Cognition refers to mental processes used for perceiving, remembering, and thinking. Most studies show that, in general, cognitive abilities are the greatest when people are in their 30s and 40s. Cognitive abilities stay about the same until the late 50s or early 60s, at which point they begin to decline, but to only a small degree. The effects of cognitive changes are not usually noticed until the 70s and beyond. These statements are based on data from studies where averages were calculated for each age group. Within each age group, however, there are wide variations in cognitive ability. The information presented here represents general findings about age-related cognitive change. They do not necessarily happen to everyone.

One study of intelligence over a lifetime found that by the age of 81, only 30-40% of study participants had a significant decline in mental ability. Two-thirds of people at this age had only a small amount of decline. And only certain cognitive abilities decline, while others may improve.

Fluid and crystallized intelligence
Attention
Processing speed
Memory

Fluid and crystallized intelligence
Different aspects of cognition are affected in various ways over time. One measure of cognitive ability is intelligence. A commonly-used system of categorizing intelligence is into "fluid" and "crystallized" intelligence.

Fluid intelligence (also called "native mental ability") is the information processing system. It refers to the ability to think and reason. It includes the speed with which information can be analyzed, and also includes attention and memory capacity.

Crystallized intelligence is accumulated information and vocabulary acquired from school and everyday life. It also encompasses the application of skills and knowledge to solving problems.

Many studies have shown that fluid intelligence is more likely to decline with age than crystallized intelligence. In fact, crystallized intelligence may continue to improve with age. Many people continue to gain expertise and skills in particular areas throughout life.

It is theorized that much of the cognitive decline with age can be traced back to deficits in the information processing system (fluid intelligence). Tasks that use well-practiced skills or familiar information are generally not affected by age. However, complex tasks that require taking in new information and analyzing it may become more difficult. Many researchers attribute this to deficits that occur in attention, speed of processing, and memory.

Attention
Attention is necessary for information to be taken in to begin with. Attention is the ability to focus on certain bits of information and to decide whether and how much to process it further. It's possible to pay attention to only a limited amount of information at any one time. Certain changes in attentional ability have been reported with older age.

Some researchers have found that many older adults have increasing difficulty distinguishing between information that is relevant and information that is irrelevant to a particular task. They have difficulty focusing only on the necessary information, and are susceptible to becoming distracted. This may slow down the speed of performing a mental task and may compromise accuracy.

Some researchers have proposed that these attentional difficulties may be the result of a general overall slowing of information processing that has been observed as people age.

Processing speed
Mental processing and reaction time become slower with age. This slowing of information processing speed actually begins in young adulthood (the late 20s), although imperceptibly at first. By the time people are past 60 or older (depending on the individual), they will generally take longer to perform mental tasks than younger people.

On tests of intelligence that require the person to perform tasks within a short time frame, older adults often do worse than younger counterparts. In the past, this was considered to be a measure of decreased cognitive functioning. However, on intelligence tests with liberal time limits, older adults are often able to perform just as well as younger people. Therefore, it's now thought by some experts that older adults don't lose mental competence, it simply takes longer to process the necessary information.

One theory holds that the slowing of processing speed is the cause of many of the cognitive difficulties experienced by older adults. However, it is not the only factor. It's not yet known what other factors may be responsible. It has been found that some mental processes are slowed more than others. The reasons for this are not known, and research continues to be conducted to figure out the exact role of slowed processing speed and to determine what other factors may be at work.

In addition to cognitive decline, slowed processing speed has also been linked to a decline in motor function. Older adults may have less dexterity and coordination than when they were younger. They may walk slower and take a longer time to react.

Some researchers have suggested that slower processing speed may also have a negative impact on some types of memory. Whether or not this is the reason, most people experience at least some degree of age-related decline in some types of memory ability.

Memory
Memory is a complex function that has been divided into different types. Only some of these are affected by age. Difficulties that occur with memory are usually small and vary widely from person to person, making generalizations difficult.

Further complicating the memory picture are the different methods by which different researchers categorize memory. However, it is widely believed that one type of memory, called working memory, is most affected by age. Working memory is the retention of information that must be manipulated or transformed in some way.

Conscious mental processing goes on in working memory. It requires taking in information from the environment and from memory stores and accomplishing a mental task. For example, a restaurant check comes to $36.43. This amount is kept in memory while figuring out which bills to use to pay the check, how much tip to leave, and how much change is due back. Everyone has limits on how much they can keep in working memory at one time. As people get older, complex mental tasks can become more difficult if they require too much information to be held in memory in order to process it.

Some researchers postulate that the problem with working memory is related to reduced speed of information processing, which reduces the efficiency of working memory.

One popular method for categorizing memory divides it into "implicit" memory and "explicit" memory. Implicit memory is the retention of skills and reflexes that have been acquired, such as the procedures for driving a car. Implicit memory generally remains intact throughout life. Explicit memory is the conscious memory of facts and events. These memories are more vulnerable to age-related decline.

Older adults may have increasing difficulty with word retrieval. In other words, recalling the name of a familiar person or object, the "tip of the tongue" phenomenon. The reasons for this are not known. One theory suggests that this also is due to slowed processing speed. As people get older, they've known more people, so searching a larger memory "database" for the right name takes longer. The information is not forgotten altogether. If someone says the name or word, it will be recognizable. There may also be a physiologic explanation for this word-finding problem, having to do with atrophy of a brain structure called the prefrontal cortex. For more information, see What physical changes happen to the brain?.

In general, memory tasks that are complex and require manipulating a lot of new information quickly become more difficult with age. Facts, names, and events that are not often accessed may become more difficult to retrieve from memory. However, knowledge that has been accumulated over a lifetime, which is repeatedly accessed and expanded, is generally retained. Well-practiced skills and abilities remain intact. And vocabulary usually continues to increase throughout life.

It's important to emphasize that the changes in cognition described here do not necessarily happen to everyone. There is wide variation among individuals. Additionally, for those who do experience declines in cognitive functioning, they are usually not disabling. The degree of decline is small and should not interfere with normal day-to-day functioning. And there are many ways to compensate for the deficits or even to regain lost function. It may take longer for an older person to learn something new, but it's still possible to learn it. Memory difficulties can be gotten around by using calendars, lists, and other memory aids.