1 NAME COURSE TITLE
2 TO BE MOTIVATED IS TO HAVE AN INCREASE IN DOPAMINE The statement to be motivated is to have an increase in dopamine implies that an increase in dopamine neurotransmitter, up-regulation of dopamine receptors, or stimulation of dopamine pathways with either drugs or enforcer is observed during motivation. Dopamine pathways are found mainly in the frontal cortex and limbic system where dopamine functions in the regulation of motivation or reward, pleasure, euphoria, fine tuning of motor function, compulsion, and preservation. Disorders such as addiction, obesity, or attention deficit hyperactive disorder are attributed to dysregulation of motivation, and the common finding in the disorders is reduced binding of dopamine in the striatum (Trifilieff, 2013). It is asserted that dopamine increases when an individual is motivated because dopamine is a neurotransmitter that is associated with regulation of motivation or reward accrued from normal activities vital for survival. The motivated behaviour, for example, the will to increase efforts towards achieving a goal is linked to the increase in dopamine, receptor over-expression, or enhanced performance of dopamine pathways (Trifilieff, 2013). The observations that link motivation to dopamine increase are the rationale for this study which aims to evaluate critically the statement to be motivated is to have an increase in dopamine by reviewing experimental studies that investigated the relationship between motivation and dopamine. Earlier studies involving songbirds observed a vital role of the medial preoptic nucleus, dopamine, and dopamine receptors regarding vocal communication when it is a season for the birds to breed (Riters et al. 2014). Male songbirds produce variations of vocal communication when sexually or agonistically motivated. The male birds are sexually motivated to sing and attract female birds to reproduce for their continued survival. Riters et al. (2014) organized an
3 experiment to investigate the hypothesis stating that stimulation of dopamine receptors or increase in dopamine is responsible for motivating male songbirds sexually. Male songbirds in breeding condition were injected with either normal saline or different dosages of dopamine receptor agonist into the hypothalamus. The findings showed that the birds that received dopamine receptor agonist produced songs to attract females sexually. The birds did not produce songs for breeding at very low or high dosages of dopamine receptor agonist and with normal saline (Riters et al. 2014). The experiment demonstrated that increase in dopamine receptor stimulation at an optimum level is responsible for motivating the male songbirds sexually. Therefore, motivation is associated with elevated dopamine levels because the increase enhances the stimulation of dopamine receptors up to an optimum level. Motivation in human beings is influenced by instrumental and Pavlovian systems interaction. Neurotransmitters such as dopamine contribute significantly in such interactions, but their mechanism has not been investigated conclusively. Hebart (2015) investigated the influence of dopamine in instrumental and Pavlovian interaction by measuring aversive and appetitive responses. The experimental group was exposed to a diet that is selectively depleted of precursor amino acids for dopamine, tyrosine or phenylalanine, and their performance compared with the control group that was exposed to a normal diet with dopamine precursor amino acids. There was a reduction in appetitive response in the experimental group which indicated that dopamine is responsible for appetitive motivation; therefore, a person s appetitive motivation decreases with depletion of dopamine due to the deprivation of amino acid precursors for dopamine (Hebart, 2015). It can be derived that dopamine is involved in motivated behaviour, for example, an increase of dopamine motivates appetitive stimuli or behaviour. Although dopamine as a
4 neurotransmitter influences the motivation of adaptive or flexible behaviour, its mechanism cannot be established conclusively. Dopamine confers antinociceptive and motivation effects necessary in enduring unpleasant stimuli to accrue reward. The mechanism of dopamine to achieve its role of motivation to get reward can be explained by inhibition of nociceptive stimuli perception or facilitation of bias which helps in avoidance or perseverance of unpleasant stimuli (Becker, 2013). Motivation is important in prioritizing reward at the expense of nociceptive input, in a benefit or cost related pattern. The motivation for essential rewards such as food comes with both cost and benefits, for example, food palatability, specific behaviour adaptation, and homeostatic state. Barbano (2009) investigated the role of endogenous dopamine in the regulation of motivation to obtain food in a set up where behavioural change and motor requirements were indispensable to access reward. In the experiment, restricted and sated rats were provided with pellets with varied palatability. Peripheral administration of both flupenthixol and naloxone were used to modify opioid neurotransmission. Motivation state was measured regarding behavioural change, motor output, and operant ratio of task. The study found that impairment of neurotransmission resulted in a reduction of motivation to obtain a reward in spite of the food being palatable (Barbano, 2009). Evidence points that dopamine is involved in motivation to get a reward such as food despite the requirements in a cost-benefit pattern. A decrease in dopamine or impairment of dopaminergic systems reduces the ability to endure unpleasant condition to obtain food. Attention-deficit hyperactive disorder (ADHD) presents with impulsivity, inattention, and motivation deficits. Considering that several studies have demonstrated the role of dopamine in
5 motivation, assessment of ADHD patients can show impaired function of dopamine pathways in the brain which explains motivation deficits in ADHD. Volkow et al. (2011) assessed dopamine motivation pathways using positron emission tomography (PET), in adult patients suffering from ADHD. The PET measurements of dopamine transporter availability and receptors obtained with cocaine and raclopride respectively were correlated with trait motivation surrogate measures in 45 ADHD patients and 41 controls. The findings showed that ADHD patients with disruption of the dopamine motivation pathways had motivation deficits (Volkow et al. 2011). Motivation deficits were also associated with attention deficits; therefore, ADHD patients require therapeutic interventions that improve their motivation. It is important to note that this study confirmed that a decrease in dopamine, disruption in dopamine pathways, or down-regulation of receptors reduces motivation significantly and vice versa. Motivation is fundamental as an element for sustaining behaviours that are successful in surviving, in dynamic environments. People are motivated to embrace actions when they predict a positive outcome as a reward for their behaviour. Discoveries in the field of neuroscience have suggested that the neurotransmitter dopamine plays a central role mediating rewarding behaviour (Gepshtein et al. 2014). The mediation is attributed to the encoding of outcome and expected rewards of active actions or behaviour during dopamine cell firing. Although dopamine cells have no direct role in specific motor movements, tonic dopamine levels in the human dorsal striatum encode for sensitivity to the cost of precise motor actions regarding energy consumption (Gepshtein et al. 2014). Dopamine increases when there is a need for humans to execute a particular rewarding normal movement; therefore, high levels of dopamine neurotransmitter is associated with signalling motor motivation.
6 Gepshtein et al. (2014) investigated the motor motivation aspect of dopamine by comparing the motor performance of patients suffering from Parkinson disease with that of healthy elderly people. The dorsal striatum of patients suffering from Parkinson disease has a significant depletion of dopamine neurotransmitter. The participants were subjected to performing rapid movements in sequence towards visible targets. The targets were associated with various energy cost, risks, and they were assisted or encountered gravity in some cases. The findings showed that Parkinson patients performed well in circumstances that required low energy cost similar to healthy elderly people. However, the performance of the patients deteriorated significantly, as compared to healthy people as the energy cost demand for performing movements increased (Gepshtein et al. 2014). The study supported the assertion claiming that a rise in dopamine increases motor motivation; therefore, Parkinson patients who have depleted dopamine levels cannot achieve the required amount of motor motivation to cope up with the high energy cost. Apart from neuronal motor deficits in Parkinson disease, there are significant aberrations with both affective and motivational aspects. Classical motor symptoms are caused by the dopaminergic neurons degeneration at the pars compacta of substantia nigra (SNc). The impairment of dopaminergic neurons affects dopamine pathways, levels, and receptors which result in the impairment of motivation observed in Parkinson patients. Impairment of motivation is also attributed to neuron loss in the ventral tegmental area (VTA) as well as psychological reactions towards debilitating motor deficits (Drui et al. 2014). In a study by Drui et al. (2014) aimed at mapping areas of the brain to find out particular regions causing motivation impairment in Parkinson disease, lesions were induced selectively in the SNc dopaminergic neurons and VTA without causing motor deficits. The outcome showed that affective and motivational
7 deficits were caused by bilateral loss of dopamine in the SNc resulting in symptoms similar to the ones in Parkinson disease. Lesions in the VTA did not cause motivational and affective deficits. The study confirmed that affective and motivational deficits, which are core impairments is Parkinson disease, are associated with degeneration of SNc dopaminergic neurons. Anhedonia hypothesis coined by Wise gives insight into the role of dopamine in the motivation of behaviours. The theory asserted that obtainment of reward results in some pleasure being experienced, and this is mediated or motivated by dopamine. However, most recent experimental studies have contested such assertions and argue that dopamine motivates behaviour by encoding for the preparation of behaviour while opioids mediate hedonic properties perceived with rewards or motivation (Barbano, 2007). In one of the studies by Barbano (2007), the role of opioids and dopamine in feeding were examined alongside components such as motivation, consumption, anticipation, physiological state, and palatability of food. The results of the reexamination indicated that dopamine is associated with preparatory or anticipatory aspects rather than use or motivational aspects of feeding. Preparatory or anticipatory role of dopamine is associated with stimuli, for example, palatability of food. Dopamine motivates feeding behaviour, but at preparatory and anticipatory stages. The argument by Wise that dopamine is vital for reward, and that increase in dopamine levels takes place during motivation has been constantly challenged (Wise, 2004). Studies have demonstrated that motivating or rewarding stimuli, for example, water, food, stimulation of the lateral hypothalamic brain, various drugs abused are sometime not effective when dopamine
8 antagonists are administered to animals at doses that spare performance (Wise, 2004). Such findings support the role of dopamine in motivation or reward and provide merit against assertions that challenge the hypothesis stating that dopamine is responsible for motivation or reward. A lot of evidence still supports the increase of dopamine and the role it plays in motivation despite different schools of thought that challenge dopamine role in motivation. For example, the efficacy of unconditional rewards is linked to the production of dopamine in the nucleus accumbens. To attach importance of motivation to neutral stimuli in the environment, dopamine must be released in various structures in the brain because the neurotransmitter stamps in the memory associated with motivation (Wise, 2004). The study by Wise has indicated that dopamine is vital for motivation and in memorizing the importance of motivation in daily activities that are indispensable for survival. The aim of this paper was to evaluate critically the statement to be motivated is to have an increase in dopamine. The evaluation has found that most evidence agrees with this statement despite some schools of thought arguing otherwise. It was found that increase in dopamine levels motivate songbirds sexually. Dopamine also functions to motivate behavior associated with appetitive stimuli. The motivation derived from dopamine helps in enduring unpleasant circumstances to obtain a reward, and impairment of dopamine pathways responsible for motivation deficits observed in Parkinson disease and ADHD. For example, signaling of motor motivation is deficient in Parkinson disease because dopamine function is diminished. It is worth understanding that dopamine helps in storage of memory about rewarding or motivating behavior. There is a gap of knowledge regarding the mechanism through which dopamine influences motivation. Contrary to the assertions that dopamine motivates behaviors that are
9 essential for survival such as feeding, new evidence shows that dopamine has a role at anticipatory or preparatory stages only and not consumption or motivational aspects of feeding.
10 References Barbano, MM 2009, 'Involvement of dopamine and opioids in the motivation to eat: influence of palatability, homeostatic state, and behavioral paradigms', Psychopharmacology, 203, 3, pp. 475-487. Barbano, MM 2007, 'Opioids for hedonic experience and dopamine to get ready for it', Psychopharmacology, 191, 3, pp. 497-506. Becker, SP 2013, 'The role of dopamine in the perceptual modulation of nociceptive stimuli by monetary wins or losses', European Journal Of Neuroscience, 38, 7, pp. 3080-3088. Drui, G, Carnicella, S, Carcenac, C, Favier, M, Bertrand, A, Boulet, S, & Savasta, M 2014, 'Loss of dopaminergic nigrostriatal neurons accounts for the motivational and affective deficits in Parkinson's disease', Molecular Psychiatry, 19, 3, pp. 358-367. Gepshtein, S, Li, X, Snider, J, Plank, M, Lee, D, & Poizner, H 2014, 'Dopamine function and the efficiency of human movement', Journal Of Cognitive Neuroscience, 26, 3, pp. 645-657. Hebart, MJ 2015, 'Serotonin and dopamine differentially affect appetitive and aversive general Pavlovian-to-instrumental transfer', Psychopharmacology, 232, 2, pp. 437-451. Riters, L, Pawlisch, B, Kelm-Nelson, C, & Stevenson, S 2014, 'Inverted-U shaped effects of D1 dopamine receptor stimulation in the medial preoptic nucleus on sexually motivated song in male European starlings', European Journal Of Neuroscience, 39, 4, pp. 650-662. Trifilieff, PA 2013, 'Increasing dopamine D2 receptor expression in the adult nucleus accumbens enhances motivation', Molecular Psychiatry, 18, 9, pp. 1025-1033. Volkow, NM 2011, 'Motivation deficit in ADHD is associated with dysfunction of the dopamine reward pathway', Molecular Psychiatry, 16, 11, pp. 1147-1154.
11 Wise, RA 2004, 'Dopamine, learning and motivation', Nature Reviews Neuroscience, 5, 6, pp. 483-12.