This this evaluation will be looking into research

This essay
will evaluate the role of neural structures in subserving emotion. The
neural structures are part of the nervous system in the human brain. The
structure 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 the
temporal lobes of the brain (Amunts
et al., 2005). The amygdala has been called by many as being part of the
neural circuitry critical for emotion (Gallagher & Chiba., 1996) (18) and it is
suggested that one of the principal roles of the amygdala is emotional
reactions. Emotions such as aggression and depression have been associated with
the amygdala, yet the prime example of the amygdala being associated with
emotion, with an overwhelming amount of evidence to support, is fear and
anxiety. However, it cannot be ignored that it is not the only neural structure
at play, with some researchers finding evidence that undermines the
significance of the amygdala and its link to fear. With the staggering amount
of research into negative emotion and the amygdala, it begs the question as to
what significance it possesses concerning positive emotions and their link to
this neural structure, with this being explored further in this evaluation. As
well as this, this evaluation will be looking into research measures and how
they may alter the reliability of the vast amount of research into emotion to
create a better evaluation concerning this specific neural structure.

 

With research into the amygdala showing links to the
psychological function, emotion, this evaluation begins with, aggression. A
study which looked at the social behaviour of a rat found that lesions to the
amygdala lessened the level of shock-induced aggression (Kolb & Nonneman., 1974).
This shows that even early on in research into the amygdala there appears to be
a link to the emotion aggression. Furthermore, an experiment which explored
facial expression recognition in bilateral amygdala-damaged patients supported
the idea that the amygdala has significant influence on aggression, as these
patients have impaired processing of facial expressions that were related to
particular negative emotions, specifically fear and anger (Sato et al., 2002). This
research comes from animal studies which conveys that when the stimulation of
the amygdala occurs, it increases aggressive behaviour. Similarly, studies that
have used brain lesions have conveyed that harm to the amygdala may generate
the reverse effect. Therefore, it would seem that this area of the brain may
play a part in the display and modulation of aggression (Brink., 2008) (15). Stimulation
of the amygdala consequences in amplified aggressive behaviour, while lesions
of this area significantly moderate an individual’s aggression. A particular
interesting study found that the volume of the amygdala may change how
aggressive an individual is. Participants who scored higher in aggression had a
16-18% reduction in amygdala volumes (Matthies et al., 2012). This suggests that the
volume of someone’s amygdala plays an important role. A further study to support this shows evidence of
amygdala-OFC dysfunction in response to processing angry faces in participants
that have a history and record of impulsive aggressive behaviour and this
further validates a link concerning a dysfunctional cortico-limbic network and
aggression (Coccaro
et al., 2007) (29). However, a study contradicts these findings, looked
into amygdala volumes in female and depressed humans. The research conveyed
that there were no significant findings linked to aggression (Elst et al., 2000) (28).
On the other hand, the study did find that depressed patients exhibited
significant enlargement of both left and right amygdala, therefore the
amygdala’s involvement in negative emotion is still prevalent. This can be
further seen in the mental disorder, major depressive disorder. This disorder
has been argued to be linked with volumetric abnormality in the amygdala, and
that the size of the amygdala is increased significantly in depressed
individuals compared to healthy people (Hamilton, Siemer & Gotlib., 2008) (30). There
is a vast amount of research which backs the theory that the amygdala
stimulates and causes depression-like emotional experiences. However, the specificity
as to how the amygdala effects this emotion is still unclear, as seen in Yang
et al (2010) (31) who
conducted a study that looked into adolescents with depression and the
involvement of the amygdala. The results found significant bilateral amygdala
activation in both the healthy and depressed teenagers. In addition, there was
greater left amygdala activation in the depressed adolescents in comparison to
the controls. More research should be conducted in adolescents and even
children 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 with
the amygdala. Fear has been defined by Ethologists as a motivational
state which is stimulated by certain stimuli that escalate to defensive
behaviour or an attempt to escape (McFarland, 1987). Anxiety can be defined as having a generalised
reaction 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 reactions
and responses (Steimer,
2002).  It
has been argued and stated that the amygdala is referred to as the ‘fear
centre’. This is evident in patients that have a genetic condition that is
extremely rare; Urbach-Wiethe disease. A particularly well-known case study is
patient S.M. Suffering from amygdala damage, patient SM appeared to have
strange fear reactions as well as a reduced experience of fear. The study
concluded 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 fear
itself (Feinstein et al.,
2011). As mentioned previously, the amygdala is referred to as the “fear
centre”, some scientists are so sure of the statement that they state that in the future they may be nearer
to helping those with debilitating fear and stress-related psychopathology (Ressler., 2010). This
suggests that they have full belief that the amygdala is in fact the neural
structure that controls fear.

There has also been a vast amount
of research which looks into the link between the amygdala and anxiety. The
amygdala has been implied in anxiety as well as mental disorders such as PTDS
and phobias where anxiety is a prominent symptom (Etkin & Wager., 2007). (14) Focusing on
Posttraumatic stress disorder (PTSD), there is research that conveys it appears
to combine features of both extreme ‘stress responsiveness and either enhanced conditioned fear or an
inability to extinguish, or inhibit conditioned fear’. (Ressler., 2010). Shin and
Liberzon (2010) stated
moderately amplified amygdala activation in response to disorder-relevant
stimuli in social phobia, PTSD, and specific phobia. In addition to this,
numerous neuroimaging studies have exhibited that participants that suffer with
PTSD have superior amygdala activation in comparison to the control group (Liberzon & Sripada., 2007).
When looking at anxiety and the
role of neural structures, a study that looked at generalised anxiety disorder
(GAD) identified and found abnormal amygdala and prefrontal cortex activation
in participants and reduced connectivity amid these areas. Additionally, it
conveyed amplified ‘grey matter volume and ‘shrunken ‘structural connectivity concerning
these structures.’ (Hilbert
et al., 2014).  This shows that
there is a distinctive ‘set of
neurobiological alterations in Generalised anxiety disorder’ and that
the amygdala as well as other neural structures play a part in anxiety as a
whole. Overall, you cannot ignore the overwhelming amount of research that
conveys that the amygdala appears to be the home to fear and also anxiety. (Change).  

 

However, when looking at
the amygdala and its role, it must also be noted that it is not solely down to
this neural structure and that others also are to be credited. Rauch and Shin (Davis., 2002) (12) state
that numerous brain areas contribute and provide vital feedback to the amygdala
including the medial frontal cortex, the hippocampus and the corticostriatothalamic circuits.
The hippocampus delivers information regarding the context of the situation, as
well as the medial frontal cortex providing ‘critical “top-down” governance over the amygdala, therefore
permitting attenuation of the fear response once danger has passed or when the
meaning of a potentially threatening stimulus has changed” (Davis., 2002). This
conveys that although the amygdala ultimately ends up being central to fear,
other neural structures are used in the process. As well as the amygdala being
heavily involved in negative emotion, there is research that suggests that the
amygdala is involved with memory. When a memory is emotionally significant to
an individual it activates brain and hormonal systems which control the strengthening
of obtained new memories. These effects are incorporated via noradrenergic activation
of the basolateral amygdala which regulates and controls memory consolidation
through interactions with various other brain regions that are linked to
consolidating memories of recent experiences (Mcgaugh & Roozendaal., 2008).

Whilst it may seem at first glance that there is an overwhelming
amount of evidence to support the statement that the amygdala is in fact ‘the
fear centre’, some researchers have contradicted this idea. Firstly, LeDoux (2015), argues that people
with damage to the amygdala are indeed less responsive to threats however they
can still feel and experience fear. He interprets previous findings by stating
that the amygdala is a vital part of the circuit that permits the brain to
identify and react to the threat but is not compulsory to feel fear. In
addition to this, there are various studies that have studied neural mechanisms
of emotion and have concentrated on individual differences. A particular study
by Adolphs et al (1999)
(11), looked at 9 participants who all suffered from bilateral damage. All
participants had issues with identifying the emotion of fear, however there was
found to be individual differences in the group of participants. Some
participants found difficulty in identifying negative emotions whereas on the
other hand two of the patients conveyed little issue with identifying emotions
in 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 that
is linked to fear. Neural structures may play various and changeable roles in
experiencing emotion subject to the person; and that further research needs to
be done to explore this idea so that these sorts of findings become relevant. Furthermore,
another study looked into neural correlates of individual difference in fear
and anxiety (Ochsner et
al., 2006). The results conclude that the findings displayed should help
explain firstly the influence of individual differences in emotion on the
neural correlates of pain, and the functions of anxiety, pain processing and
fear, participated by medial and orbitofrontal systems. With all of this in
mind, LeDoux (1996)
stated that many will be quick to conclude that the amygdala is the centre of
emotion reaction in the brain due to the vast amount of empirical evidence.
However, there are clearly other structures and networks that are involved in
emotional processing. More research should be done on the role of the neural
system in emotion so it can be fully understood. (LeDoux., 1994., LeDoux & Rogan., 1996).

 

There is also the issue that the amygdala is often only discussed
when evaluating negative emotion, suggesting that its role in effecting emotion
is limited. One emotion that has not been shown as being affected by the
amygdala is happiness. Some suggest that the neural processes of happiness are
the complete opposite to those that process depression and anxiety (Cunningham & Kirkland., 2013)
(25).  The human amygdala when in
response to emotion is most often found to show significant reactions to
fearful expression as opposed to happy ones (Morris et al., 1996) (23).  In a particular study, masked happy faces were
linked with significant bilateral activation in the amygdala and the anterior
cingulate gyrus, in comparison to masked sadness which produced only reduced
activation in the left anterior cingulate gyrus. In contrast, it was found that
masked happy faces further generated significantly higher activation in the
amygdala and anterior cingulate in relation to identically masked sad faces. These
results propose that the anterior cingulate and the amygdala are vital factors
of a network involved in identifying affective information beneath the standard
threshold of conscious visual perception (Killgore & Yurgelun-Todd., 2004) (22). However,
to some, it remains controversial as to whether the amygdala is involved in
emotions like happiness. In a study that looked into identifying expressions
from unilateral amygdala damage and complete bilateral amygdala damage, the
findings conveyed that participants with bilateral amygdala damage performed
normally at rating happy faces however the participants with right unilateral
amygdala damage performed worse overall than participants with left unilateral
amygdala damage (Adolphs
& Tranel., 2004). This leaves an area for slight confusion as to
whether individuals with right unilateral amygdala damage could not identify
happiness. Moreover, an interesting study suggests that happiness is linked
with 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 to
positive (however not negative) stimuli in happiness. Participants that were
deemed happier portrayed greater amygdala responses to stimuli that was positive.
This study indicates that happiness is related with boosted amygdala activation
to both stimuli that is negative or positive. Despite there being research that
suggests the amygdala has some sort of influence in happiness, it is clear that
the amygdala is only associated with negative emotion. 

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