| Brain: Ventral striatum | ||
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| Latin | striatum ventrale; corpus striatum ventrale | |
The ventral striatum is generally considered that part of the striatum that is connectionally associated with limbic structures, such as the amygdala, hippocampus, midline thalamus, and certain regions of the prefrontal cortex. In addition, the ventral striatum is strongly innervated by dopaminergic fibers from the ventral tegmental area (VTA), known as the mesolimbic dopamine system, and has the highest density of serotonergic inputs in the striatum. The ventral striatum consists of the nucleus accumbens and the olfactory tubercle.[1] Although, some sources also include the ventromedial parts of the caudate nucleus and putamen.[2]
In its present connotation, the term “ventral striatum” was introduced in 1975 by Lennart Heimer and Richard Wilson to differentiate it from the dorsal, sensorimotor-related part of the striatum (ie, the caudate-putamen complex). This inclusion of ventrally located striatal tissue in a “unified” striatum, along with the recognition of connectionally associated pallidal elements in the substantia innominata and deep layers of the olfactory tubercle (ie, the ventral pallidum), has had great impact on the functional-anatomical concept of the basal ganglia. Whereas traditionally, the basal ganglia were thought to be primarily involved in sensory-motor functions, it has now become accepted that the basal ganglia, as a result of their involvement in a set of parallel, functionally segregated basal ganglia-thalamocortical circuits, which primarily entertain the premotor and prefrontal cortical cortices, are also involved in cognitive and “limbic” functions.
Thus, in line with the characteristics of its inputs, the ventral striatum is functionally strongly associated with emotional and motivational aspects of behavior. Moreover, structural and functional disturbances of ventral striatal areas have been shown to be correlated with various forms of psychopathology, such as schizophrenia, addictive behavior, and obsessive–compulsive disorder. Based on the character of the afferents of the nucleus accumbens, the ventral striatum may be viewed as a site for integration of signals with emotional content (amygdala); contextual information (hippocampus); motivational significance (dopaminergic inputs); information about the state of arousal (midline thalamus); and executive/cognitive information (prefrontal cortex).
The accumbens’ outputs, directly or via ventral pallidal and dopaminergic and non-dopaminergic nigral relays, lead to brain areas involved in basic functions, such as feeding and drinking behavior (lateral hypothalamus); motivational behavior (VTA and nigral dopaminergic neurons); locomotor behavior (caudal mesencephalon); and more complex cognitive and executive functions (via medial thalamic nuclei to the prefrontal cortex). Thus, Mogenson and colleagues’ original concept of the nucleus accumbens as a functional interface between the limbic and motor systems, in general terms, is still valid. However, current insights are, of course, much more differentiated. In particular, the functional differentiation between the shell and core has received much attention in the past two decades.
Primarily based on animal experimental work, it may be concluded that the shell stands out from the core and the rest of the striatum through its involvement in the expression of certain innate, unconditioned behaviors, such as feeding or defensive behavior. The shell and core subregions play important but distinct roles in Pavlovian and instrumental conditioned learning that may be potentiated by psychostimulants. The core subregion seems to be preferentially involved in response-reinforcement learning, whereas the shell is not involved in motor or response learning, per se, rather, it integrates basic biological “drives” with the viscero-limbic and motor-effector systems. Dopamine in the nucleus accumbens may have a role in enhancing the gain by which conditioned stimuli and contexts exert control over behavior.It is considered a reward center.[3]
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