Selective attention deficits after circumscribed lesions in the human thalamus

Introduction: The theory of visual attention (TVA, Bundesen 1990) is a method that allows to measure four independent parameters of visual attention (processing speed, visual short term memory capacity, selective control, spatial weighting). Several studies in stroke patients explored the role of cortical subregions, revealing that lesions in the entire cortical attention network lead to selective attention deficits in TVA parameters. Much less is known about the role of subcortical structures, especially about the role of the thalamus. The main goal of the study was to test if specific attention deficits exist in case of distinct thalamic nuclei affected. For this purpose, we recruited patients with focal thalamic strokes in anterior, medial, ventral or posterior nuclei.

Methods: We used whole report and partial report procedures (Finke et al. 2005) to investigate the four TVA parameters. A high resolution cerebral MRI three-dimensional data set was acquired for each patient. The images were normalized and were then registered to a stereotactic atlas (Morel 2007). Additionally, each patient underwent a neuro-ophthalmological and neuropsychological testing.

Results: So far 12 patients were tested and compared to an age-matched control group (N=52). In patients with ventral lesions we found processing speed reductions in both visual fields. Any other TVA parameters were within the normal range. For patients with medial lesions values of processing speed and visual short term memory capacity were within normal range. These patients showed a spatial deficit if two targets were presented across the hemifields (i.e., visual extinction). Subtraction analysis revealed that lesions for patients with reduced processing speed are more laterally as compared to lesions with normal processing speed. Further, a patient with an anterior-medial lesion showed a selective deficit in selective control and a patient with a posterior lesion revealed a spatial bias to the ipsilesional field.

Conclusions: The results of our 12 subjects reflect that the TVA allows the detection of selective attention deficits after focal thalamic stroke. There seems to be a specificity of distinct thalamic subparts (medial nuclei=spatial weighting, ventral nuclei=processing speed). For a neuroanatomical correlation of distinct attention deficits a larger number of cases will be necessary. We intend to investigate four more patients with lesions affecting the ventral thalamic nuclei.