6. Biological Influences on Criminal Behaviour
6.2 Brain Chemistry
Dr. Gail Anderson
Neurochemistry is not often covered in criminology texts as it is highly specialised, yet some of the most exciting discoveries within biosocial criminology result from our rapidly increasing understanding of brain chemistry and its interactions with the environment. The brain controls all behaviour, and we are beginning to understand how imbalances in certain brain chemicals can affect health and behaviour. Neurotransmitters are chemicals involved in communication between nerve cells. Neurotransmitters are synthesised by the catalysis of an amino acid precursor. Once released, they bind to a receptor cell to transmit a message, then break down into their metabolites. Each of these stages is under genetic control and involves many genes. Imbalances and interactions between these neurotransmitters and our environment can have profound effects on our behaviour.
Serotonin
Low levels of serotonin, a behavioural inhibitor, have been linked to impulsive-aggressive behaviour in extensive research conducted globally over six decades. A great deal of evidence shows that serotonin plays a role in impulsive-aggressive behaviour, which makes sense because serotonin regulates the stress response in the brain, meaning that it impacts the way we handle and react to stress, in general having a calming effect.
Many studies have shown that dysfunction at any stage of the serotonergic system can reduce levels of serotonin, and alleles have been linked to increased levels of suicide (Antypa et al., 2013). For example, one such gene has two alleles referred to as S and L. We all have two alleles for every gene, so a person could have SS, SL or LL. The S allele makes a person more sensitive to stress, and the L allele makes them more resistant. In a seminal, long-term study of almost 900 people, Caspi and colleagues looked at 21- to 26-year-olds who had suffered multiple stressors (Caspi et al., 2003). They found that almost half of those with SS developed depression, and 11% attempted suicide as opposed to only 17% of those with LL who developed depression and 4% who attempted suicide (Caspi et al., 2003). This early study has been repeated many times around the world and again highlights the link between a person’s genetic background and their environment. Numerous studies have also linked low serotonin levels with aggressive behaviour (Brown et al., 1979; Glick, 2015), psychopathy (Glenn, 2011), impulsivity (Linnoila et al., 1983), and an inability to learn from negative experiences (Helmbold et al., 2015).
Overall, the studies on serotonin indicate that any sort of dysfunction in the serotonergic system has an adverse effect on behaviour. However, in many cases, we can reverse the effects. Neurotransmitters are synthesised from building blocks or precursors of basic amino acids, and the precursor for serotonin is tryptophan. This amino acid can be obtained through diet. Even peopl