Top panel: map of the gravitational torques exerted on the gas by the stellar potential in the centre of NGC 4968. The map shows in each pixel the torque derived from the HST-NIR image multiplied by the gas surface density. Both images have been de-projected to face-on (see text for details). The torques change sign as expected in a four-quadrant pattern (or butterfly diagram). The orientation of the quadrants follows the bar orientation. In this de-projected picture, the major axis of the galaxy is orientated parallel to the horizontal axis. Bottom panel: de-projected image of the CO(2−1) emission, at the same scale and with the same orientation, for comparison.