Cathodal transcranial direct current stimulation of the extrastriate visual cortex modulates implicit anti-fat bias in male, but not female, participants

Abstract

Explicit negative attitudes toward obese individuals are well documented and seem to modulate the activity of perceptual areas, such as the Extrastriate Body Area (EBA) in the lateral occipito-temporal cortex, which is critical for body-shape perception. Nevertheless, it is still unclear whether EBA serves a role in implicit weight-stereotypical bias, thus reflecting stereotypical trait attribution on the basis of perceptual cues. Here, we used an Implicit Association Test (IAT) to investigate whether applying transcranial direct current stimulation (tDCS) over bilateral extrastriate visual cortex reduces pre-existing implicit weight stereotypical associations (i.e. "Bad" with Fat and "Good" with Slim, valence-IAT). Furthermore, an esthetic-IAT, which focused on body-concepts related to esthetic dimensions (i.e. "Ugly" and "Beauty"), was developed as a control condition. Anodal, cathodal, or sham tDCS (2mA, 10min) over the right and left lateral occipito-temporal (extrastriate visual) cortex was administered to 13 female and 12male participants, before performing the IATs. Results showed that cathodal stimulation over the left extrastriate visual cortex reduced weight-bias for the evaluative dimensions (Bad vs. Good) as compared to sham stimulation over the same hemisphere. Furthermore, the effect was specific for the polarity and hemisphere of stimulation. Importantly, tDCS affected the responses only in male participants, who presented a reliable weight-bias during sham condition, but not in female participants, who did not show reliable weight-bias at sham condition. The present results suggest that negative attitudes toward obese individuals may reflect neural signals from the extrastriate visual cortex.

Dialogue intervention for youth amidst intractable conflict attenuates neural prejudice response and promotes adults’ peacemaking

“…The current findings expand this approach and show that the alpha rhythm during the IAT is significantly reduced after an intergroup dialogue intervention and this effect predicts long-lasting support of peacemaking. Consistent with our findings, Cazzato and colleagues used cathodal transcranial direct current stimulation of the occipital cortex to reduce the IAT effect ( 60 ) and similarly showed, using technology rather than dialogue intervention, that altering neural activity in occipital cortex is causally linked with reduction in intergroup bias. The findings from both studies highlight the potential of psychological and technological interventions to alter neural activity and consequently impact intergroup processes.…”

Implicit preference towards slim bodies and weight-stigma modulate the understanding of observed familiar actions

“…Participants were required to answer as fast and accurately as possible after the onset of the stimuli (i.e., single words or images presented one at a time at the centre of the screen), by pressing a left (E) or a right (I) key on a computer keyboard with the index finger of the left hand and right hand, respectively. The IAT lasted approximately 8 min and was administered in seven blocks, consisting of both congruent and incongruent conditions (blocks 3, 4, 6, and 7) and familiarization blocks (blocks 1, 2, and 5) (Greenwald, Nosek, & Banaji, 2003; Cazzato, Makris, & Urgesi, 2017). Before the first presentation of the weight-IAT, participants were shown a list with all the words belonging to the two relevant categories and were asked to carefully read all the stimuli.…”

Implicit visual sensitivity towards slim versus overweight bodies modulates motor resonance in the primary motor cortex: A tDCS study

“…More recently, we have shown that MR can be modulated by differences in the body weight between the actor and observer and that explicit negative attitudes toward overweight models can influence our ability to accurately simulate and predict the outcome of their actions (Cazzato & Makris, 2019). This is an interesting finding indicating that not only previous experience with an observed action, but also the existence of a negative stereotype (see also Cazzato, Makris, & Urgesi, 2017), can influence the level of one's ability to perceive others' actions and intentions. However, there is still limited evidence on how explicit and implicit anti-fat attitudes can influence the MR, as well as the underlying neural mechanism.…”

“…For the Weight-IAT, participants were required to answer as fast and accurately as possible after the onset of the stimuli (i.e., single words or images), by pressing a left (E) or a right (I) key on a computer keyboard with the index finger of the left hand and right hand, respectively. The IAT lasted approximately 8 minutes and was administered in seven blocks, consisting of both congruent and incongruent conditions (blocks 3, 4, 6, and 7) and familiarization blocks (blocks 1, 2, and 5) (Cazzato et al, 2017;Cazzato & Makris, 2019;Greenwald et al, 2003). Before the first presentation of the weight-IAT, participants were shown a list with all the words belonging to the two relevant categories and were asked to read carefully all of the stimuli.…”