Neuroscience Letters 403 (2006) 90–95 Differential time course and intensity of PFC activation for men and women in response to emotional stimuli: A functional near-infrared spectroscopy (fNIRS) study Jose Leon-Carrion a,b,∗ , Jes ´ us Damas b,d , Kurtulus Izzetoglu c , Kambiz Pourrezai c , Juan Francisco Mart´ ın-Rodr´ ıguez a,b , Juan Manuel Barroso y Martin a , Maria Rosario Dominguez-Morales b a Human Neuropsychology Laboratory, School of Psychology, Department of Experimental Psychology, C/Camilo Jos´ e Cela s/n, University of Seville, Spain b Center for Brain Injury Rehabilitation (CRECER), Seville, Spain c School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia d Applied Mathematics Department, School of Optics, Universidad Complutense de Madrid, Spain Received 29 September 2005; received in revised form 8 March 2006; accepted 19 April 2006 Abstract Using functional near-infrared spectroscopy (fNIRS) we recorded prefrontal cortex (PFC) activation during positive, negative and neutral film clips, based on affective ratings according to their valence and arousal, to assess gender differences in cerebral activation in 15 male and 15 female volunteers. To record PFC activation, five movie clips were presented on a 17-in. TFT screen. The recordings included a pre-stimulus 5-s local baseline and “on” and “off” segments of data, referring to fNIRS Oxy-Hb levels while stimulation (movie clip) was present and during an inter-stimulus blank screen. Our data showed gender differences in the delay period to initial PFC activation and in the course and intensity of activation produced by affective visual stimuli. During the exposure or “on” period of the stimuli we observed more pronounced overshoot and undershoot in men versus women across the range of emotions elicited. This effect was even more pronounced following stimulus cessation (“off” period). The results indicate that gender and the duration of recordings may affect the results of emotional neuroimaging studies. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Gender differences; Emotion; Functional near-infrared spectroscopy; Temporal course; Prefrontal cortex Although previous studies on emotion have found certain dif- ferences in the way male and female brains process emotional stimuli [2,8,11–13,21,23,31,34], little is yet known about the possible associated neural correlates [18,23,31,35], and even less about the function of prefrontal cortex (PFC) in these gender differences. The main difference reported in a study by Kemp et al. [21] was associated with widespread frontal latency reduc- tions (predominantly right sided), in females but not in males, when processing unpleasant images. In another study, Wrase et al. [35] found stronger activity in the frontal lobe (inferior and medial frontal gyrus) for positive visual stimuli in men, and stronger activation in the anterior and medial cingulate gyrus for affectively negative pictures in women. Although studies ∗ Corresponding author. E-mail address: leoncarrion@us.es (J. Leon-Carrion). suggest that gender differences in processing visual emotional stimuli do exist, the search for clear and conclusive evidence of frontal gender differences remains [34]. To study gender differences associated to PFC activation in emotion studies, emotions must first be classified according to their valence and arousal. Most emotion studies have generally used standardized methods to evoke and assess these psycho- logical dimensions in neuroimaging studies [5,12]. Although studies have provided functional images of activated areas of the brain associated to emotional tasks, they have seldom addressed the temporal course of the activation. Functional near-infrared spectroscopy (fNIRS) is a new technique that can be used to mea- sure hemodynamic changes in the brain that closely correlate to specific tasks, and to plot the temporal course of the changes. The validity of this method has been demonstrated by differ- ent authors in both human [5,16,19,24,25] and animal studies [15,28,29]. The degree of change in cerebral blood flow volume 0304-3940/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2006.04.050