Thursday, August 11, 2016

How our brain and visceral monitoring encode the ‘self’

Babo-Rebelo et al. show that two seemingly distinct roles of the default brain network (DN), in self-related cognition on the one hand, and in the monitoring of bodily signals for autonomous function regulation, on the other, are functionally coupled. They do this by testing whether the amplitudes of heartbeat-evoked responses (HERs) during thoughts systematically covary with their self-relatedness, and whether this mechanism engages the DN. They employ two scales of self-relatedness. The “Me” scale described the content of the thought oriented either toward oneself or toward an external object, event, or person. The “I” scale described the engagement of the participant as the protagonist or the agent in the thought. Here is their abstract:
The default network (DN) has been consistently associated with self-related cognition, but also to bodily state monitoring and autonomic regulation. We hypothesized that these two seemingly disparate functional roles of the DN are functionally coupled, in line with theories proposing that selfhood is grounded in the neural monitoring of internal organs, such as the heart. We measured with magnetoencephalograhy neural responses evoked by heartbeats while human participants freely mind-wandered. When interrupted by a visual stimulus at random intervals, participants scored the self-relatedness of the interrupted thought. They evaluated their involvement as the first-person perspective subject or agent in the thought (“I”), and on another scale to what degree they were thinking about themselves (“Me”). During the interrupted thought, neural responses to heartbeats in two regions of the DN, the ventral precuneus and the ventromedial prefrontal cortex, covaried, respectively, with the “I” and the “Me” dimensions of the self, even at the single-trial level. No covariation between self-relatedness and peripheral autonomic measures (heart rate, heart rate variability, pupil diameter, electrodermal activity, respiration rate, and phase) or alpha power was observed. Our results reveal a direct link between selfhood and neural responses to heartbeats in the DN and thus directly support theories grounding selfhood in the neural monitoring of visceral inputs. More generally, the tight functional coupling between self-related processing and cardiac monitoring observed here implies that, even in the absence of measured changes in peripheral bodily measures, physiological and cognitive functions have to be considered jointly in the DN.

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