The thalamus interrupts top-down attentional control for permitting exploratory shiftings to sensory signals.

When attention is involuntarily drawn in a direction different to that of the target, slower motor response times are observed (i.e. the meridian effect). Previous data suggested that the thalamus might participate in the generation of visual salience. What may be the role of the thalamus in the capture by luminance transients when attentional control is in action? A single experiment was administrated in a group of ten healthy volunteers as well as in a group of three patients with unilateral thalamic infarcts. Subjects participated in a task where attentional control was interrupted by a distractor. The meridian effect was present only in the performance of the healthy volunteers and when distractors occurred in the ipsilesional (intact) hemifield of the thalamic patients. These results suggest that when an important signal appears during attentional focalization, the thalamus interrupts current focalization and permits the compilation of an attentional program in the midbrain aiming at generating an orienting response towards the source of this signal.