Age affects both intellectual level and intellectual pattern. There is evidence, however, that intellectual level continues to grow into adulthood, and even into middle and old age for those who remain intellectually active; the rate.of growth, however, gradually declines after the age of about 25. In old age, skills that derive from earlier learning, for example, vocabulary knowledge, tend to decay slowly, and those that require new learning such as solving unfamiliar logical problems, become more difficult to acquire and to retain.
Memory failure is almost universal in old age, particularly forgetfulness for names. This impairment is thought to be the result of functional changes in the brain. Because, however, knowledge of the physiological basis of memory is uncertain it cannot be assumed that loss of memory in elderly people is caused by the reduction in the number of neurons in the brain. It is probable that rapid neuron loss, as well as other abnormalities observed in aging brains. Results not from aging itself, but from disorders of the brain that often accompany aging. Many elderly people, who have suffered from impaired memory function have, on examination after death, shown evidence of brain disorder. Memory impairment may, therefore, be an early sign of brain disorders such as senility or cerebral arteriosclerosis – in which the brain arteries harden, which reduces the oxygen available to areas of the brain by reducing thesupply. Symptoms of such disorders may be exhibited as an exaggerated forgetfulness for recent events and for events immediately preceding the disorder. As the condition worsens there may be a reduced ability to remember past events as well as personal experiences and general or common information. Severe memory defects are rare and may have a psychological, rather than organic, cause.