The effect of the simple
The effect of the simple dopaminergic tonic/phasic model on cognitive processing has been investigated by a few studies (Nolan et al., 2004; Rosa et al., 2010). Rosa et al. (2010), using a Stroop task that requires different levels of cognitive flexibility and stability, observed an association between the Met allele and a better cognitive stability for both clinical and non-clinical samples. However, Val allele did not seem to benefit cognitive flexibility or stability. Malloy-Diniz et al. (2013) used two tests to analyze neuropsychological functions in non-clinical subjects: the Iowa Gambling Task (IGT) test to analyze impulsivity related to lack of planning and the Continuous Performance Test (CPT) to assess attentional and motor impulsivities. As a result, Met homozygous individuals showed worse performance at IGT, which required greater cognitive flexibility. Groups did not differ at CPT, which required cognitive stability. Nolan et al. (2004) also observed the tonic/phasic effect associated with COMT Val158Met polymorphism. Met homozygotes showed better acquisition of a task requiring cognitive stability, but greater deficit in a task that requires flexibility. Val homozygotes, in turn showed worse performance when cognitive stability was required. Authors concluded that the Met allele, by increasing tonic dopamine, promotes cognitive stability but limits cognitive flexibility.
Motor learning and control require many cognitive functions associated with the COMT Val158Met polymorphism. Thus, an association between this polymorphism and motor behavior is expected. For instance, working memory (WM) is one of the cognitive functions associated with COMT. Spatial working memory has an important role in the initial phases of motor learning and in the learning rate in both visuomotor EPZ005687 and sequential motor tasks (Hikosaka et al., 2002; Anguera et al., 2010; Seidler et al., 2012). Visuomotor adaptation tasks have a greater demand of cognitive flexibility as their perturbations require adaptation, whereas sequential motor tasks require cognitive stability to learn a motor pattern that is refined and well defined. Thus, this study aimed to review the literature on studies that investigated the association between the COMT Val158Met polymorphism and motor behavior. Two main questions oriented our study review: 1) is there an association between the COMT Val158Met polymorphism and motor behavior? ; 2) is the tonic/phasic effect of COMT Val/Met associated with the stability or flexibility promoted by the motor task? Since the COMT polymorphism is associated with both psychiatric and developmental disorders such as Schizophrenia (Sagud et al., 2010) and Attention Deficit Hyperactivity Disorder (ADHD) (Sun et al., 2014) respectively, only studies carried out with non-clinical populations were included.
Methods The current integrative review consisted of the following steps: elaboration of the research questions that need to be answered, selection of articles, descriptions of the studies and their results, and interpretation of the results. This type of review was chosen due to the heterogeneity of the studies (Lage et al., 2015). For the database PubMed, the following terms were used in an advanced search: “catecholmethyltransferase” and “motor behavior” (n = 165), “COMT” and “motor learning” (n = 23), and “catecholmethyltransferase” and “motor control” (n = 68) [All fields]. A total of 256 articles were identified. On the databases ISI Web of Science, we found a total of 222 articles using the search terms “catechol-O-methyltransferase" and "motor behavior" (n = 35), “COMT” and “motor learning” (n = 15), and “Catechol-o-methyltransferase” and “motor control” (n = 172) [Topic]. On the database Scopus, a total of 74 articles were found by searching the keywords "catechol-o-methyltransferase" and "motor behavior" (n = 46), “COMT” and “motor learning” (n = 9), and “catechol-o-methyltransferase” and “motor control” (n = 19) [Keywords]. A total of 552 articles were found in our initial search on the three databases (Fig. 1).