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.

Impairment of the supervisory attentional system in early untreated patients with Parkinson's disease.

The aim of this study was to specify the frontal type dysfunction widely reported in Parkinson's disease (PD) early in the course of the disease and before dopaminergic therapy. Seventeen "de novo" PD patients and 17 healthy control subjects performed modified versions of the Stroop word-color test and the Brown Peterson paradigm. A dissociation between results on the two tasks was observed in PD patients. They had difficulties in inhibiting a strong habitual response and establishing a new, better adapted pattern of response; but they performed as well as controls in a dual-task paradigm requiring correct allocation of the processing resources of working memory. Early in the course of the disease, untreated PD patients suffer from dysfunction of the supervisory attentional system. However, the present findings suggest that this system is not a single unit but rather could be composed of multiple subsystems whose sensitivity depends on the origin of frontal dysfunction. Indeed, only a few of these subsystems seemed to be impaired in de novo PD patients. It can be hypothesized that those involved in the phenomena of adaptation and consolidation of currently appropriate responses depend on the dorsolateral prefrontal loop, which is affected by the dopaminergic innervation of the caudate nucleus.