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Autori: Šimić, Goran
Naslov: Functional neuroanatomy of the brain reward system and the impact of early emotional experience on adult capacity for social attachment
Dio CC časopisa: NE
Skup: 9. Zagreb International Medical Summit - Opening lecture
Mjesto i datum: Zagreb, Hrvatska, 12-15.11.2009.
Ključne riječi: amygdala; autism; mesolimbic and mesocortical dopaminergic projections; drug abuse; emotional development; fMRI; maternal bonding; orbitofrontal cortex; oxytocin; paternal behavior; rearing conditions; social attachment; stress
There is accumulated evidence that the core of the brain reward system is composed of dopaminergic projections from ventral tegmental area (VTA) to amygdaloid complex of nuclei (AMY) and orbito-frontal cortex (OFC). These mesolimbic and mesocortical projections release dopamine at higher rate during pleasant experiences of eating food, having sex or bonding with a child (behavioral activation, step 1). Many drugs such as cocaine, amphetamines, opioids, canabinoids, nicotine and (to a lesser extent) alcohol, are acting the same way. It has been shown that the firing frequency of these dopaminergic projections is the signaling mechanism coding for an error value in prediction of reward, which directly correlates with the motivational levels (Arrias-Carrion and Poppel, Acta Neurobiol Exp, 2007). When a reward is greater than expected, the firing of certain VTA dopaminergic neurons increases, consequently increasing the desire or motivation toward the reward in OFC. As documented in experimental models using "water vs. cocaine" paradigm it is the OFC glutamatergic projections that regulate activation of motor responses to such "motivation-related events" through thalamic motor nuclei and n. accumbens septi, while e.g. blocking dopamine D1 receptors in OFC prevents drug-seeking behavior (direction of behavior or "choice", step 2). In the case of a failure to achieve planned goals, particularly in the long term (chronic stress) where free cortisol levels are elevated, the reward mechanism is often activated by the compensatory "displaced behavior", such as overeating. While many people also experiment with drugs, relatively few individuals develop a true addiction. It has been hypothesized that such individual differences might be determined by early emotional experience. In one of the experimental models (Brake et al., Eur J Neurosci, 2004) maternally separated and non-handled animals were shown to be hyperactive when placed in a novel setting and displayed a dose-dependent higher sensitivity to cocaine and amphetamine-induced locomotor activity. They also responded to a mild stressor (tail-pinch) with significantly greater increases in nucleus accumbens dopamine levels, and increased dopamine D3 receptor binding and mRNA levels. Due to change in regulation of motivation circuit and pathological long-term changes in synaptic plasticity of OFC neurons that project to ventral striatum, in the last phase (dependence and drug abuse, step 3) such patients are taking drugs compulsively. Together, these findings provide evidence that early postnatal rearing conditions can lead to profound and lasting changes in the responsiveness of mesocorticolimbic dopamine neurons to stress and stimulants. The early social attachment lies at the heart of emotional and social development of mammals. Several recent studies are adding to a body of literature that shows various neuropeptides, mainly oxytocin, vasopressin and corticotropin-releasing factor systems play a key role in maternal bonding and social affiliation (Ahern and Young, Front Behav Neurosci, 2009). Feldman and colleagues (Psychol Sci, 2007) demonstrated this association for the first time in people. Plasma oxytocin levels across pregnancy and postpartum period in 62 pregnant women predicted mother-infant bonding. Women with higher levels of oxytocin bonded better with their babies since oxytocin levels positively correlated with a clearly defined set of maternal behaviors, including gaze, vocalization, positive affect, affectionate touch, attachment-related thoughts and to frequent checking of the infant. Furthermore, it has been recently shown that mothers with secure attachment show greater activation of medial OFC, ventral striatum and the oxytocin-associated hypothalamic regions, while insecure/dismissing mothers showed greater insular activation in response to their own infant’ s sad faces (Strathearn et al., Neuropsychopharmacology, 2009). Likewise, animal studies demonstrated a developmental relationship between exposure to extra oxytocin in early life and subsequent maternal and social behaviors (Bales et al., Horm Behav, 2007). For instance, when prairie voles had received a low dose of oxytocin in early life, adult females were slow to approach pups ; when they received higher doses of the hormone were more likely to care for them (and no longer displayed a partner preference too). In one of the earlier studies (Wismer Fries et al., PNAS USA, 2005), urine levels of oxytocin and vasopressin were compared in two sets of children—one raised from birth with their biological parents and one adopted after living in orphanages in Russia and Romania—following contact with their mothers. The levels of oxytocin rose in the biological children but remained the same in the adopted children. These findings suggest there may be biological underpinnings for the observation that some adopted children, in particular those from deprived circumstances, have difficulty forming secure relationships, despite living in loving homes. Slight modulation in serotonin levels, turnover and metabolism, or in receptor type activation, density and binding activity is particularly important in this respect because it may strongly affect aggressive behavior. The recent data obtained by Nelson and Trainor (Nature Rev Neurosci, 2007) suggested that children carrying the short form of the MAOA promoter gene, which confers decreased MAOA activity, are more likely to develop conduct disorders and increased antisocial behaviour when exposed to abusive home environments (Casni et al., Science, 2002). Finally, it has been shown that children with autism have lower levels of circulating oxytocin (Modahl et al., Biol Psychiatry, 1998), while adults diagnosed with autism or Asperger's syndrome who received oxytocin showed an improved ability to identify emotional content on a speech comprehension task (while those on a placebo did not) (Hollander et al., Biol Psychiatry, 2007).
Vrsta sudjelovanja: Plenarno
Vrsta prezentacije u zborniku: Sažetak
Vrsta recenzije: Domaća recenzija
Projekt / tema: 108-1081870-1942
Izvorni jezik: ENG
Kategorija: Stručni
Znanstvena područja:
Temeljne medicinske znanosti,Kliničke medicinske znanosti,Psihologija
Tiskani medij: da
Upisao u CROSBI: (, 23. Stu. 2009. u 13:05 sati

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