Motivation and emotion/Book/2021/Neurostimulation and emotion

Overview
Emotions are feelings or neural states trigger by experiences occurring around an individual which can cause dysfunction if expressed to a great intensity (Adolphs, 2010). This is when emotion regulation comes in place – it is when an individual has conscious control and can bring their emotions to a normal level (Clarke et al., 2020). Activities in the brain lead to emotional responses, and modulation of the brain through neurostimulation can trigger the production of neurotransmitters that control emotions involved when individuals experience an inhibition in the brain (Knotkova et al., 2016). This chapter discusses what neurostimulation is and its effects on emotion.


 * What is neurostimulation?
 * What is the relationship between neurostimulation and the brain?
 * How does neurostimulation affect emotional responses?

 Aciel is a 20-year-old university student studying full-time and working part-time. He was diagnosed with depression as a teen and is taking prescription medication for it. He often feels gloomy at random times and at great intensity. One day, he had an episode that put him in a state that he has not experienced before. He then wonders if the medication is working at all as he seems to think that it does not change the state of his emotions. He then starts looking for other options to help his condition.

What is neurostimulation?


Neurostimulation is an emerging topic in neuroscience research (Dubreuil-Vall et al., 2019). It is the modification of the neural activity that can be used to help with the treatment of neuropsychological disorders and the improvement of cognitive functions (Westwood & Romani, 2017). Neurostimulation aims to help areas of the body surrounded by the nervous system - namely the brain and the spinal cord (Knotkova et al., 2016). All processes involve sending electric signals to target various parts of the body for pain relief and/or modulation of neurotransmitters’ activity in the brain (Knotkova et al., 2016).

Neurostimulation comprises a variety of procedures that aim to stimulate neural activities in the brain and the spinal cord when inhibition of neurotransmitters occurs (Knotkova et al., 2016). Due to the nature of the procedures, it is now widely used in clinical settings such as hospitals and clinics that specialise in administering neurostimulation therapy.

Means of modulation
There are various types of neurostimulation devices with different delivery methods. They can either be invasive or non-invasive (Knotkova et al., 2016).

Invasive
Invasive stimulations involve direct contact with the target part of the organ of concern which can be done through neurosurgery implantation of electrodes into the nerves (Plow & Machado, 2013; Schwedt & Vargas, 2015). There are several kinds of invasive neurostimulation, but the most common procedures are deep brain stimulation and vagal nerve stimulation (Schwedt & Vargas, 2015).

Deep brain stimulation is conducted by implanting electrodes in parts of the brain that is affected by trauma or injury (Schwedt & Vargas, 2015). It was also described by Schwedt and Vargas (2015) that it is mostly used to reduce motor movement injuries. On the other hand, vagal nerve stimulation is conducted similarly but only targets the vagus nerve of the nervous system.

Non-invasive
Compared to invasive stimulations, non-invasive stimulations are deemed to be safer and more ethical in terms of the procedures as the process occurs externally through shockwaves delivered through a piece of equipment (Kelly et al., 2019). It is also considered to be more practical and convenient about the reliability of the measure – with some procedures having to be repeated in a given length of time between sessions (Dubreuil-Vall et al., 2019). Examples include transcranial direct stimulation (tCDS) (as shown in figure 1) and transcranial magnetic stimulation (TMS) (Grazzi, 2015).

tDCS and TMS are often used when the patients' bodies' are resistant to the primary treatment they have - either their prescribed medicine or therapy (De Raedt et al., 2015). It is perceived to be an additional type of treatment especially for patients with psychological disorders. As it does not require surgical procedures, people might find it more convenient to take it as a treatment.

Treatment of illnesses using neurostimulation
Many studies have shown the use of neurostimulation as a treatment for various illnesses. It has been known that tCDS responses to the decreased neuroplasticity (the ability to recover neural activities) in the brain of individuals with diagnosed psychotic disorders like schizophrenia (Brunoni et al., 2014). It is also widely used in treating mood disorders such as depression and bipolar disorders in clinical settings as well as neurological conditions such as chronic migraines and headaches (Schwedt & Vargas, 2015).

Neurostimulation is also used to treat physical illnesses caused by injuries or trauma of the sensory organs and the nerves involved in the physical movements (Patel et al., 2017). Examples are highlighted in Plow and Machado’s (2013) study where invasive stimulation is used to treat stroke patients and guide them into recovery and in Schwedt and Vargas' (2015) research about vagal nerve stimulation which is mainly used for the treatment of epilepsy.

Physiological mechanisms


With the nature of emotions, it is important to know what part of the body is in charge of facilitating it. As the main core of emotional responses, the brain is targeted during neurostimulation with the purpose of emotion regulation (Knotkova et al., 2016). There are different regions in the brain, however, the limbic system contains the primary parts involved in triggering emotions (Boggio et al., 2009).

The brain and emotion
Areas of the brain are classified into cortical and subcortical (Reeve, 2018). For further elaboration, the cortical area of the brain is concerned about cognitive functions whilst the subcortical area assists in emotional urges. It is underpinned that with the identification of the emotional brain, the limbic system would be found in the cerebral cortex of the brain as it houses the subcortical region (Reeve, 2018).

Limbic system
There are different regions in the brain, however, the limbic system contains the primary parts involved in triggering emotions (Boggio et al., 2009). The limbic system contains the following parts with their respective functions in emotions (Guy-Evans, 2021):


 * Amygdala – main area for emotional responses (happiness, sadness, and anger)
 * Hypothalamus – regulation of the body’s homeostasis but if impairment occurs, it can cause imbalances of hormones that can ultimately lead to mood disorders
 * Cingulate gyrus – regulation of emotions (fear and avoidance), damage to this area can lead to improper responses (dysfunction)

Neurotransmitters
The brain contains neurotransmitters, produced by the body to deliver signals to cells to regulate bodily functions, that are mainly responsible for emotions (Wang et al., 2020).

As they carry a fundamental role in regulating emotions, imbalance in these neurotransmitters can cause dysfunctional responses to external stimuli (Reeve, 2018). This can also lead to the development of psychological disorders, i.e depression is there is lack of serotonin, schizophrenia for lack of dopamine, and attention deficit hyperactivity disorder (ADHD) for lack of norepinephrine (Wang et al., 2020).

The brain and neurostimulation
During neurostimulation, the effectiveness of cognitive functions and brain activity increases as intensity levels are manipulated (Dubreuil-Vall et al., 2019). Extensively mentioned by Adolphs (2010), the brain has countless links with the body’s responses caused by stimuli through neurons. Conduction of neurostimulation not only stimulates the brain but also increases neural plasticity through the elevated activation of action potential in neurons achieved by the electric signals imposed (Thibaut et al., 2017).

 After the episode, he decided to go to the doctors and was hopeful to get a proper diagnosis due to what has occurred. From then, his doctor notified him that he has now been diagnosed with clinical depression. He got offered a new treatment approach - neurostimulation.

How does neurostimulation affect emotion?


Research has shown the relevance of neurostimulation in terms of emotion regulation (Clarke et al., 2020). If there is inhibition of certain neurotransmitters, neurostimulation processes can trigger the firing of neurons to balance neural activities in the brain (Thibaut et al., 2017).

Use of non-invasive neurostimulation
Although there are various types of neurostimulation procedures, not all can apply to the regulation of emotions. It is perceived that the use of non-invasive neurostimulation can be more efficient to use for procedures involving modulation of the emotional brain (Kelly et al., 2019). Two of the most commonly used neurostimulation devices are transcranial magnetic stimulation (TMS) (as seen in figure 3) and transcranial direct current stimulation (tDCS) – which might appear to be the same for some but has their distinctiveness (De Raedt et al., 2015).

Process of neurostimulation in emotion regulation
Both procedures (TMS and tDCS) involve the use of equipment on the patient’s head and can both be used for situations of depressive and anxious symptoms but the procedures differ in how long and intense the electric signals are. De Raedt et al. (2015) stated that TMS activates the neurons themselves but tDCS can only control the action potentials (start-up) of neurons. However, both procedures are still effective as a treatment for some mental illnesses.



The neurotransmitters serotonin and dopamine are in charge of the emotions of sadness and happiness respectively (Wang et al., 2020). Low levels of production of serotonin can cause depressive and anxious symptoms which then leads to physicians prescribing selective serotonin reuptake inhibitors (SSRIs) as one of the primary treatments (De Raedt et al., 2015). In cases where medicine is not as effective as they were ought to be, the use of neurostimulation might be used to reduce the symptoms of depression and anxiety (Cirillo et al., 2019).

For TMS, a metal rod with a magnetic coil at the end is used to stimulate neurons by generating electrical signals to allow the production of neural synapses (De Raedt et al., 2015). With tDCS, electrode patches are placed into several specific parts of the scalp to match with the parts underneath in the brain to ensure equal distribution of electrical signals (De Raedt et al., 2015).

Both of the procedures are conducted just above the patient's head which creates a magnetic field for the primary electrical current to reach the neurons in the brain. There needs to be a second electric current to be conducted for action potential (see figure 4) to happen and signals the neurons to release the neurotransmitter that the patient is lacking (Cirillo et al., 2019). In parts of the brain that has a disparity of emotional responses, neurostimulation will be able to balance it out by "forcing" the neurons to release neurotransmitters through the emission of electric current or voltage and stabilise the level of emotions (De Raedt et al., 2015).

Application to psychological disorders
As it is applicable for various disorders, studies have shown that neurostimulation is turning out to be one of the treatments that specialists can use along with the medicinal prescription or therapy that clients or patients might be taking (Andò et al., 2021; De Raedt et al., 2015). Cirillo et al.'s review (2019) of TMS showed positive results as participants with posttraumatic stress disorder (PTSD) and generalised anxiety disorder (GAD) were found to have improved symptoms after conducting TMS. It is also applied in the treatment of the major depressive disorder (MDD) in addition to the conduction of initial treatments (De Raedt et al., 2015). There was not enough research about tDCS as it is a fairly new procedure based on TMS but it can be depicted from surfacing meta-analyses, it is very likely to be more available for treatment (Clarke et al., 2020; De Raedt et al., 2015).

 Aciel explored the different types of neurostimulation and narrowed it down to two - transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). Ultimately, he decided to go with tDCS as it works better with his schedule - with it being time-effective and accessible.

Two months after regular sessions of tDCS, Aciel found himself to have less intense depressive episodes. tDCS did not completely get rid of his depression symptoms, but he is glad to have found a process to help him put his emotions on a more normal level.

Conclusion
Neurostimulation regulates the body’s nervous system in a way that can be direct (invasive) or indirect (non-invasive). It is also one of the many techniques in neuroscience that is constantly being developed to reach a wide scope of applicability. It allows the modification of neural activity in the brain to achieve chemical balance and avoid the lack of neurotransmitters that can potentially lead to disorders. As the centre for emotional responses, it is evident that neurostimulation can be of great help when an imbalance between the neurological messengers in the brain occurs. Albeit relevant to many fields of neurology, it is emerging as a promising approach to treating psychological illnesses, especially in mood disorders like depression and bipolar disorder, as well as anxiety and PTSD.

Take-home message:  Neurostimulation presents positive effects on the regulation of emotions and can be used as a treatment for psychological disorders.