Interactions between the client (Cl) and therapist (Th) evolve therapeutic relationships in psychotherapy. An interpersonal link or therapeutic space is implicitly developed wherein certain important elements are expressed and shared.  However, neural basis of psychotherapy, especially of non-verbal modalities, have scarcely been explored. Therefore, we examined the neural backgrounds of such therapeutic alliances during sandplay, a powerful art/play therapy technique. Real-time and simultaneous measurement of hemodynamics was conducted in the prefrontal cortex (PFC) of Cl-Th pairs participating in sandplay and subsequent interview sessions through multichannel near-infrared spectroscopy. As sandplay is highly individualized, and no two sessions and products (sandtrays) are the same, we expected variation in interactive patterns in the Cl–Th pairs. Nevertheless, we observed a statistically significant correlation between the spatio-temporal patterns in signals produced by the homologous regions of the brains. During the sandplay condition, significant correlations were obtained in the lateral PFC and frontopolar (FP) regions in the real Cl-Th pairs. Furthermore, a significant correlation was observed in the FP region for the interview condition. The correlations found in our study were explained as a “remote” synchronization (i.e., unconnected peripheral oscillators synchronizing through a hub maintaining free desynchronized dynamics) between two subjects in a pair, possibly representing the neural foundation of empathy which arises commonly in sandplay therapy.

Six clients (Cls＝ healthy volunteer students) and six volunteer therapists (Ths) participated in this study. The age of Cls ranged from 19 to 28 years (i.e., mean age = 21.5 years, SD = 2.99) and between 23 to 49 years for Ths (i.e., mean age = 39.7 years, SD = 8.21). They formed six (one male-male, one male-female, four female-female) pairs; however, due to technical problems with NIRS data acquisition, one female-female pair was excluded from the analysis, and the remaining five pairs were analyzed.

We used multichannel NIRS (FOIRE-3000; Shimadzu, Kyoto, Japan) to measure the time courses of concentration changes regarding oxy- and deoxy-Hb during a simulated sandplay session (i.e., 10 minutes at maximum) and post-sandplay interviews (i.e., approximately 5 minutes). Near-infrared light was used at wavelengths of 780 nm, 805 nm, and 830 nm, and the time resolution was set to 0.13 seconds. From the sandplay task period and the interview session, which lasted approximately 10 minutes, a sampling window of 200 seconds was selected for each session, with relatively stable signals, and without apparent artifacts.

Please use these datasets only for quantitative analyses. We are refraining from uploading the sandtrays (i.e. sandplay pictures ) made by the Cls, as no consents for analyzing their sandtrays in any other ways, such as interpreting the individual sandplayers' personalities or psychological problems which might be presented in their sandtrays.

In the first column,

task-start indicates the starting point of sandtray

task-end indicates the end poing of sandtray

interview-start indicates the starting point of interview

interview-end indicates the end point of interview

The graphs of NIRS signals and heatmaps were obtained using the R script "analysis6_Study1_task_20180914.R " and "analysis7_Study1_interview_20180914.R", and the cross-correlograms were obtained by "correlogramviewer1.R".