Recovery from hemineglect: differential neurobiological effects of optokinetic stimulation and alertness training

We prospectively investigated by means of neuropsychological tests and functional magnetic resonance imaging (fMRI) the behavioural and neural effects of a 3-week optokinetic stimulation (OKS) training in 7 patients with chronic visuospatial neglect resulting from right-hemisphere lesions. Behaviourally, OKS caused both a short- and a long-term (4 weeks) improvement of performance in a neglect test battery (compared to a 3-week baseline period). This amelioration of neglect symptoms was associated with increases of neural activity during an fMRI spatial attention task bilaterally in the middle frontal gyrus and the precuneus. Additional left hemisphere increases in neural activity were observed in the cingulate gyrus, angular gyrus, middle temporal gyrus and occipital cortex. This pattern of activation represents a combination of areas normally involved in spatial attention plus a compensatory recruitment of left hemisphere areas. These results were then compared with data from our previous study (Thimm et al., 2006) which employed an alertness training (AIXTENT) with an otherwise identical treatment study design. After the OKS training there was more activation bilaterally in the precuneus than after the AIXTENT training. In contrast, after AIXTENT training there was more activation bilaterally in frontal cortex. Taken together, the results show that amelioration of neglect can be induced by both OKS and alertness training. The data furthermore suggest that the differential activations of frontal or parietal areas may reflect the specific impact of the two types of training either on an anterior system for the control of attention intensity (AIXTENT) or on the posterior system of spatial attention (OKS).