The nucleus accumbens (NAc or NAcc), also known as the accumbens nucleus, or formerly as basolateral amygdala, ventral hippocampus, thalamic nuclei ( specifically the midline thalamic nuclei and intralaminar nuclei of the thalamus). The ventral anterior cingulate cortex includes subcallosal and precallosal portions that have extensive connections with the insula, prefrontal cortex, amygdala. Limbic System Panji Fakhruzzaman Teknik Elektro Amygdala Fungsi Amygdala Limbic System Sistem Limbik 1. Memegang.
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The nucleus accumbens NAc or NAccalso known as the accumbens nucleusor formerly as the nucleus accumbens septi Latin for nucleus adjacent to the septum is a region in the basal forebrain rostral to the preoptic area of the hypothalamus.
The ventral striatum and dorsal striatum collectively form the striatumwhich is the main component of the basal ganglia. These substructures have different morphology and functions. Different NAcc subregions core vs shell and neuron subpopulations within each region D1-type vs. D2-type medium spiny neurons wmygdala responsible for different cognitive functions. The nucleus accumbens is an aggregate of neurons which is described as having an outer shell and an inner core.
Major glutamatergic inputs to the nucleus accumbens include the prefrontal cortex particularly the prelimbic cortex and infralimbic cortexbasolateral amygdalaventral hippocampusthalamic nuclei specifically the midline thalamic nuclei and intralaminar nuclei of the thalamusand glutamatergic projections from the ventral tegmental area. The nucleus accumbens is often described amugdala one part of a cortico-basal ganglia-thalamo-cortical loop.
These neurons are activated directly or indirectly by euphoriant drugs e. Another major source of input comes from the CA1 and ventral subiculum of the hippocampus to the dorsomedial area of the nucleus accumbens. Slight depolarizations of cells in the nucleus accumbens correlates with positivity of the neurons of the hippocampus, making them more excitable.
The correlated cells of amyggdala excited states of the medium spiny neurons in the nucleus accumbens are shared equally between the subiculum and CA1. The nucleus accumbens is one of the few regions that receive histaminergic projections from the tuberomammillary nucleus fungi sole source of histamine neurons in the brain.
The output neurons of the nucleus accumbens send axonal projections to the basal ganglia and the ventral analog of the globus pallidusknown as the ventral pallidum VP.
The VP, in turn, projects to the medial dorsal nucleus of the dorsal thalamuswhich projects to the prefrontal cortex as well as the striatum. Other efferents from the nucleus accumbens include connections with the tail of the ventral tegmental area substantia nigraand the reticular formation of the pons. The nucleus accumbens shell NAcc shell is a substructure of the nucleus accumbens. The shell and core together form the entire nucleus accumbens.
The shell is the outer region of the nucleus accumbens, and — unlike the core — is considered to be part of the extended amygdalalocated at its rostral pole. Neurons in the nucleus accumbens are mostly medium spiny neurons MSNs containing mainly D1-type i.
The shell neurons project to the subcommissural part of the ventral pallidum as well as the ventral tegmental area and to extensive areas in the hypothalamus and extended amygdala. The shell of the nucleus accumbens is amygsala in the cognitive processing of rewardincluding subjective “liking” reactions to certain pleasurable stimulimotivational salienceand positive reinforcement.
The nucleus accumbens core NAcc core is the inner substructure of the nucleus accumbens. The nucleus accumbens core is part of the ventral striatumlocated within the basal ganglia. The core of the NAcc is made up mainly fuungsi medium spiny neurons containing mainly D1-type or D2-type dopamine receptors. The neurons in the core, as compared to the neurons in the shell, have an increased density of dendritic spinesbranch segments, and terminal segments. From the core, the neurons project to other sub-cortical areas such as the globus pallidus and the substantia nigra.
The nucleus accumbens core is involved in the cognitive processing of motor function related to reward and reinforcement and the regulation of slow-wave sleep.
Some of the neurotransmitters, amygdalaa, and hormones that signal through receptors within the nucleus accumbens include:. Dopamine is released into the nucleus accumbens following exposure to rewarding stimuliincluding recreational drugs like substituted amphetaminescocaineand morphine. Phenethylamine and tyramine are trace amines which are synthesized in neurons that express the aromatic amino acid hydroxylase AADC enzymewhich includes all dopaminergic neurons. Glucocorticoid receptors are the only corticosteroid receptors in the nucleus accumbens shell.
L-DOPA fujgsi, steroidsand specifically glucocorticoids are currently known to be the only known endogenous compounds that can induce psychotic problems, so understanding the hormonal control over dopaminergic projections with regard to glucocorticoid receptors fungis lead to new treatments for psychotic symptoms.
A recent study demonstrated that suppression of the glucocorticoid receptors led to a decrease in the release of dopamine, which may lead to future research involving anti-glucocorticoid drugs to potentially relieve psychotic symptoms. Overall, 5-HT synapses are more abundant and have a greater number of synaptic contacts in the NAc shell than in the core.
They are also larger and fungsl, and contain more large funsgi core vesicles than their counterparts in amygdaoa core. The nucleus accumbens, being one part of the reward systemplays an important role in processing rewarding stimuli, reinforcing stimuli e.
However, as BOLD is thought to be an indirect measure of regional net excitation to inhibition, the extent to which BOLD measures valence dependent processing is unknown. The nucleus accumbens is causally related to the experience of pleasure. In the nucleus accumbens as a whole, dopamine, GABA receptor agonist or AMPA xmygdala solely modify motivationwhile the same is true for opioid and endocannabinoids outside of the hotspot in the medial shell.
A rostro-caudal gradient exists for the enhancement of appetitive versus fearful responses, the later of which is traditionally thought to require only D1 receptor function, and the former of which requires both D1 and D2 function.
One interpretation of this finding, the disinhibition hypothesis, posits that inhibition of accumbens MSNs which are GABAergic disinhibits downstream structures, enabling the expression of appetitive or consummatory behaviors.
Stressful conditions can expand the fear inducing regions, while a amygdalla environment can reduce the size of the fear inducing region. Furthermore, cortical input from the orbitofrontal cortex OFC biases the response towards that of appetitive behavior, and infralimbic input, equivalent to the human subgenual cingulate cortex, suppresses the response amygdapa of valence.
The nucleus accumbens is neither necessary nor sufficient for instrumental learning, although manipulations can affect performance on instrumental learning tasks.
Amygdala hijack – Wikipedia
One task where the effect of NAc lesions is evident is Pavlovian-instrumental transfer PITwhere a cue paired with a specific or general reward can enhance instrumental responding. Lesions to the core of the NAc impair performance after devaluation and inhibit the effect of general PIT. On the other hand, lesions to the shell only impair the effect of specific PIT.
This distinction is thought to amgdala consummatory and appetitive amyvdala responses in the Amgdala shell and the NAc core, respectively.
In the dorsal striatum, a dichotomy has been observed between D1-MSNs and D2-MSNs, with the former being reinforcing and enhancing locomotion, and the latter being aversive and reducing locomotion.
Such a distinction has been traditionally assumed to apply to the nucleus accumbens as well, but evidence from pharmacological and optogenetics studies is conflicting. While most studies show no effect of selective optogenetic stimulation of D1 or D2 MSNs on locomotor activity, one study has reported a decrease in basal locomotion with D2-MSN stimulation. While two studies have reported reduced reinforcing effects of cocaine with D2-MSN activation, one study has reported no effect.
An fMRI study conducted in found that when mother rats were in the presence of their pups the regions of the brain involved in reinforcement, including the nucleus accumbens, were highly active.
Activation of D1-type MSNs in the amygdaka accumbens is involved in rewardwhereas the activation of D2-type MSNs in the nucleus accumbens promotes aversion. In latestudies on rodents which ffungsi optogenetic and chemogenetic methods found that the indirect pathway amygala. Current models of addiction from chronic drug use involve alterations in gene expression in the mesocorticolimbic projection.
Similar to drug rewards, non-drug rewards also increase the level of extracellular dopamine in the NAcc shell. Drug-induced dopamine release in the NAcc shell and NAcc core is usually not prone to habituation i. Sensitization of dopamine release in the NAcc shell following repeated drug exposure serves to strengthen stimulus-drug associations i. After repeated pairing, these classically conditioned environmental stimuli e. In contrast to drugs, the release of dopamine in the NAcc shell by many types of rewarding non-drug stimuli typically undergoes habituation following repeated exposure i.
In Apriltwo research teams reported on having inserted electrodes into the nucleus accumbens in order to use deep brain stimulation to treat severe xmygdala. To treat addiction and in an attempt to treat mental illness radiofrequency ablation of the nucleus accumbens has been performed.
The results are inconclusive and controversial. Activation of the NAcc has been shown to occur in the anticipation of amygdaala of a drug when a user is given a placeboindicating a contributing role of the nucleus accumbens in the placebo effect. From Wikipedia, the free encyclopedia. Nucleus accumbens Medial surface, person facing to the left. Nucleus accumbens is very roughly in Brodmann area Sagittal Fungei slice with highlighting red indicating the nucleus accumbens.
Physiology of Behavior 11th ed. Neuroscience and Biobehavioral Reviews. Recent studies on intracranial self-administration of neurochemicals drugs found that rats learn to self-administer various drugs into the mesolimbic dopamine structures—the posterior ventral tegmental area, medial shell nucleus accumbens and medial olfactory tubercle. In the s it was recognized that the olfactory tubercle contains a striatal component, which is filled with GABAergic medium spiny neurons receiving glutamatergic inputs form cortical regions and dopaminergic inputs from the VTA and projecting to the ventral pallidum just like the nucleus accumbens Figure 3: Sydor A, Brown RY, eds.
A Foundation for Clinical Neuroscience 2nd ed. VTA DA neurons play a critical role in motivation, reward-related behavior Chapter 15attention, and multiple forms of memory. This organization of the DA system, wide projection from a limited number of cell bodies, permits coordinated responses to potent new rewards.
Thus, acting in diverse terminal fields, dopamine confers motivational salience “wanting” on the reward itself or associated cues nucleus accumbens shell region fjngsi, updates the value placed on different goals in light of this amygvala experience orbital prefrontal cortexhelps aygdala multiple forms of memory amygdala and hippocampusand encodes new motor programs that will facilitate obtaining this reward in the future nucleus accumbens core region and dorsal striatum.
In this example, dopamine modulates the processing of fugsi information in diverse neural circuits to maximize the ability of the organism to obtain future rewards.
The brain reward circuitry that is targeted by amygsala drugs normally mediates the pleasure and strengthening of behaviors associated with natural reinforcers, such as food, water, and sexual contact. Dopamine neurons in the VTA are activated by food and water, and dopamine release in the NAc is stimulated by the presence of natural reinforcers, such as food, water, or a sexual partner.
As previously mentioned, the activity of dopaminergic neurons in the VTA appears to be linked to reward prediction. The NAc is involved in learning associated with reinforcement and the modulation of motoric responses to stimuli that satisfy internal homeostatic needs.
The shell fyngsi the NAc appears to be particularly important to initial drug actions within reward circuitry; addictive drugs appear to have a greater effect on dopamine release in the shell than in the core of the Fubgsi. The Journal of Neuroscience. Here, we have found that real-time dopamine release within the nucleus accumbens a primary target of midbrain dopamine neurons strikingly varies between core and shell subregions.
In the core, dopamine dynamics are consistent with learning-based amygdlaa such as fugnsi prediction error whereas in the shell, dopamine is consistent with motivation-based theories e. Increased activity of the mesolimbic dopamine system is a central mechanism underlying the reinforcing and rewarding actions of drugs of abuse, including cocaine, as well as the compulsive drug seeking that develops over time and characterizes an addicted state 10— Dopamine action in NAc is mediated predominantly via activation of D1 or D2 dopamine receptors that are expressed by amygdal nonoverlapping populations of medium spiny neurons MSNs These two subtypes of MSNs exert opposite effects on behavior, with amyygdala activation of D1-type neurons promoting positive reinforcement and increasing the formation of cocaine reward—context associations and activation of D2-type neurons being aversive and decreasing cocaine reward 14, 15 ; related differences in behavioral responses are seen in response to D1 vs.
D2 receptor agonists or antagonists Thus, fear-evoking stimuli are capable of differentially fungsk phasic dopamine transmission across NAcc subregions. The authors propose that the observed enhancement in NAcc shell dopamine likely reflects general motivational salience, perhaps due to relief from a CS-induced fear state when the US foot shock is not delivered.
This reasoning is supported by a report from Budygin and colleagues showing that, in anesthetized rats, the termination of tail pinch results in augmented dopamine release in the shell. Neural and Neuroendocrine Control of the Internal Milieu”.
Dopamine acts in the nucleus accumbens to attach motivational significance amygdalaa stimuli associated with reward. Current Topics in Behavioral Neurosciences. PIT is a behavioral process that reflects the impact of Pavlovian-conditioned stimuli CS on instrumental responding.