7-Tesla evidence for columnar and rostral–caudal organization of the human periaqueductal grey response in the absence of threat: a working memory study

The periaqueductal grey (PAG) is a small midbrain structure that surrounds the cerebral aqueduct, regulates brain–body communication, and is often studied for its role in “fight-or-flight” defense responses. We used ultra-high field 7-Tesla fMRI to resolve the PAG in humans and distinguish it from the cerebral aqueduct, examining its in vivo function in humans during a working memory task (N = 87)—i.e., a setting that required physiological mobilization, but no “threat”. During both low and moderate task-elicited cognitive demand, we observed BOLD signal intensity increases in bilateral ventrolateral PAG (vlPAG), consistent with the columnar organization of PAG function identified in non-human animal research. Changes in physiological activity during the task (phasic skin conductance response (SCR) amplitudes, cardiac interbeat interval, respiratory rate) were correlated with PAG BOLD estimates across subjects, and showed some evidence of spatial organization within the PAG, but no spatial organization overlapping with the task-elicited increase in bilateral vlPAG. These findings suggest that the PAG coordinates and regulates bodily activity, even in the absence of threat.