periods of brain imaging when individuals are not engaged in any active task.
default or intrinsic network: neural network that is active during internal processing
executive functions: cognitive functions involved in planning, understanding new situations, and cognitive flexibility
Figure 2.23 The Brain’s Default Network
Source: James King-Holmes/Henry Luckhoo/Science Source
Overall, the default network is involved during internal or private considerations that do not require processing external sensory information. In fact, it appears as if there is a negative correlation between activities in the default network versus networks associated with processing information from the environment. That is, when someone begins some cognitive activity, then new networks associated with that task become active and the default network becomes less active. This suggests that separate brain mechanisms evolved for dealing with information involving the external environment as opposed to considerations internal to the person. A variety of psychopathology disorders show problems with the default network in terms of being able to turn it off and engage in a more active external task. People with schizophrenia are one group that has difficulty turning off the default network and moving to an active task that uses a different network.
Different Networks Are Involved in Different Tasks
In addition to the default network, the executive and salience networks are dysfunctional in different psychopathologies (Menon, 2011). The central executive network is involved in performing such tasks as planning, goal setting, directing attention, performing, inhibiting the management of actions, and the coding of representations in working memory (Eisenberg & Berman, 2010). These are sometimes referred to as frontal lobe tasks, since damage to the frontal areas of the brain compromises performance of these tasks. These tasks are also referred to as executive functions, because they assist in planning, understanding new situations, and having cognitive flexibility. The salience network, as the name implies, is involved in monitoring and noting important (i.e., salient) changes in biological and cognitive systems.
The three networks—default, executive, and salience—show deficits in individuals with specific psychopathologies. Menon (2011) has reviewed the research literature and suggests that these networks play a prominent role in schizophrenia, depression, anxiety, dementia, and autism. As you will see throughout this book, the role of these networks may be dysfunctional in the network itself or in the ability to activate or deactivate specific networks in changing situations.
Figure 2.24 shows those areas of the brain that Menon (2011) found to be associated with each of these networks. The figure shows an MRI structural image of the brain in black and white. The areas that are activated during the task are displayed in color. The brain is shown in terms of a three-dimensional image along an x-, y-, and z-axis. The x-axis shows the brain from the side, the y-axis from the back; and the z-axis from above. The numbers below the image represent the location along each axis. Using these three numbers, brain imaging programs can identify the areas in relation to traditional anatomical structures.
In Figure 2.24, the central executive network, which is involved in higher order cognitive and attentional demands including planning for the future and remembering concepts, is shown in blue. The salience network, which is important for monitoring critical external events and internal states, is shown in yellow. The default network, which is active during mind wandering and when the person is not engaged in active problem solving, is shown in red.
modularity: the concept that specific areas of the brain are dedicated to certain types of processing
Let’s take a moment to understand how researchers describe brain function in terms of networks. One important concept is modularity. Modularity describes how specific areas of the brain are dedicated to certain types of processing. For example, as discussed early in the chapter, we know that a particular part of the temporal lobe, the FFA, is involved in processing responses to the human face. fMRI measures, for example, would show greater brain activation in this area when observing the human face as opposed to nonhuman faces.
Another important concept is connectivity. This asks how different areas of the brain work together in specific conditions. To determine connectivity, researchers examine fMRI or EEG measures from a large number of locations throughout the brain. It is assumed that those areas whose activity is correlated are in some way working together.
Figure 2.24 Structural Image of Three Brain Networks
Source: Reprinted from Vinod Menon, Large-Scale Brain Networks and Psychopathology: A Unifying Triple-Network Model, Trends in Cognitive Sciences, Vol. 15, pp. 483–506, Copyright © 2011, with permission from Elsevier.
connectivity: the concept that different areas of the brain work together in specific conditions
Concept Check
How does the brain operate as a “small world framework,” and why is this significant?
How is the brain’s default or intrinsic network different from the central executive and salience networks?
Researchers are concerned with modularity and connectivity in terms of neural networks. What are modularity and connectivity, and how are they important in thinking about psychopathology?
Genetics and Psychopathology
In this section, we consider the genetic level of analysis. This discussion includes a historical understanding of the study of genes as well as their structure. You will then learn about the role of DNA, how genes influence behavior, epigenetics, mitochondria, and endophenotypes.
Genes form the blueprint that determines what an organism is to become. Specific genes have been associated with a variety of disorders as will be described throughout this book. However, the original hope of finding a few genes that were involved in particular mental disorders has not panned out. What has become apparent is that there is a complex interaction of genetic and environmental factors involved in mental illness. Just having a gene does not mean that it is active—it turns on or off under a complex set of circumstances.
As the factors involved have become more complicated, there has been a search for particular processes related to psychopathology. For example, there exists a gene (SERT) that is involved in the removal of the neurotransmitter serotonin from the synapse. A variant of the SERT gene has been associated with depression, alcoholism, eating disorders, ADHD, and autism (Serretti, Calati, Mandelli, & De Ronchi, 2006). Likewise, a variant of the gene (DßH), which is associated with the synthesis of norepinephrine from dopamine, is associated with schizophrenia, cocaine-induced paranoia, depression, ADHD, and alcoholism (Cubells & Zabetian, 2004). It is suggested that the lower level of the proteins produced by the DßH gene is associated with a vulnerability to psychotic symptoms.
As researchers discover genes related to specific forms of mental illness, there may be a need to reorganize the manner in which we view mental illness. One study analyzed the genes from 33,332 individuals with a mental disorder in comparison with 27,888 without a disorder (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2013). This research suggests that similar genetic risk factors involved in calcium channel signaling exist for what we have considered to be separate disorders. These five disorders are autism spectrum disorder, schizophrenia, bipolar disorder, major depressive disorder, and ADHD. This study implies that a particular genetic makeup may put some individuals at higher risk for developing a variety of disorders. There is also research that suggests that having certain mental disorders such as schizophrenia may actually protect these individuals from getting certain types of cancer (Tabarés-Seisdedos & Rubenstein, 2013).