Inducing representational change in the hippocampus through real-time neurofeedback

When you perceive or remember something, other related things come to mind, affecting how these competing items are subsequently perceived and remembered. Such behavioral consequences are believed to result from changes in the overlap of neural representations of these items, especially in the hippocampus. According to multiple theories, hippocampal overlap should increase (integration) when there is high coactivation between cortical representations. However, prior studies used indirect proxies for coactivation, by manipulating stimulus similarity or task demands. Here we induce coactivation in the visual cortex more directly using closed-loop neurofeedback from real-time fMRI. While viewing one object, participants were rewarded for activating the representation of another object as strongly as possible. Across multiple real-time fMRI sessions, they succeeded in using the neurofeedback to induce coactivation. Compared with untrained objects, this coactivation led to memory integration in behavior and the brain: Trained objects became harder for participants to discriminate behaviorally in a categorical perception task and harder to discriminate neurally from patterns of fMRI activity in their hippocampus as a result of losing unique features. These findings demonstrate that neurofeedback can be used to alter and combine memories.

Methods
Data were acquired using a 3T Siemens Prisma scanner with a 64-channel head coil at the Brain Imaging Center at Yale University.

The scan sequences are as follows:

For recognition and feedback functional runs, an echo-planar imaging (EPI) sequence was used to collect BOLD data (TR=2 s; TE=30 ms; voxel size=3 mm isotropic; FA=90°; IPAT GRAPPA acceleration factor=2; distance factor=25%), yielding 36 axial slices. Each recognition run contained 145 volumes and each feedback run contained 176 volumes. Two field map volumes (TR=5 s; TE=80 ms; otherwise matching the EPI scans) were acquired in opposite phase encoding directions. For anatomical alignment and visualization, we collected a 3D T1-weighted magnetization-prepared rapid acquisition gradient echo (MPRAGE) scan (TR=2.5 s; TE=2.9 ms; voxel size=1 mm isotropic; FA=8°; 176 sagittal slices; IPAT GRAPPA acceleration factor=2), and a 3D T2-weighted fast spin echo scan with variable flip angle (TR=3.2 s; TE=565 ms; voxel size=1 mm isotropic; 176 sagittal slices; IPAT GRAPPA acceleration factor=2).