Theta Oscillations Gate the Transmission of Reliable Sequences in the Medial Entorhinal Cortex

Interoception Underlies Therapeutic Effects of Mindfulness Meditation for Posttraumatic Stress Disorder: A Randomized Clinical Trial

BACKGROUND

Mindfulness-based interventions have proven efficacy in treating posttraumatic stress disorder (PTSD), but the neurobiological mechanism underlying the therapeutic effects is unknown. As mindfulness meditation cultivates attention to the present moment and bodily sensations, neural functions related to interoception (i.e., central processes of bodily signals) might be such a mechanism.

METHODS

We conducted a clinical trial in which veterans with PTSD were randomly assigned to receive an 8-week mindfulness-based stress reduction (MBSR) intervention (n = 47) or an active control intervention (present-centered group therapy; n = 51). We assessed pre- and postintervention PTSD symptoms and electroencephalography measures of neural outcomes, including spontaneous brain activity, cognitive task-related brain responses, and interoceptive brain responses (heartbeat-evoked brain responses). We conducted statistical causal mediation analyses using treatment type as a predictor, pre- and postintervention measures of symptom severity as treatment response, and the neural outcomes as mediators.

RESULTS

Compared with the control group, the MBSR group had greater improvements in PTSD symptoms and increases in spontaneous alpha power (8-13 Hz), task-related frontal theta power (4-7 Hz in 140-220 ms after stimulus), and frontal theta heartbeat-evoked brain responses (3-5 Hz and 265-336 ms after R peak). The mediation analysis using latent difference score modeling revealed that only changes in frontal theta heartbeat-evoked brain responses mediated the MBSR treatment effect.

CONCLUSIONS

Mindfulness meditation improves brain functions of attentional control and resting brain states reflective of internally oriented relaxation. However, interoceptive neural functions enhanced by MBSR seem to be a primary cerebral mechanism that improves symptoms of PTSD.

Dynamical self-organization and efficient representation of space by grid cells

To plan trajectories and navigate, animals must maintain a mental representation of the environment and their own position within it. This "cognitive map" is thought to be supported in part by the entorhinal cortex, where grid cells are active when an animal occupies the vertices of a scaling hierarchy of periodic lattices of locations in an enclosure. Here, we review computational developments which suggest that the grid cell network is: (a) efficient, providing required spatial resolution with a minimum number of neurons, (b) self-organizing, dynamically coordinating the structure and scale of the responses, and (c) adaptive, re-organizing in response to changes in landmarks and the structure of the boundaries of spaces. We consider these ideas in light of recent discoveries of similar structures in the mental representation of abstract spaces of shapes and smells, and in other brain areas, and highlight promising directions for future research.