During recent decades, sexual affiliation has been an exponentially explored functional context within socioaffective neuroscience, especially with respect to the motivational component of inter-attraction, which can be either positive or negative within social relationships. As appearing in international databases, sexual visual stimuli are often reported as the most arousing stimuli and are therefore ideal to increase knowledge of the influence of the arousal dimension on the neural (central and peripheral) and psychological correlates of emotional information processing, which is at the center of the theory presented by Mather et al.. Here, we focus on recent results regarding the motor correlates of visual sexual information corroborating the complex modulatory role of arousal as developed in the GANE (glutamate amplifies noradrenergic effects) theory.

Within the framework of sexual behavior, emotion can be conceptualized partly as an action disposition characterized by a context-dependent (e.g., approach vs. avoidance) behavioral component, which may be mediated by automatic responses (Campbell et al. Reference Campbell, Wood, McBride, Lang, Simons, Balaban and Simons1997; Panksepp & Biven Reference Panksepp and Biven2012). In that sense, emotion should influence several steps of the motor response (Bradley et al. Reference Bradley, Greenwald, Petry and Lang1992; Helbig et al. Reference Helbig, Borod, Frisina, Tse, Voustianiouk, Olanow and Gracies2011; Williams et al. Reference Williams, Mathews and MacLeod1996) by inducing an approach behavior to what promotes our well-being and our survival and an avoidance behavior in response to painful experiences (Elliot & Covington Reference Elliot and Covington2001). Albeit recent, most neuroimaging studies of sexual arousal made central in their theoretical model a motivational component. Several incentive motivation theories state that approach behavior is activated by appropriate incentives (Agmo Reference Agmo1999; Bindra Reference Bindra1974; Singer & Toates Reference Singer and Toates1987). This theoretical framework is supported by recent results indicating that, in sexual conditions, behavioral responsiveness and interest (Both et al. Reference Both, Spiering, Everaerd and Laan2004) and spinal tendon reflexes (Both et al. Reference Both, Boxtel, Stekelenburg, Everaerd and Laan2005) increase linearly with the arousal level of the stimuli.

Posture is a good index of motor correlates of emotional information processing and can be quantified by determining the body's center-of-pressure (Gurfinkel Reference Gurfinkel1973) displacements. Previous studies reported the influence of emotion on decision-making processes (Damasio et al. Reference Damasio, Everitt and Bishop1996) through emotional biasing of action selection, which might indicate the functioning of a Pavlovian system that innately regulates specified responses to reward- or punishment-predictive stimuli (Ly et al. Reference Ly, Huys, Stins, Roelofs and Cools2014). This is supported by numerous studies reporting, respectively, behavioral activation versus inhibition in response to reward versus punishment (Cavanagh et al. Reference Cavanagh, Eisenberg, Guitart-Masip, Huys and Frank2013; Crockett et al. Reference Crockett, Clark and Robbins2009; Guitart-Masip et al. Reference Guitart-Masip, Fuentemilla, Bach, Huys, Dayan, Dolan and Duzel2011; Reference Guitart-Masip, Huys, Fuentemilla, Dayan, Duzel and Dolan2012; Reference Guitart-Masip, Duzel, Dolan and Dayan2014).

Contrary to the primary hypothesis of an approach-type behavior, our recent study (Mouras et al. Reference Mouras, Lelard, Ahmadi, Godefroy and Krystkowiak2015) demonstrated a freezing-type response to sexually explicit stimuli (Fig. 1).

Figure 1.

Means and standard deviations of postural indices as a function of the stimulus. (A) Amplitude of the sway of the center of pressure (COP) in the mediolateral direction (Amp [COP]-ML). (B) Amplitude of the sway of the COP in the anteroposterior direction (Amp [COP]-AP). (C) Standard displacement of the COP in the mediolateral direction (SD [COP]-ML). (D) Standard displacement of the COP in the anteroposterior direction (SD [COP]-AP). (E) Area encompassed by displacements of the COP (COP-area). *p < 0.05, **p < 0.01 when comparing stimuli. (From Mouras et al. Reference Mouras, Lelard, Ahmadi, Godefroy and Krystkowiak2015).

These results were quite surprising – and in accordance with the GANE theory's interpretation of the effect of arousal on perception and memory. Previous studies reported a freezing strategy in response to aversive visual images (Facchinetti et al. Reference Facchinetti, Imbiriba, Azevedo, Vargas and Volchan2006; Hillman et al. Reference Hillman, Rosengren and Smith2004; Stins & Beek Reference Stins and Beek2007) or a defense-type response to unpleasant compared with both pleasant and neutral videos (Hagenaars et al. Reference Hagenaars, Roelofs and Stins2014b). Interestingly, Horslen and Carpenter (Reference Horslen and Carpenter2011) argued that arousal only modulated the freezing strategy. Hagenaars et al. (Reference Hagenaars, Oitzl and Roelofs2014a) reported that freezing (a) is usually considered a threat-related defense strategy and (b) could be similar to immobility occurring in orienting or behavioral inhibition. The temporal dimension of the motor correlates may be central as demonstrated by early (1–2 s after stimulus onset) freezing behavior in response to unpleasant films (Hagenaars et al. Reference Hagenaars, Oitzl and Roelofs2014a) that would be associated with an optimal body position for concealment from the predator (McNaughton & Corr Reference McNaughton and Corr2004). Therefore, sexual arousal could be partly associated not only with positive emotions, but also with a certain anxiety in accordance with a freezing response to angry faces and related to anxiety (Roelofs et al. Reference Roelofs, Hagenaars and Stins2010). Facchinetti et al. (Reference Facchinetti, Imbiriba, Azevedo, Vargas and Volchan2006) reported that body sway reductions were observed in response to both unpleasant and pleasant pictures and suggested that “baby and family pictures may have elicited (for subjects) a predisposition to social bonding and that the pre-activation of muscles involved in the anterior-posterior displacement could reflect preparation for processes like attachment and reduction of social distance.”