A NIRS STUDY OF THE HEMODYNAMIC CORRELATES OF COGNITIVEFUNCTIONS

Sustained attention (SA) is a function within the construct of attention, defined as the ability to maintain a consistent level of vigilance and detect unpredictably occurring stimuli over time [1]. Working memory (WM) is a component of memory which encompasses the temporary on-line maintenance of information and its manipulation [2]. Neuroimaging studies converge to suggest a prominent role of the prefrontal cortex (PFC) in processes affecting both SA (primarily in the right hemisphere) and WM [2]. Enhanced brain activity associated with cognitive effort induces an increased metabolic consumption which leads to local hemodynamic changes that modify the optical properties of the cerebral tissue. Near Infrared Spectroscopy (NIRS) is an optical imaging method that capitalizes on the absorption and scattering properties of near-infrared light to monitor the hemodynamic changes occurring in response to functional activation [3]. NIRS has advantages over more common imaging methods including noninvasivity, portability, better motion tolerance and increased comfort for the participants and is being widely used to investigate cortical activation related to cognitive processes [3]. One of the most popular WM experimental paradigms is the n-back task, in which participants are required to monitor a series of stimuli and to respond whenever the currently presented stimulus is the same as the one presented n trials before [4]. In the 0-back condition the target stimulus is previously specified and the task is therefore expected to elicit the activation of SA mechanisms to maintain high vigilance and receptivity levels over time and promptly respond to task-relevant stimuli. In the other conditions (1-, 2-, ..., n-back) the task requires not only continuous vigilance, but also the storage, updating and manipulation of newly presented information and is therefore assumed to place great demands on key processes within WM, inasmuch as the cognitive load increases. The aims of the present study are to use NIRS to evaluate PFC activation during SA and WM processes and to investigate the relationships between the cognitive load variation and the cortical activation patterns.