Striatum
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In the brain, the striatum or neostriatum is a subcortical part of the telencephalon consisting of the caudate nucleus and the putamen. It is part of the basal ganglia. The striatum is best known for its role in the planning and modulation of movement pathways but is also involved in a variety of other cognitive processes involving executive function.
The striatum consists mainly of GABAergic 'medium spiny neurons', but medium aspiny neurons and large aspiny neurons can also be found along with cholinergic interneurons. These interneurons correspond to Tonically Active Neurons (TANs) recorded in vivo that briefly stop firing in concomitance to behaviourally salient situations and reward-related events. It is organized into areas called 'striosomes' and 'matrisomes' which receive inputs from the limbic system (e.g. amygdala) and cortex respectively.
Function
In humans the striatum is activated by stimuli associated with reward, but also by aversive, novel, unexpected or intense stimuli, and cues associated with such events. Recent fMRI evidence suggests that the common property linking these stimuli, to which the striatum is reacting, is saliency under the conditions of presentation. A number of other brain areas and circuits are also related to reward, including the nucleus accumbens and other frontal areas.The main efferent target of the striatum is the globus pallidus, which is primarily inhibited by GABAergic synapses from the striatum. The main afferent region to the striatum is neocortex. Glutamatergic cortical pyramidal cells project to the striatum, exciting striatal neurons. The substantia nigra projects dopaminergic axons to the striatum via the nigrostriatal pathway, which is part of the medial forebrain bundle. While cortical axons synapse mainly on spine heads of medium spiny neurons, nigral axons synapse mainly on spine shafts. Metabotropic dopamine receptors are present both on medium spiny neurons and on cortical axon terminals. Second messenger cascades triggered by activation of these dopamine receptors can modulate pre- and postsynaptic function, both in the short term and in the long term.
Parkinson's disease results from loss of dopaminergic innervation to the striatum. It is also thought that addiction involves plasticity at striatal synapses.
External links
References
- Aosaki T, Kiuchi K & Kawaguchi Y (1998) Dopamine D1-like receptor activation excites rat striatal large aspiny neurons in vitro. J Neurosci 15, 5180–90
- Apicella P (2002) Tonically active neurons in the primate striatum and their role in the processing of information about motivationally relevant events. Eur J Neurosci 16, 2017–26
- Holt DJ, Graybiel AM & Saper CB (1997) Neurochemical architecture of the human striatum. J Comp Neurol 21, 1–25
- Morris G, Arkadir D, Nevet A, Vaadia E & Bergman H (2004) Coincident but distinct messages of midbrain dopamine and striatal tonically active neurons. Neuron 8, 133–43
- Tepper JM & Bolam JP (2004) Functional diversity and specificity of neostriatal interneurons. Curr Opin Neurobiol 14, 685–92
- Yamada H, Matsumoto N & Kimura M (2004) Tonically active neurons in the primate caudate nucleus and putamen differentially encode instructed motivational outcomes of action. J Neurosci 7, 3500–10
- Zink, CF, Pagnoni G, Martin-Skurski ME, Chappelow JC, & Berns GS (2004). Human striatal responses to monetary reward depend on saliency. Neuron 42, 509-17
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