[SOUND] The prefrontal cortex shows this slow development up until about age 25 and then it starts to show a gradual decline. So, on neuroanatomical studies there have been changes that are associated with age. In general, the brain becomes flatter across age into old age and the ventricles which hold the cerebral spinal fluid become larger. And so the brain starts to slowly lose some of it's mass, much like the rest of the body does across age. The prefrontal cortex shows an early degradation relative to other parts of the brain. This would predict that older adults would have difficulty with these prefrontal types of tasks. That they would show a larger degradation in these prefrontal types of tasks relative to other types of tasks that did not require the prefrontal cortex. There are also other types of changes that occur within sensory systems. The sensory systems are not as sensitive in older age as they are for adults and for adolescents. When researchers looked at the brain activity associated with the simple task of looking at a blinking light, either blinking twice, once, or none at all. Researchers noticed that in fact what happened was that the young adults showed activity in the occipital cortex for this blinking light. And older adults showed activity in the dorsolateral prefrontal cortex. Again, this suggests because the sensory systems are not as sensitive in older age, the dorsolateral prefrontal cortex, an area involved in control, must come in and play a role to compensate for this less efficient sensory process. In young adults, the sensory process is enough for them to detect the stimulus. In a study looking at the effect of task switching, Jimura and Braver asked a group of subjects to perform different types of semantic tasks. So one task was something like man made or natural, and then they asked people to switch between these different tasks. The young adults, when asked to switch between tasks showed activity in the dorsolateral prefrontal cortex. And also in the parietal lobe. But, interestingly, the older adults showed activity only in the parietal lobe. When they encountered this cue they told them what they were going to have to do with the next stimulus. So this suggests that the young adults are actually being pro-active, they're actually planning out the next task and that the older adults are being reactive. That the fact that they are now processing information differently, means that they're using this cue in a very reactive type of manner. Now, both groups were able to do the task, but this suggests that some of the brain systems and the strategies that are used by older adults and young adults differ. In a follow up study, Madden and Cabeza and colleagues looked at the inter-connectivity of these brain areas when subjects were doing this task. In the young adults, what they found was that the interconnectivity was strong at the cue when they got the Madden ask. There the dorsolateral prefrontal cortex and the inferior parietal lobule were strongly interconnected when young adults were told what they were going to have to do with the next stimulus. The older adults showed that strong interconnectivity but only when they got the word. Suggesting again, that the older adults were waiting for the word, and then executing this type of strategy. This suggests again, that there are differences in the way that older adults and young adults process information. And specifically in the ways that they are able to do these executive types of tasks. What we've shown so far and what we've seen in the last two sections is that the ability to perform task switching changes with age. And that the brain activity observed also changes with age up until adulthood. In addition, there's a further change later in development, later in older adulthood, in which there are again changes in the way the brain activity occurs and the types of task switching that older adults can engage in and the size of that switching effect.
