Neuroscience Letters 422 (2007) 147–152 A lasting post-stimulus activation on dorsolateral prefrontal cortex is produced when processing valence and arousal in visual affective stimuli Jose Le ´ on-Carri´ on a,b,∗ , Juan Francisco Mart´ ın-Rodr´ ıguez a,b , Jes´ us Damas-L ´ opez b , Kambiz Pourrezai c , Kurtulus Izzetoglu c , Juan Manuel Barroso y Martin a , Mar´ ıa Rosario Dom´ ınguez-Morales b a Human Neuropsychology Laboratory, School of Psychology, Department of Experimental Psychology, C/Camilo Jos´ e Cela s/n, University of Seville, Seville, Spain b Center for Brain Injury Rehabilitation (C.RE.CER.), Torneo 23, Seville, Spain c School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania, USA Received 2 March 2007; received in revised form 30 April 2007; accepted 30 April 2007 Abstract This paper introduces a new paradigm in the study of emotional processes through functional neuroimaging. We study whether the valence and arousal of visual stimuli influence neuroimaging of the evoked hemodynamic changes. Using functional near-infrared spectroscopy (fNIRS), we investigate evoked-cerebral blood oxygenation (CBO) changes in dorsolateral prefrontal cortex (DLPFC) during direct exposure to different emotion-eliciting stimuli (‘on’ period), and during the period directly following stimulus cessation (‘off’ period). We hypothesize that the evoked- CBO, rather than return to baseline after stimulus cessation, would show either overshoot or undershoot. The study includes 30 healthy subjects and a total of 9 stimuli, which consist of video-clips with different emotional content. The total sample of trials studied (270) is classified according to the valence and arousal ratings given by the subjects. Results show a more robust activation in DLPFC during the ‘off’ period than during the ‘on’ period, depending on the subjective degree of arousal given to the stimulus. Our findings provide the first fNIRS evidence showing that an increment in subjective arousal leads to activation in DLPFC which persists after stimulus cessation and this does not occur with non-arousing stimuli. Neuroimaging studies must consider the duration and affective dimensions of the stimulus as well as the duration of the scanning to specify how much of the recorded response is analyzed. Not accounting for this difference may contribute to confusion in the data interpretation. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Arousal; Valence; fNIRS; Emotion; DLPFC; Neuroimaging Two affective dimensions have been studied extensively in neu- roimaging research on emotional stimuli: arousal (exciting or calming) and valence (positive or negative) [4,49]. These dimen- sions have been found to have dissociable effects in different neurophysiological systems [1,50]. Since degrees of arousal and valence can be manipulated independently, e.g., negative and arousing [5], or positive and arousing [15,16], investigating the impact of the affective dimensions of visual emotional stimuli on ∗ Corresponding author at: Human Neuropsychology Laboratory, School of Psychology, Department of Experimental Psychology, C/Camilo Jos´ e Cela s/n, University of Seville, Seville, Spain. Tel.: +34 95 457 4137; fax: +34 95 437 4588. E-mail address: leoncarrion@us.es (J. Le ´ on-Carri´ on). brain activation is extremely important. It is generally accepted that brain activation is elicited by direct cognitive/affective stim- ulation and that this activation decreases with stimulus cessation [30]. Thus, the majority of neuroimaging studies have tended to focus on signal changes simultaneous with exposure to stimuli. However, two points require further investigation: the dura- tion of an emotionally-evoked activation and its dependence on the affective dimensions (valence and arousal) of the stimulus. Another question that needs to be studied is whether the value (valence) and intensity (arousal) of an emotional stimulus evoke the same type of neural activation. It is difficult to determine differences in evoked-cerebral blood oxygenation (CBO) changes, particularly in duration and level of neuronal activation within a brain region or between 0304-3940/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2007.04.087