Body-centered encoding of passive tactile pattern memories.

The human brain stores and retrieves tactile experiences, allowing object recognition by touch, the definition of haptic preferences, and the retrieval of past bodily experiences. However, little is known about the spatial code of tactile body memories, particularly whether encoding takes place in a body-centered (tactile) reference frame, not influenced by hand posture or visual cues, or whether it takes place in an external reference frame, where tactile information is integrated with proprioceptive and visual information. Here, we combined a passive tactile pattern memory task with the crossed-hands paradigm to investigate if tactile pattern retrieval accuracy is influenced by in-/congruent hand position during learning and retrieval (experiment 1) and/or the spatial context surrounding the hand (experiment 2). We hypothesized that significant effects of hand position and/or visual context on retrieval accuracy evidence external encoding, whereas the absence of such effects are more consistent with body-centered encoding. Our data is in accordance with the latter hypothesis, and do not support external encoding. The results can be considered plausible in light of clinical evidence where bodily sensations related to past memories are often confined to specific body locations rather than remapped to external space.