The structure of the brain and aggression Flashcards
Brain structure : Role of the limbic system
Papez and Maclean linked limbic structures to emotional behaviours such as aggression
The key structure for aggression is the amygdala, located in the limbic system. This has a central role in how an organism assesses and responds to environmental threats and challenges.
Coccaro et al studied people with intermittent explosive disorder (IED), a major feature of which outbursts of extreme reactive (hot-blooded, impulsive) aggression. Participants brains were scanned by fMRI while they viewed images of faces. IED participants showed high levels of amygdala activity when viewing angry faces (not found in non-IED controls)
This association between amygdala reactivity and aggression is especially meaningful because an angry facial expression is an ecologically valid sign of threat (it exists in the real world)
Brain structure : Role of the prefrontal cortex
The amygdala functions in tandem with the OFC
The OFC is a region of the prefrontal cortex just above the eye sockets. It plays an important role in higher cognitive functions ( rational thinking, decision making) and is also involved in self-control, impulse regulation and inhibition of aggressive behaviours
In people with psychiatric disorders that feature aggression, OFC activity is reduced, which disrupts its impulse-control function (coccaro)
Raine et al used PET scans to study murderes whose crimes included reactive aggression. There was greater glucose metabolism (more activity) in the amygdala, but abnormally low metabolism in the prefrontal cortex (including OFC) compared with matched controls
Brain function: Role of serotonin
Neurotransmitter with widespread inhibitory effects on neural transmission (slows down and dampens activity of neurons)
Normal levels of serotonin in the OFC are associated with behavioural self-control but decreased serotonin may disturb this link, reducing self-control and leading to more impulsive behaviours including aggression (denson et al)
Virkkunen at al compared levels of a serotonin metabolite (5-HIAA) in the cerebrospinal fluid of violent non-impulsive offenders, who also suffered from more sleep irregularities. This is an interesting find because serotonin helps regulate sleep patterns. Disturbance of sleep strongly implies disruption of serotonin functioning
Brain function : Role of dopamine
Neurotransmitter with inhibitory effects in some area of the brain and excitatory effects in others
Dopamine is involved in regulating motivated behaviour and our experience of reward. Its main influence on aggression comes through its interaction with serotonin.
Seo et al claim that serotonin under activity stimulated dopamine overactivity and both are linked with impulsivity and aggression
So serotonin hypofunction is the primary cause of impulsive aggression and dopamine hyper function makes an additional contribution
A weakness is that research into neural influences is often correlational
Studies typically find links between high levels of aggression and a brain function, dysfunction or structure
There are ethical reasons for doing correlational research because experiments would have to make people be aggressive (an alternative is to do animal studies, raising other practical and ethical issues)
This means it is impossible to establish whether a particular structure or function/ dysfunction Is a cause or effect of aggressive behaviour, or whether a third variable is involved
A strength is support from longitudinal research for the role of the amygdala
Pardini et al found that over a 20 year period, 56 males consistently behaved aggressively (including serious criminal violence). fMRI scans found a strong negative correlation between aggression and amygdala volumes
The findings is particularly significant because it could not be explained by potential cofounding variables (e.g. race, age, substance abuse0 or y earlier levels of aggression, because these were all controlled in the study
This is strong support for the influence of the amygdala, especially as it shows the explanation has predictive validity
Competing argument
Some researchers have tried to overcome this problem by using drugs known to increase serotonin activity, e.g. participants given paroxetine administered fever and less intense electrical shocks to others (Berman et al ) This is evidence of a link between serotonin and aggression that goes beyond the usual correlational findings
Application: There are practical benefits to understanding neural influences
For example, one goal of research is to discover a drug that affects the brains serotonin system , reducing aggressive behaviour with minimal side effects
A category of serotonin agonist drugs called serenics has significant anti-aggressive effects in animals and humans (Verhoeven and Tuinier)
This may be invaluable given that human aggression is at there root of so many personal, social and economic costs
Issues and debate
amygdala dysfunction is not an inevitable cause of aggression. Whether or not aggression occurs depends on many interacting risk factors (social, psychological and environmental)
These interact with biological predisposition to behave aggressively, but the diathesis is not enough on its own to trigger aggression
The problem with any reductionism explanation is that it rarely reflects the true complexity of a behaviour, in this case oversimplifying the causes of aggression
