This essaywill evaluate the role of neural structures in subserving emotion.
Theneural structures are part of the nervous system in the human brain. Thestructure that will be the main focus of this evaluation will be the amygdala.Part of the limbic system, the amygdala is almond-shaped and located within thetemporal lobes of the brain (Amuntset al.
, 2005). The amygdala has been called by many as being part of theneural circuitry critical for emotion (Gallagher & Chiba., 1996) (18) and it issuggested that one of the principal roles of the amygdala is emotionalreactions. Emotions such as aggression and depression have been associated withthe amygdala, yet the prime example of the amygdala being associated withemotion, with an overwhelming amount of evidence to support, is fear andanxiety. However, it cannot be ignored that it is not the only neural structureat play, with some researchers finding evidence that undermines thesignificance of the amygdala and its link to fear.
With the staggering amountof research into negative emotion and the amygdala, it begs the question as towhat significance it possesses concerning positive emotions and their link tothis neural structure, with this being explored further in this evaluation. Aswell as this, this evaluation will be looking into research measures and howthey may alter the reliability of the vast amount of research into emotion tocreate a better evaluation concerning this specific neural structure. With research into the amygdala showing links to thepsychological function, emotion, this evaluation begins with, aggression.
Astudy which looked at the social behaviour of a rat found that lesions to theamygdala lessened the level of shock-induced aggression (Kolb & Nonneman., 1974).This shows that even early on in research into the amygdala there appears to bea link to the emotion aggression. Furthermore, an experiment which exploredfacial expression recognition in bilateral amygdala-damaged patients supportedthe idea that the amygdala has significant influence on aggression, as thesepatients have impaired processing of facial expressions that were related toparticular negative emotions, specifically fear and anger (Sato et al., 2002). Thisresearch comes from animal studies which conveys that when the stimulation ofthe amygdala occurs, it increases aggressive behaviour. Similarly, studies thathave used brain lesions have conveyed that harm to the amygdala may generatethe reverse effect.
Therefore, it would seem that this area of the brain mayplay a part in the display and modulation of aggression (Brink., 2008) (15). Stimulationof the amygdala consequences in amplified aggressive behaviour, while lesionsof this area significantly moderate an individual’s aggression. A particularinteresting study found that the volume of the amygdala may change howaggressive an individual is. Participants who scored higher in aggression had a16-18% reduction in amygdala volumes (Matthies et al.
, 2012). This suggests that thevolume of someone’s amygdala plays an important role. A further study to support this shows evidence ofamygdala-OFC dysfunction in response to processing angry faces in participantsthat have a history and record of impulsive aggressive behaviour and thisfurther validates a link concerning a dysfunctional cortico-limbic network andaggression (Coccaroet al., 2007) (29). However, a study contradicts these findings, lookedinto amygdala volumes in female and depressed humans.
The research conveyedthat there were no significant findings linked to aggression (Elst et al., 2000) (28).On the other hand, the study did find that depressed patients exhibitedsignificant enlargement of both left and right amygdala, therefore theamygdala’s involvement in negative emotion is still prevalent. This can befurther seen in the mental disorder, major depressive disorder. This disorderhas been argued to be linked with volumetric abnormality in the amygdala, andthat the size of the amygdala is increased significantly in depressedindividuals compared to healthy people (Hamilton, Siemer & Gotlib., 2008) (30).
Thereis a vast amount of research which backs the theory that the amygdalastimulates and causes depression-like emotional experiences. However, the specificityas to how the amygdala effects this emotion is still unclear, as seen in Yanget al (2010) (31) whoconducted a study that looked into adolescents with depression and theinvolvement of the amygdala. The results found significant bilateral amygdalaactivation in both the healthy and depressed teenagers. In addition, there wasgreater left amygdala activation in the depressed adolescents in comparison tothe controls.
More research should be conducted in adolescents and evenchildren to gain more of an understanding of the amygdala’s role in emotion,seeing as the brain continues to mature and develop well into the 20’s (Johnson, Blum & Giedd., 2009). In research,the emotions fear and anxiety have taken centre stage in being associated withthe amygdala. Fear has been defined by Ethologists as a motivationalstate which is stimulated by certain stimuli that escalate to defensivebehaviour or an attempt to escape (McFarland, 1987). Anxiety can be defined as having a generalisedreaction to an internal conflict or a threat which is unknown (Craig, Brown and Baum, 1995).
The principal function of anxiety and fear is to act as a signal of danger,threat, or motivational conflict, and to trigger suitable adaptive reactionsand responses (Steimer,2002). Ithas been argued and stated that the amygdala is referred to as the ‘fearcentre’. This is evident in patients that have a genetic condition that isextremely rare; Urbach-Wiethe disease. A particularly well-known case study ispatient S.M. Suffering from amygdala damage, patient SM appeared to havestrange fear reactions as well as a reduced experience of fear. The studyconcluded that the amygdala plays a central role in creating a state of fear,and the deficiency of such a neural structure prevents the capability of fearitself (Feinstein et al.
,2011). As mentioned previously, the amygdala is referred to as the “fearcentre”, some scientists are so sure of the statement that they state that in the future they may be nearerto helping those with debilitating fear and stress-related psychopathology (Ressler., 2010).
Thissuggests that they have full belief that the amygdala is in fact the neuralstructure that controls fear. There has also been a vast amountof research which looks into the link between the amygdala and anxiety. Theamygdala has been implied in anxiety as well as mental disorders such as PTDSand phobias where anxiety is a prominent symptom (Etkin & Wager., 2007). (14) Focusing onPosttraumatic stress disorder (PTSD), there is research that conveys it appearsto combine features of both extreme ‘stress responsiveness and either enhanced conditioned fear or aninability to extinguish, or inhibit conditioned fear’. (Ressler., 2010). Shin andLiberzon (2010) statedmoderately amplified amygdala activation in response to disorder-relevantstimuli in social phobia, PTSD, and specific phobia.
In addition to this,numerous neuroimaging studies have exhibited that participants that suffer withPTSD have superior amygdala activation in comparison to the control group (Liberzon & Sripada., 2007).When looking at anxiety and therole of neural structures, a study that looked at generalised anxiety disorder(GAD) identified and found abnormal amygdala and prefrontal cortex activationin participants and reduced connectivity amid these areas. Additionally, itconveyed amplified ‘grey matter volume and ‘shrunken ‘structural connectivity concerningthese structures.’ (Hilbertet al., 2014).
This shows thatthere is a distinctive ‘set ofneurobiological alterations in Generalised anxiety disorder’ and thatthe amygdala as well as other neural structures play a part in anxiety as awhole. Overall, you cannot ignore the overwhelming amount of research thatconveys that the amygdala appears to be the home to fear and also anxiety. (Change). However, when looking atthe amygdala and its role, it must also be noted that it is not solely down tothis neural structure and that others also are to be credited.
Rauch and Shin (Davis., 2002) (12) statethat numerous brain areas contribute and provide vital feedback to the amygdalaincluding the medial frontal cortex, the hippocampus and the corticostriatothalamic circuits.The hippocampus delivers information regarding the context of the situation, aswell as the medial frontal cortex providing ‘critical “top-down” governance over the amygdala, thereforepermitting attenuation of the fear response once danger has passed or when themeaning of a potentially threatening stimulus has changed” (Davis., 2002). Thisconveys that although the amygdala ultimately ends up being central to fear,other neural structures are used in the process. As well as the amygdala beingheavily involved in negative emotion, there is research that suggests that theamygdala is involved with memory. When a memory is emotionally significant toan individual it activates brain and hormonal systems which control the strengtheningof obtained new memories.
These effects are incorporated via noradrenergic activationof the basolateral amygdala which regulates and controls memory consolidationthrough interactions with various other brain regions that are linked toconsolidating memories of recent experiences (Mcgaugh & Roozendaal., 2008). Whilst it may seem at first glance that there is an overwhelmingamount of evidence to support the statement that the amygdala is in fact ‘thefear centre’, some researchers have contradicted this idea. Firstly, LeDoux (2015), argues that peoplewith damage to the amygdala are indeed less responsive to threats however theycan still feel and experience fear. He interprets previous findings by statingthat the amygdala is a vital part of the circuit that permits the brain toidentify and react to the threat but is not compulsory to feel fear. Inaddition to this, there are various studies that have studied neural mechanismsof emotion and have concentrated on individual differences. A particular studyby Adolphs et al (1999)(11), looked at 9 participants who all suffered from bilateral damage.
Allparticipants had issues with identifying the emotion of fear, however there wasfound to be individual differences in the group of participants. Someparticipants found difficulty in identifying negative emotions whereas on theother hand two of the patients conveyed little issue with identifying emotionsin facial expression at all despite them both having bilateral amygdala lesions(Adolphs et al., 1999).
This suggests that perhaps the amygdala is not the only neural structure thatis linked to fear. Neural structures may play various and changeable roles inexperiencing emotion subject to the person; and that further research needs tobe done to explore this idea so that these sorts of findings become relevant. Furthermore,another study looked into neural correlates of individual difference in fearand anxiety (Ochsner etal.
, 2006). The results conclude that the findings displayed should helpexplain firstly the influence of individual differences in emotion on theneural correlates of pain, and the functions of anxiety, pain processing andfear, participated by medial and orbitofrontal systems. With all of this inmind, LeDoux (1996)stated that many will be quick to conclude that the amygdala is the centre ofemotion reaction in the brain due to the vast amount of empirical evidence.However, there are clearly other structures and networks that are involved inemotional processing. More research should be done on the role of the neuralsystem in emotion so it can be fully understood.
(LeDoux., 1994., LeDoux & Rogan., 1996). There is also the issue that the amygdala is often only discussedwhen evaluating negative emotion, suggesting that its role in effecting emotionis limited.
One emotion that has not been shown as being affected by theamygdala is happiness. Some suggest that the neural processes of happiness arethe complete opposite to those that process depression and anxiety (Cunningham & Kirkland., 2013)(25). The human amygdala when inresponse to emotion is most often found to show significant reactions tofearful expression as opposed to happy ones (Morris et al., 1996) (23). In a particular study, masked happy faces werelinked with significant bilateral activation in the amygdala and the anteriorcingulate gyrus, in comparison to masked sadness which produced only reducedactivation in the left anterior cingulate gyrus. In contrast, it was found thatmasked happy faces further generated significantly higher activation in theamygdala and anterior cingulate in relation to identically masked sad faces.
Theseresults propose that the anterior cingulate and the amygdala are vital factorsof a network involved in identifying affective information beneath the standardthreshold of conscious visual perception (Killgore & Yurgelun-Todd., 2004) (22). However,to some, it remains controversial as to whether the amygdala is involved inemotions like happiness. In a study that looked into identifying expressionsfrom unilateral amygdala damage and complete bilateral amygdala damage, thefindings conveyed that participants with bilateral amygdala damage performednormally at rating happy faces however the participants with right unilateralamygdala damage performed worse overall than participants with left unilateralamygdala damage (Adolphs& Tranel., 2004). This leaves an area for slight confusion as towhether individuals with right unilateral amygdala damage could not identifyhappiness.
Moreover, an interesting study suggests that happiness is linkedwith a balanced and stable amygdala response to negativity and positivity (Cunningham & Tabitha., 2013)(25). This is due to their research which looks into moderate responses topositive (however not negative) stimuli in happiness. Participants that weredeemed happier portrayed greater amygdala responses to stimuli that was positive.
This study indicates that happiness is related with boosted amygdala activationto both stimuli that is negative or positive. Despite there being research thatsuggests the amygdala has some sort of influence in happiness, it is clear thatthe amygdala is only associated with negative emotion.