The insula has been identified as a key region involved in interoceptive awareness. Whilst imaging studies have investigated the neural activation patterns in this region involved in intero- and exteroceptive awareness, the underlying biochemical mechanisms still remain unclear.In order to investigate these, a well-established fMRI task targeting interoceptive awareness (heartbeat counting) and exteroceptive awareness (tone counting) was combined with magnetic resonance spectroscopy (MRS). Controlling for physiological noise, neural activity in the insula during intero- and exteroceptive awareness was confirmed in an independent data sample using the same fMRI design.Focussing on MRS values from the left insula and combining them with neural activity during intero- and exteroceptive awareness in the same healthy individuals, we demonstrated that GABA concentration in a region highly involved in interoceptive processing is correlated with neural responses to interoceptive stimuli, as opposed to exteroceptive stimuli. In addition, both GABA and interoceptive signal changes in the insula predicted the degree of depressed affect, as measured by the Beck Hopelessness Scale. On the one hand, the association between GABA concentration and neural activity during interoceptive awareness provides novel insight into the biochemical underpinnings of insula function and interoception. On the other, through the additional association of both GABA and neural activity during interoception with depressed affect, these data also bear potentially important implications for psychiatric disorders like depression and anxiety, where GABAergic deficits, altered insula function and abnormal affect coincide.
Bibliographical noteFunding Information:
The authors would like to thank O. Lyttelton and the staff from the MNI as well as from the University of Montréal for their excellent technical support. Thanks also to K. Dedovic and A. Perna for helping with participant recruitment and screening procedures. The authors thank Edward J. Auerbach, Ph.D. (Center for Magnetic Resonance Research, University of Minnesota) for implementing the MEGA-PRESS sequence on Siemens, and Romain Valabregue, Ph.D. (Centre de NeuroImagerie de Recherche, Paris, France) for developing processing tools. MM acknowledges support from Biotechnology Research Center grant P41 RR008079 (NCRR) and P41 EB015894 (NIBIB), and NCC P30 NS057091 . GN acknowledges support from the Hope of Depression Research Foundation (HDRF) , the Canadian Institutes of Health Research (CIHR) and the EJLB-Michael Smith Foundation (CIHR–EJLB) . DJH was funded by a CIHR Postdoctoral Fellowship.
- Depressed affect