Article

Prismatic adaptation effects on spatial representation of time in neglect patients.

Department of Psychology, University of Palermo, Palermo, Italy; Fondazione "Santa Lucia" IRCCS, Rome, Italy.
Cortex (Impact Factor: 6.04). 11/2011; DOI: 10.1016/j.cortex.2011.11.010
Source: PubMed

ABSTRACT Processing of temporal information may require the use of spatial attention to represent time along a mental time line. We used prismatic adaptation (PA) to explore the contribution of spatial attention to the spatial representation of time in right brain damaged patients with and without neglect of left space and in age-matched healthy controls. Right brain damaged patients presented time underestimation deficits, that were significantly greater in patients with neglect than in patients without neglect. PA inducing leftward attentional deviation reduced time underestimation deficit in patients with neglect. The results support the hypothesis that a right hemispheric network has a role, per se, in time perception. Moreover, they suggest that right hemisphere is important in time perception for its control of spatial attention, engaged in spatial representation of time. Procedures that ameliorate left spatial deficits could also be useful for modulating temporal deficits in right brain damaged patients with neglect.

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    ABSTRACT: Prismatic Adaptation (PA) has been shown to affect left-to-right spatial representations of temporal durations. A leftward aftereffect usually distorts time representation toward an underestimation, while rightward aftereffect usually results in an overestimation of temporal durations. Here, we used functional magnetic resonance imaging (fMRI) to study the neural mechanisms that underlie PA effects on time perception. Additionally, we investigated whether the effect of PA on time is transient or stable and, in the case of stability, which cortical areas are responsible of its maintenance. Functional brain images were acquired while participants (n=17) performed a time reproduction task and a control task before, immediately after and 30 minutes after PA inducing a leftward aftereffect, administered outside the scanner. The leftward aftereffect induced an underestimation of time intervals that lasted for at least 30 minutes. The left anterior insula and the left superior frontal gyrus showed increased functional activation immediately after versus before PA in the time versus the control task, suggesting these brain areas to be involved in the executive spatial manipulation of the representation of time. The left middle frontal gyrus showed an increase of activation after 30 minutes with respect to before PA. This suggests that this brain region may play a key role in the maintenance of the PA effect over time.
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    ABSTRACT: Background The prismatic adaptation (PA) is a visuo-motor procedure that has captured the attention of neuroscientists in the last decades, hence it seems to affect high-order cognition. However, the basic neural processes related to PA and its effects on cortical plasticity are not clear yet. Objective/Hypothesis The aim of the present study is to explore whether PA induces a direct effect on the motor cortices (M1) excitability. Methods Fourteen healthy participants were submitted to paired-pulse TMS to measure short-intracortical-inhibition (SICI) and intracortical-facilitation (ICF) on both the left and the right M1, before and after PA, that could induce a leftward or rightward after-effect. Results An increase of intracortical-facilitation was found in the M1 controlateral to the after-effect direction. Moreover the extent of facilitation and of the after-effect were correlated to each others. Conclusion This finding reveals that PA influences M1 cortices directly, raising their excitability. The present investigation represents an innovative step for the understanding of neurophysiological processes by which PA affects brain functions.
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