientists now think are distributed all around the brain. What a rose looks like, smells like, the pain of the thorn and emotions attached to it are all in different parts. When you think of a rose, its like your frontal cortex does a Google search through every part of your brain for an association with rose thats been stored, says Dr. Doraiswamy.

The richer you can make the experience, the more memorable it is, says Dr. Devi. If you have a fantastic evening with the best bottle of wine in a lovely setting, youll remember that event because the trace thats created is very wide. And every time you play it back in your mind, you are physically reinforcing it.

Repetition also helps reinforce abstract things like names or numbers, as does a mnemonic association, like noting that Jane is far from plain. Such tricks are often automatic for people who pride themselves on remembering names. But its harder if you are sleep-deprived, anxious or under stress -- like, say, a new CEO who starts to thank the chairman from the podium and suddenly blanks on his name.

Its just as important to forget extraneous things and minimize mental clutter, says Dr. Devi. You cant dump those 1960s TV jingles from long-term memory, but you can free up your short-term memory by using calendars, lists and personal-digital assistants. Put the burden on gadgets, says Dr. Doraiswamy.

When should you be concerned about memory lapses?

In Alzheimers, people often retain obscure old memories, but have trouble recalling recent events and conversations. Or they may forget the names of simple things. If a person cant find their car in a six-floor garage at JFK because they forgot to look at the number, thats probably just a senior moment, says Dr. Doraiswamy. But if they cant remember the color or make of the car theyve been driving for years, that could be more serious.

Changes in behavior or mood or memory can also signal early Alzheimers. If youve always been a ditz, its not so unusual if you cant remember well, says Dr. Devi. But if you had a remarkable memory and now you cant remember things, thats more cause for concern.

Some of these distinctions are subtle -- and theres a vast middle ground of mild cognitive impairment in between normal aging and Alzheimers. If youre concerned, get evaluated by a family doctor or a memory specialist, and the sooner, the better. A host of other conditions can cause memory problems -- including depression, alcohol abuse, thyroid problems, vitamin deficiencies and hormone fluctuations -- and many are treatable. If it is Alzheimers, getting help early may be able to reduce symptoms and slow the progress of the disease.

年华老去的各种迹象中，最可怕的莫过于智力衰退。我有时会脑子想着一个词，指下却打出另外一个词；对于一个记者来说，这是令人不安的状况。一般来说，打错的词总是接近于我所想的那个，比如说把“for”打成“of”，或是把“their”打成“there”。

这个问题还专门有个术语──语音错语症；这只是老年失忆症中的一种，后者是各种智力衰退问题的俗称。最常见的症状就是一下子想不起一个名字、一个数字或是打算作什么。

杜克大学医学院(Duke University Medical School)的生物精神病学项目负责人穆拉利•多雷斯瓦米(P. Murali Doraiswamy)表示，我们认为绝大多数此类问题可能都是良性的，但这也是许多老年痴呆症患者的最初症状。多雷斯瓦米是新书《老年痴呆症行动计划》(The Alzheimers Action Plan)作者之一。

即使在正常衰老的情况下，人的认知功能也会从五六十岁开始整体变慢。在我们的大脑中，保证神经细胞交换信息的化学物质神经递质会慢慢衰减。大脑自身也在萎缩。连接脑前部与存储区域的神经纤维脑白质会发生变化，导致信息处理时间延长，就好像电脑在读取文件时出现暂时死机一样。

多雷斯瓦米说，我们一下想不起来某些名字与日期，这通常是因为没有对这些信息作恰当的“存档”工作。可我们在第一次接触这些信息时就没有给于充分关注，尤其在同时处理多项工作时更是如此。纽约记忆研究中心(New York Memory Center)负责人、精神病与神经学家加亚特里•德维(Gayatri Devi)表示，“人类大脑的存储容量是无穷的，但你不能同时运行过多程序，或很难同时兼顾这些程序。”这或许可以解释困扰很多人的“左耳进右耳出”现象。

用心是记忆的关键。科学家目前认为，记忆分布在大脑的各个区域。有关玫瑰的形状、香味、刺痛的感觉及相关情感的信息分别存储在大脑的不同部位。多雷斯瓦米表示，当你想到玫瑰时，大脑的活动就像是额叶皮质在你大脑的每个部位作google式的搜索、寻找与玫瑰有关的存储信息一样。

德维谈到，你对一个事物的体验越丰富，你的记忆就越深。他进一步解释说，如果你在美景佳酿陪伴下度过了一个迷人的夜晚，你一定不会忘记这个夜晚，因为那一晚给你留下了很多印记。而每次你在脑海回放那些情景的时候，就会再一次加强这些记忆。

重复也有助于增强名字或数字等抽象事物的记忆，记忆联想也是这样。那些在记名字方面很有一套的人通常会下意识地这么做。但如果你处在睡眠不足、紧张焦虑或者面临压力的情况下，做到这点会比较困难。举例说，新上任的首席执行长上台致词感谢董事长的时候，可能突然磕磕巴巴地说不出董事长的名字了。

德维说，排除无关事物、去粗取精也是记忆的重要因素。你或许无法从久远记忆中回想出1960年代的电视广告词，但你完全可以借助日历、清单以及个人数码助手等工具解放你的短期记忆。多雷斯瓦米建议道，让那些小东西来帮你分担记忆任务。

到什么时候你需要为记忆衰退感到担忧呢？

老年痴呆症患者通常能记得很久以前、模糊不清的事，但却难以想起近期的事情和谈话，或者想不起简单的名字。多雷斯瓦米谈到，如果一个人因为忘记看车位编码而无法在肯尼迪机场的6层停车场里找到自己的车，那可能只是普通的老年失忆。但如果他连开了多年的车子是什么颜色或车型都想不起来的话，问题可能就比较严重了。

行为、脾气或记忆出现变化也是老年痴呆症患者的早期症状。德维说，如果你一贯昏头昏脑，那么记性不好也没什么奇怪的；但如果你以往记忆非凡，现在却开始记不住事情，这就比较让人担心了。

有时候，两者之间的差别并不明显，在正常的衰老与老年痴呆之间存在大量有“轻微智能缺损”的人群。如果你对此感到担心的话，那么就请家庭医生或记忆专家给你做个评估。事不宜迟，越早越好。当然，也有诸多其他因素会影响记忆，例如情绪低落、酗酒、甲状腺问题、维生素缺乏以及内分泌失调等等；许多原因都是可以治愈的。但如果这是老年痴呆症引起的，那么提早就医可能有助于减轻症状，延缓疾病的发展。