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Fronto-cerebellar dissociation
Fronto-cerebellar dissociation is the disconnection and independent function of frontal and cerebellar regions of the brain. It is characterized by inhibited communication between the two regions, and is notably observed in cases of ADHD, schizophrenia, alcohol abuse, and heroin abuse. The frontal and cerebellar regions make distinctive contributions to cognitive performance, with the left-frontal activations being responsible for selecting a response to a stimulus, while the right-cerebellar activation is responsible for the search for a given response to a stimulus. Left-frontal activation increases when there are many appropriate responses to a stimulus, and right-cerebellar activation increases when there is a single appropriate response to a stimulus. A person with dissociated frontal and cerebellar regions may have difficulties with selecting a response to a stimuli, or difficulties with response initiation. Fronto-cerebellar dissociation can often result in either the frontal lobe or the cerebellum becoming more active in place of the less active region as a compensatory effect. 〔Cubillo, A., Halari, R., Smith, A., Taylor, E., & Rubia, K. (2012). A review of fronto-striatal and fronto-cortical brain abnormalities in children and adults with Attention Deficit Hyperactivity Disorder (ADHD) and new evidence for dysfunction in adults with ADHD during motivation and attention. Cortex, 48(2), 194-215. doi: 10.1016/j.cortex.2011.04.007〕〔de Zeeuw, P., Weusten, J., van Dijk, S., van Belle, J., & Durston, S. (2012). Deficits in Cognitive Control, Timing and Reward Sensitivity Appear to be Dissociable in ADHD. Plos One, 7(12). doi: 10.1371/journal.pone.0051416〕
==Background==
Neuroanatomical studies in non-human primates have shown connections between the cerebellum and non-motor cortical areas of the frontal lobe.〔Strick, P. L., Dum, R. P., and Fiez, J. A. (2009). Cerebellum and nonmotor function. Annu. Rev. Neurosci. 32, 413–434.〕 Fronto-cerebellar circuitry is important to processes such as language, memory, and thought. Positron emission tomography has shown that when a subject was shown a noun and asked to state an associated verb, left-frontal and right-cerebellar activation was greater than if asked to simply speak the noun aloud. Generating an associated word required more fronto-cerebellar coactivation, indicating a difference between semantic retrieval and verbal working memory. Additionally, completing a word when presented a stem of the word resulted in greater left-frontal activation when there were many possible completions to the stem. Right-cerebellar activation was greater when there were fewer possible completions to the stem. These results indicate that the left-frontal activations correlate with selection of a response among many possible responses.〔Desmond, J. E., Gabrieli, J. D. E., & Glover, G. H. (1998). Dissociation of frontal and cerebellar activity in a cognitive task: Evidence for a distinction between selection and search. Neuroimage, 7(4), 368-376. doi: 10.1006/nimg.1998.0340〕〔Hogan, M. J. (2004). The cerebellum in thought and action: a fronto-cerebellar aging hypothesis. New Ideas in Psychology, 22(2), 97-125. doi: 10.1016/j.newideapsych.2004.09.002〕
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