Although gait disorders were described in schizophrenia, motor imagery of gait has not yet been studied in this pathology. We compared gait, motor imagery of gait and the difference between these two conditions in patients with schizophrenia and healthy age-matched controls. The mean ± standard deviation (S.D.) of Timed Up and Go (TUG), imagined TUG (iTUG) and delta time (i.e.; difference between TUG and iTUG), was used as outcomes. Covariables include Mini Mental State Examination, the Frontal Assessment Battery (FAB), FAB's subitems, the Positive and Negative Syndrome Scale and the Unified Parkinson's Disease Rating Scale (UPDRS). Seventeen patients with early schizophrenia and 15 healthy age-matched controls were assessed. Schizophrenia patients performed the TUG and the iTUG slower than the controls. Multivariate linear regressions showed that iTUG and delta time were associated with the conflicting instruction of the FAB. The present study provides the first evidence that patients with schizophrenia performed gait and motor imagery of gait slower than healthy controls. These deficits could be in part explained by impaired executive function and specifically by a disturbance in the sensitivity to interference.
Before the advent of neuroleptics, gait disorders were described in patients with schizophrenia as a characteristic of the illness (Bleuler, 1911). Quantitative gait analysis confirmed these descriptions and showed a decrease of gait velocity due to a shorter stride length (Putzhammer et al., 2005). Ataxic gait in patients with schizophrenia seems also to be more frequent than in control subjects, and is related to old age and previous history of alcohol abuse, involving a dysfunction of the visuo-cerebellar circuit (Jeon et al., 2007). In addition, it was shown in patients with schizophrenia that infant motor developmental delay was associated with deficits in cognitive function involving executive function in adults (Murray et al., 2006). This last description suggests that executive function could contribute to motor disorders in schizophrenia (Brebion et al., 2000).
Motor imagery (MI) refers to the mental simulation of an action without its actual execution (Jeannerod, 1995). Previous reports on Parkinson's disease in particular suggested that MI shares common neural structures with motor execution (Jeannerod, 1994 and Dominey et al., 1995) and the frontostriatal structures is one of these regions (Dominey et al., 1995). Furthermore, in the realization of motor representations into motor performances, the dopaminergic system seems to play an important role (Yaguez et al., 1999). A recent study on MI of locomotion showed that practice of MI modulates brain networks including supplementary motor area, basal ganglia, bilateral thalamus and right cerebellum (Ionta et al., 2010). Concerning schizophrenia, a review on MI in this pathology suggested an important role of the posterior parietal cortex in attentional dysfunctions and impairments in MI (Danckert et al., 2004).
To assess gait and MI of gait, we recently adapted an imagined version of the Timed Up and Go (TUG) (Beauchet et al., 2010). TUG is a basic test for the evaluation of functional mobility, measuring time while standing up, walking, turning and sitting down and it has been used to evaluate gait and balance performance (Podsiadlo and Richardson, 1991). We showed a relationship between the discrepancy of the time to perform the TUG and the imagined time to perform the TUG (delta time) and Mini Mental State Examination (MMSE) (Folstein et al., 1975) in a sample of older adults (Beauchet et al., 2010). Due to the absence of study on MI of locomotion in schizophrenia, we used this adapted version of the TUG in this population. Because of the role of the dopaminergic system and the suspected relationship between, on the one hand, gait disorders and cognitive function and, on the other, deficits in MI and cognitive function in schizophrenia, we hypothesized that slower TUG and imagined TUG (iTUG) would be observed in patients with schizophrenia. The objective of this prospective cross-sectional study was 1) to measure and compare the time of TUG, iTUG and the difference of time between these two conditions of realization (i.e., delta time) in a sample of patients with schizophrenia and healthy matched controls and 2) to examine whether there was an association between the performances of TUG, iTUG and delta time and the cognitive status.
The global cognitive score assessed by MMSE was statistically different between both groups (30 ± 0 for the control group; 28 ± 2 for patients with schizophrenia; P < 0.001). All the tests assessing the performance of executive functioning was worse in the schizophrenic group compared to the control group (P < 0.050) with the exception of the subtest of the FAB assessing programming (P = 1.000). Motor performance assessed by the UPDRS and its gait subscore presented significant deficits in the patients' group with schizophrenia compared to the control group (P < 0.001) ( Table 1a). The PANSS scores for the positive and the negative symptoms were respectively 21 ± 7 and 21 ± 15 and the general score was 47 ± 11 in schizophrenic patients ( Table 1b).
