Sunday, 2 June 2013

Prefrontal Cortex

The prefrontal cortex is the part of the brain located directly above the eyes. It is involved in cognitive analysis and abstract thought, it receives information from all of the senses and is responsible for future planning and goal achievement.

The prefrontal cortex is one of the last brain regions to develop and usually finishes its maturation in the mid-twenties, around the age of 25.  Usually it is said that the brain finishes development in the mid twenties, and this is referring solely to the prefrontal cortex as most other areas should have matured before this.

A brief overview of everything that the prefrontal cortex does is the following;

- Centering attention

- Organising thoughts and solving problems

- Predicting various scenarios and risk assessment

- Planning future appropriate behaviours

- Weighing up short-term gratification and comparing to long-term rewards, e.g. video games or studying

- Controlling impulses and emotions

These are known as "executive functions" of the brain.

Teenagers have less white matter (myelin) in their frontal lobes than adults do although this increases with age. As myelin increases the amount and strength of interconnections within the brain increases. This allows for better communication between cells of the brain. As the myelin in the brain increases with age the frontal cortex becomes better equipped to modulate the emotions of the more primitive and reactive brain centres such as the limbic system. This is part of an idea called 'frontalisation' whereby the prefrontal cortex gains more and more control with age.

As teenagers have reduced interconnections with their prefrontal cortex and less myelin, they are more likely to engage in risky behaviour. This is due in part to lack of impulse control. At around the age of 15 a teenager is able to work out the most appropriate behaviour in a circumstance when asked about it (compared to fully grown adults). However, whenever they are placed into these circumstances, they may do the exact opposite to how they feel they 'should' respond. This is probably due to the limbic system's power of the underdeveloped prefrontal cortex. That is, they cannot control themselves when faced with strong emotions. During adolescence the amount of white matter in the brain increases linearly, while the amount of grey matter in the brain follows an inverted-U pattern. During this time unused neuronal connections are eliminated and the total amount of grey matter is reduced. This is known as synaptic pruning, where the unnecessary synaptic connections are 'undone'. Despite losing grey matter, the brain does not lose functionality, rather it just becomes more efficient at performing its tasks. The overall effect is increased myelination (insulation of axons resulting in faster communication between nerve cells) and reduction of unused neural pathways.

Development of the dorsolateral prefrontal cortex are involved in impulse control and future planning while ventromedial prefrontal cortex development is associated with better decision making. Also, changes in the orbitofrontal are important for evaluating rewards and risks. This period of brain development is important as the thoughts and ideas developed at this point in life greatly influence the formation of adult character and personality.

Studies have indicated that reduced volume and interconnectivity between the frontal lobes and other brain regions are observed in patients with ADHD, schizophrenia, depression, bipolar disorder, suicide victims, criminals, sociopaths, drug addicts and people in high stress environments.

It is important to be able to control stress during this time as well as high stress levels are toxic for the brain and hinder neurogenesis (growth of nerve cells) and can impede development at this time.

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