Differences in attentional selective control after rostral and dorsal putaminal lesions

Introduction: The classic view of putaminal function is dominated by its involvement in the motor loop of the basal ganglia. Yet functional imaging in healthy subjects and patients suggest a role in attention and working memory. Specific cortical regions and thalamic structures are connected with specific putaminal regions. The dorsolateral prefrontal cortex (DLPFC) projects to the rostral part, motor areas project to the dorsal part. This functional topography is maintained in the output structures of the basal ganglia and in the thalamus (Haber et al. 2001). The DLPFC is part of the attention network. Therefore, it is of interest to investigate if selective attentional deficits can be observed after focal lesions in distinct subparts of the putamen.

Methods: So far two patients (61, 54 years) with a singular and circumscribed lesion predominantly in the rostral (13×15×5mm) and dorsal (9×12×5mm) putamen, respectively, were examined 6 month after the stroke. The rostral lesion extends to the head of the caudate nucleus. Whole report and partial report procedures (Finke et al. 2005) were used to investigate four attention parameters (processing speed, short term memory capacity, selective control, spatial weighting). In addition, both patients underwent a neuro-ophthalmological and neuropsychological testing.

Results: The patient with the rostral lesion showed a clear reduction in processing speed (C=9.15), as well as extinction of contralesional targets if two targets were presented across the hemifields (w-lambda=0.62). In contrast, the patient with the dorsal lesion did not show a reduction in processing speed (C=20.77) or any spatial bias (w-lambda=0.50). But this patient showed for both hemifields a clearly increased selective control (α=0.07).

Conclusions: Our findings indicate the high specificity of distinct subparts of the putamen in attentional selective control. Both the spatial bias and the reduced processing speed in the patient with a rostral putaminal lesion are consistent with the findings of Finke et al. (2006) and Habekost & Rostrup (2006) showing that lesions affecting the caudate nucleus lead to a spatial bias and that lesion affecting the putamen lead to reduced processing speed. For an exact neuroanatomical correlation a larger number of cases will be necessary. More patients have been recruited and will be investigated within the next month.