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Linking structure and function - Coggle Diagram

- - - - Brodmann was certain that specific brain regions were responsible for different functions but he also suggests that disease states may be associated with changes in these regions.
- - - - From the Phineas Gage case study, the front part of the brain is involved in controlling aggression and moderating behaviour. What are the problems with inferring a conclusion such as this?
        
        This is a case study based on one individual and we should therefore be cautious in making generalisations about brain function on this basis.
        
        Examination of Gage’s skull occurred post-mortem and other changes may have occurred in the period between sustaining the injury and his death.
        
        Due to the nature of the injury, any damage was unlikely to be specific to one particular region of his brain.
        
        There may not be accurate reports of Gage’s behaviour prior to the accident so it’s difficult to know precisely what types of behavioural changes occurred.
        
        An alternative useful approach is the post-mortem study of the brains of people who have suffered from a particular condition (Figure 2.16). In Parkinson’s disease for example, studies of post-mortem brains show loss of neurons in a region of the brain known as the substantia nigra. It would be tempting to propose from this observation that the loss of neurons from this region is responsible for the movement impairments that are characteristic of Parkinson’s disease and therefore that the substantia nigra is involved in movement. In fact, the substantia nigra is important for movement, but it’s also involved in reward and addiction, so conclusions about the role of the substantia nigra are not based on studies of this type alone.
        
        While post-mortem studies of patients who have experienced a disease can be useful, there can be issues in interpreting these studies. For example, the post-mortem brain may display changes that are age-related rather than being due to the condition, or medications for the condition may have affected the structures of interest.
- - - - Functional MRI uses the same principle as MRI but looks at changes in the way that water molecules in the brain behave during a given task. A baseline recording is taken during which the participant isn’t engaged in any particular task. When the participant is engaged in a task of interest, blood flow to the relevant brain regions will increase and this will affect the behaviour of the water molecules in those brain regions. This altered behaviour of the water molecules can be measured and converted into coloured areas on a scan. fMRI can therefore be used to determine which parts of the brain are active when the subject is engaged in a particular task.
        
        The default mode network is a collection of brain regions which are seen to be activated when an individual is in a so-called ‘resting state’. The brain is never truly at rest but in this state, an individual is not engaged in any particular cognitively demanding task. Instead they are free to let their mind wander and daydream, perhaps thinking about their past or planning the rest of their day. Whilst there is no consensus on which brain regions are involved in the DMN, it is thought to include the medial prefrontal cortex, the parietal cortex and the posterior cingulate cortex.
        
        Other networks include the salience network, thought to be involved in choosing which aspects of the external environment most need focus of attention at any given time and the central executive network, a network of brain regions activated when engaged in complex, cognitively demanding tasks.
        
        Numerous studies suggest that defects in the default mode network are implicated in various mental health and neurodevelopmental conditions, including depression, ADHD, autism and schizophrenia (Hu et al., 2017; Mowinckel et al., 2017; Padmanabhan et al., 2017; Wise et al., 2017). The observed effects on the DMN vary from one condition to the next, with some conditions seeming to show an increase in activity and some showing a decrease in activity. Much more work needs to be done in this area, but an understanding of how brain regions operate together in a coordinated way is likely to result in a richer understanding of mental health conditions.
- - - - Changes in individual brain structures may also underly some mental health conditions and there is a large amount of emerging evidence in this area. For example, there is some evidence of a correlation between clinical depression and atrophy of the hippocampus, which can be as much as 20% in some cases.