A research team led by Dr. WANG Liang from the Institute of Psychology of the Chinese Academy of Sciences has found that right hippocampal theta power hierarchically encodes the distance between the current position and a goal destination.
The study was published online on May 5, 2023 in Current biology.
Successfully navigating to goal is crucial for animals in nature as well as human in the modern life. Computational models show that Euclidean distance to the goal is calculated in goal-directed navigation. Representing goal distance at multi-scale is extremely efficient and less susceptible to interference from background noise than coding at a single scale. However, the neural signatures underlying multi-scale goal coding remain poorly understood, particularly in the human brain.
By examining intracranial electroencephalography (iEEG) recordings of refractory epilepsy patients when they performed a virtual spatial navigation task, this study found that high theta power (6-9 Hz) of right hippocampus was significantly modulated by goal distance and decreased as participants approaching the goal.
Furthermore, this goal distance modulation showed gradual changes along the hippocampal longitudinal axis, with the posterior hippocampal theta power more tightly coupled to the goal distance.
Cognitive processing characteristics eventually determined by the temporal hierarchy of brain regions. The current study further found that the neural timescales showed a gradual increase from posterior to anterior hippocampus.
"This is the first study to explore the electrophysiological neural signatures of goal distance in human.” said Dr. WANG, corresponding author of the study.
The current results provide empirical evidence for a multi-scale goal distance representation in the human hippocampus, and link the hippocampal processing of spatial information to its intrinsic temporal dynamics.
This study was supported by the STI2030-Major Projects, the National Natural Science Foundation of China, the Ministry Key Project, the CAS Interdisciplinary Innovation Team, the Scientific Foundation of the Institute of Psychology, Chinese Academy of Sciences, the National Natural Science Foundation of China, China Postdoctoral Science Foundation, and the CAS Special Research Assistant Project, the ERC grant agreement.
Figure 1.a Fine-to-coarse Goal Distance Coding Along Posterior-anterior Axis. Image by Dr. WANG Liang.
A Experiment paradigm: Each trial began with a fixation lasting for 3 to 5 s (randomly jittered). The cue present for 2 s. Participants freely navigated to the target. After participants had made a button-press response at the assumed goal location, feedback was shown for 1.5 s. Finally, the target object for that trial was presented in its correct location and participants collected the object from there, allowing for further learning.
B Important experiment variable: Drop error was defined as the Euclidean distance between the response location (yellow hexagon) and the actual object location (orange pentagram). Goal distance was calculated as the instantaneous Euclidean distance between the current location (brown circle) and the correct object location. The blue curve is an example of movement trajectory.
C Significant modulation of right hippocampal theta power by goal distance in good trials, but not in bad trials and for non-target goals.
D Example contact in the right hippocampus showing a positive correlation between theta power and goal distance.
E Goal distance modulation correlates with recording locations along the right hippocampal posterior-anterior axis (left). As examples (right), the goal distance is plotted against theta power for the circled blue and pink dots marked at the top panel.
F Neural timescale showed a gradual increase from posterior to anterior hippocampus.
Institute of Psychology Chinese Academy of Sciences
Beijing 100101, China.