Hypnotic susceptibility explains differences in resting state functional connectivity

Introduction: Hypnotic susceptibility (HS) is a measurable cognitive trait defined as the generalized tendency to respond to hypnotic suggestions [1]. Very little is known about the neural bases of HS [2]. Our aim was to assess HS-related differences in resting state func tional c onnec tivity. Methods: N=35 healthy women (3 ambidextrous, 4 left-handed; age range 19-56 yrs, mean 36.9 yrs) partic ipated in the study. HS was assessed with the Stanford Hypnotic Susc eptibility Sc ale – Form A (SHSS:A), mental absorption with the T ellegen Absorption Sc ale (T AS) and trait anxiety with the State-T rait Anxiety Inventory Form Y (ST AI-Y2). Subjec ts were not in any way pre-selec ted for SHSS sc ore. T o measure spontaneous BOLD signal fluc tuations at rest, two runs of EPI sc ans were ac quired while subjec ts lay in the sc anner relaxed with eyes c losed (for eac h run: 200 volumes; T R 2 s; isometric voxel size 3.6 mm; 35 axial slic es without gap; matrix 80 x 63 voxels; FOV 286 x 229 mm; ac quisition time 7 min), using a 3T Philips Ac hieva MR sc anner. A T 1-weighted brain image (isotropic voxel size 0.5 mm) was ac quired for inter-subjec t alignment. EPI data were analysed using AFNI. Preproc essing inc luded the removal of physiologic al, white matter and hardware related noise using RET ROICOR and ANAT ICOR proc edures, lowpass filtering to remove frequenc ies >0.1 Hz, and 6-mm FWHM spatial smoothing. Seed-based func tional c onnec tivity (FC) was quantified as the z-transformed Pearson c orrelation with the seed signal (average BOLD signal within a sphere of 6mm radius). Seeds were plac ed (a) within key regions of the Default Mode Network (DMN) taken from the literature; (b) in the two areas (anterior c ingulate c ortex – ACC; dorsolateral prefrontal c ortex – DLPFC) desc ribed in Hoeft et al. [2]; and (c ) in 15 seeds ad-hoc plac ed along the c ingulate c ortex in eac h hemisphere. HS-related differenc es in FC were assessed by using SHSS sc ore as a between-subjec ts linear regressor to explain FC z-sc ores. Furthermore, some of the c lusters whic h resulted signific antly c onnec ted with the above mentioned seeds, e.g. orbitofrontal c ortex (OFC), were, in turn, used as seeds (d). Results: SHSS sc ores ranged from 0-10 (mean 3.6). Eighteen subjec ts had low (SHSS<4), 14 medium (SHSS=4-7) and 3 high SHSS sc ores (SHSS>7). SHSS was independent of age, educ ational level, handedness, trait anxiety and mental absorption. SHSS was positively c orrelated with FC (a) of DMN seeds, i.e., the right medial PFC, left posterior c ingulate c ortex (PCC) and left posterior insula with c erebellar foc i, and (b) of Hoeft et al.'s [2] ACC seed with c erebellar regions, and of right DLPFC with left OFC. When foc using on the c ingulate c ortex (c ), SHSS was positively c orrelated with FC of ACC with mid-c ingulate c ortex (MCC), of various seeds in the ACC and MCC with c erebellar foc i, and of MCC with bilateral OFC. SHSS was also positively c orrelated with FC of the OFC foc i (d) with a wide network of regions, inc luding MCC, bilateral DLPFC (see Fig. 1), pre- and postcentral gyri, superior temporal gyri and insula as well as cerebellum and contralateral precuneus (Fig. 2). Conclusions:Among healthy women, individuals with higher HS show higher resting state FC between OFC, DLPFC, cingulate cortex and cerebellum. Further researc h is needed to c onfirm these relationships in men, and to assess their cognitive correlates.