The Effects of Aging on Intelligence, and the Idea of g

Intelligence is generally thought to decline with age. That is, in many ways, a flawed belief. There are various cognitive processes, linked with changes in brain area mass that do deteriorate with time. However, there are other brain areas that increase their activity in older age.  This is thought to perhaps be a compensatory mechanism.

There are two areas whose function levels change over time.  The dorsolateral prefrontal cortex is more active in younger adults during high cognitive load working memory tasks.  The rostrolateral prefrontal cortex's activity actually increases in older adults.  This is thought to be a compensatory mechanism for changes in the working memory system.  It ties in most closely with the system described by Baddeley and Hitch.  This model ties in three subsystems that comprise working memory. There is the phonological loop, the visuospatial sketchpad. and the central executive. The phonological loop handles verbal memory, such as rehearsal. The visuospatial sketchpad handles tasks involving visual memory and mental imaging. It is thought of as a sketchpad, in that it is the theoretical system that allows for humans to visualize information. This information can be modified in tasks like mental rotation. The central executive manages memory consolidation, and handles suprathreshold cognitive load. The central executive is the least well theorized part of the system. It can be thought of as an attentional control mechanism that coordinates the activity of the two other slave systems.

Much of the evidence for this dual system was developed by Baddeley and Hitch in a long series of experiments.  It was found that such things as listening to American football descriptions on the radio impaired driving ability. This means that there must exist a control system (controlling the driving task) that is getting overtaxed by listening to and comprehending the football game.

Intelligence must be closely related to these systems, since much of intelligence could be explained on the basis of verbal fluency (the phonological loop), visuospatial skills (the visuospatial sketchpad), or logical processing (the central executive).

In the remaining parts of this section, the effects of age on certain types of tasks will be assessed. Additionally, the effects of certain types of lesions to white matter will be assessed for their effects on intelligence. These white matter lesions are closely related to aging and certain forms of dementia.  In the final portion, the idea of a general intelligence factor that applies to all ages, and could also thus explain why different people are differently affected by the aging process.