Figure 2.

fMRI paradigms. Schematic representation of the fMRI paradigms used to investigate the effect of autonomic perturbation on the brain in subjects at rest (experiment 1; panel A), and when engaged in performing a visuo‐spatial attention task (experiment 2; panel B). In experiment 1, subjects were required to lie still in the scanner, without thinking of anything in particular. Fifty efficacious (−60 mm Hg) and 30 nonefficacious (−10 mm Hg) neck suction (NS) pulses with a duration of 8 s each were randomly administered over 16 min of continuous fMRI data acquisition. Each NS pulse was followed by a random interpulse interval at atmospheric pressure ranging from 3.0 to 5.2 s. In experiment 2 (total fMRI acquisition = 16 min), the visuo‐spatial attention task included 32 blocks, with a duration of 30 s each, half of them requiring the active task (A = active), and half of them requiring a control condition (C = control). Each block started with instructions (duration = 3.2 s, followed by 0.8 s of black screen) and included the presentation of 14 stimuli (duration = 0.3 s each) separated from each other by intervals of black screen (duration = 1.7 s each). The effective intertrial interval was 2 s. The total number of trials was 896, with 224 repetitions for each of four trial‐types (active task under efficacious NS stimulation, active task under nonefficacious NS stimulation, control task under efficacious NS stimulation, and control task under nonefficacious NS stimulation). During the active condition, subjects were requested to press (as soon as possible) a button with the right index for items presenting with a symmetrical bisection of a colored horizontal line by a shorter vertical line and not to press in case of asymmetrical bisection. In the control condition, subjects were requested to press (as soon as possible) the same button when the items were presented in yellow and not to press in any other case. During task performance, NS was delivered in 60 s duration blocks, alternating half of them with a pressure of −60 mm Hg (efficacious stimulation), and the other half with a pressure of −10 mm Hg (nonefficacious stimulation). The active and control 30 s duration blocks were pseudo‐randomly administered in order to obtain half of them under efficacious and half under nonefficacious NS stimulation. Each block of NS consisted of 8 s duration pulses (either −60 or −10 mm Hg) interleaved with 4‐s duration intervals of suction release (cuffs at atmospheric pressure) to avoid the risk of accommodation for the mechanoreceptors. This allowed us to obtain a continuous stimulation of the mechanoreceptors over the entire block of efficacious NS stimulation. See text for further details.