BOLD imaging is performed with a 3-T MRI scanner (Philips Achieva 3.0T, X series, Quasar Dual MRI system). Each study consists of axial T1-weighted spin echo images (matrix of at least 192 × 256) covering the whole brain for anatomical correlation. Functional scan is performed using a single-shot echo planar pulse sequence in an interleaved multislice format with a field of view of 24 cm and a matrix size of at least 64 × 64, resulting in a in-plane resolution of 3.75 × 3.75. The pulse sequence parameters include a 90° flip-angle with a TE (time to echo)/TR (repetition time) of 60 ms/4000 ms. Each paradigm consists of 5 periods. Each period will consist of rest and stimulation (tube inflation causing rectal distension). In each period, 50 dynamics are performed. Each dynamic will last for 2 seconds. The scans will be performed with the rectal tube inflated to render: