So we've talked about structural neuroimaging studies so far. What I want to talk about now is about functional neuroimaging studies. There are many fewer functional neuroimaging studies, in fact, current estimates suggest that there somewhere in the area of upwards of about 40 of these studies now and people with schizophrenia. And in these studies, in functional neuroimaging, we are looking for activity in the brain, rather than simply the structure of the brain. These are imaging studies that are conducted in an MRI, just the way a structural MRI study would be conducted. But in these studies, there is measurement of oxygen levels. In fact, the signal that is measured is known as what is called the BOLD signal, blood-oxygen-level dependent signal. And the logic behind these types of studies, is that the more oxygen it's being delivered to a specific part of the brain while someone does a specific task, indicates what areas of the brain are more active during their cognitive task. Functional neuroimaging studies as well, have revealed a lot of very important findings about schizophrenia. Some of the cognitive areas that have been studied most closely in functional neuroimaging studies, are studies of attention and working memory, attention, of course, as the ability to focus on a specific stimulus, or to be able to focus on a specific stimulus and ignore distracting stimuli. Right? That's a form of attention. Working memory includes the ability to remember things over a short period of time, seconds or minutes. And even more importantly, to manipulate that information. Probably the best example would be remembering a phone number. So reciting that phone number to oneself, that would be an example of working memory over a period of seconds or minutes. But then also, being able to remember the numbers of the phone number and reverse them in your head. That would be truly active working memory. So studies of attention and working memory and functional neuroimaging have converged on some very important findings. The tasks that have been used to measure attention, typically been a task called the CPT or Continuous Performance Test and measures of working memory of typically included what's called an n-back task. For the continuous performance task, studies have shown that when people are actually involved in a continuous performance test where they are trying to track a target, and then this task typically a series of stimuli are shown, many of them are distractor stimuli, and periodically, a target stimuli will show up. In some cases, it's remembering, for example, to respond to way X whenever an A precedes it. So you see a series of stimuli and you respond to an X whenever a precedes it. In other versions of the task, you're looking for a specific target, but the stimuli may be degraded visually, so it's hard to detect where the stimuli are. So you're trying to pay attention to these sort of visually degraded stimuli responding when you see a target. In these types of studies using continuous performance tasks, studies have shown quite decisively, that one area of the frontal cortex, specifically the dorsolateral prefrontal cortex, is reduced in activation in people with schizophrenia as compared to healthy controls. This finding is particularly powerful because when the finding or the study has been replicated in first episode samples, people who've just been diagnosed with schizophrenia and have minimal exposure to anti-psychotic medication. These findings are still evident. That is, when people do this task and they have schizophrenia, their activation in this area of the brain, known as the dorsolateral prefrontal cortex, is reduced. So again, this suggests a close relationship between a decrease in brain activity. We had talked before about brain structure. Now, we're talking about activity, but decrease in activity and performance on a specific cognitive task.
